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Using sulfur isotope to determine the sources of vermillion in ancient burial mounds in Japan
This study represents an attempt to determine the sources of vermillion found in ancient Japanese burial mounds of the 1st-6th centuries A.D., by comparing their ratios of sulfur isotopes with those of cinnabar ore samples collected in Japan and China. Cinnabar ore samples were taken from three mines in central Japan (Niu in Mie, Yamato in Nara, and Sui in Tokushima prefectures), and from Wanshan in China, where mining activity has been recorded back to the 6th century A.D. and earlier. When the ratios of 34S and 32S were compared with the Canyon Diablo meteorite standard, a high δ34S value of + 22.6 ± 3.60‰ was found for the Wanshan mine, as opposed to low values ranging from -7.3 ± 1.9 to -2.1 ± 1.6‰ for the Japanese mines. The ratios of sulfur isotopes in vermillion collected from ancient Japanese burial mounds also divided into two groups. High ratios (+11.1 to +22.8‰) were found in 1st- and 2nd- century burials in the western regions of northern Kyushu and San'in, suggesting that local, powerful chiefs obtained vermillion through relations with China. Lower ratios (-8.4 to -2.0‰) were found in burials of the 2nd through 6th centuries in central Japan, where the ancient Yamato dynasty emerged as the first unified polity around the end of the 2nd century A.D. We, therefore, conclude that the Yamato dynasty exploited local sources of vermillion, rather than depending solely on China. The present study demonstrates the feasibility of determining sources of vermillion using sulfur isotope ratios, and the relevance of such findings for archaeological research. © 2005 Wiley Periodicals, Inc.

DOI： 10.1002/gea.20035

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Geochronological constraints using 40Ar/39Ar dating on the mineralization of the Hishikari epithermal gold deposit, Japan
Ages for thirty adularia samples collected from various veins were in the Hishikari gold deposit determined by 40Ar/39Ar dating to constrain the timing of adularia-quartz vein formation and to determine the temporal change in temperature of hydrothermal fluid. Plateau ages were obtained from all adularia samples, and significant excess 40Ar is not recognized from inverse isochrones. The duration of mineralization within individual veins was determined by adularia ages from the early and late stages of mineralization within the same vein. The durations of mineralization in the Daisen-1, Daisen-3, Hosen-2 and Keisen-3 veins in the Honko-Sanjin zone were 7,000, 140,000, 160,000 and 170,000 years, respectively. The durations of mineralization in the Seisen-2 and Yusen-1-2 veins in the Yamada zones were 360,000 and 320,000 years, respectively. Mineralization lasted for a relatively longer period in individual veins at the Yamada zone. Mineralization ages from the Honko-Sanjin zone range from 1.04 to 0.75 Ma, and most mineralization ages are concentrated in a short period from 1.01 to 0.88 Ma. In contrast, mineralization ages for the Yamada zone range from 1.21 to 0.64 Ma. These results indicate that fracturing and subsequent vein formation lasted for a longer period in the Yamada zone (about 570,000 years) compared with those events in the Honko-Sanjin zone (about 290,000 years). The homogenization temperatures of liquid-rich fluid inclusions in columnar adularia used for age determination were determined to be 223°C on average, and most of these temperatures range from 180 to 258°C. No significant temporal change in homogenization temperature is recognized in this study. However, adularia in the Keisen veins indicated higher homogenization temperatures compared with elsewhere in the deposit, suggesting that the principal ascent of mineralizing hydrothermal fluid was via the Keisen veins.

DOI： 10.1111/j.1751-3928.2005.tb00246.x

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Metallogenesis of porphyry Cu-Au deposits of the western Luzon arc, Philippines: K-Ar ages, SO3 contents of microphenocrystic apatite and significance of intrusive rocks.

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Mineral paragenesis, fluid inclusions and sulfur isotope systematics of the Lepanto Far Southeast porphyry Cu-Au deposit, Mankayan, Benguet, Philippines.

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Genesis of the Mamut porphyry Cu deposit, Sabah, East Malaysia.

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Spinifex texture of native sulfur: A cooling product of sulfur flow eruptions at Shiretoko-Iwozan volcano, Hokkaido, Japan

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Polymetallic mineralization at the Shin-Ohtoyo deposit, Harukayama district, Hokkaido, Japan.

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A Kuroko-type polymetallic sulfide deposit in a submarine silicic caldera.

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Geology, alteration, and formation environment of the disseminated gold-silver telluride Bulawan deposit, Negros Occidental, Philippines.

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"Brown Ore" from the Fukasawa kuroko deposits, northeast Japan: Its characteristics and formation process.

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Tectonic implication of the hydrated garnet peridotites near Mt. Kinabalu, Sabah, East Malaysia

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The Cretaceous Luk Ulo Complex (LUC) in Central Java, Indonesia, hosts orogenic gold-type ores with S derived from metapelite. The host rock consists of accreted metapelite, metamorphosed under temperature up to 510 ± 30 °C. We investigated the textural and chemical evolution of pyrite and carbonaceous matter (CM), and analyzed the hosts phases for trace elements (TEs) such as As, Pb, Cu, Sb, Te, Ag, Zn, Bi, Se, Hg, and Au, with the aim of documenting the behavior of these elements during prograde metamorphism and evaluate the implications on gold mineralization. With increasing metamorphic grade, the texture and chemical composition of pyrite evolved through different stages: 1) framboidal pyrite and pyrite nodules in the sedimentary–diagenetic facies, 2) anhedral–subhedral pyrite in sub-greenschist facies (SGSF), 3) euhedral pyrite in lower greenschist facies (LGSF), 4) elongated pyrite in middle greenschist facies (MGSF), and 5) replacement of pyrite by pyrrhotite in upper greenschist facies (UGSF). The framboidal pyrite and pyrite nodules contain measurable TEs. Recrystallization of such pyrite into euhedral pyrite in LGSF resulted in significant depletion of TEs, except for Se, by pressure-solution. With increasing metamorphic grade, the recrystallization of organic matter to “cooked” CM in LGSF was accompanied by significant depletion in most TEs, with only Fe and S being retained. The transformation of cooked CM into graphite in MGSF, and of elongated pyrite into pyrrhotite in UGSF resulted in further removal of remaining TEs. These observations and the absence of para-amphibolite in the LUC suggest that remobilization of TEs and S from sedimentary pyrite and CM might have occurred in the LGSF, much earlier than previously proposed (UGSF-amphibolite transition).

DOI： 10.1016/j.oregeorev.2024.105966

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In the Olkaria geothermal field, Kenya, a silica scale formed from geothermal water at the OW-35 production well was geochemically investigated. The geothermal water is highly alkaline, with a pH of 10.13, while the salinity is low, with a total Cl concentration of 432.4 ppm. The silica scale was precipitated from geothermal water with a high temperature (150–190 °C) in the OW-35 separator. For the mineral composition of the scale sample, it is mainly amorphous Opal-A and crystalline quartz. The SiO2 content was 85.47 wt.%, and the Al2O3 and Fe2O3 contents were high at 3.16 and 1.11%, respectively, despite the fact that Al and Fe concentrations in the geothermal water were low. Based on the enrichment factor, Al was extremely concentrated from the geothermal water onto the silica scale during the formation, suggesting that Al may participate in the formation of the silica scale. For Fe, there was no contribution of Fe to the formation of silica scale, which was present as magnetite. This silica scale is a mixture of crystalline quartz and amorphous opal-A. The deposition mechanism was considered as follows. The quartz was formed by continuous and slow adsorption of monosilicic acid on the surface of the solid due to the slight supersaturated condition. On the other hand, opal-A was formed by a reaction between aluminate ion and monosilicic acid or monosilicate ion on the solid surface.

DOI： 10.1016/j.geothermics.2023.102871

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Boiling and mixing are thought to be the most important processes for mineralization in the low-sulfidation epithermal gold‑silver deposits. Some low-sulfidation epithermal gold‑silver deposits show vertical zoning of metals including gold, silver, copper, lead, and zinc, but effect of boiling and mixing for the vertical zoning of metals through mineralization has been scarcely debated. Therefore, we applied geochemical modeling for an open-isenthalpic boiling system, with a hydrothermal fluid with different initial temperatures, carbon dioxide contents, salinities, and total sulfur contents to numerically evaluate the effect of boiling phenomenon for the vertical zoning in low-sulfidation epithermal gold‑silver deposits. Geochemical modeling of boiling phenomenon suggests that boiling is effective for depositing gold, silver, copper, lead, and zinc and that it could form a bonanza zone enriched in gold and silver in the shallow zone above the lead and zinc-rich zone. Temperature, carbon dioxide content, salinity, and hydrogen sulfide content affect the deposited amount of metals, vertical extent, depth of mineralization, and gold/silver ratio of the ore zone, although other factors such as permeability, gangue mineralogy, duration of mineralization, kinetics of mineral precipitation, change in porosity, thermal conductivity, and fractures of host rocks could affect mineralization as well. Our modeling of boiling phenomenon demonstrates similar characteristics with natural low-sulfidation epithermal gold‑silver deposits, suggesting that boiling is an important mechanism to cause vertical metal zoning in the low-sulfidation epithermal gold‑silver deposits, even though mixing could also be important to precipitate metals in some deposits.

DOI： 10.1016/j.gexplo.2023.107378

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Zuun Mod is a porphyry-type Mo-Cu deposit located in the Edren terrane in Southwest Mongolia. The deposit has estimated resources of 218 Mt with an average Mo grade of 0.057% and Cu grade of 0.069%, and significant amounts of Re. The deposit is characterized by multiple pulses of magmatism and exsolution of magmatic ore fluids and associated alteration and mineralization. The timing of these events and the tectonic environment were unconstrained, and the deposit's origin remains controversial. Based on drill core and field examinations, four lithological units of the Bayanbulag intrusive complex are identified in the deposit area including quartz syenite, quartz monzonite, granodiorite, and granite. The majority of Mo mineralization at Zuun Mod occurs in sheeted and stockwork quartz veins that crosscut units of the Bayanbulag complex as well as disseminations within altered granitoids wherein the mineralized quartz veins occur with potassic and phyllic alteration selvages. Zircon U-Pb age dating for quartz monzonite and granodiorite defined the timing of magmatic events at 305.3 ± 3.6 Ma and 301.8 ± 2.7 Ma, respectively. Molybdenite Re-Os geochronology on grains from a quartz vein with potassic alteration selvage determined the age of Mo mineralization at 297 ± 4.8 Ma. Lithogeochemical data of intrusive units suggest the granitoid rocks show calc-alkaline to high-K calc-alkaline, I-type, and metaluminous to slightly peraluminous affinities that formed in a post-collisional setting and were likely sourced from subduction-modified lithosphere. Lithogeochemical signatures and the tectonic environment classify Zuun Mod into neither Climax nor Endako-types, but as a Mo-rich porphyry Cu deposit.

DOI： 10.1016/j.jseaes.2023.105857

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Lateral sampling of each blasting interval (~ 2.6 m) along a 79 m strike length was conducted for the Hosen 8-2 vein on the −5 ML (mining level, meters relative to sea level) of the Main ore zone in the Hishikari epithermal Au deposit, Kagoshima, Japan. The horizontal variation of mineral textures, bulk chemical compositions, and fluid inclusion temperatures and apparent salinity of ore fluids were determined. The major gangue minerals of the quartz veins studied include quartz and adularia with minor amounts of calcite and smectite. The major ore minerals include electrum, galena, and sphalerite with minor pyrite, petzite, and hessite. Electrum commonly occurs in a discrete band with microcrystalline quartz, granular adularia, and smectite. The electrum-bearing band is followed by tabular adularia, and finally by granular or comb quartz. Mineral textures that indicate high degrees of supersaturation with respect to amorphous silica (presently quartz with microcrystalline/mosaic and feathery textures) and adularia (with tabular, rhombic, and granular textures) were common throughout the vein strike. Bulk chemical analyses indicate that Au grade is positively correlated with Ag, Bi, Pb, and Te contents. A bonanza zone with Au grades up to 10,800 ppm occurs in the central part of the Hosen 8-2 vein on the −5 ML, and is associated with high adularia content, calculated as adularia / (quartz + adularia). The wide lateral variation in the geochemical composition contrasts with the consistent association of electrum with microcrystalline quartz, granular adularia, and smectite throughout the Hosen 8-2 vein on the −5 ML. Fluid inclusion microthermometry of primary and pseudosecondary inclusions in quartz and adularia yielded histogram modes of homogenization temperature between 160 and 240°C; the most frequent mode is 200–210°C, with most data within ±10°C from this value. The maximum ice-melting temperature of most samples excluding late comb quartz is −1.5°C, which is equivalent to an apparent salinity of 2.6 wt% NaCl eq. The wide variation in ice-melting temperatures and apparent salinities (up to 5.2 wt% NaCl eq.) may be due to dissolved CO2 in the fluids, while the sharp decrease in apparent salinity with temperature decrease indicates CO2 loss due to fluid boiling during vein formation. The intimate association of electrum with microcrystalline quartz that recrystallized from amorphous silica indicate sharp boiling and vapor loss as the primary mechanism of Au deposition in the Hosen 8-2 vein.

DOI： 10.1111/rge.12318

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The gold mineralization at the Tau deposit in northeastern Botswana can be distinguished into two stages. The first stage of mineralization consists of invisible gold associated with early, sulfur-rich arsenopyrite (Apy1). The second stage is characterized by native gold associated with late, sulfur-poor arsenopyrite (Apy2). This study aims to constrain the nature of the ore-forming fluid at the Tau deposit on the basis of fluid inclusion microthermometry and arsenopyrite geothermometry. Quartz crystals closely associated with gold-bearing sulfides (Apy1) from the host rock host three types of fluid inclusions occurring in the same assemblages: Type I, two-phase aqueous fluid inclusions, Type II three-phase aqueous-carbonic fluid inclusions and Type III one- or two-phase CO2-rich fluid inclusions. Microthermometric and Raman spectroscopic studies revealed the dominance of coexisting H2O+NaCl (Type I) and CO2-N2-CH4 (Type III) fluid inclusions. The coexisting Type I and Type III fluid inclusions could represent products of the immiscibility of a homogenous H2O-CO2-NaCl-N2-CH4 primary ore fluid. The salinity of Type I (calculated from melting temperature of ice) and Type II (calculated from dissolution temperature of clathrate) fluid inclusions vary from 3.4 to 9.2 wt% NaCl equiv. and 5.8 to 9.8 wt% NaCl equiv., respectively. The overall fluid inclusion salinity range (<10 wt% NaCl equiv.) and gas compositions of fluids suggest that the primary ore-forming fluid at the Tau deposit was of low salinity and H2O-CO2-N2-CH4-NaCl composition. Integration of fluid inclusion microthermometry and arsenopyrite geothermometer results suggest that the first stage and second stages of gold mineralization and the associated alteration at the Tau deposit occurred at pressure and temperature conditions of 75–145 MPa and 290–370°C and 85–160 MPa and 330–370°C, respectively. These results suggest that there was an increase in temperature from the first stage to the second stage of mineralization, resulting in the recrystallization of invisible gold-bearing arsenopyrite in the first stage to form native gold-bearing arsenopyrite in the second stage. Fluid composition and the estimated physico-chemical conditions at the Tau deposit confirm that gold was transported as reduced bisulfide complexes and initial gold deposition was likely caused by a reduction in sulfur contents as a result of sulfidation reactions and pressure-induced phase separation (fluid immiscibility).

DOI： 10.1111/rge.12316

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Auriferous quartz veins in the Namicupo gold prospect occur parallel to the foliation of metasedimentary host rocks of the Xixano Complex in northeastern Mozambique. The geochemistry and ore-forming mechanism of the Namicupo prospect have never been scientifically investigated. This study discusses the ore mineralogy, fluid inclusion, and stable isotope (S-O) characteristics of the prospect. The mineralization in the Namicupo prospect is divided into two stages. The Stage I, primary mineralization, is represented by electrum with Ag contents of 15–26 at.%, associated with pyrite and chalcopyrite. The Stage II is supergene mineralization, characterized by electrum with Ag contents of 39–46 at.%, intergrown with goethite, barite, and minium, which replaced primary sulfides. Quartz from the mineralized veins hosts three types of primary fluid inclusions coexisting in the same fluid inclusion assemblage. Type A inclusions are three-phase aqueous‑carbonic inclusions (aqueous liquid, CO2 liquid and vapor), with final homogenization temperature and salinity varying from 140 to 241 °C, and 1.0 to 7.8 wt% NaCl eq., respectively. Type B inclusions occur either as mono-phase (vapor or liquid) or two-phase (vapor and liquid) CO2-rich, N2-H2O-bearing inclusions, with homogenization temperature varying from +12.9 to +29.3 °C. The Type C inclusions are two-phase (liquid and vapor) aqueous inclusions, which homogenize to liquid phase at temperatures between 209 and 337 °C. The salinity of the Type C inclusions varies from 4.0 to 10.8 wt% NaCl eq. The sulfur isotopic ratios (δ34SCDT) of sulfides associated with Stage I mineralization and the oxygen isotopic ratios (δ18OSMOW) of water calculated from those of quartz from the quartz veins vary from −3.5 to +0.9 ‰ and −1.0 to +2.5 ‰, respectively. The primary mineralization at the prospect is classified as an orogenic-type gold mineralization, formed by aqueous‑carbonic metamorphic fluids. The precipitation of primary gold mineralization in the Namicupo prospect resulted dominantly from fluid immiscibility. The considerable amount of S up to 0.1 wt% and the high Ag contents of electrum intergrown with goethite, minium and barite suggest that the supergene mineralization in the Stage II was caused by oxidation of primary gold-bearing sulfides and Au-rich electrum under moderately acidic and oxidizing conditions, which resulted in Au and Ag liberation, likely by thiosulfate. Dissolution of primary mineralization and supergene gold enrichment in the Namicupo prospect appear to have occurred largely in situ, with little evidence of distant mobilization.

DOI： 10.1016/j.gexplo.2023.107220

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The Mupane gold deposit, which is one of the numerous gold occurrences in the Tati Greenstone Belt in the northeastern part of Botswana, consists of four orebodies, namely Tau, Tawana, Kwena, and Tholo deposits. The present research, which focuses on the genesis of the Tau deposit, was based on ore petrography, mineral chemistry of sulfides, and sulfur isotope data. Mineralogical characteristics of the host rocks indicate that banded iron formation at the Tau deposit includes iron oxides (magnetite), carbonates (siderite and ankerite), silicates (chlorite and amphibole), and sulfides (arsenopyrite and pyrrhotite). The deposit features arsenopyrite-rich zones associated with biotite-chlorite veins, which are indicative of the precipitation of arsenopyrite concomitant with potassic alteration. The replacement of magnetite by pyrrhotite in some samples suggests that sulfidation was likely the dominant gold precipitation mechanism because it is considered to have destabilized gold-thiocomplexes in the ore-forming fluids. Based on textural relationships and chemical composition, arsenopyrite is interpreted to reflect two generations. Arsenopyrite 1 is possibly early in origin, sieve textured with abundant inclusions of pyrrhotite. Arsenopyrite 1 was then overgrown by late arsenopyrite 2 with no porous textures and rare inclusions of pyrrhotite. Gold mineralization was initiated by focused fluid flow and sulfidation of the oxide facies banded iron formation, leading to an epigenetic gold mineralization. The mineralogical assemblages, textures, and mineral chemistry data at the Tau gold deposit revealed two-stage gold mineralizations commencing with the deposition of invisible gold in arsenopyrite 1 followed by the later formation of native gold during hydrothermal alteration and post-depositional recrystallization of arsenopyrite 1. Laser ablation inductively coupled plasma mass spectrometric analysis of arsenopyrite from the Tau deposit revealed that the hydrothermal event responsible for the formation of late native gold also affected the distribution of other trace elements within the grains as evidenced by varying trace elements contents in arsenopyrite 1 and arsenopyrite 2. The range of δ34S of gold-bearing assemblages from the Tau deposit is restricted from +1.6 to +3.9‰, which is typical of Archean orogenic gold deposits and indicates that overall reduced hydrothermal conditions prevailed during the gold mineralization process at the Tau deposit. The results from this study suggest that gold mineralization involved multi-processes such as sulfidation, metamorphism, deformation, hydrothermal alteration, and gold remobilization.

DOI： 10.1111/rge.12305

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The Chifumbazi gold deposit is located in the Chifunde District, Tete Province, northwestern Mozambique. The geology of the study area is composed of the Proterozoic Mualadzi Group comprising ultramafic metavolcanic rocks, quartzite, biotite-schist, Macanda Mafic Metavolcanics, conglomerate, and granitoid of the Furancungo Suite. The geological characteristics and metallogenesis of gold mineralization in the Tete Province are poorly understood. This study describes the gold mineralization and associated hydrothermal alteration in the Chifumbazi deposit on the basis of petrography, whole-rock geochemistry, mineral chemistry, fluid inclusion and sulfur isotope analyses. The mineralization in the Chifumbazi deposit includes auriferous quartz, calcite, dolomite and ankerite quartz-chlorite, and chlorite-pyrite veins and veinlets as well as sulfide dissemination hosted by altered meta-granodiorite along shear zones and fracture zones. On a larger scale, the mineralized veins and veinlets occur along a discordant fracture system within a Pan-African shear zone. The meta-granodiorite host-rock of the mineralization consists mainly of plagioclase, biotite, actinolite, and quartz, and alteration minerals calcite, dolomite, sericite, and chlorite. The meta-granodiorite is enriched in LREE compared to HREE and shows negative Eu anomalies. The mineralization in the Chifumbazi deposit formed through three hypogene mineralization stages (Stages I–III) and one supergene stage (Stage IV). Stage I comprises quartz, calcite, dolomite, ankerite, pyrite, chalcopyrite, pyrrhotite and galena. Stage II comprises quartz, pyrrhotite, pyrite, chalcopyrite and native gold. Stage III comprises chlorite and pyrite; and Stage IV comprises secondary minerals goethite, bornite and covellite. Bulk chemical analysis of ores detected gold contents up to 5 ppm for a quartz vein of Stage II, where visible native gold is present in pyrite. The δ34SCDT values of pyrite and chalcopyrite of the Stages I–III range from +0.9 to +2.4 ‰. On the basis of the geological setting, mineralogy, and sulfur isotope signatures, the Chifumbazi deposit can be classified as orogenic.

DOI： 10.1111/rge.12308

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The Xiangzhong metallogenic province (XZMP), the largest polymetallic mineralization province in southern China, is known for its large number of Sb and Sb-polymetallic deposits (>100). In this study, detailed microscope observation, trace element, and sulfur isotopic analyses were performed on stibnite from the Xikuangshan, Woxi, and Banxi deposits in the XZMP to constrain the ore genesis. Stibnite from three deposits appears similar under backscattered electron imaging and has similar major elements contents. Detectable trace elements in stibnite are Fe, Cu, Zn, As, and Pb. Base metals (Cu, Pb, and Zn) are enriched in stibnite from the Woxi deposit but are depleted in stibnite from the Xikuangshan and Banxi deposits. Gold is detectable only in stibnite from the Woxi deposit. Cu, As, and Pb mainly occur as solid solutions within the crystal lattice in stibnite, while micro-scale inclusions of Fe- and/or Zn-rich phases are also observed. The δ34S values of stibnite from three deposits are distinct but with narrow ranges: +6.8 to +10.2 ‰; +5.5 to +6.5 ‰; −4.2 to +0.1 ‰ for the Xikuangshan, Banxi, and Woxi deposits, respectively. The δ34S values of stibnite suggest that the underlying basement rocks are the potential source of sulfur for the Sb mineralization in the Xikuangshan and Banxi districts while sulfur for the Sb mineralization of the Woxi district may have originated from a deep magmatic source. In addition, a positive trend between the δ34S values of stibnite and sampling depth suggests an input of the 34S-rich basin brine during the mineralization in the Woxi district. We propose a genetic model for the Sb mineralization in the XZMP: Fluids rich in Sb, Au, W, Cu, Pb, and Zn related to igneous activities ascended via regional deep faults and mixed with 34S-rich basin brine. Ore minerals of Sb, Au, and W were deposited within structural traps resulting in the Woxi-type deposits. The basement-derived deep fluids driven by orogenic leached Sb and related metals from the basement metamorphic rocks, which migrated via the regional faults and mixed with cold near surface meteoric water to form the Xikuangshan-type deposits.

DOI： 10.1016/j.gexplo.2023.107177

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The Luk Ulo Metamorphic Complex, Central Java is a product of the Cretaceous subduction and accretion, and includes diverse types of protoliths. Two-types of primary mineralization have been recognized in this area, namely, (1) seafloor basalt-hosted massive sulfide mineralization and (2) low-grade metamorphic rocks-hosted vein type mineralization. Later erosion of these types of primary mineralization formed placer gold deposits along rivers. However, the source has never been identified. Thus, this study aims at understanding the source of placer gold, the characteristics of the primary mineralization, and the tectonic evolution of the study area on the basis of mineralogy, mineral chemistry, whole-rock geochemistry, and sulfur isotope analyses. Volcanogenic massive sulfide (VMS)-type mineralization was identified in the seafloor basalt and few deep-sea sedimentary rocks, and both the ores and host rocks preserved pre-metamorphic textures and minerals. The characteristics of this VMS-type mineralization include (1) crustiform quartz veins with pyrite cutting the host rocks, (2) zonation of local silicification to interlayered chlorite/smectite-chlorite-laumontite-calcite-epidote alteration from central to outer zone, (3) pyrite-dominated ores with minor amounts of arsenian pyrite, chalcopyrite, and marcasite, (4) unmetamorphosed host rocks and ores, and (5) sulfur isotope signature with a median δ34S of +3.1‰ suggesting sulfur derived from magmatic source and/or sulfur extracted from basaltic rocks with a small contribution of biogenic sulfur. On the other hand, low-grade metamorphic rocks-hosted vein type mineralization was identified as orogenic-type gold mineralization, and the mineralized veins formed after the peak of metamorphism. It is characterized by (1) pyrite-arsenian pyrite ores with minor amounts of arsenopyrite, galena, tetrahedrite, chalcopyrite, and sphalerite, (2) quartz-illite-graphite alteration assemblage, (3) mineralized veins cross-cutting the foliation of metamorphic host rocks, (4) high antimony contents of pyrite (up to 1.7 wt%) and rutile (up to 160 ppm), (5) relatively high ore-forming temperature (423 ± 9°C, calculated from arsenopyrite and graphite geothermometers), and (6) remobilized-sedimentary sulfur signature of the ores with a median δ34S of −9.8‰. Several lines of evidence suggest that placer gold was likely derived from the erosion of orogenic-type gold ores in the surrounding areas. This evidence includes the presence of gold-bearing ores hosted by low-grade metapelites and metagranitoid with characteristics of orogenic-type gold mineralization, whereas the VMS-type ores are barren in gold. The occurrence of the mid-oceanic ridge- and accretion zone-related mineralization in this area reflects the subduction and amalgamation of oceanic and continental crustal blocks during the Cretaceous period. Discovery of gold mineralization hosted in the Cretaceous basement rocks of the Sunda arc indicates the importance to broaden the gold exploration targets to include not only young volcanic rocks, but also relatively old metamorphic basement rocks.

DOI： 10.1111/rge.12300

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The Sanjin deposit is one of three major ore zones hosted by Pleistocene quartz-adularia veins being mined at the Hishikari low-sulfidation epithermal gold mine, which has produced more than 242 t of gold at an extraordinary average grade since 1985. Hydrothermal alteration zoning of the Sanjin deposit was examined with respect to mineralogy, geochemistry, fluid inclusion microthermometry, and oxygen and hydrogen isotopes. Clay minerals are dominated by interstratified chlorite-smectite (C/S) and interstratified illite-smectite (I/S) with <20% smectite. Epidote and prehnite are recorded for the first time at Hishikari in the southeastern part of the Sanjin deposit, typically coexisting with chlorite. Trapping temperatures of fluid inclusions from associated ore zone quartz veins typically range from 195 to 230 °C, with higher temperatures prevalent in the southeastern part of the Sanjin deposit. The calculated fluid δ18O and δ2H values from clay minerals and quartz cannot be explained by a simple water-rock interaction or a simple fluid mixing model, since variable isotopic exchange temperature and endmembers have to be considered. This suggests that both water-rock interaction and mixing of fluids occurred between dynamically variable end members during mineralization. The average estimated formation temperature of chlorites in the Sanjin deposit using chlorite geothermometry is 233 ± 19 °C, in agreement with the highest temperature zone in Hishikari, estimated by homogenization temperature of fluid inclusions of ore veins. In addition, the estimated formation temperatures of chlorite in epidote- and/or prehnite-rich altered rocks are higher (avg. 240 ± 17 °C) than those in epidote- and/or prehnite-poor altered rocks (avg. 216 ± 9 °C). Thus, the chlorite-epidote/prehnite assemblage can be an index of a high temperature alteration zone in the Sanjin deposit. Considering the position of the paleo-water table of the three ore zones, these factors are consistent with the formation of the Sanjin deposit proximal to the upflow zone responsible for gold mineralization at Hishikari. We suggest that our approach could be utilized to understand the thermal structure of epithermal gold system, which may be important to explore for blind veins at mature mining districts.

DOI： 10.1016/j.gexplo.2022.107018

Language：English   Publishing type：Research paper (scientific journal)  

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The Tagun-Khin-Dan gold deposit in the Mogok-Mandalay-Mergui Belt, Central Myanmar, is characterized by an array of quartz-veins hosted in mudstone of the Kogwe Formation of the Carboniferous Mergui Group. Two major deformational stages were recorded in the area; (1) N-S shortening and (2) uplifting and emplacement of various dykes and quartz veinlets. The N-S shortening within the area lead the development of km-scale faults, determined largely by the presence of a zone of major WNW-ESE trending dextral strike-slip faulting. Quartz veins in the deposit include: (1) type-A quartz veins, parallel to the dextral NW-SE trending major fault; and (2) type-B quartz veins which occur as isolated parallel veins. Gold in the type-A quartz vein is present as native gold and electrum locked within pyrite and associated with pyrite and galena and in the type-B quartz veins as electrum associated with sulfide minerals such as pyrite, chalcopyrite, galena and sphalerite. The mineralization stages can be classified into the type-A quartz vein stage and the type-B quartz vein stage. Two type of fluid inclusions; liquid-rich aqueous inclusions (L-type) and vapor-rich aqueous inclusions (V-type) are identified in the type-A quartz veins. The homogenization temperature of L-type fluid inclusions of the type-A quartz veins ranges from 203 to 321°C and salinity of the fluid inclusions varies from 0.4 to 1.6 wt% NaCl equiv. The homogenization temperature of V-type fluid inclusions of type-A quartz veins ranges from 290 to 340°C with a salinity ranging from 0.4 to 1.9 wt% NaCl equivalent. In the type-B quartz veins, only liquid-rich aqueous inclusions (L-type) are identified. The type-B quartz veins yielded low homogenization temperatures from 160 to 220°C, with low salinities from 0.2 to 1.9 wt% NaCl equiv. compared with those of the type-A veins. The depth range of ore formation is estimated to be a shallow depth of less than 0.2 km based on fluid inclusion microthermometry. Fluid boiling is evident during the type-A quartz vein stage, and fluid cooling and mixing in the later type-B quartz vein stage. Precipitation of pyrite in the ore zone occurred as four recognized types: arsenic-rich pyrite-1, 2, 3 in the type-A quartz veins and pyrite-4 in the type-B quartz veins. A positive relation between Au and As contents of pyrites suggests that the gold is present together with arsenic in the structure of pyrites of the type-A quartz veins as solid solution in addition to as nanoparticle inclusions. The high Co and Ni contents of pyrites of both the type-A and the type-B quartz veins, with no evidence of CO2 in the system indicate that the ore-forming fluids were epizonal magmatic-hydrothermal fluids rather than metamorphic fluid. The hydrothermal fluids of the Tagun-Khin-Dan deposit were driven by faulting to form the mudstone-hosted epithermal gold mineralization and related to continuing northwards movement of the Indian Plate that initiated the displacement on the strike-slip Sagaing Fault.

DOI： 10.1111/rge.12298

Language：English   Publishing type：Research paper (scientific journal)  

The lithocap at Mankayan is a contiguous zone of alunite + quartz + pyrite that occur as pervasive alteration of the metavolcanic basement and dacitic pyroclastic rocks. Alunite + quartz + pyrite assemblage also occurs within hydrothermal gold-bearing veins and breccias. Several high-sulfidation epithermal gold orebodies have been previously delineated in the Lepanto Main Enargite orebody, and in the Northwest, Carmen, Florence West and Florence East quartz-pyrite-gold (QPG) veins. This study presents new data of mineral composition and sulfur isotopic ratios of alunites from different zones of the lithocap at Mankayan. Elemental composition maps and point analysis of alunites indicate compositional heterogeneity within a single alunite crystal. Common substituents to the K+ site are Na+ and H3O+, with few Ca2+ substitution in some sites. Limited occurrences of PO43- substitution to SO42- were also documented. Sulfur isotopic ratios (delta 34SCDT) of alunite range from + 13 &#37;o to + 24 &#37;o, which are typical of hypogene alunite. Sulfur isotopic ratios of coexisting pyrite are mostly negative, ranging from -5.4 to -1.0 &#37;o. Few samples of alunite from the Northwest and Florence West quartz-pyrite-gold veins have sulfur isotopic ratios similar to the values of its coexisting pyrite. The estimated temperature of formation using sulfur isotope geothermometry of alunite-pyrite pairs ranges from 197 degrees C to 364 degrees C, with most of the samples varying within 220 to 270 degrees C. The calculated bulk delta 34S of the hydrothermal fluid was found to be + 5 to + 6 &#37;o for the different mineralization events in Mankayan. The alunite crystals are heterogeneous even in the microscopic scale. Compositional maps show that K and Na concentration vary within single crystals, as well as among different crystals of a sample. The variations of K and Na content mostly follow the crystal growth structure, however, some alunite crystals with irregular variations are also present. Some samples contain aluminum-phosphate-sulfate (APS) minerals intergrown with alunite. Electron probe microanalysis of the alunite crystals showed a generally wide range of composition between the alunite - natroalunite solid solution. Using thermodynamic functions, a relationship between temperature and K+/Na+ of the hydrothermal fluids was determined across the range of alunite-natroalunite solid solution system. The model curves suggest that at temperatures less than ~ 250 degrees C a slight change in fluid composition and/or temperature can vary the number of Na atoms per formula unit by 0.3 units. At higher temperatures, a more significant change in the physicochemical conditions is required for a substitution to occur. This explains the wide range of Na content in the alunites from the different parts of the lithocap. The characteristics compiled in this study reflect the fluctuations in temperature and fluid compositions that occurred during the multiple hydrothermal events in the Mankayan District.

DOI： 10.1016/j.oregeorev.2022.104959

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The Mazua ultramafic intrusion is among the most promising intrusions hosting Fe-Ti oxide ores in Mozambique. Fe-Ti oxide ores are mainly composed of ilmenite occurring as lenses, veins and layers, either massive or disseminated in hornblende pyroxenite. This study discusses the nature and origin of the intrusion and related ilmenite ore body on the basis of whole-rock and mineral chemistry. Textural and structural evidences support a cumulate origin for these rocks, including the occurrence of relict cumulate textures, layering of alternating oxides and silicate-rich rocks, and size-grading of silicate-rich layers. Primary magmatic features have, however, largely been overprinted by subsolidus processes. The occurrence of the cumulate assemblage (Fe-Ti oxides and clinopyroxene), without plagioclase and olivine, suggests that the magma underwent differentiation before its emplacement. The evolved magmatic nature of the intrusion is consistent with the calculated Mg-number of approximately 50 for the melt in equilibrium with clinopyroxene crystals. The high TiO2 concentrations (>4 wt&#37;) of the evolved magma, by differentiation, are interpreted as the main factors controlling the crystallization of Fe-Ti oxides. We propose that the ores formed from crystallization and settling of Fe-Ti oxide minerals from an evolved basaltic magma. This model is consistent with (1) the occurrence of Fe-Ti oxides and clinopyroxene as cumulates in relation to the coexisting amphibole, (2) the layering structures of alternating oxides and silicate matrix, (3) the scarcity of apatite supported by the extremely low whole-rock P2O5 concentrations and (4) the restricted occurrence of ore veins, excluding the formation from immiscible oxide melts.

DOI： 10.1016/j.oregeorev.2022.104760

Language：English   Publishing type：Research paper (scientific journal)  

Language：Others   Publishing type：Research paper (scientific journal)  

The Mowana hydrothermal Cu deposit is located within the Matsitama–Motloutse Complex in the southwestern part of the Zimbabwe Craton in the northeastern part of Botswana. This study aims to document the characteristics of the mineralization based on geology, quartz textures, ore mineralogy, chlorite geothermometry, and sulfur isotope analyses. The deposit is hosted by the NNE-striking and nearly vertically dipping (70–80°) Bushman Lineament, within the graphitic schist lenses in the carbonaceous and argillaceous metasedimentary rocks of the Neoarchean to Paleoproterozoic Matsitama Sedimentary Group. The hydrothermal alteration of the host rocks is characterized by silicification, chloritization, epidotization, sericitization, hematite, and calcite alteration. Based on the alteration mineral assemblage, the main mineralization stage is attributed to near neutral pH fluids at temperatures between ~200 and ~340°C. The base metal mineralization of the Mowana deposit was evolved in at least two vein types. The first mineralization type, represented by the quartz+calcite±K-feldspar veins and breccias is characterized by the precipitation of principal chalcopyrite with pyrite, minor bornite, and trace amounts of galena. The Type 2 veins represented by the quartz+calcite±fluorite veins, host appreciable amounts of galena. The supergene mineralization widely distributed in the shallow levels of the deposit is manifested by the significant presence of chalcocite, bornite, covellite, anglesite, malachite, and hematite. The temperature obtained from the chlorite geothermometry in the Type 1 veins indicate that the mineralization associated with chlorite alteration formed at a temperature ranging from 340 to 400°C. The ore mineral assemblage: pyrite, bornite, and chalcopyrite, paired with the chlorite geothermometry data indicate that the Type 1 veins formed at an intemediate to high sulfidation state. Sulfur isotopic ratios determined on the sulfides indicate the magmatic S and/or leaching of the host metasedimentary rocks and closed system reduction of seawater sulfate as the sources of S.

DOI： 10.1111/rge.12263

Language：Others   Publishing type：Research paper (scientific journal)  

Northern Mozambique hosts numerous occurrences of gold mineralization in metamorphic terranes, which are little known because of the insufficient studies. In this work, we describe the main geological and geochemical characteristics of the Nanlia and Makorongo gold prospects located in the Namuno district, northeastern Mozambique. We report the mode of occurrence of gold, petrography and mineralogy of the host rocks and ores, fluid inclusion characteristics and stable isotope data, to understand the genesis of gold mineralization in the study area. The gold mineralization in the Nanlia and Makorongo prospects is hosted by the Neoproterozoic Xixano Metamorphic Complex in the Mozambique Belt, which is composed of mafic granulite, amphibolite, paragneiss and marble. The host rock amphibolite consists mainly of amphibole, plagioclase, biotite and minor quartz, titanite and sulfides. The gold mineralization is associated with E-W to ENE-WSW trending quartz veins, oriented parallel to low angle to the foliation of the host rock amphibolite. The ore mineralogy consists of pyrite, pyrrhotite, chalcopyrite, magnetite, galena and sphalerite, with minor tellurides, xilingolite, electrum and native gold. Mineralized quartz veins in the Nanlia and Makorongo prospects host two types of fluid inclusions which locally coexist in the same assemblage: type 1, one-phase CO2 inclusions with final melting temperature between −58 and −52 °C; and type 2, two-phase H2O + NaCl (±CO2 ± N2 ± CH4) inclusions with homogenization temperature ranging from 246 to 370 °C and 239 to 382 °C in the Nanlia and Makorongo prospects, respectively, and salinity of 12–21 wt&#37; NaCl eq. Pressure and temperature (P-T) conditions of ore-formation were estimated from fluid inclusions and sphalerite geobarometry at 420–620 °C and 160–280 MPa, and 330–440 °C and 150–200 MPa in the Nanlia and Makorongo prospects, respectively. The Nanlia and Makorongo gold prospects are classified as orogenic-type gold deposits. We suggest that gold mineralization was caused by an aqueous-carbonic fluid with low-moderate salinity originated by devolatilization during prograde metamorphism of underlying rocks. The gold mineralization post-dates the peak of metamorphism of the host rocks, thus formed during the retrograde metamorphism of the host rocks. The precipitation of gold in the Nanlia and Makorongo prospects was caused by fluid phase separation induced by pressure drop as the mineralizing fluid migrated to shallower depths.

DOI： 10.1016/j.oregeorev.2021.104195

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Several gold deposits are found in the Central Magmatic-Volcanic Belt (CMVB) of Myanmar, which forms a nearly N–S-trending, 1500-km-long arc extending from the Andaman Sea to northern Myanmar. The CMVB consists of Cretaceous granitoids intruded into folded andesites and pillow basalts (Mawgyi Andesite) which rest on cherts, talc-schists, mudstones and phyllites. The EE3 gold deposit is part of gold mineralization in the Thone Myae Song area, located in the Kawlin–Wuntho block in the northern part of the CMVB. The orebodies occur as sulfide-bearing massive quartz veins hosted by Mawgyi Andesite. Based on the mineral assemblages and cross-cutting relationships, three mineralization stages are identified in the EE3 gold deposit: Stage-I quartz-carbonate-sulfide veins; Stage-II quartz-carbonate veins intersecting the Stage-I veins; and Stage-III quartz-carbonate-sulfide veins parallel to the Stage-I veins. The main hydrothermal alteration minerals are sericite, epidote, chlorite and calcite. Three main types of fluid inclusions were distinguished from the mineralized quartz veins hosted by Mawgyi Andesite: liquid-rich aqueous fluid inclusions (Type A), vapor-rich aqueous inclusions (Type B), and H₂O-CO₂-NaCl inclusions (Type C). The latter occurs only in the Stage-I veins. The ore-forming conditions are estimated from fluid inclusions in the Stage-I, Stage-II and Stage-III veins to be at 180 °C and 28 bars, 176 °C and 26 bars, and 158 °C and 21 bars, respectively. The formation pressures of the Stage-I, Stage-II and Stage-III mineralization correspond to a shallow depth of 300 m, 280 m, and 225 m, respectively. Based on the ore and alteration mineral assemblages, and estimated temperature and pressure conditions of the mineralization, the EE3 gold deposit was formed in an epithermal condition.

DOI： 10.1016/j.jseaes.2021.104749

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The Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper-gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry-type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry-type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn-mineralization early-mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite-rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late-mineralization Late Diorite (LD). High XMg of calcic amphiboles (>0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite-rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K-Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K-Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K-Ar ages also indicate earlier formed intrusive rocks in the Southwest prospect, possibly coeval to the earliest “dark diorite” intrusion in the Sto. Tomas II deposit. In addition, the range of δ34S of sulfide minerals from +1.8‰ to +5.1‰ in the Southwest prospect closely overlaps with the rest of the porphyry copper and epithermal deposits in the Sto. Tomas II deposit and its vicinity. This indicates that the sulfides may have formed from a homogeneous source of the porphyry copper deposits and epithermal deposits in the Sto. Tomas II orebody and its vicinity. The evidence presented in this work proves that the porphyry copper-type veinlets and the adjacent potassic alteration in the Southwest prospect are formed earlier and at a shallower level in contrast with the other porphyry deposits in the Baguio District.

DOI： 10.1111/rge.12242

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The Woxi Au-Sb-W deposit is one of the largest polymetallic ore deposits in the Xuefengshan Range, southern China, hosted in low-grade metamorphosed Neoproterozoic volcaniclastic rocks. The orebodies of the deposit are predominantly composed of banded quartz veins, which are strictly controlled by bedding and faults. Petrographic observations and geochemical results are reported on the occurrence of Au and properties of the ore-forming processes for different stages in the deposit. The veins extend vertically up to 2 km without obvious vertical metal zoning. The ore-forming process can be subdivided into four mineralization stages: Pre-ore stage; Early stage (scheelite-quartz stage); Middle stage (pyrite-stibnite-quartz stage); and Late stage (stibnite-quartz sage). Four types of pyrite (Py0, Py1, Py2, and Py3) were identified in the ores and host-rock: Py0 occurs as euhedral grains with voids in the core, ranging in size from 50 to 100 μm and formed mainly in the Pre-ore stage and Early stage; Py1 occurs as subhedral grains. Small grains (around 10 μm) of Py1 form irregularly shaped clusters of variable size ranging from tens to hundreds of μm and mainly formed in the Middle stage; Euhedral-subhedral fine-grained Py2 formed in the Late stage; Minor subhedral fine-grained Py3 was deposited in the Late-stage. Stibnite is widely distributed in the Middle and Late stage ore veins. No systemic difference was recognized in mineralogical features among stibnite formed in different stages. In addition to native gold, the lattice bound Au+1 widely exists in Py1 and Py2 in the deposit, and widespread Py1 is considered as the main Au-bearing mineral with the highest Au contents. Most elements (such as Co, Ni, Cu, As, Sb, Ba, and Pb) are considered to occur as solid solution within the crystal lattice and/or invisible nanoparticles in sulfides minerals. The Co/Ni ratio of most pyrite is lower than 1, suggesting that the metals in the ore-forming fluid are sourced from sedimentary rocks. The coupled behavior between Au and As; Au and Sb suggests that the substitution of As and Sb in pyrite can enhance the incorporation of Au. Variation of trace elements in pyrites of different stages suggests some information on the mineralization processes: Large ion lithophile elements (such as Ba and Pb) are enriched in Py0 indicating that water-rock reaction occurred in the Early stage; Fine-grained Py1 with a heterogeneous distribution of elements suggests fast crystallization of pyrite in the Middle stage.

DOI： 10.1111/rge.12279

Language：English  

The Molopo Farms Complex (MFC) is located near the western margin of the Archean Kaapvaal Craton, in southern Botswana. The complex hosts low grade disseminated Ni-Cu and platinum group elements (PGE) mineralization restricted to the lower ultramafic cumulates, notably in the feldspathic orthopyroxenites. The mineralized feldspathic orthopyroxenites contain up to 0.47 ppm Pt + Pd + Au manifested in the form of platinum group mineral (PGM) assemblages dominated by PGE bismuthotellurides, asernides and minor Au and Ag alloys. The PGM encountered are froodite (PdBi₂), moncheite (PtTe₂), michenerite (PdBiTe), sperrylite (PtAs₂) largely associated with altered silicates and sulfide minerals. The association of PGM with sulfides suggests that they were originally concentrated by sulfide melt, while late stage reaction of sulfides with hydrothermal fluids resulted in the observed spatial proximity of PGM with altered silicates. The Cu/Pd ratios of most of the rocks fall within the primitive mantle range. However, the Cu/Pd ratios of the feldspathic orthopyroxenites are more variable, with few samples falling above and below the primitive mantle range suggesting the prior sulfide extraction from the magmas and the presence of cumulus sulfides. This is supported by the Cu/Zr ratios of these rocks which are also variable above and below unity. Trace element ratios on the (Th/Yb) _PM versus (Nb/Th) _PM plot indicate strong crustal contamination across all units including those not in proximity to the country rocks. The δ³⁴S of the magmatic rocks are variable between −6.3‰ and −11.4‰. In contrast, the δ³⁴S of dolomitic siltstones of the Transvaal Supergroup which constitute the immediate country rocks vary from −4.1‰ to +0.6‰. These data indicate that crustal contamination largely occurred prior to magma emplacement. It is inferred that the most important contaminant and source of crustal S were the Ramotswa and Ditlhojana Formations that include sulfidic shales at depth. We consider that magnesian basaltic magmas of B1 Bushveld magma composition underwent crustal contamination, assimilation of crustal S and segregation of sulfide melt in the feeder conduit or staging-chamber prior to final magma emplacement. The feeder conduit or staging-chamber was subsequently invaded by further B1 magma. This magma entrained some of the sulfides lodged in the plumbing system and flushed them to the final MFC chamber studied here. After the staging-chamber had already partially solidified, it was invaded by yet another influx of magma, possibly even more primitive than the B1 Bushveld magma. Being a crystal mush, this magma assimilated and entrained some of the previously formed orthopyroxenites manifested by fragments of orthopyroxenite in the harzburgites of the final MFC chamber. The presence of centimeter-sized globular sulfides and fragments of orthopyroxenite within harzburgites suggests that the complex was emplaced as separate pulses of magmas. Therefore, it is considered that sulfide accumulations may remain undiscovered in the feeder zones or the staging-chamber.

DOI： 10.1016/j.oregeorev.2020.103731

Language：English  

The overprinting episodes of porphyry-type and epithermal-type mineralization in the Mankayan District, northern Luzon, Philippines allow an investigation on variation of geochemical signatures with different alteration assemblages. Due to the multiple hydrothermal activities in Mankayan, some older porphyry-type deposits have been overprinted by acid-sulfate alteration that is commonly associated with high-sulfidation epithermal mineralization. In this study, we analyzed metavolcanic basement rocks and dioritic rocks that host porphyry-type mineralization in the Far Southeast deposit, Honeycomb prospect and Christine prospect, which all have near-neutral pH alteration assemblage of illite/muscovite + chlorite ± quartz. We compared their geochemical data with those of the Fatima porphyry deposit, which was overprinted by quartz + alunite ± kaolinite/dickite alteration. Furthermore, we also compared the geochemical data of the metavolcanic and dioritic rocks in the Carmen and Florence prospects hosting quartz-pyrite-gold and enargite veins which overprinted earlier porphyry-type mineralization. N-MORB-normalized multi-element diagrams show that the host rocks preserve negative anomalies of high field strength elements (HFSEs) that are typical of magmas generated in a supra-subduction zone setting. The non-mineralized metavolcanic and dioritic rocks show variable signature of the large ion lithophiles (LILEs), while the altered metavolcanic and dioritic rocks show a more consistent signature. Negative anomaly of Rb is associated with acid-sulfate alteration, while positive anomaly of Rb was observed in the dioritic rocks that have been altered by near-neutral pH fluids. Furthermore, acid-sulfate alteration significantly added LREEs and depleted HREEs compared to the near-neutral pH alteration. Mass changes in altered rocks were determined using the isocon technique. Mass changes are generally more pronounced in the acid-sulfate altered rocks compared to the near-neutral pH altered rocks. The metavolcanic rocks altered to quartz + alunite in Carmen and Florence significantly gained SiO₂, Al₂O₃ and S, and lost Na₂O, CaO, MgO and Fe₂O₃. The dioritic and metavolcanic rocks altered to chlorite + illite in the Far Southeast, Honeycomb, Christine and Fatima porphyry deposits lost SiO₂ and Al₂O₃, while the concentrations of other elements remain relatively unchanged. The pH-dependence of the geochemical behavior of Rb in hydrothermal conditions was utilized to construct new molar element ratios that could differentiate the rocks that underwent K-metasomatism either under near-neutral pH or acidic conditions. The recognition of this behavior could be useful in a routine lithogeochemical analysis that is being used in exploration.

DOI： 10.1016/j.gexplo.2020.106612

Language：Others   Publishing type：Research paper (scientific journal)  

© 2020 Elsevier B.V. The Molopo Farms Complex (MFC) is located near the western margin of the Archean Kaapvaal Craton, in southern Botswana. The complex hosts low grade disseminated Ni-Cu and platinum group elements (PGE) mineralization restricted to the lower ultramafic cumulates, notably in the feldspathic orthopyroxenites. The mineralized feldspathic orthopyroxenites contain up to 0.47 ppm Pt + Pd + Au manifested in the form of platinum group mineral (PGM) assemblages dominated by PGE bismuthotellurides, asernides and minor Au and Ag alloys. The PGM encountered are froodite (PdBi2), moncheite (PtTe2), michenerite (PdBiTe), sperrylite (PtAs2) largely associated with altered silicates and sulfide minerals. The association of PGM with sulfides suggests that they were originally concentrated by sulfide melt, while late stage reaction of sulfides with hydrothermal fluids resulted in the observed spatial proximity of PGM with altered silicates. The Cu/Pd ratios of most of the rocks fall within the primitive mantle range. However, the Cu/Pd ratios of the feldspathic orthopyroxenites are more variable, with few samples falling above and below the primitive mantle range suggesting the prior sulfide extraction from the magmas and the presence of cumulus sulfides. This is supported by the Cu/Zr ratios of these rocks which are also variable above and below unity. Trace element ratios on the (Th/Yb) PM versus (Nb/Th) PM plot indicate strong crustal contamination across all units including those not in proximity to the country rocks. The δ34S of the magmatic rocks are variable between −6.3‰ and −11.4‰. In contrast, the δ34S of dolomitic siltstones of the Transvaal Supergroup which constitute the immediate country rocks vary from −4.1‰ to +0.6‰. These data indicate that crustal contamination largely occurred prior to magma emplacement. It is inferred that the most important contaminant and source of crustal S were the Ramotswa and Ditlhojana Formations that include sulfidic shales at depth. We consider that magnesian basaltic magmas of B1 Bushveld magma composition underwent crustal contamination, assimilation of crustal S and segregation of sulfide melt in the feeder conduit or staging-chamber prior to final magma emplacement. The feeder conduit or staging-chamber was subsequently invaded by further B1 magma. This magma entrained some of the sulfides lodged in the plumbing system and flushed them to the final MFC chamber studied here. After the staging-chamber had already partially solidified, it was invaded by yet another influx of magma, possibly even more primitive than the B1 Bushveld magma. Being a crystal mush, this magma assimilated and entrained some of the previously formed orthopyroxenites manifested by fragments of orthopyroxenite in the harzburgites of the final MFC chamber. The presence of centimeter-sized globular sulfides and fragments of orthopyroxenite within harzburgites suggests that the complex was emplaced as separate pulses of magmas. Therefore, it is considered that sulfide accumulations may remain undiscovered in the feeder zones or the staging-chamber.

DOI： 10.1016/j.oregeorev.2020.103731

Language：Others   Publishing type：Research paper (scientific journal)  

© 2020 Elsevier B.V. The overprinting episodes of porphyry-type and epithermal-type mineralization in the Mankayan District, northern Luzon, Philippines allow an investigation on variation of geochemical signatures with different alteration assemblages. Due to the multiple hydrothermal activities in Mankayan, some older porphyry-type deposits have been overprinted by acid-sulfate alteration that is commonly associated with high-sulfidation epithermal mineralization. In this study, we analyzed metavolcanic basement rocks and dioritic rocks that host porphyry-type mineralization in the Far Southeast deposit, Honeycomb prospect and Christine prospect, which all have near-neutral pH alteration assemblage of illite/muscovite + chlorite ± quartz. We compared their geochemical data with those of the Fatima porphyry deposit, which was overprinted by quartz + alunite ± kaolinite/dickite alteration. Furthermore, we also compared the geochemical data of the metavolcanic and dioritic rocks in the Carmen and Florence prospects hosting quartz-pyrite-gold and enargite veins which overprinted earlier porphyry-type mineralization. N-MORB-normalized multi-element diagrams show that the host rocks preserve negative anomalies of high field strength elements (HFSEs) that are typical of magmas generated in a supra-subduction zone setting. The non-mineralized metavolcanic and dioritic rocks show variable signature of the large ion lithophiles (LILEs), while the altered metavolcanic and dioritic rocks show a more consistent signature. Negative anomaly of Rb is associated with acid-sulfate alteration, while positive anomaly of Rb was observed in the dioritic rocks that have been altered by near-neutral pH fluids. Furthermore, acid-sulfate alteration significantly added LREEs and depleted HREEs compared to the near-neutral pH alteration. Mass changes in altered rocks were determined using the isocon technique. Mass changes are generally more pronounced in the acid-sulfate altered rocks compared to the near-neutral pH altered rocks. The metavolcanic rocks altered to quartz + alunite in Carmen and Florence significantly gained SiO2, Al2O3 and S, and lost Na2O, CaO, MgO and Fe2O3. The dioritic and metavolcanic rocks altered to chlorite + illite in the Far Southeast, Honeycomb, Christine and Fatima porphyry deposits lost SiO2 and Al2O3, while the concentrations of other elements remain relatively unchanged. The pH-dependence of the geochemical behavior of Rb in hydrothermal conditions was utilized to construct new molar element ratios that could differentiate the rocks that underwent K-metasomatism either under near-neutral pH or acidic conditions. The recognition of this behavior could be useful in a routine lithogeochemical analysis that is being used in exploration.

DOI： 10.1016/j.gexplo.2020.106612

Language：English   Publishing type：Research paper (scientific journal)  

Several high-sulfidation epithermal gold orebodies in the Mankayan Mineral District were formed in an environment that has been already affected by earlier porphyry-type mineralization. This study reports the geologic and geochemical characteristics of the Carmen and Florence epithermal orebodies, which are located in the south of the Lepanto main enargite–gold orebody. The gold-bearing epithermal quartz veins in the Carmen and Florence areas are of two types: (i) the enargite-rich veins and (ii) the quartz–pyrite–gold (QPG) veins. The two types of veins are mainly hosted by the Cretaceous Lepanto Metavolcanics basement rocks, with minor veins cutting the Pleistocene Imbanguila Dacite Pyroclastics. The mineral assemblages and homogenization temperatures of fluid inclusions indicate that the Carmen and Florence orebodies were deposited by fluids varying from high to very high sulfidation state. The enargite and QPG epithermal veins of Carmen and Florence cut porphyry-type quartz veinlet stockworks and veins that host polyphase hypersaline fluid inclusions that did not homogenize at or below 400°C. These high-temperature quartz exhibits distinctly different mineral chemistry from the quartz of the QPG and enargite-rich epithermal veins. In particular, the Ti content of quartz of the porphyry-type veinlet stockwork is elevated (>100 ppm), whereas the Ti concentration of the epithermal vein quartz crystals are below detection limits. The Fe concentration of quartz is high in epithermal vein quartz (>300 ppm), whereas nearly undetected in the porphyry-type stockwork veinlet quartz. Multiple generations of quartz with different mineral chemistry, fluid inclusions morphology, temperature, salinity and bulk gas compositions, and stable isotopic ratios indicate the variable hydrothermal conditions throughout the mineralization history of the Mankayan District. The temperature, pH, sulfidation state, oxidation state, and fluid composition vary among the orebodies in Carmen and Florence areas. Furthermore, the characteristics of earlier alteration affected the apparent characteristics of subsequent mineralization.

DOI： 10.1111/rge.12214

Language：Others   Publishing type：Research paper (scientific journal)  

© 2019 The Society of Resource Geology The Kay Tanda epithermal Au deposit in Lobo, Batangas is one of the Au deposits situated in the Batangas Mineral District in southern Luzon, Philippines. This study aims to document the geological, alteration, and mineralization characteristics and to determine the age of the mineralization, the mechanism of ore deposition, and the hydrothermal fluid characteristics of the Kay Tanda deposit. The geology of Kay Tanda consists of (i) the Talahib Volcanic Sequence, a Middle Miocene dacitic to andesitic volcaniclastic sequence that served as the host rock of the mineralization; (ii) the Balibago Diorite Complex, a cogenetic intrusive complex intruding the Talahib Volcanic Sequence; (iii) the Calatagan Formation, a Late Miocene to Early Pliocene volcanosedimentary formation unconformably overlying the Talahib Volcanic Sequence; (iv) the Dacite Porphyry Intrusives, which intruded the older lithological units; and (v) the Balibago Andesite, a Pliocene postmineralization volcaniclastic unit. K-Ar dating on illite collected from the alteration haloes around quartz veins demonstrated that the age of mineralization is around 5.9 ± 0.2 to 5.5 ± 0.2 Ma (Late Miocene). Two main styles of mineralization are identified in Kay Tanda. The first style is an early-stage extensive epithermal mineralization characterized by stratabound Au-Ag-bearing quartz stockworks hosted at the shallower levels of the Talahib Volcanic Sequence. The second style is a late-stage base metal (Zn, Pb, and Cu) epithermal mineralization with local bonanza-grade Au mineralization hosted in veins and hydrothermal breccias that are intersected at deeper levels of the Talahib Volcanic Sequence and at the shallower levels of the Balibago Intrusive Complex. Paragenetic studies on the mineralization in Kay Tanda defined six stages of mineralization; the first two belong to the first mineralization style, while the last four belong to the second mineralization style. Stage 1 is composed of quartz ± pyrophyllite ± dickite/kaolinite ± diaspore alteration, which is cut by quartz veins. Stage 2 is composed of Au-Ag-bearing quartz stockworks associated with pervasive illite ± quartz ± smectite ± kaolinite alteration. Stage 3 is composed of carbonate veins with minor base metal sulfides. Stage 4 is composed of quartz ± adularia ± calcite veins and hydrothermal breccias, hosting the main base metal and bonanza-grade Au mineralization, and is associated with chlorite-illite-quartz alteration. Stage 5 is composed of epidote-carbonate veins associated with epidote-calcite-chlorite alteration. Stage 6 is composed of anhydrite-gypsum veins with minor base metal mineralization. The alteration assemblage of the deposit evolved from an acidic mineral assemblage caused by the condensation of magmatic volatiles from the Balibago Intrusive Complex into the groundwater to a slightly acidic mineral assemblage caused by the interaction of the host rocks and the circulating hydrothermal waters being heated up by the Dacite Porphyry Intrusives to a near-neutral pH toward the later parts of the mineralization. Fluid inclusion microthermometry indicates that the temperature of the system started to increase during Stage 1 (T = 220–250°C) and remained at high temperatures (T = 250–290°C) toward Stage 6 due to the continuous intrusion of Dacite Porphyry Intrusives at depth. Salinity slightly decreased toward the later stages due to the contribution of more meteoric waters into the hydrothermal system. Boiling is considered the main mechanism of ore deposition based on the occurrence of rhombic adularia, the heterogeneous trapping of fluid inclusions of variable liquid–vapor ratios, the distribution of homogenization temperatures, and the gas ratios obtained from the quantitative fluid inclusion gas analysis of quartz. Ore mineral assemblage and sulfur fugacity determined from the FeS content of sphalerite at temperatures estimated by fluid inclusion microthermometry indicate that the base metal mineralization at Kay Tanda evolved from a high sulfidation to an intermediate sulfidation condition.

DOI： 10.1111/rge.12205

Language：English  

The Utanobori gold deposit is a low-sulfidation, epithermal vein-type deposit located in northern Hokkaido, Japan. The deposit is hosted by conglomerate, sandstone, and tuff of the Middle to Late Miocene Esashi Formation. These rocks were hydrothermally altered. Silica sinters and quartz-adularia veins are common in the deposit. The quartz-adularia veins either contain a ginguro band, which corresponds to the main gold-bearing vein (Type 1 Veins), or do not contain a ginguro band but contain minor adularia (Type 2 Veins). Type 1 Veins are divided into three stages with 12–14 substages. Ore minerals identified include electrum, naumannite, chlorargyrite, bromargyrite, an unidentified Fe-Sb mineral, and an Fe-(Sb)-As mineral. These ore minerals formed in the main mineralization stages I (bands I-b and I-d) and II (band II-a). Scanning electron microscopy with cathodoluminescence images show that cathodoluminescence-dark microcrystalline quartz exhibiting colloform (ghost-sphere) texture is closely associated with ore minerals in the Type 1 Vein and Type 2 Vein, and the Al and K contents of such quartz are commonly '1000 ppm. This indicates that the ore minerals were crystallized from alkaline, silica-saturated fluids at temperatures '200°C, which initially deposited amorphous silica that was recrystallized to microcrystalline quartz. The average Au content of electrum is 52.5 at&#37; Au (n = 10), 65.7 at&#37; Au (n = 20), and 55.5 at&#37; Au (n = 5) in bands I-b, I-d, and II-a, respectively, of Type 1 Veins. The δ³⁴S_CDT values of two fine-grained disseminated pyrites in the altered conglomerate and bedded tuff in the argillic altered zone are −4.3 and −4.2‰. Ar-Ar dating on adularia yielded 13.6 ± 0.06 Ma, 13.6 ± 0.07 Ma, and 13.6 ± 0.06 Ma for the stages I, II, and III of the Type 1 Vein, respectively. K-Ar ages determined on adularia in the silica sinter and on whole-rock of glassy rhyolite of the Esashi Formation are 15.0 ± 0.4 Ma and 14.6 ± 0.4 Ma, respectively. These radiometric ages indicate that silica sinter associated with the rhyolitic volcanic rocks formed prior to the main gold mineralization.

DOI： 10.1111/rge.12211

Language：English  

The Poboya Prospect lies along the North Northwest - South Southeast Palu-Koro Fault Zone in the central part of the West Sulawesi Arc. The geology of the area consists of the Palu Metamorphic Complex overlain by the Paleogene-Neogene Tinombo Formation of volcanosedimentary rocks, the Celebes Molasse sediment, and Late Cenozoic granitic rocks. Petrography, scanning electron microscope with energy-dispersive spectrometry (SEM-EDS), electron probe microanalyzer (EPMA), and fluid inclusion microthermometry were carried out to examine vein textures, ore mineralogy, and characteristics of the ore-forming fluid responsible for mineralization in the River Reef Zone, the Poboya Prospect. Textures of quartz-carbonate veins in the River Reef Zone include massive micro-comb, moss, colloform, crustiform, mosaic, feathery, flamboyant, lattice bladed, ghost bladed, parallel bladed, and saccharoidal textures representing primary growth, recrystallization, and replacement. The homogenization temperature and fluid salinity are 240–250°C and 0.3–0.7 wt&#37; NaCl eq., respectively. Ore minerals precipitated in the early stage consist of electrum, naumannite-aguilarite, chalcopyrite, pyrite, marcasite, sphalerite, and pyrrhotite. Apart from pyrrhotite, these ore minerals were also precipitated in the late stage along with selenopolybasite, freibergite, argyrodite, pyrargyrite, and galena. Selenium more preferably occurs as the crystallographic replacement of sulfur in naumannite-aguilarite, argyrodite, pyrargyrite, selenopolybasite, and freibergite instead of as independent selenide minerals. The low-sulfidation epithermal deposit in the River Reef Zone, the Poboya Prospect, illustrates the potential of the West Sulawesi Arc, particularly along the Palu-Koro Fault Zone, to host epithermal gold mineralization.

DOI： 10.1111/rge.12206

Language：Others   Publishing type：Research paper (scientific journal)  

© 2019 The Society of Resource Geology The Utanobori gold deposit is a low-sulfidation, epithermal vein-type deposit located in northern Hokkaido, Japan. The deposit is hosted by conglomerate, sandstone, and tuff of the Middle to Late Miocene Esashi Formation. These rocks were hydrothermally altered. Silica sinters and quartz-adularia veins are common in the deposit. The quartz-adularia veins either contain a ginguro band, which corresponds to the main gold-bearing vein (Type 1 Veins), or do not contain a ginguro band but contain minor adularia (Type 2 Veins). Type 1 Veins are divided into three stages with 12–14 substages. Ore minerals identified include electrum, naumannite, chlorargyrite, bromargyrite, an unidentified Fe-Sb mineral, and an Fe-(Sb)-As mineral. These ore minerals formed in the main mineralization stages I (bands I-b and I-d) and II (band II-a). Scanning electron microscopy with cathodoluminescence images show that cathodoluminescence-dark microcrystalline quartz exhibiting colloform (ghost-sphere) texture is closely associated with ore minerals in the Type 1 Vein and Type 2 Vein, and the Al and K contents of such quartz are commonly '1000 ppm. This indicates that the ore minerals were crystallized from alkaline, silica-saturated fluids at temperatures '200°C, which initially deposited amorphous silica that was recrystallized to microcrystalline quartz. The average Au content of electrum is 52.5 at&#37; Au (n = 10), 65.7 at&#37; Au (n = 20), and 55.5 at&#37; Au (n = 5) in bands I-b, I-d, and II-a, respectively, of Type 1 Veins. The δ34SCDT values of two fine-grained disseminated pyrites in the altered conglomerate and bedded tuff in the argillic altered zone are −4.3 and −4.2‰. Ar-Ar dating on adularia yielded 13.6 ± 0.06 Ma, 13.6 ± 0.07 Ma, and 13.6 ± 0.06 Ma for the stages I, II, and III of the Type 1 Vein, respectively. K-Ar ages determined on adularia in the silica sinter and on whole-rock of glassy rhyolite of the Esashi Formation are 15.0 ± 0.4 Ma and 14.6 ± 0.4 Ma, respectively. These radiometric ages indicate that silica sinter associated with the rhyolitic volcanic rocks formed prior to the main gold mineralization.

DOI： 10.1111/rge.12211

Language：Others   Publishing type：Research paper (scientific journal)  

© 2019 The Society of Resource Geology The Poboya Prospect lies along the North Northwest - South Southeast Palu-Koro Fault Zone in the central part of the West Sulawesi Arc. The geology of the area consists of the Palu Metamorphic Complex overlain by the Paleogene-Neogene Tinombo Formation of volcanosedimentary rocks, the Celebes Molasse sediment, and Late Cenozoic granitic rocks. Petrography, scanning electron microscope with energy-dispersive spectrometry (SEM-EDS), electron probe microanalyzer (EPMA), and fluid inclusion microthermometry were carried out to examine vein textures, ore mineralogy, and characteristics of the ore-forming fluid responsible for mineralization in the River Reef Zone, the Poboya Prospect. Textures of quartz-carbonate veins in the River Reef Zone include massive micro-comb, moss, colloform, crustiform, mosaic, feathery, flamboyant, lattice bladed, ghost bladed, parallel bladed, and saccharoidal textures representing primary growth, recrystallization, and replacement. The homogenization temperature and fluid salinity are 240–250°C and 0.3–0.7 wt&#37; NaCl eq., respectively. Ore minerals precipitated in the early stage consist of electrum, naumannite-aguilarite, chalcopyrite, pyrite, marcasite, sphalerite, and pyrrhotite. Apart from pyrrhotite, these ore minerals were also precipitated in the late stage along with selenopolybasite, freibergite, argyrodite, pyrargyrite, and galena. Selenium more preferably occurs as the crystallographic replacement of sulfur in naumannite-aguilarite, argyrodite, pyrargyrite, selenopolybasite, and freibergite instead of as independent selenide minerals. The low-sulfidation epithermal deposit in the River Reef Zone, the Poboya Prospect, illustrates the potential of the West Sulawesi Arc, particularly along the Palu-Koro Fault Zone, to host epithermal gold mineralization.

DOI： 10.1111/rge.12206

Language：English  

The Kay Tanda epithermal Au deposit in Lobo, Batangas is one of the Au deposits situated in the Batangas Mineral District in southern Luzon, Philippines. This study aims to document the geological, alteration, and mineralization characteristics and to determine the age of the mineralization, the mechanism of ore deposition, and the hydrothermal fluid characteristics of the Kay Tanda deposit. The geology of Kay Tanda consists of (i) the Talahib Volcanic Sequence, a Middle Miocene dacitic to andesitic volcaniclastic sequence that served as the host rock of the mineralization; (ii) the Balibago Diorite Complex, a cogenetic intrusive complex intruding the Talahib Volcanic Sequence; (iii) the Calatagan Formation, a Late Miocene to Early Pliocene volcanosedimentary formation unconformably overlying the Talahib Volcanic Sequence; (iv) the Dacite Porphyry Intrusives, which intruded the older lithological units; and (v) the Balibago Andesite, a Pliocene postmineralization volcaniclastic unit. K-Ar dating on illite collected from the alteration haloes around quartz veins demonstrated that the age of mineralization is around 5.9 ± 0.2 to 5.5 ± 0.2 Ma (Late Miocene). Two main styles of mineralization are identified in Kay Tanda. The first style is an early-stage extensive epithermal mineralization characterized by stratabound Au-Ag-bearing quartz stockworks hosted at the shallower levels of the Talahib Volcanic Sequence. The second style is a late-stage base metal (Zn, Pb, and Cu) epithermal mineralization with local bonanza-grade Au mineralization hosted in veins and hydrothermal breccias that are intersected at deeper levels of the Talahib Volcanic Sequence and at the shallower levels of the Balibago Intrusive Complex. Paragenetic studies on the mineralization in Kay Tanda defined six stages of mineralization; the first two belong to the first mineralization style, while the last four belong to the second mineralization style. Stage 1 is composed of quartz ± pyrophyllite ± dickite/kaolinite ± diaspore alteration, which is cut by quartz veins. Stage 2 is composed of Au-Ag-bearing quartz stockworks associated with pervasive illite ± quartz ± smectite ± kaolinite alteration. Stage 3 is composed of carbonate veins with minor base metal sulfides. Stage 4 is composed of quartz ± adularia ± calcite veins and hydrothermal breccias, hosting the main base metal and bonanza-grade Au mineralization, and is associated with chlorite-illite-quartz alteration. Stage 5 is composed of epidote-carbonate veins associated with epidote-calcite-chlorite alteration. Stage 6 is composed of anhydrite-gypsum veins with minor base metal mineralization. The alteration assemblage of the deposit evolved from an acidic mineral assemblage caused by the condensation of magmatic volatiles from the Balibago Intrusive Complex into the groundwater to a slightly acidic mineral assemblage caused by the interaction of the host rocks and the circulating hydrothermal waters being heated up by the Dacite Porphyry Intrusives to a near-neutral pH toward the later parts of the mineralization. Fluid inclusion microthermometry indicates that the temperature of the system started to increase during Stage 1 (T = 220–250°C) and remained at high temperatures (T = 250–290°C) toward Stage 6 due to the continuous intrusion of Dacite Porphyry Intrusives at depth. Salinity slightly decreased toward the later stages due to the contribution of more meteoric waters into the hydrothermal system. Boiling is considered the main mechanism of ore deposition based on the occurrence of rhombic adularia, the heterogeneous trapping of fluid inclusions of variable liquid–vapor ratios, the distribution of homogenization temperatures, and the gas ratios obtained from the quantitative fluid inclusion gas analysis of quartz. Ore mineral assemblage and sulfur fugacity determined from the FeS content of sphalerite at temperatures estimated by fluid inclusion microthermometry indicate that the base metal mineralization at Kay Tanda evolved from a high sulfidation to an intermediate sulfidation condition.

DOI： 10.1111/rge.12205

Language：English   Publishing type：Research paper (scientific journal)  

The Salu Bulo prospect is one of the gold prospects in the Awak Mas project in the central part of the western province, Sulawesi, Indonesia. The gold mineralization is hosted by the meta-sedimentary rocks intercalated with the meta-volcanic and volcaniclastic rocks of the Latimojong Metamorphic Complex. The ores are approximately three meters thick, consisting of veins, stockwork, and breccias. The veins can be classified into three stages, namely, early, main, and late stages, and gold mineralization is related to the main stage. The mineral assemblage of the matrix of breccia and the veins are both composed of quartz, carbonate (mainly ankerite), and albite. High-grade gold ores in the Salu Bulo prospect are accompanied by intense alteration, such as carbonatization, albitization, silicification, and sulfidation along the main stage veins and breccia. Alteration mineral assemblage includes ankerite ± calcite, quartz, albite, and pyrite along with minor sericite. Pyrite is the most abundant sulfide mineral that is spatially related to native gold and electrum (<2–42 μm in size). It is more abundant as dissemination in the altered host rocks than those in veins. This suggests that water–rock interaction played a role to precipitate pyrite and Au in the Salu Bulo prospect. The Au contents of intensely altered host rocks and ores have positive correlations with Ag, Ni, Mo, and Na. Fluid inclusions in the veins of the main stage and the matrix of breccia are mainly two-phase liquid-rich inclusions with minor two-phase, vapor-rich, and single-phase liquid or vapor inclusions. CO
₂
and N
₂
gases are detected in the fluid inclusions by Laser Raman microspectrometry. Fluid boiling probably occurred when the fluid was trapped at approximately 120–190 m below the paleo water table. δ
¹⁸
O
_SMOW
values of fluid, +5.8 and +7.6‰, calculated from δ
¹⁸
O
_SMOW
of quartz from the main stage vein indicate oxygen isotopic exchange with wall rocks during deep circulation. δ
³⁴
S
_CDT
of pyrite narrowly ranges from −2.0 to +3.4‰, suggesting a single source of sulfur. Gold mineralization in the Salu Bulo prospect occurred in an epithermal condition, after the metamorphism of the host rocks. It formed at a relatively shallow depth from fluids with low to moderate salinity (3.0–8.5 wt&#37; NaCl equiv.). The temperature and pressure of ore formation range from 190 to 210°C and 1.2 to 1.9 MPa, respectively.

DOI： 10.1111/rge.12193

Language：Others   Publishing type：Research paper (scientific journal)  

© 2018 The Society of Resource Geology The Shwe Min Bon Cu–Au skarn deposit lies within one of the largest Au–Cu belts in Myanmar. The deposit is situated along the Shan scarp zone, which marks the boundary between the Myanmar central basin to the west and the Shan plateau to the east. The Shwe Min Bon deposit comprises skarn-type metasomatic alteration, and the Cu–Au mineralization occurs along the contact face between the Nwabangyi Dolomite and Shweminbon Formation and the Cretaceous dioritic rocks. The metasomatic process resulted in pro- and retrograde mineral assemblages in exoskarn. Hydrothermal activities in the Shwe Min Bon deposit are classified into prograde, retrograde stage I, and retrograde stage II. The prograde skarn is classified into a proximal garnet skarn with minor clinopyroxene and a distal wollastonite skarn. Chlorite, epidote, and tremolite–actinolite were formed during the retrograde stage I. Cu–Au mineralization mainly occurred in retrograde stage I, which was characterized by moderate temperatures (260–320 °C) and fluid with a moderate salinity (5.0–6.0&#37; NaCl equiv.). Low temperature (180–200 °C) and low salinity (2.0–3.0&#37; NaCl equiv.) were responsible for retrograde stage II. Au mineralization is mainly associated with chalcopyrite and tennantite in retrograde stage I and with tellurobismuthite in retrograde stage II.

DOI： 10.1111/rge.12187

Language：English  

The Shwe Min Bon Cu–Au skarn deposit lies within one of the largest Au–Cu belts in Myanmar. The deposit is situated along the Shan scarp zone, which marks the boundary between the Myanmar central basin to the west and the Shan plateau to the east. The Shwe Min Bon deposit comprises skarn-type metasomatic alteration, and the Cu–Au mineralization occurs along the contact face between the Nwabangyi Dolomite and Shweminbon Formation and the Cretaceous dioritic rocks. The metasomatic process resulted in pro- and retrograde mineral assemblages in exoskarn. Hydrothermal activities in the Shwe Min Bon deposit are classified into prograde, retrograde stage I, and retrograde stage II. The prograde skarn is classified into a proximal garnet skarn with minor clinopyroxene and a distal wollastonite skarn. Chlorite, epidote, and tremolite–actinolite were formed during the retrograde stage I. Cu–Au mineralization mainly occurred in retrograde stage I, which was characterized by moderate temperatures (260–320 °C) and fluid with a moderate salinity (5.0–6.0&#37; NaCl equiv.). Low temperature (180–200 °C) and low salinity (2.0–3.0&#37; NaCl equiv.) were responsible for retrograde stage II. Au mineralization is mainly associated with chalcopyrite and tennantite in retrograde stage I and with tellurobismuthite in retrograde stage II.

DOI： 10.1111/rge.12187

Language：English  

The Northwest quartz-pyrite-gold veins are situated 500 m east of the Lepanto fault in Mankayan, Luzon, Philippines. Most vein mineralization is hosted by the Lepanto metavolcanic basement rocks at an elevation between 700 and 1,050 m. The earliest stage, stage 1, is characterized by sphalerite + chalcopyrite + pyrite ± magnetite veins cutting the host rocks that were altered to chlorite + illite + epidote. Precious metal deposition started in stage 2 as electrum, native gold, and gold-silver tellurides deposited with pyrite, quartz, and carbonate. Deposition of gold and silver tellurides continued in stage 3a with abundant pyrite and tennantite-tetrahedrite solid solution intergrown with chalcopyrite, bornite, and minor sphalerite. The stage 3a veins and host-rock alteration are characterized by abundant muscovite and quartz, while the stage 3b veins and alteration consist of quartz, pyrophyllite, alunite, and dickite. Enargite and luzonite are the dominant sulfide minerals in stage 4, which are either disseminated in silicified host rock or within wide quartz veins. Lesser amounts of quartz and abundant pyrite with inclusions of enargite and luzonite were precipitated in stage 5. Microthermometry on fluid inclusions in quartz of stages 2, 3a, and 4 indicates boiling of the hydrothermal fluids. Bulk gas analysis on fluid inclusions in quartz shows that the stage 2 and 4 fluids had components derived from basaltic and andesitic magma, respectively. Fluids that formed stage 4 quartz were more diluted by meteoric water than the fluids that formed the stage 2 veins. Radiometric 40Ar/39Ar dating on alunite separated from the stage 3b advanced argillic alteration zone yielded 2.2 ± 0.1 Ma. Sulfur isotope compositions of the Northwest quartz-pyrite-gold deposit reveal a bulk δ34S of approximately 5, similar to the calculated value for the adjacent Far Southeast porphyry deposit. Calculated oxygen and hydrogen isotope ratios of the fluids of the Northwest quartz-pyrite-gold deposit stage 3b dickites are similar to those that formed the illite alteration in the Far Southeast porphyry deposit but are higher in δ18O when compared to the fluids that formed the kandites in the Lepanto enargite deposit. The northward cooling of mineralizing fluids previously reported in the Lepanto enargite deposit is not consistent with the mineralogic indications in the Northwest quartz-pyrite-gold deposit. These data indicate multiple mineralization events in the Mankayan district, which is one of the largest mineral districts in the western Pacific.

DOI： 10.5382/econgeo.2018.4606

Language：Others   Publishing type：Research paper (scientific journal)  

© 2017 Elsevier B.V. The Kago deposit is a small deposit located at the southern tip of the Satsuma Peninsula of Southern Kyushu, Japan. It lies proximal to the well-known Nansatsu-type mineralisation province dominated by high-sulfidation type epithermal deposits. The deposit was heavily mined in the 18 th Century, largely for its relatively higher gold compared to that of surrounding and regional deposits. The Kago deposit is a typical low-sulfidation deposit, characterised by adularia-quartz veins, composed of electrum, Ag-tetrahedrite, polybasite, chalcopyrite and pyrite. Based on mine records, the grade ranged from 4.1 to 13.3 g/t Au and 2.6–6.6 g/t Ag. Alteration grades from low to high temperature argillic into a propylitic zone at the extremes of the vein exposures. Carbonate is absent. Fluid inclusion microthermometry reveals a typical temperature range of 220–240 °C with salinity of 0.7–2.6 NaCl eq. wt&#37;. Electrum from high-grade ore ranges from 66 to 69 wt&#37; Au. 40Ar/39Ar age dating of adularia bearing colloform/crustiform and brecciated veins, suggests a mineralisation event from 4.23 to 4.0 Ma. δ18O of veined and silicified quartz ranges from +4.0 to +18.4‰. δ18OH2O of fluids in equilibrium with quartz, in the dominant range of measured fluid inclusion temperatures, ranges from −6.5‰ to −0.2‰. δ34S of pyrite has a narrow range from −1.8 to 2.7‰. The deposit lies at the northern extent of the classic Nansatsu high-sulfidation epithermal area, in which a number of silicified bodies punctuate the region in a roughly semi-circular shape. The Kago deposit lies within the principle mineralisation age range of the high-sulfidation deposits, which range from 5.5 to 3.7 Ma. The structural displacement of the Kago deposit from the Nansatsu mineralisation and the differing host rocks has greatly influenced alteration, ore and rock-water interaction of the ore depositing fluids. Here we seek to establish the relationship that this extended mineral province has between the differing styles of mineralisation.

DOI： 10.1016/j.oregeorev.2017.10.027

Language：Others   Publishing type：Research paper (scientific journal)  

© 2018 Society of Economic Geologists, Inc.All Rights Reserved. The Northwest quartz-pyrite-gold veins are situated 500 m east of the Lepanto fault in Mankayan, Luzon, Philippines. Most vein mineralization is hosted by the Lepanto metavolcanic basement rocks at an elevation between 700 and 1,050 m. The earliest stage, stage 1, is characterized by sphalerite + chalcopyrite + pyrite ± magnetite veins cutting the host rocks that were altered to chlorite + illite + epidote. Precious metal deposition started in stage 2 as electrum, native gold, and gold-silver tellurides deposited with pyrite, quartz, and carbonate. Deposition of gold and silver tellurides continued in stage 3a with abundant pyrite and tennantite-tetrahedrite solid solution intergrown with chalcopyrite, bornite, and minor sphalerite. The stage 3a veins and host-rock alteration are characterized by abundant muscovite and quartz, while the stage 3b veins and alteration consist of quartz, pyrophyllite, alunite, and dickite. Enargite and luzonite are the dominant sulfide minerals in stage 4, which are either disseminated in silicified host rock or within wide quartz veins. Lesser amounts of quartz and abundant pyrite with inclusions of enargite and luzonite were precipitated in stage 5. Microthermometry on fluid inclusions in quartz of stages 2, 3a, and 4 indicates boiling of the hydrothermal fluids. Bulk gas analysis on fluid inclusions in quartz shows that the stage 2 and 4 fluids had components derived from basaltic and andesitic magma, respectively. Fluids that formed stage 4 quartz were more diluted by meteoric water than the fluids that formed the stage 2 veins. Radiometric 40Ar/39Ar dating on alunite separated from the stage 3b advanced argillic alteration zone yielded 2.2 ± 0.1 Ma. Sulfur isotope compositions of the Northwest quartz-pyrite-gold deposit reveal a bulk δ34S of approximately 5, similar to the calculated value for the adjacent Far Southeast porphyry deposit. Calculated oxygen and hydrogen isotope ratios of the fluids of the Northwest quartz-pyrite-gold deposit stage 3b dickites are similar to those that formed the illite alteration in the Far Southeast porphyry deposit but are higher in δ18O when compared to the fluids that formed the kandites in the Lepanto enargite deposit. The northward cooling of mineralizing fluids previously reported in the Lepanto enargite deposit is not consistent with the mineralogic indications in the Northwest quartz-pyrite-gold deposit. These data indicate multiple mineralization events in the Mankayan district, which is one of the largest mineral districts in the western Pacific.

DOI： 10.5382/econgeo.2018.4606

Language：English  

The Kago deposit is a small deposit located at the southern tip of the Satsuma Peninsula of Southern Kyushu, Japan. It lies proximal to the well-known Nansatsu-type mineralisation province dominated by high-sulfidation type epithermal deposits. The deposit was heavily mined in the 18 ^th Century, largely for its relatively higher gold compared to that of surrounding and regional deposits. The Kago deposit is a typical low-sulfidation deposit, characterised by adularia-quartz veins, composed of electrum, Ag-tetrahedrite, polybasite, chalcopyrite and pyrite. Based on mine records, the grade ranged from 4.1 to 13.3 g/t Au and 2.6–6.6 g/t Ag. Alteration grades from low to high temperature argillic into a propylitic zone at the extremes of the vein exposures. Carbonate is absent. Fluid inclusion microthermometry reveals a typical temperature range of 220–240 °C with salinity of 0.7–2.6 NaCl eq. wt&#37;. Electrum from high-grade ore ranges from 66 to 69 wt&#37; Au. ⁴⁰Ar/³⁹Ar age dating of adularia bearing colloform/crustiform and brecciated veins, suggests a mineralisation event from 4.23 to 4.0 Ma. δ¹⁸O of veined and silicified quartz ranges from +4.0 to +18.4‰. δ¹⁸OH₂O of fluids in equilibrium with quartz, in the dominant range of measured fluid inclusion temperatures, ranges from −6.5‰ to −0.2‰. δ³⁴S of pyrite has a narrow range from −1.8 to 2.7‰. The deposit lies at the northern extent of the classic Nansatsu high-sulfidation epithermal area, in which a number of silicified bodies punctuate the region in a roughly semi-circular shape. The Kago deposit lies within the principle mineralisation age range of the high-sulfidation deposits, which range from 5.5 to 3.7 Ma. The structural displacement of the Kago deposit from the Nansatsu mineralisation and the differing host rocks has greatly influenced alteration, ore and rock-water interaction of the ore depositing fluids. Here we seek to establish the relationship that this extended mineral province has between the differing styles of mineralisation.

DOI： 10.1016/j.oregeorev.2017.10.027

Language：English  

Petrochemical characteristics of Permo-Triassic granitoids from five regions (i) Mung Loei, (ii) Phu Thap Fah – Phu Thep, (iii) Phetchabun, (iv) Nakon Sawan – Lobburi, and (v) Rayong – Chantaburi along the Loei Fold Belt (LFB), northeastern Thailand were studied. The LFB is a north–south trending 800 km fold belt that hosts several gold and base-metal deposits. The granitoids consist of monzogranite, granodiorite, monzodiorite, tonalite, quartz-syenite, and quartz-rich granitoids. These are composed of quartz, plagioclase, and K-feldspar with mafic minerals such as hornblende and biotite. Accessory minerals, such as titanite, zircon, magnetite, ilmenite, apatite, garnet, rutile, and allanite are also present. Magnetic susceptibilities in the SI unit of granitoids vary from 6.5 × 10
⁻³
to 15.2 × 10
⁻³
in Muang Loei, from 0.1 × 10
⁻³
to 29.4 × 10
⁻³
in Phu Thap Fah – Phu Thep, from 2.7 × 10
⁻³
to 34.6 × 10
⁻³
in Petchabun, from 2.4 × 10
⁻³
to 14.1 × 10
⁻³
in Nakon Sawan – Lobburi, and from 0.03 × 10
⁻³
to 2.8 × 10
⁻³
in Rayong – Chantaburi. Concentration of major elements suggests that these intermediate to felsic plutonic rocks have calc-alkaline affinities. Concentration of REE of the granitoids normalized to chondrite displays moderately elevated light REE (LREE) and relatively flat heavy (HREE) patterns, with distinct depletion of Eu. Rb versus Y/Nb and Nb/Y tectonic discrimination diagrams illustrate that the granitoids from Muang Loei, Phu Thap Fah – Phu Thep, Phetchabun, Nakon Sawan – Lobburi, and Rayong – Chantaburi formed in continental volcanic-arc setting. New age data from radiometric K-Ar dating on K-feldspar from granodiorite in Loei and Nakhon Sawan areas yielded 171 ± 3 and 221 ± 5 Ma, respectively. K-Ar dating on hornblende separated from diorite in Lobburi yielded 219 ± 8 Ma. These ages suggest that magmatism of Muang Loei occurred in the Middle Jurassic, and Nakon Sawan – Lobburi occurred in Late Triassic. Both Nb versus Y and Rb versus (Y + Nb) diagrams and age data indicate that Nakon Sawan – Lobburi granitoids intruded in Late Triassic at Nong Bua, Nakon Sawan province and Khao Wong Phra Jun, Lobburi province in volcanic arc setting. Muang Loei granitoids at the Loei province formed later in Middle Jurassic also in volcanic arc setting. The negative δ
³⁴
S
_CDT
values of ore minerals from the skarn deposit suggest that the I-type magma has been influenced by light biogenic sulfur from local country rocks. The Au-Cu-Fe-Sb deposits correlate with the magnetite-series granitoids in Phetchabun, Nakon Sawan – Lobburi and Rayong – Chantaburi areas. Metallogeny of the Au and Cu-Au skarn deposits and the epithermal Au deposit is related to adakitic rocks of magnetite-series granitoids from Phetchabun and Nakon Sawan areas. All mineralizations along the LFB are generated in the volcanic arc related to the subduction of Paleo-Tethys. The total Al (
^T
Al) content of biotite of granitoids increases in the following order: granitoids associated with Fe and Au deposit < with Cu deposit < barren granitoids. X
_Mg
of biotite in granitoids in Muang Loei indicates the crystallization of biotite in magnetite-series granitoids under high oxygen fugacity conditions. On the other hand, low X
_Mg
(<0.4) of biotite in magnetite-series granitoids in Phu Thap Fah – Phu Thep and Rayong – Chantaburi indicates a reduced environment and low oxygen fugacity, associated with Au skarn deposit (Phu Thap Fah) and Sb-Au deposit (Bo Thong), respectively. The magnetite-series granitoids at Phu Thap Fah having low magnetic susceptibilities and low X
_Mg
of biotite were formed by reduction of initially oxidizing magnetite-series granitic magma by interaction with reducing sedimentary country rocks as suggested by negative δ
³⁴
S
_CDT
values.

DOI： 10.1111/rge.12176

Language：English  

Talc deposits in Nangarhar Province, are hosted by Paleoproterozoic carbonate rocks, metamorphosed to amphibolite facies in the east–west (E–W) trending Spinghar Fault Block. Many deposits in this province have potential economic importance. However, detailed geologic and petrological studies on ore genesis are still lacking. In this study, eight talc deposits and two prospects of the Spinghar Fault Block were investigated. Talc is mainly formed by alteration of the host dolomite marble, magnesite rocks, and tremolitite. Talc ore bodies occur parallel to subparallel to the beddings of the host carbonate rocks. Dolerite occur as dikes and sills and are mostly metamorphosed to amphibolite. Although the amphibolite occurs mostly parallel to subparallel to the beddings of the host carbonate rocks, and talc orebodies, it partly crosscuts the host rocks. Massive layers of tremolitite were observed with most of the talc ore bodies. Quartz veins occur along the gneissosity of gneiss all over the study area. SiO₂ and MgO content in talc rocks from all deposits ranged from 49.1 to 65.1 wt&#37; and from 26.1 to 32.9 wt&#37;, respectively. CaO content in talc rocks and magnesite rocks are less than 1 wt&#37;. ƩREE content in talc rocks ranged from 0.1 to 8.9 ppm. Chemical compositions of host carbonate rocks are close to the ideal composition. Concentrations of Al, Ta, Hf, Zr, Th, Cr, Ni, Co, and ƩREE in talc ores and host carbonate rocks were very low and inconsistent with mafic and ultramafic rocks protolith. Therefore, the metamorphosed sedimentary carbonate rocks were likely to be the protolith of the talc ores. The occurrence of parallel to subparallel quartz veins to the gneissosity of gneiss, as well as the presence of hydrous minerals in host carbonate rocks, suggested that hydrothermal fluids were most probably supplied through the gneiss.

DOI： 10.1111/rge.12174

Language：English  

Despite showing favorable geology, there are no known porphyry-type deposits in Japan. This, therefore, provides an ideal porphyry-“barren” case area on which to test the recently developed plagioclase-based discriminator for porphyry-“fertile” calc-alkaline systems. The discriminator was applied to plagioclase data for Japan in the online GEOROC database for convergent margin settings. Of the 3933 data points available, and considered reliable, 91&#37; fall in the “barren” field, which compares with 73&#37; for equivalent data worldwide. “Fertile” signatures in certain parts of Kyushu and central Honshu should be further investigated, as well as areas where there are magnetite-series magmatic systems with elevated whole-rock Sr/Y but for which there are currently little or no plagioclase data (SW-, N-central-, and NE-Honshu). Why the Japanese arcs appear to show anomalously poor potential for porphyry deposits compared with other arcs worldwide, including Western Luzon, is as yet unclear but possibly relates to tectonic factors or the nature of the magmatic source or because melt PH₂O in many of the magmatic systems was too low, as suggested from low average excess Al in plagioclase.

DOI： 10.1111/rge.12162

Language：English   Publishing type：Research paper (other academic)  

Uluwai Prospect is located in the northern part of South Arm of Sulawesi along the eastern part of the Kalosi Fold Belt and Latimojong Mountain. The area is generally characterized by moderate to rugged topography area with elevation in the range of 700 to 1400 m above sea level in the mountainous complex called Latimojong Mountain Complex. The mineralization is characterized by a relatively simple sulphide ore mineral assemblage consists of pyrite, sphalerite and chalcopyrite. Samples were collected in areas showing abundant sulphide minerals where younger faults cut the bedding and foliation of country rocks. A number of silicified zones have been observed, as well as float material containing disseminated pyrite, chalcopyrite, and sphalerite with hematite, goethite and limonite. Some alteration types have been observed including sericitization, albitization, carbonatization and silisification. The samples collected indicated that the mineralisation is contained within metasedimentary (sandstone to mudstone) and greenschist. Geochemical analyses from 16 samples including 5 stream sediment samples indicated that the most promising mineralization occur in the prospect area are copper (Cu) and zinc (Zn). This is also supported by the abundance of chalcopyrite and sphalerite in some highly altered samples. Assaying of the collected samples revealed most of samples contain relatively low gold (Au) concentration. However, two samples contain 0.007 and 0.01 ppm of Au. In the mineralized area, Zn concentrations are up to 134 ppm, Cu up to 120 ppm and Pb up to 18 ppm and As up to 70 ppm. There is no clear relationship that exists between Au and the base metals except that one of the samples with highest Au values tend to have high Zn and As. This unclear pattern also shown by Cu, Pb and Zn. Base metal concentration in stream sediment samples show a relatively stable pattern than in rock samples. Arsenic tends to be elevated in base metal rich samples. Sb and Mo are relatively low in all sample type. However, Mo values will be high in the samples which contain highest Cu and Zn.

DOI： 10.1088/1742-6596/962/1/012011

Language：English  

DOI： 10.1111/rge.12123

Language：English  

Petrochemical studies were conducted on granitoids in Sibolga and surrounding areas in North Sumatra, Indonesia. The granitoids presented the characteristics of A- and I-type ilmenite series. The syenogranites from Sarudik, the syenogranite, quartz syenite, and quartz alkali feldspar syenite from Sibuluhan Sihaporas, and the monzogranites from Sibolga Julu are A-type granitoids that have high SiO₂, CaO, Al₂O₃, Na₂O + K₂O, and Rb content, a high FeO/MgO ratio, and low Ba, Sr, and Zr content. The alkali feldspar syenite from Sarudik, the quartz alkali feldspar syenite from Tukka, and the quartz syenite from Adian Koting show I-type characteristics. I-type granitoids have lower SiO₂, Na₂O + K₂O, Rb, Yb, and total REE (ΣREE) content and low FeO/MgO ratio. However, quartz syenite from the Sibolga Julu, which exhibits I-type characteristics, has high ΣREE content but a low FeO/MgO ratio. The granitoids consisted mainly of K-feldspar megacrysts, quartz, plagioclase, and biotite with hornblende in some cases. Accessory minerals were zircon, apatite, allanite, and titanite. Cordierite and corundum occurred as xenocrysts and inclusions in K-feldspar in syenogranite (Sarudik) and quartz syenite (Adian Koting). SiO₂ and ΣREE content and the Rb/Sr ratio are positively correlated to each other. The REE are enriched in quartz alkali feldspar syenites from Sibolga Julu and Sarudik, quartz syenite from Tarutung, and quartz alkali feldspar syenite, syenogranite, and quartz syenite from Sibuluhan Sihaporas. These highly-differentiated granitoids were formed within the plate settings. In contrast, the ΣREE content of hornblende-bearing granitoids that were formed in volcanic arc settings is low. The coexistence of cordierite and corundum with biotite and hornblende indicates that the metaluminous magma was contaminated by metasedimentary basement rocks.

DOI： 10.1111/rge.12132

Language：English  

DOI： 10.1016/j.jseaes.2017.01.027

Language：English  

DOI： 10.1111/rge.12136

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

A laboratory geochemical study was conducted using a drill core sample of cap rock from the Surat Basin, Australia, to investigate the effect of NO2 contained in the CO2 gas exhausted from the oxyfuel combustion process (oxyfuel combustion CO2) on the cap rock. A gas (CO2 containing NO2) was prepared to simulate the exhaust gas produced from the oxyfuel combustion process. Two types of gases (pure CO2 and CO2 containing SO2) were also prepared as reference gases. The effect of NO2 on cap rock was studied experimentally using these gases. No differences in the amounts of leached ions and pH changes for CO2 containing NO2 (36 ppmv), pure CO2, and CO2 containing SO2 (35 ppmv) existed. The pH values decreased immediately after CO2 gas injection but increased with time as a result of mineral buffering. Leaching of Fe, Mg, Ca, and K was suggested to have occurred as the result of dissolution of Fe-chlorite, prehnite and illite-smectite mixed layer clay in the shale sample. The amounts of Ca, Fe, and Mg leached with CO2 containing NO2 (318 ppmv) were higher than those for pure CO2. For the mixture containing 318 ppmv NO2, the pH increased more than that for the other gas conditions immediately after the pH fall at the start of the experiment, because oxidation-reduction reactions occurred between Fe2+ and NO3-. Moreover, the results indicated that some of the leached Ca and Fe were deposited on the shale sample because of the pH increase. Therefore, we concluded that the effects of NO2 on mineral dissolution and pH changes of formation water are negligible when oxyfuel combustion CO2 containing about 30 ppmv of NO2 is injected into an underground aquifer. In addition, even if about 300 ppmv NO2 is accidentally injected into the underground aquifer, mineral dissolution is suppressed due to the buffering of pH decrease after gas injection.

DOI： 10.1016/j.apgeochem.2016.04.007

Language：English   Publishing type：Research paper (scientific journal)  

Late Cenozoic granitoids are widespread in a 1600 km long belt forming the Western and Northern Sulawesi tectono-magmatic provinces. They can be divided into three rock series: shoshonitic (HK), high-K felsic calc-alkaline (CAK), and normal calc-alkaline to tholeiitic (CA-TH). Representative samples collected from eleven plutons, which were subjected to petrography, major element, trace element, Sr, Nd, Pb isotope and whole-rock δ¹⁸O analyses, are all I-type and metaluminous to weakly peraluminous. The occurrence of the two K-rich series is restricted to Western Sulawesi, where they formed in an extensional, post-subduction tectonic setting with astenospheric upwelling providing thermal perturbation and adiabatic decompression. Two parental magma sources are proposed: enriched mantle or lower crustal equivalent for HK magmas, and Triassic igneous rocks in a Gondwana-derived fragment thrust beneath the cental and northern parts of Western Sulawesi for CAK magmas. The latter interpretation is based on striking similarities in radiogenic isotope and trace element signatures. CA-TH granitoids are found mostly in Northern Sulawesi. Partial melting of lower-middle crust amphibolites in an active subduction environment is the proposed origin of these rocks. Fractional crystallization and crustal contamination have played a significant role in magma petrogenesis, particularly in the case of the HK and CAK series. Contamination by organic carbon-bearing sedimentary rocks of the HK and CAK granitoids in the central part of Western Sulawesi is suggested by their ilmenite-series (reduced) character. The CAK granitoids further to the north and CA-TH granitoids in Northern Sulawesi are typical magnetite-series (oxidized). This may explain differences in mineralization styles in the two regions.

DOI： 10.1016/j.jseaes.2016.04.018

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Fluid Inclusion and Stable Isotope Study at the Southeastern Martabe Deposit Purnama, Barani and Horas Ore Bodies, North Sumatra, Indonesia
The Martabe Au-Ag deposit, North Sumatra Province, Indonesia, is a high sulfidation epithermal deposit, which is hosted by Neogene sandstone, siltstone, volcanic breccia, and andesite to basaltic andesite of Angkola Formation. The deposit consists of six ore bodies that occurred as silicified massive ore (enargite-luzonite-pyrite-tetrahedrite-tellurides), quartz veins (tetrahedrite-galena-sphalerite-chalcopyrite), banded sulfide veins (pyrite-tetrahedrite-sphalerite-galena) and cavity filling. All ore bodies are controlled by N-S and NW-SE trending faults. The Barani and Horas ore bodies are located in the southeast of the Purnama ore body. Fluid inclusion microthermometry, and alunite-pyrite and barite-pyrite pairs sulfur isotopic geothermometry show slightly different formation temperatures among the ore bodies. Formation temperature and salinity of fluid inclusions of the Purnama ore body range from 200 to 260C and from 6 to 8wt.&#37; NaCl equivalent, respectively. Formation temperature and salinity of fluid inclusions of the Barani ore body range from 200 to 220°C and from 0 to 2.5wt.&#37; NaCl equivalent and those of the Horas ore body range from 240 to 275°C and from 2 to 3wt.&#37; NaCl equivalent, respectively. The Barani and Horas ore bodies are less silicified and sulfides are less abundant than the Purnama ore body. A relationship between enthalpy and chloride content indicates mixing of hot saline fluids with cooler dilute fluids during the mineralization of each of the ore bodies. The δ¹⁸O values of quartz samples from the southeast ore bodies exhibit a wide range from +4.2 to +12.9‰ with an average value of +7.0‰. The δ¹⁸O values of H₂O estimated from δ¹⁸O values of quartz, barite and calcite confirm the oxygen isotopic shift to near meteoric water trend, which support the incorporation of meteoric water. Salinity of the fluid inclusions decrease from >5wt.&#37; NaCl equivalent in the Purnama ore body to <3wt.&#37; NaCl equivalent in the Barani ore body, indicating different fluid systems during mineralization. The δ³⁴S values of sulfide and sulfate in Purnama range from-4.2 to +5.5‰ and from +1.2 to +26.7‰, those in the Barani range from-4.3 to +26.4‰ and from +3.9 to +18.5‰ and those in the Horas ore body range from-11.8 to +3.5‰ and from +1.4 to +25.7‰, respectively. The δ³⁴S of total bulk sulfur in southeastern ore bodies (Σδ³⁴S) was estimated to be approximately +6‰. The estimated sulfur fugacity during formation of the Purnama and Horas ore bodies is relatively high. It was between 10^-4.8 and 10^-10.8 atm at 220 to 260°C. Tellurium fugacity was between 10^-7.8 and 10^-9.5 atm at 260°C and between 10^-9 and 10^-10.6 atm at 220°C in the Purnama ore body. The Barani ore body was formed at lower fS₂, lower than about 10^-14 atm at 200 to 220°C based on the presence of arsenopyrite and pyrrhotite in the early stage, and between 10^-14 and 10^-12 atm based on the existence of enargite and tennantite in the last stage.

DOI： 10.1111/rge.12093

Language：English   Publishing type：Research paper (scientific journal)  

We analyzed new radiometric dating and petrological data of DVC in an attempt to reconstruct volcanic history as groundwork to understand magmatic temporal and spatial evolution. The magma of DVC can be divided on the basis of mineral composition into three types: olivine bearing basalt-basaltic andesite, pyroxene basaltic andesite-andesite, and biotite andesite-dacite, which coincide with three volcanic episodes of DVC: pre-caldera, second, and youngest episode, respectively. The pre-caldera episode was active no later than 1Ma, the second episode occurred between 0.3 and 0.4Ma, and the youngest occurred after 0.27Ma. Plots of CaO, K2O, Al2O3, and Rb/Sr against FeO*/MgO and/or MgO suggest that each volcanic episode has distinct differentiation trends, indicating the presence of multiple shallow magma chambers. The close spatial relationship between the geothermal manifestation, geophysical anomalies, geothermal production zones and volcanic edifices supports the presence of multiple shallow magma chambers beneath DVC, which act as a heat source for the existing geothermal system.

DOI： 10.1016/j.jvolgeores.2015.12.010

Language：English   Publishing type：Research paper (scientific journal)  

The Permo-Jurassic North Thai (NT) Granites and the Late Cretaceous to Paleogene Western Province (WP) Granites in Thailand are contrasting in terms of tectonic settings and chemical compositions. The NT Granites, which are dominated by S-type features, are characterized by lower SiO<inf>2</inf> contents and higher P<inf>2</inf>O<inf>5</inf> contents than the WP Granites in this study. In order to compare the mobility and adsorption of rare earth elements (REEs) during weathering of the two granite suites, geochemical analyses were conducted on the granite and weathered granites. The weathered WP Granites show wider ranges of REEs+Y (REY) contents, percentages of ion-exchangeable REY and Ce anomalies than the weathered NT Granites. These results indicate that REEs were less mobile during weathering of the NT Granites than those of the WP Granites. The low mobility of REEs can be explained by the occurrences of residual monazite and secondary REE phosphates which immobilize REEs during weathering. Therefore, in the weathered NT Granites, REEs are mostly contained in the phosphate minerals. In contrast, the weathered WP Granites are dominated by ion-exchangeable REEs (adsorbed REEs) which are likely to exist on the surface of clays. Previous studies and our study results suggest that the ion-exchangeable REEs in the weathered granites were probably sourced from weatherable allanite, titanite, apatite and/or REE fluorocarbonate, and rarely from monazite and zircon, which are resistant to weathering. The weathered granites of low phosphate contents potentially show high percentages of ion-exchangeable REY, although they can be influenced by the degree of hydrothermal alteration or weathering of granites.

DOI： 10.1016/j.jseaes.2015.05.018

Language：English   Publishing type：Research paper (international conference proceedings)  

Northwest Panay consists of two terranes that form part of the Central Philippine collision zone: Buruanga Peninsula and Antique Range. The Buruanga Peninsula consists of a Jurassic chert-clastic-limestone sequence, typical of oceanic plate stratigraphy of the Palawan Micro-continental Block. The Antique Range is characterized by Antique Ophiolite Complex peridotites and Miocene volcanic and clastic rocks, representing obducted oceanic crust that serves as the oceanic leading edge of the collision with the Philippine Mobile Belt. The Nabas Fault is identified as the boundary between the two terranes. This study employed the gravity method to characterize the Northwest Panay subsurface structure. Results indicate higher Bouguer anomaly values for Buruanga Peninsula than those for Antique Range, separated by a sudden decrease in gravity values toward the east-southeast (ESE) direction. Forward gravity data modeling indicates the presence of an underlying basaltic subducted slab in the Buruanga Peninsula. Furthermore, the Nabas Fault is characterized as an east-dipping thrust structure formed by Buruanga Peninsula basement leading edge subduction beneath Antique Range. Additional geophysical constraints were provided by shallow seismic refraction and electrical resistivity surveys. Results from both methods delineated the shallow subsurface signature of the Nabas Fault buried beneath alluvium deposits. The gravity, seismic refraction and electrical resistivity methods were consistent in identifying the Nabas Fault as the terrane boundary between the Buruanga Peninsula and the Antique Range. The three geophysical methods helped constrain the subsurface configuration in Northwest Panay.

DOI： 10.3319/TAO.2015.05.11.03(TC)

Language：English   Publishing type：Research paper (scientific journal)  

Textural and Chemical Evolution of Unidirectional Solidification Textures in Highly Differentiated Granitic Rocks at Kharaatyagaan, Central Mongolia
Unidirectional solidification texture (UST) in an aplite body is recognized in the Neoproterozoic highly differentiated granitic rocks at Kharaatyagaan, central Mongolia. On the basis of crystal morphology, two main types of UST were identified in the aplite body: (i) thin crenulate UST layers; and (ii) thick intergrowth UST layers. Bulk geochemistry indicates that the Kharaatyagaan UST-bearing aplite and aplite dike are alkaline, and are enriched in light rare-earth elements. Scanning electron microscopy and cathadoluminescence imaging of UST quartz from Kharaatyagaan show four types of quartz: euhedral quartz phenocrysts with well-developed concentric growth zoning (Qa1) in the aplite; euhedral quartz with weak growth zoning in the aplite (Qa2); UST quartz exhibiting distinct growth zones (Qu1); and UST quartz showing mosaic texture (Qu2). Crystallization temperatures determined by the Ti-in-quartz geothermometer of Qa1 and Qu1 quartz range between around 500°C and 780°C and Qa2 and Qu2 range between about 490° and 630°C. The cathodoluminescence textures of quartz are predominantly caused by variations in the trace elements contents of quartz. The Qa1 and Qu1 quartz crystals are characterized by high Ti and Al concentrations in the quartz lattice, and are observed in the bottom of the Kharaatyagaan hill, which formed in the early, less evolved magmatic stage. The Qa2 and Qu2 UST quartz characterized by low Ti and variable Al concentrations are found at the top. The UST layers crystallized along the upper part of the magma chamber in the presence of fluid phases exsolved from felsic magma.

DOI： 10.1111/rge.12050

Language：English   Publishing type：Research paper (scientific journal)  

Gold-mineralized quartz veins at the Trenggalek district of the Southern Mountains Range in East Java, Indonesia, are hosted by Oligo-Miocene volcaniclastic and volcanic rocks, and are distributed close to andesitic plugs in the northern prospects (Dalangturu, Suruh, Jati, Gregah, Jombok, Salak, and Kojan) and the southern prospects (Sentul and Buluroto). The plugs are subalkaline tholeiitic basaltic-andesite to calc-alkaline andesite in composition. ⁴⁰Ar-³⁹Ar dating of a quartz-adularia vein at the Dalangturu prospect yielded an age of 16.29 ± 0.56 Ma (2σ), and a crystal tuff of a limestone-pyroclastic rock sequence at the southwest of the Dalangturu prospect was determined as 15.6 ± 0.5 Ma (2σ). Statistic overlap of ages suggests that the gold mineralization in the northern prospects took place in a shallow marine to subaerial transitional environment. Hydrothermal alteration of the host rocks is characterized by the replacement of quartz, illite and adularia. Quartz veins in surface outcrops are up to 50cm wide in the northern prospects and up to 3m wide in the southern prospects, showing a banded or brecciated texture, and are composed of quartz, adularia, carbonates with pyrite, electrum, sphalerite, galena, and polybasite. Gold contents of quartz veins are positively correlated with Ag, Zn, Pb, and Cu contents in both the northern and southern prospects. The quartz veins at the Jati, Gregah, and Sentul prospects have relatively lower gold-silver ratios (Ag/Au = 23.2) compared to those at the Kojan, Dalangturu, Salak, and Suruh prospects (Ag/Au = 66.8). The quartz veins at the Dalangturu prospect are relatively rich in base metal sulfides. Ag/(Au+Ag) ratios of electrum in the Dalangturu prospect range from 45.2 to 65.0 at%, and FeS contents of sphalerite range from 1.2 to 6.4 mol%. Fluid inclusion microthermometry indicates ore-forming temperatures of 190-200°C and 220-230°C at the Sentul and Kojan prospects, respectively. Widely variable vapor/liquid ratio of fluid inclusions indicates that fluid boiling took place within the hydrothermal system at the Sentul prospect. Salinities of ore-fluids range from 0 to 0.7 wt% (av. 0.4 wt% NaCl equiv.) and from 0.5 to 1.4 wt% (av. 0.9 wt%) for the Sentul and Kojan prospects, respectively. The boiling of hydrothermal fluid was one of the gold deposition mechanisms in the Sentul prospect.

DOI： 10.1111/rge.12034

Language：English   Publishing type：Research paper (scientific journal)  

We present the first data on bulk-rock major and trace element compositions for a suite of eclogite- and blueschist-facies rocks from the Bantimala Complex, Indonesia, with the aim of better constraining the protolith origins and nature of the subducted crust. The eclogites can be classified into two groups: glaucophane-rich eclogite and glaucophane-free eclogite, whereas the blueschists are divided into albite-epidote glaucophanite and quartz-glaucophane schists. SiO2 contents of the eclogites are 43.3-49.6 wt&#37;, with Na2O+K2O contents 3.7-4.7 wt&#37;. The blueschists show a wider range of compositions, with SiO2=40.7-63.8 wt&#37; and Na2O+K2O=2.7-4.5 wt&#37;. Trace element data suggest that the eclogite protoliths include both enriched and normal mid-oceanic ridge basalt (E-MORB and N-MORB) and also gabbroic cumulates. The blueschists show more variation in protoliths, which include N-MORB, Oceanic Island Basalt (OIB) and Island Arc Basalt (IAB). Plots of element concentrations against the immobile Zr show considerable mobility of large ion lithophiles but not of high field-strength elements during high-pressure metamorphism, and indicate that the high SiO2 content of some blueschists is probably due to metasomatism by a LILE-rich siliceous aqueous fluid. Strong correlations between K, Rb, Ba and Cs suggests that enrichment of these elements occurred by a single process. All the protoliths were subducted, metamorphosed to blueschist/eclogite-facies and subsequently exhumed. It is noteworthy that the samples deduced to have come from thicker-crust environments (OIB, IAB) were subducted to shallower depths (blueschist-facies) than MORB-derived samples, all except one of which reached eclogite-facies conditions. The geochemical data of this study demonstrate the variety of ocean floor types that were subducted under the southeast margin of Sundaland in the late Jurassic period. © 2013 Wiley Publishing Asia Pty Ltd.

DOI： 10.1111/iar.12037

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In Kamchatka, Central Koryak, Central Kamchatka and East Kamchatka metallogenic belts are distributed from northwest to southeast. K-Ar age, sulfur isotopic composition of sulfide minerals, and bulk chemical compositions of ores were analyzed for 13 ore deposits including hydrothermal gold-silver and base metal, in order to elucidate the geological time periods of ore formation, relationship to regional volcanic belts, type of mineralization, and origin of sulfur in sulfides. The dating yielded ore-forming ages of 41Ma for the Ametistovoe deposit in the Central Koryak, 17.1Ma for the Zolotoe deposit and 6.9Ma for the Aginskoe deposit in the Central Kamchatka, and 7.4Ma for the Porozhistoe deposit and 5.1Ma for the Vilyuchinskoe deposit in the East Kamchatka metallogenic belt. The data combined with previous data of ore-forming ages indicate that the time periods of ore formation in these metallogenic belts become young towards the southeast. The averaged δ34SCDT of sulfides are -2.8‰ for the Ametistovoe deposit in Central Koryak, -1.8‰ to +2.0‰ (av. -0.1‰) for the Zolotoe, Aginskoe, Baranievskoe and Ozernovskoe deposits in Central Kamchatka, and -0.7 to +3.8‰ (av. +1.7‰) for Bolshe-Bannoe, Kumroch, Vilyuchinskoe, Bystrinskoe, Asachinskoe, Rodnikovoe, and Mutnovskoe deposits in East Kamchatka. The negative δ34SCDT value from the Ametistovoe deposit in Central Koryak is ascribed to the contamination of 32S-enriched sedimentary sulfur in the Ukelayat-Lesnaya River trough of basement rock. Comparison of the sulfur isotope compositions of the mineral deposits shows similarity between the Central Koryak and Magadan metallogenic belts, and East Kamchatka and Kuril Islands belts. The Central Kamchatka belt is intermediate between these two groups in term of sulfur isotopic composition. © 2013 The Society of Resource Geology.

DOI： 10.1111/rge.12005

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DOI： 10.1007/s00126-011-0380-5

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Geochemical studies done on the Baguio Mineral District had dominantly looked at the igneous rocks. A major gap is the scarcity of studies dealing with the sedimentary rock geochemistry for this district which this paper intends to address. The petrographic data and major and trace element compositions of the siltstones-sandstones from the lower member of the Late Oligocene to Early Miocene Zigzag Formation show that they are generally quartz-rich and have high K2O, Th and La/Sc contents. The chondrite-normalized REE pattern exhibits a negative Eu anomaly, enrichment in LREEs and flat HREEs similar to typical post-Archean shales. Taken together, the data indicate derivation of the lower member of the Zigzag Formation from intermediate to acid igneous rock sources generated in an active margin setting. A likely candidate source is the Cordon Syenite Complex/Palali Formation in the Northern Sierra Madre - Caraballo Mountains. Derivation from mafic source rocks in an oceanic island arc setting is inferred for samples of the Middle to Late Miocene Klondyke, Late Miocene to Early Pliocene Amlang and Late Pliocene Cataguintingan Formations. These samples are characterized by low K2O, Th and La/Sc but high Cr/Th values. Unroofing of the Pugo Metavolcanics and the younger plutons in the Central Cordillera provided the materials which eventually produced the Klondyke and Amlang Formations. Continuous uplift and shallowing of the basin resulted in the deposition of the Cataguintingan Formation. The petrography, geochemistry and geological features of the sedimentary rocks clearly define the change in sediment provenance from quartz-rich during the Oligocene to quartz-deficit in the Miocene. This offers additional constraints in understanding the geological evolution of the mineral district. © 2012 Elsevier Ltd.

DOI： 10.1016/j.jseaes.2012.09.026

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Geochemical studies were conducted on the hydrothermally altered granitic rocks in the Ranong and Takua Pa tin-fields in southern Thailand in order to investigate the mode of occurrence of REE (rare earth elements), with emphasis placed on a potential REE resource associated with granitic rocks in the Southeast Asian Tin Belt. The total REE (ΣREE) content of altered granitic rocks ranges from 130 to 350ppm at Haad Son Paen (which is presently mined for kaolin clay) in the Ranong tin-field, and that of altered granitic rocks and kaolinite veinlets reaches up to 424ppm and 872ppm, respectively, at Nok Hook in the Takua Pa tin-field. Rare earth elements in the altered granitic rocks and kaolinite veinlets show a relatively flat chondrite-normalized pattern, thus enriched in heavy REE compared with the original granitic rocks and their weathered crusts. At Nok Hook (Takua Pa), the ΣREE content of kaolinite separated from an altered granitic rock by elutriation is 1313ppm, a ΣREE amount about four times higher than that of whole-rock composition of the altered granitic rock. Chondrite-normalized REE patterns of the elutriated kaolinite and of the altered granite are relatively flat. Sequential extraction experiments suggest that 41 and 85 percent of REE are present as ion exchangeable-form in the altered granitic rock, and in the kaolinite veinlets, respectively. In addition, more than 90% of REE in the kaolinite veinlets are present as the acid-soluble state. On the other hand, the ΣREE content of kaolinite veinlets and of the kaolinite concentrated by elutriation from an altered granitic rock at Haad Som Paen (Ranong) is 70ppm and 75ppm, respectively, thus enrichment of REE in kaolinite was not confirmed. In addition, by the sequential extraction experiments, 23% and 4% of REE were extracted from the altered granitic rock and the kaolinite veinlets at Haad Som Paen. In the altered granitic rocks at Haad Som Paen, REE are present as refractory phases, and REE in the acid-soluble states had been leached by hydrothermal fluid.

DOI： 10.1111/j.1751-3928.2012.00212.x

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Petrological and geochemical investigations of the sedimentary Lasala formation in northwest Mindoro, Philippines, offer new insights into the origin of this geologically contentious region. Mindoro island's position at the boundary between Sundaland and the Philippine Mobile Belt has led to variable suggestions as to how much of it is continent derived or not. The Eocene Lasala formation overlies the Jurassic Halcon metamorphics, a regionally metamorphosed suite generally thought to have formed as a result of arc-continent collision processes. The sedimentary formation consists mainly of sandstones and shales interbedded with mudstones, basalt flows, and subordinate limestones and conglomerates. Petrographic information on the Lasala clastic rocks demonstrates a uniform framework composition that is predominantly quartzose. Major oxide, trace element abundances, and various elemental ratios similarly impart a strongly felsic signature. These characteristics are taken to indicate a chiefly continental, passive margin derivation and deposition of the Lasala sediments during the Eocene. The weak indication of active margin influence is suggested to be an inherited signature, supported by paleogeographic models of the southeastern Asian margin area during the pre-Cenozoic. © 2011 Springer-Verlag.

DOI： 10.1007/s00531-011-0643-5

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Luzonite-Famatinite Series Minerals at the Victoria Gold Deposit, Northern Luzon, Philippines
The Victoria gold deposit was classified as a low-sulfidation epithermal deposit. However, high-sulfidation state minerals are identified at deeper levels in the Victoria gold deposit in this study (e.g. luzonite, enargite and colusite). luzonite group minerals and chalcopyrite often overprinted the pre-existing vein materials. Luzonite group minerals of this type often replace tetrahedrite group minerals, and often show a small scale flaky intergrowth structure and banding structure of submicron order, with chalcopyrite. It is considered that these structures are formed by decomposition of intermediate-products which replaced tetrahedrite group minerals. The sulfidation-state of a mineralizing fluid during the last stage corresponds to high-sulfidation.

DOI： 10.14824/jakoka.2010.0.254.0

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In the Namosi district, of Viti Levu Island, Republic of the Fiji Islands, we conducted chemical analysis on intrusive rocks and attempted to clarify the relationship between petrological characteristics and mineralization. Samples were collected from the Waisoi copper deposit, Waivaka corridor, Waisomo, Wailutelevu and Wainabama Southwest localities. The intrusive rocks in the district show the overall characteristics of calc-alkaline magnetite series. Using the normative composition diagram for granite classification, most of the intrusive rocks plot in the tonalite, granodiorite, quartz monzodiorite and quartz diorite fields. Rare earth element (REE) analysis revealed that at Waisoi the intrusive rocks tend towards an Eu positive anomaly, whereas most of those at Waisomo tend to have a negative anomaly. The (Cecn/Ybcn)/Ybcn ratio shows that the intrusive rocks in the Namosi district may be derived from a mantle origin magma possibly contaminated by crustal materials. Waisoi rocks have less contamination with continental crust and show higher gold content compared to those of the Waivaka corridor. The observed differences between Waisoi and Waivaka corridor in the Cu/Au ratio might also be caused by varying amounts of contamination by crustal materials. There is no clear correlation between the La/Yb ratio and K-Ar ages, however, the La/Yb ratio of the Waivaka corridor rocks has a wide range, suggesting a variable amount of crustal contamination of the magma from 7 to 5 Ma. The less crustal contamination and generation of relatively high silica contents under relatively oxidized conditions in the Waisoi magmas is correlated with Au-rich porphyry copper mineralization and in contrast more crustal contamination produced Au-poor porphyry copper mineralization at the Waivaka Corridor in the Namosi district. © 2010 The Authors. Journal compilation © 2010 The Society of Resource Geology.

DOI： 10.1111/j.1751-3928.2010.00113.x

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Whole-rock geochemical analysis of samples from the clastic sequences in Northwestern Panay revealed different compositional ranges for the Buruanga Peninsula and Antique Range. The results provide additional evidence that Northwestern Panay consists of two distinct terranes as a result of the arc-continent collision between the Palawan Microcontinental Block and the Philippine Mobile Belt. Major element compositions of clastic rocks from the Buruanga Peninsula (Saboncogon Formation) revealed that they belong to a continental margin tectonic setting whereas the Antique Range sedimentary rocks (Lagdo Formation) show an affinity to an oceanic island arc setting. The Fragante Formation of the Antique Range shows some similarities in tectonic setting and provenance with Buruanga Peninsula clastic rocks, which suggests a Buruanga Peninsula sediment contribution during its time of formation. Furthermore, provenance analyses from combined major and trace element data indicate a more silicic source for the Buruanga Peninsula clastics and a more mafic derivation for the sedimentary rocks of the Antique Range. These findings are consistent with previous studies suggesting that the Buruanga Peninsula forms part of the Palawan Microcontinental Block and the Antique Range belongs to the Philippine Mobile Belt. The Palawan Microcontinental Block is believed to be a drifted continental fragment from the Mesozoic East Asian accretionary complex in the southern part of the Eurasian mainland, which represents the continental margin setting and felsic source of the Buruanga Peninsula clastic rocks. Meanwhile, the oceanic island setting and mafic source of the Antique Range clastic rocks represent the volcanic rocks of the Philippine Mobile Belt that were formed as a result of the subduction of the leading oceanic edge of the Palawan Microcontinental Block.

DOI： 10.1016/j.tecto.2009.02.004

Other Link： doi:10.1016/jtecto.2009.02.004

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Whole-rock geochemical analysis of samples from the clastic sequences in Northwestern Panay revealed different compositional ranges for the Buruanga Peninsula and Antique Range. The results provide additional evidence that Northwestern Panay consists of two distinct terranes as a result of the arc-continent collision between the Palawan Microcontinental Block and the Philippine Mobile Belt. Major element compositions of clastic rocks from the Buruanga Peninsula (Saboncogon Formation) revealed that they belong to a continental margin tectonic setting whereas the Antique Range sedimentary rocks (Lagdo Formation) show an affinity to an oceanic island arc setting. The Fragante Formation of the Antique Range shows some similarities in tectonic setting and provenance with Buruanga Peninsula clastic rocks, which suggests a Buruanga Peninsula sediment contribution during its time of formation. Furthermore, provenance analyses from combined major and trace element data indicate a more silicic source for the Buruanga Peninsula clastics and a more mafic derivation for the sedimentary rocks of the Antique Range. These findings are consistent with previous studies suggesting that the Buruanga Peninsula forms part of the Palawan Microcontinental Block and the Antique Range belongs to the Philippine Mobile Belt. The Palawan Microcontinental Block is believed to be a drifted continental fragment from the Mesozoic East Asian accretionary complex in the southern part of the Eurasian mainland, which represents the continental margin setting and felsic source of the Buruanga Peninsula clastic rocks. Meanwhile, the oceanic island setting and mafic source of the Antique Range clastic rocks represent the volcanic rocks of the Philippine Mobile Belt that were formed as a result of the subduction of the leading oceanic edge of the Palawan Microcontinental Block.

DOI： 10.1016/j.tecto.2009.02.004

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Themetic issue Collection of achievements on earth resources from AUN/ SEED-Net, Part III

DOI： 10.1111/j.1751-3928.2009.00091.x

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Origin of bornite pods in intrusive rocks at the kingking porphyry copper-gold Deposit, Southeastern Mindanao, Philippines
At the Kingking porphyry copper-gold deposit, Compostela Valley, south-eastern Mindanao, Philippines, bornite pods occur in the brecciated parts in the biotite diorite porphyry, together with the volcanic rock and diorite fragments without associated stockworks of quartz veinlets. These pods are generally elongated in shape and measure several centimeters across their longest axes. They are composed of bornite and chalcopyrite with traces of calaverite. The δ³⁴ S of bornite and subordinate chalcopyrite of bornite pods ranging from -2.2‰ to +0.1‰ are similar to the δ³⁴ S of sulfides associated with quartz veinlets such as bornite and chalcopyrite ranging from -4.7‰ to ±0.0‰. This suggests that the ultimate source of sulfur is identical for bornite pods and sulfides associated with quartz veinlets. Bornite pods are associated with volcanic rock and dioritic fragments in the brecciated portion of the biotite diorite porphyry. It was observed that some dioritic fragments contain quartz veinlets, which may indicate an earlier episode of mineralization. Fragments of the earlier dioritic intrusive rocks and the volcanic rocks, together with the sulfides were incorporated into the biotite diorite porphyry magma. A molten sulfide is possible for the composition between bornite and intermediate solid solution at ∼800°C. The sulfides from the earlier dioritic intrusive rocks in the molten state were segregated and then eventually coalesce to form the bornite pods in the brecciated section of the biotite diorite porphyry.

DOI： 10.1111/j.1751-3928.2009.00098.x

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Geochemical characteristics of intrusive rocks, Southeastern Mindanao, Philippines Implication to metallogenesis of porphyry copper-gold deposits
This paper describes petrologic and geochemical characteristics of intrusive rocks associated with porphyry copper deposits in south-eastern Mindanao, the Philippines, where the Kingking deposit is located. Intrusive rocks at the Kingking deposit, are classified into biotite-bearing diorite porphyry, hornblende diorite porphyry and diorite porphyry. Intrusive rocks in other areas in south-eastern Mindanao, including Batoto, Bukal, Maragusan, Masara, Amacan and Sumlog, are hornblende diorite porphyry and hornblende quartz diorite. They are adakitic in Sr/Y-Y diagram, but not in La/Yb-Yb diagram due to relatively low REE contents. The magmas are oxidizing as suggested by the high X Mg of mafic silicate phenocrysts and SO 3 contents of microphenocrystic apatite. An Oligocene-Miocene diorite intrusive complex formed by calc-alkaline, hydrous, oxidizing magma is considered to be associated with porphyry-type copper-gold mineralization.

DOI： 10.1111/j.1751-3928.2009.00094.x

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Fluid inclusion study and opaque mineral assemblage at the deep and shallow part of the batu hijau porphyry copper-gold deposit, Sumbawa, Indonesia
The Batu Hijau deposit is the only porphyry type deposit in production in the Sunda-Banda arc, Indonesia. This study discusses the reason for the localization of copper grade at the deep part of the deposit based on the observation of opaque mineral assemblage. In addition, the formation condition of quartz veins and opaque minerals is discussed on the basis of the fluid inclusion microthermometry. Samples were selected from drill holes SBD100, SBD168, SBD194, SBD254, and SBD257 to cover the wide vertical range. At the Batu Hijau deposit, quartz veins have been classified mainly into four types called A, B, C and D veins, and the A veins contain mainly bornite, often associated with digenite and chalcocite. In addition, magnetite occurs in A veins. However, at the deep part of the deposit, there are quartz veins associated with magnetite, but few copper sulfides such as bornite and chalcopyrite in quartz veins, as observed in SBD257. Quartz veins at depth in SBD257 have abundant magnetite and pyrite. Pyrite in quartz veins at depth in SBD257 mainly occur at the rim of magnetite grains or interstices between them. In quartz veins in SBD254, there are abundant copper sulfides such as bornite and chalcopyrite in spite of the depth. Bornite and chalcopyrite occur as inclusions in magnetite grains in quartz veins in SBD254. Pyrite which often occurs in low grade zone in quartz veins in SBD254 is also recognized at the rims of copper sulfides. This indicates that pyrite in SBD257 and SBD254 formed later than magnetite. On the other hand, blebs of bornite and chalcopyrite inclusions in magnetite grains, which are recognized in quartz veins in SBD168 at shallow high grade part, suggest that the hydrothermal fluid, from which magnetite was deposited also brought the copper sulfides such as bornite and chalcopyrite to the deep part of the Batu Hijau deposit. Therefore, it is concluded that initially the high grade ore zone extended to depth without localization. However due to the later overprinting hydrothermal activity, copper sulfides and magnetite were replaced or dissolved and pyrite was formed, resulting the low grade zone at the deep part of the deposit. Dissolution temperatures (Td) of halite obtained by from fluid inclusion microthermometry show significant differences between SBD168 and other drill holes. The high Td obtained in SBD168 may indicate larger volume of NaCl crystals in hydrothermal fluid at the time of entrapment of the fluid inclusions and formation of other opaque minerals such as magnetite and copper-iron sulfides. It suggests that the ratio of vapor to brine is also higher at the shallow part of the deposit. The higher vapor to brine ratio may suggest a higher degree of boiling. Removal of vapor phase separated from brine during boiling increases the concentration of substances dissolved in the brine, and this will result in saturation, as evidenced by the salinity and NaCl saturation. The higher degree of boiling suggested by the higher vapor to brine ratio at shallow part may have increased the copper concentration in the brine that may have lead the saturation, resulted in the deposition of copper-bearing minerals.

DOI： 10.1111/j.1751-3928.2009.00093.x

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Reactivities of various andesites and some other volcanic rocks were investigated by an accelerated mortar bar test in saturated NaCl solution (saturated NaCl method). In Japan, because of its low alkali content of Portland cement, total alkali amount in concrete can be controlled under 3.0 kg/m ³ for most cases. However, environmental alkalis such as deicing salt may add extra alkalis to concrete and ASR risks may increase. This risk is thought to be able to be checked by saturated NaCl method. The experiment shows that the most reactive andesites contain tridymite. Cristobalite is the second reactive phase. Glass seems non-reactive in the saturated NaCl method. Glassy andesite without silica minerals is judged as reactive by chemical method but innocuous by saturated NaCl method. Glass phase has been believed reactive in high alkali condition but there is a possibility that it is less reactive in specific environments such as deicing salt.

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In this study, we successfully integrated geological data, potential field data, and remote sensing data with the aim of investigating and improving our knowledge of the structural setting of the Eljufra area, northwestern Libya. SPOT-5 panchromatic band and digital elevation models (DEM) were used to construct surface shaded maps, and gravity and aeromagnetic surveys were used to provide information on subsurface structures and the nature of intrusive bodies. The results revealed that the prevailing trend of lineaments is NNW-SSE and NNE-SSW. A Bouguer anomaly map revealed that horst and graben blocks occur inside the large graben. An analytic signal method was applied to the aeromagnetic data to estimate locations and the minimum depths to the contact. A comparison of gravity and magnetic data provided information on hydrothermally altered basalt and sediment density. An anticlinal structure was detected in the western part of the study area. The effects of faults on basalt rocks indicated geological time for volcanic activity.

DOI： 10.1186/BF03353116

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Characteristics of porphyry Cu mineralization at Waisoi (Namosi District), Viti Levu, Fiji
The porphyry Cu deposits at Waisoi in Namosi district, Viti Levu are separated into two deposits: the Waisoi East deposit and the Waisoi West deposit. In the Waisoi East deposit, quartz porphyry is exposed and in the Waisoi West deposit, diorite porphyry is sporadically exposed in addition to a small body of quartz porphyry. The mineralization in the Waisoi East deposit is characterized by the bornite-chalcopyrite-pyrite assemblage associated with traces of molybdenite and native gold. Polyphase fluid inclusions in stockwork quartz veinlets show homogenization temperatures ranging from 210 to >500°C. The high-grade Cu mineralization in the Waisoi West deposit is characterized by the bornite-chalcopyrite-pyrite assemblage accompanied with sheeted and stockwork quartz veinlets. Polyphase fluid inclusions occasionally containing hematite flakes in quartz veinlets in the center of the Waisoi West deposit homogenize at temperatures ranging from 450°C to >500°C. However, fluid inclusions in stockwork quartz veinlets in the periphery, homogenize at lower temperatures around 210°C. Both in the Waisoi East and Waisoi West deposits, primary bornite-chalcopyrite-pyrite assemblage in the high Cu-grade zone was deposited at the upper stability limit of chalcopyrite with respect to sulfur fugacity. Thus, the principal Cu mineralization at the Waisoi deposits occurred at a relatively high sulfur fugacity, that is, in a high-sulfidation environment.

DOI： 10.1111/j.1751-3928.2007.00031.x

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About the special issue Collection of achievements on earth resources from AUN/SEED-Net, part II

DOI： 10.1111/j.1751-3928.2007.00009.x

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The Selogiri area, situated in Wonogiri regency, Central Java, is one of several gold prospecting areas in the Southern areas Mountain Range in Java, Indonesia. Three types of dioritic-andesitic intrusive rocks occur in the Selogiri area, namely, hornblende andesite porphyry, hornblende diorite porphyry and hornblende diorite, exposed in a half-circular depression where volcanic breccia and tuff are widely distributed. The occurrence of stockwork quartz veinlets and associated with magnetite and malachite coating along the cracks in the diorite porphyry suggests porphyry type mineralization. This is also supported by the occurrence of polyphase hypersaline fluid inclusions in the stockwork veinlet quartz. Small-scale miners are mining NS-trending quartz veins for gold associated with base metal sulfides. These veins are probably epithermal-type mineralization that overprinted porphyry-type mineralization. The Neogene intermediate to silicic hydrous magmatism in Java could have formed the porphyry-type mineralization in Selogiri, as in the rest of the Sunda-Banda arc.

DOI： 10.1111/j.1751-3928.2007.00019.x

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The Pongkor gold-silver mine is situated at the northeastern flank of the Bayah dome, which is a product of volcanism in the Sunda-Banda Arc. The hydrothermal alteration minerals in the Ciurug-Cikoret area are typical of those formed from acid to near-neutral pH thermal waters. On the surface, illite/smectite mixed layer mineral (I/Sm), smectite and kaolinite, and spotting illite, I/Sm and K-feldspar alteration occur at the top of the mineralized zone. Silicification, K-feldspar and I/Sm zones are commonly formed in the wall rock, and gradually grade outwards into a propylitic zone. The mineralization of precious metal ore zone is constrained by fluid temperatures between 180 and 220°C, and with low salinity (<0.2 wt% NaCl equivalent) and boiling condition. The minimum depth of vein formation below the paleo-water table is approximately 90-130 m for the hydrostatic column. Hydrogen and oxygen isotope data for quartz and calcite show relatively homogeneous fluid composition (-53 to -68‰ δD and -5.7 to +0.3‰ δ¹⁸O H₂O). There is no specific trend in the data with respect to the mineralization stages and elevation, which suggests that the ore-forming fluids did not significantly change spatially during the vein formation. The stable isotope data indicate mixing between the hydrothermal fluids and meteoric water and interaction between the hydrothermal fluids and the host rock.

DOI： 10.1111/j.1751-3928.2007.00013.x

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The Kingking deposit is a gold-rich porphyry copper deposit and the southernmost deposit at the eastern Mindanao mineralized belt, Philippines. It is underlain by Cretaceous-Paleogene sedimentary and volcanic rocks that are intruded by mineralized Miocene diorite porphyries and by barren Miocene-Pliocene dacite and diorite porphyries. The main alteration zones in the deposit are the inner potassic zone and the outer propylitic zone. The biotite-bearing diorite and hornblende diorite porphyries are the primary host rocks of mineralization. Two dominant copper minerals, bornite and chalcopyrite, which usually occur as fracture fillings, are associated with fine crystalline quartz veinlet stockworks in the mineralized diorites. Minor secondary covellite, chalcocite and digenite are also observed. The primary Cu-Fe sulfide phases initially deposited from ore fluids consisted of bornite solid solution (bnss) and intermediate solid solution (iss), which decomposed to form the bornite and chalcopyrite. Peculiar bornite pods that are different from dissemination and are associated with volcanic rock xenoliths in biotite-bearing diorite porphyry are noted in a drill hole. These pods of bornite are not associated with quartz veinlet stockworks. Fluid inclusion analyses show three types of inclusions contained in Kingking samples: two-phase fluid-rich and vapor-rich inclusions and polyphase hypersaline inclusions from porphyry-type quartz veinlet stockworks. The liquid-vapor homogenization temperatures (T_H) and the dissolution temperature of halite daughter crystals (T_M) from the polyphase hypersaline inclusions predominantly range from 400°C up to >500°C. The wide range of T_H and T_M may be due to heterogeneous trapping of variable ratios of vapor and brine. For some inclusions, T_H > T_M and in some cases, T_H < T_M, indicating that some of the brine was supersaturated or saturated with NaCl at the time of entrapment. Calculated salinity of the polyphase hypersaline inclusions ranges from 40 to 60% NaCl equivalent. Temperature and vapor pressure of mineralized fluid were estimated to be 400°C and 16 MPa.

DOI： 10.1111/j.1751-3928.2007.00018.x

Language：English   Publishing type：Research paper (other academic)  

Characteristics of the Cibaliung gold deposit Miocene low-sulfidation-type epithermal gold deposit in Western Java, Indonesia
Middle Miocene (11.18-10.65 Ma) low sulfidation-type epithermal gold mineralization occurred in the Cibaliung area, southwestern part of Java Island, Indonesia. It is hosted by andesitic to basaltic andesitic lavas of the Middle Miocene Honje Formation (11.4 Ma) and is covered by Pliocene Cibaliung tuff (4.9 Ma). The exploration estimates mineral resource of approximately 1.3 million tonnes at 10.42 g/t gold and 60.7 g/t silver at a 3 g/t Au cut-off. This equates to approximately 435,000 ounces of gold and 2.54 million ounces of silver. That resource resulted from two ore shoots: Cibitung and Cikoneng. Studies on ore mineralogy, hydrothermal alteration, geology, fluid inclusion, stable isotopes and age dating were conducted in order to characterize the deposit and to understand a possible mechanism of preservation of the deposit. The ore mineral assemblage of the deposit consists of electrum, naumannite, Ag-Se-Te sulfide minerals, chalcopyrite, pyrite, sphalerite and galena. Those ore minerals occur in quartz veins showing colloform-crustiform texture. They are enveloped by mixed layer clay illite/smectite zone, which grades into smectite zone outward. The temperature of mineralization revealed by fluid inclusion study on quartz in the veins ranges from 170 and 220°C at shallow and deep level, respectively. The temperature range is in agreement with the temperature deduced from the hydrothermal alteration mineral assemblage including mixed layered illite/smectite and laumontite. The mineralizing fluid is dilute, with a salinity <1 wt&#37; NaCl equivalent and has stable isotopes of oxygen and hydrogen composition indicating a meteoric water origin. Although the deposit is old enough that it would have been eroded in a tropical island arc setting, the coverage by younger volcanic deposits such as the Citeluk tuff and the Cibaliung tuff most probably prevented this erosion.

DOI： 10.1111/j.1751-3928.2007.00011.x

Language：Japanese  

Rare Earth Element Geochemistry on the Formation Environment of the Hishikari Epithermal Gold Deposit, Japan

Language：English  

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Language：English   Publishing type：Research paper (scientific journal)  

Implication of the temporal sulphur isotopic variation during the 2000 eruption of Miyakejima Volcano, Japan
The variation of sulphur isotopic composition during the 2000 eruption of the Miyakejima Volcano was examined in order to monitor the temporal change of the volcanic activity. The δ³⁴S values of water-soluble sulphate leached from volcanic ash effused during intermittent eruptions from July to September 2005 range from +5 to +11‰ with a fluctuation of ca 3‰ within a single eruption. The δ³⁴S value of sulphuric acid mist collected with 'Cu-metal trap' placed on the flank of the volcano from December 2000 to January 2001 is +6.2‰. These sulphur isotopic compositions of sulphate, which were isotopically equilibrated in the subvolcanic hydrothermal system, indicate that the temperature of the hydrothermal system beneath the caldera increased after the period of intermittent phreatic and phreatomagmatic eruptions. Then, the δ³⁴S value of sulphuric acid trapped from January to March 2001 was +9.0‰ and the δ³⁴S value of water-soluble sulphate on volcanic ash emitted with minor eruption in May 2001 was +11.0‰, suggesting a decrease in temperature of the subvolcanic hydrothermal system.

DOI： 10.1111/j.1440-1738.2007.00549.x

Language：English   Publishing type：Research paper (scientific journal)  

Java island, regarded as a classic example of island arcs, is built through multi events of Cenozoic arc magmatism produced by the subduction of Indian-Australian oceanic crusts along the southern margin of Eurasian plate. Regional crustal compositions, subducted slabs, and tectonics determined the spatial-geochemical evolution of arc magmatism and regional metallogeny. Tertiary geodynamics of island arc was dominated by backarc-ward migrations of volcanic centers. Only after the Miocene-Pliocene roll-back effects of retreating slab, slab detachment, and backarc magmatism took place in central Java. The source of arc magmas is mainly partial melting of mantle wedge, triggered by fluids released from dehydrated slabs. Increasing potassium contents of arc magmas towards the backarc-side and younger magmas is typical for all magmas, while alkali and incompatible trace elements ratios are characteristics for different settings of volcanic centers. The oceanic nature of crust and the likely presence of hot slab subducted beneath the eastern Java determine the occurrences of adakitic magmas. Backarc magmatism has a deeper mantle source with or without contributions from subduction-related materials. The domination of magnetite-series magmatism determines the sulfide mineralization for the whole island. District geology, geodynamics, and magma compositions in turn control particular styles and scales of precious metals concentrations. Deep-seated crustal faults have focused the locations of overlapping volcanic centers and metalliferous fluids into few major gold districts. Porphyry deposits are mostly concentrated within Lower Tertiary (early stage) volcanic centers in eastern Java which are not covered by younger volcanic centers, and whose sulfides are derived from partial melting of basaltic parental materials. On the other hand, high-grade low-sulfidation epithermal gold deposits formed in later stages of arc development and are spatially located within younger volcanic centers (Upper Miocene-Pliocene) that overlap the older ones. Gold in low-sulfidation epithermal system is likely to be derived from crustal materials. The overall interacting factors resulting in the petrochemical systematics that are applicable for exploration: 1) early-stage volcanic centers with high Sr/Y and Na₂O/K₂O ratios are more prospective for porphyry mineralization, while 2) later-stage volcanic centers with high K₂O, total alkali, and K₂O/Na₂O ratios are more prospective for low-sulfidation epithermal mineralization.

DOI： 10.1111/j.1751-3928.2006.tb00284.x

Language：English   Publishing type：Research paper (scientific journal)  

Sulfur isotope ratios of cinnabar from Hg deposits and stibnite, jamesonite and berthierite from Sb deposits in Japan are examined in order to understand metallogeneses of Hg and Sb deposits in Japanese island arcs. The studied Hg and Sb deposits include the Hg deposit at Yamato-suigin (Honshu) and the Sb deposit at Ichinokawa (Shikoku) in the Southwest Japan arc. In addition, Hg deposits including Itomuka and Ryushoden in central Hokkaido and Hg and Sb mineralizations in Northeast Japan arc are examined. The δ³⁴S values of cinnabar from the Hidaka-Kitami district, central Hokkaido, including the Itomuka and Ryushoden deposits range widely, from -10 to +16 ‰, the highest values encountered at the Samani deposit. The δ³⁴S values of cinnabar from other areas in Japan range from -12 to +5 ‰, having δ ³⁴S values higher than +2 ‰ from southwestern Hokkaido (Meiji deposit), Shikoku (Suii deposit) and Kyushu (Hasami and Yamagano deposits). On the other hand, the δ³⁴S values of stibnite from all areas in Japan range from -14 to +5 ‰, having positive δ³⁴S values higher than +2 ‰ up to +5 ‰ from southwestern Hokkaido (Yakumo, Toyotomi and Teine deposits) and eastern-central Honshu (Hachiman and Daikoku deposits). The variation in δ³⁴S values of Hg and Sb deposits may reflect the variation in δ³⁴S values of country rocks or variation in mixing ratio of sulfur extracted from the country rocks, sulfur derived from seawater sulfate, and sulfur derived from magmatic emanations. The relatively high δ³⁴S values of cinnabar and stibnite higher than +2 ‰ from southwestern Hokkaido, eastern-central Honshu and Kyushu are probably caused by contribution of volcanic emanation from arc magmas having positive Σδ ³⁴S values, whereas the positive δ³⁴S values of cinnabar higher than +2 ‰ from Suii deposit in Shikoku may be attributed to structurally substituted sulfate in limestone country rocks and/or sulfur derived from seawater sulfate. However, the wide range of the δ³⁴S values of cinnabar from the Hidaka-Kitami district, central Hokkaido, is difficult to explain at this moment. Other relatively low, negative δ³⁴S values of cinnabar and stibnite, berthierite from other areas in Japan may be attributed to 1) incorporation of isotopically light sedimentary sulfur or sulfur derived from ilmenite-series silicic magma, or 2) less contribution of volcanic emanation from arc magmas having positive Σδ³⁴S values.

DOI： 10.1111/j.1751-3928.2006.tb00266.x

Language：English   Publishing type：Research paper (other academic)  

Phanerozoic granitoids have been classified into magnetite and ilmenite series based on the abundance of magnetite, which is related to the Fe ₂ O ₃ /FeO ratio of the rock and the oxygen fugacity ( f _O2 ) of its parent magma. We have examined the temporal and spatial distributions of both series in Archean granitoids from the Barberton region and the Johannesburg Dome of the Kaapvaal Craton, South Africa. The oldest syntectonic TTG (tonalite-trondhjemite-granodiorite) granitoids (ca. 3450 Ma in age) were found to be ilmenite series, whereas some intermediate-series granitoids occurred locally. Younger and larger syntectonic TTGs (e.g., the 3230 Ma Kaap Valley plutons) comprise nearly equal quantities of magnetite and ilmenite series. The major 3105 Ma calc-alkaline batholiths (e.g., Nelspruit batholith), emplaced during the late-tectonic stage, comprise mostly magnetite-series granitoids, suggesting that an oxidized continental crust already existed by this time. The rare earth element ratios and δ ¹⁸ O values, as well as the Fe ₂ O ₃ /FeO ratios, of the Archean magnetite-series granitoids suggest that their magmas were generated from the partial melting of subducted oceanic basalts that had been oxidized by interaction with seawater on mid-oceanic ridges; the processes of magma generation were much like those for Phanerozoic magnetite-series granitoids. This further suggests that the concentrations of oxidants (O ₂ and/or SO ₄ ^2- ) in the Archean oceans were similar to those in Phanerozoic oceans. Low concentrations of chlorine in the magmas, as well as deep levels of granite erosion, appear to explain the absence of major mineral deposits associated with the Kaapvaal granitoids.

DOI： 10.1130/2006.1198(04)

Language：English   Publishing type：Research paper (scientific journal)  

Characteristics of gold mineralization at the Ciurug vein, Pongkor gold-silver deposit, West Java, Indonesia
The Pongkor Gold-Silver Mine, Bogor district, West Java, is approximately 80 km southwest of Jakarta. The gold and silver mineralization in the area is present in a deposit consisting of an epithermal vein-system named individually as the Pasir Jawa, Gudang Handak, Ciguha, Pamoyanan, Kubang Cicau, and Ciurug veins. In the area studied, rocks of basaltic-andesitic composition are dominated by volcanic breccia and lapilli tuff, with andesite lava and siltstone present locally. The hydrothermal alteration minerals in the Ciurug are a are typical of those formed from acid to near-neutral pH thermal waters, where the acid alteration is distributed from the surface to shallow depth, while the near-neutral pH alteration becomes dominant at depths. The Ciurug vein shows four main mineralization stages where each discrete stage is characterized by a specific facies; these are, from early to late: carbonate-quartz, manganese carbonate-quartz, banded-massive quartz and gray sulfide-quartz facies. The major metallic minerals are pyrite, sph alerite, chalcopyrite and galena; they occur in almost each mineralization stage. Bornite was observed only in the southern part of the Ciurug vein at a depth of 515 m, and the occurrence of this mineral is reported here for the first time. Electrum and silver sulfides (mostly acanthite) are minor, whereas silver sulfosalts, stromeyerite and mckinstryite, and covellite are in trace amounts. The silver sulfosalts have compositional ranges of pearceite, antimonpearceite and polybasite. Most of the electrum, occurs coexisting with other sulfide minerals, as inclusions in pyrite grains, with very little as inclusions in chalcopyrite or sphalerite. Gold grades within the Ciurug vein vary from 1.2 to hundreds of ppm, where the highest gold grade occurs in the latest mineralization stage in a thin sulfide band in vein quartz. Fluid inclusion microthermometry of c alcite and quartz indicates deposition throughout the mineralized veins in the range from 170 to 230°C and from low salinity fluids (predominantly lower than 0.2 wt&#37; NaCl equiv.). Fluid inclusions occur with features of boiling.

DOI： 10.1111/j.1751-3928.2005.tb00244.x

Language：English   Publishing type：Research paper (scientific journal)  

Primary ore mineral assemblage and fluid inclusion study of the Batu Hijau porphyry Cu-Au deposit, Sumbawa, Indonesia
The Batu Hijan porphyry Cu-Au deposit, Sumbawa Island, Indonesia, is associated with a tonalitic intrusive complex. The temperature-pressure condition of mineralization at the Batu Hijau deposit is discussed on the basis of fluid inclusion microthermometry. Then, the initial Cu-Fe sulfide mineral assemblage is discussed. Bornite and chalcopyrite are m ajor copper ore minerals associated with quartz veinlets. The quartz veinlets have been classified into 'A' veinlets associated with bornite, digenite, chalcocite and chalcopyrite, 'B' veinlets having chalcopyrite± bornite along vuggy center-line, rare 'C' chalcopyrite-quartz veinlets, and late 'D' veinlets consisting of massive pyrite and quartz (Clode et al., 1999). Copper and gold mineralization is associated with abundant 'A' quartz veinlets. Abundant fluid inclusions are found in veinlet quartz consisting mainly of gas-rich inclusions and polyphase inclusions throughout the veinlet types. The hydrothermal activity occurred in temperature-pressure conditions of aqueous fluid immiscibility into hypersaline brine and dilute vapor. The halite dissolution (Tm[halite]) and liquid-vapor homogenization (Th) temperatures of the polyphase inclusions in veinlet quartz range from 270 to 472°C and from 280 to 454°C, respectively. The estimated salinity ranges from 36 to 47 wt&#37; (NaCl equiv.). The apparent pressures lower than 300 bars are estimated to have been along the liquid-vapor-halite curve for the fluid inclusions having the Th lower than the Tm that trapped the brine saturated with halite, or at slightly higher pressure relative to liquid-vapor-halite curve for the fluid inclusions having the Th higher than the Tm that trapped the brine unsaturated with halite. The actual temperature and pressure during the hydrothermal activity at the Batu Hijau deposit are estimated to have been around 300°C and 50 bars. At such temperature-pressure conditions, the principal and initial Cu-Fe sulfide mineral assemblages are thought to be chalcopyrite + bornite solid solution (bnss) for the chalcopyrite-bearing assemblage, and chalcocite-digenite solid solution and bnss for the chalcopyrite-free assemblage.

DOI： 10.1111/j.1751-3928.2005.tb00245.x

Language：English   Publishing type：Research paper (scientific journal)  

Evolution of hydrothermal system at the Dizon porphyry Cu-Au deposit, Zambales, Philippines
Evolution of hydrothermal system from initial porphyry Cu mineralization to overlapping epithermal system at the Dizon porphyry Cu-Au deposit in western central Luzon, Zambales, Philippines, is documented in terms of mineral paragenesis, fluid inclusion petrography and microthermometry, and sulfur isotope systematics. The paragenetic stages throughout the deposit are summarized as follows; 1) stockwork amethystic quartz veinlets associated with chalcopyrite, bomite, magnetite and Au enveloped by chlorite alteration overprinting biotite alteration, 2) stockwork quartz veinlets with chalcopyrite and pyrite associated with Au and chalcopyrite and pyrite stringers in sericite alteration, 3) stringer quartz veinlets associated with molybdenite in sericite alteration, and 4) WNW-trending quartz veins associated with sphalerite and galena at deeper part, while enargite and stibnite at shallower levels associated with advanced argillic alteration. Chalcopyrite and bomite associated with magnetite in quartz veinlet stockwork (stage 1) have precipitated initially as intermediate solid solution (iss) and bomite solid solution (bnss), respectively. Fluid inclusions in the stockwork veinlet quartz consist of gas-rich inclusions and polyphase inclusions. Halite in polyphase inclusions dissolves at temperatures ranging from 360°C to >500°C but liquid (brine) and gas (vapor) do not homogenize at <500°C. The maximum pressure and minimum temperature during the deposition of iss and bnss with stockwork quartz veinlets are estimated to be 460 bars and 500°C. Fluid inclusions in veinlet stockwork quartz enveloped in sericite alte ration (stage 2) consist mainly of gas-rich inclusions and polyphase inclusions. In addition to the possible presence of saturated NaCl crystals at the time of entrapment of fluid inclusions that exhibit the liquid-vapor homogenization temperatures lower than the halite dissolution temperatures in some samples, wide range of temperatures of halite dissolution and liquid-vapor homogenization of polyphase inclusions from 230°C to >500°C and from 270°C to >500°C, respectively, suggests heterogeneous entrapment of gaseous vapor and hypersaline brine. The minimum pressure and temperature are estimated to be about 25 bars and 245°C. Fluid inclusions in veinlet quartz associated with molybdenite (stage 3) are dominated by gas-rich inclusions accompanied with minor liquid-rich inclusions that homogenize at temperatures between 350°C and 490°C. Fluid inclusions in vuggy veinlet quartz associated with stibnite (stage 4) consist mainly of gas-rich inclusions with subordinate polyphase inclusions that do not homogenize below 500°C. Fluid inclusions in veinlet quartz associated with galena and sphalerite (stage 4) are composed of liquid-rich two-phase inclusions, and they homogenize into liquid phase at temperatures ranging widely from 190°C to 300°C (suggesting boiling) and the salinity ranges from 1.0 wt&#37; to 3.4 wt&#37; NaCl equivalent. A pressure of about 15 bars is estimated for the dilute aqueous solution of 190°C from which veinlet quartz associated with galena and sphalerite precipitated. In addition to a change in temperature-pressure regime from lithostatic pressure during the deposition of iss and bnss with stockwork quartz veinlets to hydrostatic pressure during fracture-controlled quartz veinlet associated with galena and sphalerite, a decrease in pressure is supposed to have occurred due to unroofing or removal of the overlying piles during the temperature decrease in the evolution of hydrothermal system. The majority of the sulfur isotopic composition of sulfides ranges from ±0‰, to +5 ‰. Sulfur originated from an isotopically uniform and homogeneous source, and the mineralization occurred in a single hydrothermal system.

DOI： 10.1111/j.1751-3928.2005.tb00230.x

Language：English   Publishing type：Research paper (scientific journal)  

Silica scales containing large amounts of smectite were recently found in the pipelines for geothermal water at a geothermal power plant. To elucidate the mechanism of smectite formation, seven silica scale samples were characterized by powder X-ray diffraction, chemical analysis and ²⁷Al MAS NMR. Smectite was present in samples with MgO levels above 10 wt&#37; and Al₂O₃ levels below 10 wt&#37;. In ²⁷Al MAS NMR spectra, peaks assigned to both tetrahedrally and octahedrally coordinated aluminum (Al(4) and Al(6)) were observed for Mg-rich samples, whereas a peak due to Al(4) alone appeared in Mg-poor samples. From these observation and comparison between ²⁷Al MAS NMR spectra for synthesized precipitates of Al₂O₃-SiO₂ containing MgO and not containing MgO, it is concluded that magnesium plays an important role in the stabilization of Al(6), and results in the formation of smectite.

DOI： 10.1111/j.1751-3928.2005.tb00248.x

Language：English  

This study represents an attempt to determine the sources of vermillion found in ancient Japanese burial mounds of the 1st-6th centuries A.D., by comparing their ratios of sulfur isotopes with those of cinnabar ore samples collected in Japan and China. Cinnabar ore samples were taken from three mines in central Japan (Niu in Mie, Yamato in Nara, and Sui in Tokushima prefectures), and from Wanshan in China, where mining activity has been recorded back to the 6th century A.D. and earlier. When the ratios of ³⁴S and ³²S were compared with the Canyon Diablo meteorite standard, a high δ³⁴S value of + 22.6 ± 3.60‰ was found for the Wanshan mine, as opposed to low values ranging from -7.3 ± 1.9 to -2.1 ± 1.6‰ for the Japanese mines. The ratios of sulfur isotopes in vermillion collected from ancient Japanese burial mounds also divided into two groups. High ratios (+11.1 to +22.8‰) were found in 1st- and 2nd- century burials in the western regions of northern Kyushu and San'in, suggesting that local, powerful chiefs obtained vermillion through relations with China. Lower ratios (-8.4 to -2.0‰) were found in burials of the 2nd through 6th centuries in central Japan, where the ancient Yamato dynasty emerged as the first unified polity around the end of the 2nd century A.D. We, therefore, conclude that the Yamato dynasty exploited local sources of vermillion, rather than depending solely on China. The present study demonstrates the feasibility of determining sources of vermillion using sulfur isotope ratios, and the relevance of such findings for archaeological research.

DOI： 10.1002/gea.20035

Language：English  

Ages for thirty adularia samples collected from various veins were in the Hishikari gold deposit determined by ⁴⁰Ar/³⁹Ar dating to constrain the timing of adularia-quartz vein formation and to determine the temporal change in temperature of hydrothermal fluid. Plateau ages were obtained from all adularia samples, and significant excess ⁴⁰Ar is not recognized from inverse isochrones. The duration of mineralization within individual veins was determined by adularia ages from the early and late stages of mineralization within the same vein. The durations of mineralization in the Daisen-1, Daisen-3, Hosen-2 and Keisen-3 veins in the Honko-Sanjin zone were 7,000, 140,000, 160,000 and 170,000 years, respectively. The durations of mineralization in the Seisen-2 and Yusen-1-2 veins in the Yamada zones were 360,000 and 320,000 years, respectively. Mineralization lasted for a relatively longer period in individual veins at the Yamada zone. Mineralization ages from the Honko-Sanjin zone range from 1.04 to 0.75 Ma, and most mineralization ages are concentrated in a short period from 1.01 to 0.88 Ma. In contrast, mineralization ages for the Yamada zone range from 1.21 to 0.64 Ma. These results indicate that fracturing and subsequent vein formation lasted for a longer period in the Yamada zone (about 570,000 years) compared with those events in the Honko-Sanjin zone (about 290,000 years). The homogenization temperatures of liquid-rich fluid inclusions in columnar adularia used for age determination were determined to be 223°C on average, and most of these temperatures range from 180 to 258°C. No significant temporal change in homogenization temperature is recognized in this study. However, adularia in the Keisen veins indicated higher homogenization temperatures compared with elsewhere in the deposit, suggesting that the principal ascent of mineralizing hydrothermal fluid was via the Keisen veins.

DOI： 10.1111/j.1751-3928.2005.tb00246.x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/j.1751-3928.2005.tb00236.x

Language：English   Publishing type：Research paper (scientific journal)  

Occurrence of halogen-rich phlogopite in Late Cenozoic volcanic rocks in the Japanese arcs
Halogen-rich phlogopite occurs in the groundmass of andesite and dacite lavas from Late Tertiary to Quaternary volcanoes associated with native sulfur and limonite deposits (Shiretoko-Iwozan, Hachimantai, Adatara, Omeshidake, Masaki) and hydrothermal ore deposits (Harukayama, Muineyama, Hishikari) in Japan. The F contents of the halogen-rich phlogopite range from 3.6 to 5.7 wt&#37;, corresponding to atomic F/(F+Cl+OH) ratios ranging from 0.45 to 0.69. On the other hand, the Cl contents of the halogen-rich phlogopite are around 0.2 wt&#37;. The atomic Mg/(Mg+Fe) ratios range from 0.69 to 0.83. The fluorine intercept value [IV(F)] defined by Munoz (1984) of the phlogopites ranges from 0.79 to 3.17, and the chlorine intercept value [IV(Cl)] ranges from -7.11 to -7.77. The observed IV(F) of the phlogopites broadly overlap the range of the IV (F) for biotites from porphyry copper deposits. On the other hand, the observed IV(Cl) are significantly lower than the IV(Cl) for biotites from porphyry copper deposits. Whereas the F contents of the phlogopite appear more prominent compared to the Cl contents, the calculation of halogen intercept values revealed that the phlogopites are enriched in Cl with respect to the element distribution effect of Mg-Fe substitution. Since the degree of Cl enrichment of the phlogopite is more significant compared to that of biotite in porphyry copper deposits, the phlogopites are considered to have formed under the condition of significantly high activity of halogens. Hydrothermal ore deposits may be formed in magmatic hydrothermal system associated with volcanoes where halogen-rich phlogopite is formed by hypersaline fluid.

DOI： 10.1111/j.1751-3928.2004.tb00196.x

Language：English   Publishing type：Research paper (scientific journal)  

Variation of Cl and SO₃ contents of microphenocrystic apatite in intermediate to silicic igneous rocks of Cenozoic Japanese island arcs Implications for porphyry Cu metallogenesis in the western Pacific island arcs
Determinations of SO₃ and Cl contents of igneous accessory apatite were carried out on Late Cenozoic intermediate to silicic intrusive and volcanic rocks in the Japanese island arcs of the western Pacific rim including the southwestern Kuril arc (eastern Hokkaido), Northeast Japan arc (southwestern Hokkaido through northeastern Honshu to central Honshu), Izu-Bonin arc, Kyushu-Palau ridge, Southwest Japan arc (northern Kyushu) and northern Ryukyu arc (southern Kyushu). These were compared to those from the Western Luzon arc, Philippines, to better understand the metallogenesis of porphyry Cu deposits in the western Pacific island arcs. In addition, SO₃ and Cl contents of accessory apatite in the Cretaceous magnetite-series granitic rocks in the Kitakami belt (northeastern Honshu) and the Miocene ilmenite-series granitic rocks in the Outer Zone of Southwest Japan (southern Kyushu) were also examined. Microphenocrystic apatites in shallow intrusions associated with porphyry Cu deposits in the Western Luzon arc contain >0.1 wt&#37; S as SO₃. Such high SO₃ contents of microphenocrystic apatite are a common characteristic of hydrous magmatism in the Western Luzon arc, from 15 Ma old tonalitic plutonic rocks of the Luzon Central Cordillera to present-day volcanism at Mount Pinatubo. The accessory apatite in intrusive rocks associated with porphyry Cu deposits, especially those at the Santo Tomas II deposit, show significantly high Cl contents (>2 wt&#37;). The SO₃ contents of microphenocrystic apatite in most of the hydrous silicic rocks along the volcanic front, in andesites related to native sulfur deposits, and in Miocene and younger shallow granitic intrusions in northeastern Honshu, are generally <0.1 wt&#37;. On the other hand, the SO₃ contents of apatite in such rocks from eastern Hokkaido, southwestern Hokkaido, Izu, northern Kyushu and southern Kyushu are similar to those from the Western Luzon arc. The SO ₃ contents of accessory apatite in the Cretaceous magnetite-series granitic rocks in the Kitakami belt are variable, whereas those of the Miocene ilmenite-series granitic rocks in southern Kyushu are extremely low. The Cl contents of accessory apatite in some rocks of the Northeast Japan arc, Izu-Bonin arc and Southwest Japan arc are significantly high. In terms of the Cl and SO₃ contents of microphenocrystic apatite, Cenozoic Japanese arc magmatism show similarities with arc magmatism associated elsewhere with porphyry Cu mineralization, except for the most of northeastern Honshu of the Northeast Japan arc. Apatite commonly occurs as inclusions in other phenocrystic phases. Thus the variation in SO₃ contents of apatite is a feature of early stage magmatic differentiation. The SO ₃ contents of microphenocrystic apatite are considered to reflect the redox state of the magma source region or fluids encountered during magma generation.

DOI： 10.1111/j.1751-3928.2004.tb00211.x

Language：English   Publishing type：Research paper (scientific journal)  

Association of electrum and calcite and its significance to the genesis of the Hishikari gold deposits, southern Kyushu, Japan.

Language：English   Publishing type：Research paper (scientific journal)  

The Victoria gold deposit is a low-sulfidation style epithermal carbonate-base metal gold deposit discovered in 1995 in the Mankayan mineral district, northern Luzon, Philippines. It occurs just south of a high-sulfidation copper-gold orebody (Lepanto enargite deposit) and a porphyry copper-gold orebody (Far Southeast (FSE) deposit). Radiometrie dating of the Victoria mineralization yields ages from 1.6 to 1.1 Ma, similar to ages of the Lepanto enargite deposit. Mineralogical, geochemical, fluid inclusion and sulfur isotope studies suggest that the Victoria deposit is not directly related to the late stage of hydrothermal activity that produced the FSE porphyry copper-gold and the Lepanto enargite deposits. The hydrothermal fluids from which Victoria was formed appear to have been derived from the south, and not from the FSE intrusive center to the northeast. This would suggest a regional south to north hydrothermal gradient, consistent with the similar flow within the FSE porphyry-Lepanto enargite system. On a district scale, structures similar to those of the Victoria deposit in trend and nature would be highly prospective, especially if they occur north of identified plutons and volcanic centers.

DOI： 10.1111/j.1751-3928.2002.tb00142.x

Language：English   Publishing type：Research paper (scientific journal)  

Mineral assemblage, precipitation sequence and textures of the gold-bearing veins from the Hishikari epithermal vein-type deposits, southern Kyushu, Japan, were examined. In addition, fluid inclusion microthermometry and carbon and oxygen isotopic compositions of calcite were determined. Calcite, and that replaced by quartz, were commonly observed throughout the precipitation sequence of the veins. Thus, calcite must be a more common gangue constituent initially than observed presently. Association of calcite and electrum is observed immediately subsequent to columnar adularia in some vein samples. In addition, close association of electrum with pseudo-acicular quartz, and electrum with truscottite were observed. The initial coprecipitation of electrum and calcite might be a common phenomenon in the gold-bearing veins at the Hishikari deposits. The Th (homogenization temperature) data from the Honko-Sanjin deposits are generally higher than those from the Yamada deposit. Samples that show association of calcite and electrum yielded higher Th (206-217°C, average) than the Th data from calcite associated with low-grade Au ore or barren (180-204°C, average). The measured Tm (temperature of last melting point of ice) range from -0.4 to 0.0°C. The result suggests that the salinity of the hydrothermal solution was low during the precipitation both of calcite associated with Au mineralization and of barren calcite. Fluid inclusion evidence suggestive of boiling of hydrothermal solution for the precipitation of calcite was not recognized in the present work. The δ13C and δ18O values of calcite range from -10.8 to -4.7 ‰ and from +3.2 to +15.2 ‰, respectively. The δ13C value of H2CO3 and the δ18O value of H2O in the hydrothermal fluids calculated assuming isotopic equilibrium with calcite using the temperature obtained by fluid inclusion microthermometry, range from -14.4 to -9.1 ‰, and from -6.2 to +5.5 ‰, respectively. Thus, the calculated δ18O values of H2O for calcite further confirm the presence of the 18O-enriched ore fluids during the mineralization at the Hishikari deposits. The hydrothermal solution isotopically equilibrated with the sedimentary basement rocks was responsible for the gold mineralization associated with calcite.

DOI： 10.1111/j.1751-3928.2002.tb00148.x

Language：English   Publishing type：Research paper (scientific journal)  

Victoria carbonate-base metal gold deposit and its significance in the Mankayan mineral district, Luzon, Philippines.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Zeolite-bearing veins pervaded in the Shirahama Formation Upper Pliocene) of the Chikura Group at the southern end of Boso Peninsula, Chiba Prefecture

Language：English   Publishing type：Research paper (scientific journal)  

Magnetic susceptibilities were measured on a representative collection of Archaean granitoids of the Barberton region using a portable KT5 magnetic susceptibility meter. The studied granitoids comprise, (1) syn-tectonic tonalite-trondhjemite-granodiorite (TTG) granitoids (132 samples), (2) late-tectonic calc-alkaline granitoids (402 samples) and (3) post-tectonic low-Ca and high-Ca granitoids (12 samples). Most of the early-stage syn-tectonic granitoids (similar to3450 Ma) have low magnetic susceptibilities, less than 3 x 10(-3) SI units, and correspond to ilmenite-series granitoids. The late-stage Kaap Valley tonalite pluton (similar to3230 Ma) contains sporadically distributed higher magnetic susceptibility values (greater than 3 x 10(-3) SI units), which are less than one-third in magnetic susceptibility of typical magnetite-series TTG of the Japanese Island Arc and thus strictly belong to an intermediate series. The Barberton TTG suite is essentially derived from reduced amphibolitic lower crust that reflects the anoxic nature of the Earth surface during the Archaean Eon. The more oxidized nature of the Kaap Valley tonalite may be generated in an oxidized lower crust by fluids squeezed out of the subducting plate.
Late-tectonic granodiorite - adamellite batholithic complexes (similar to3105 Ma) belong mostly to the magnetite series, and seem to suggest that relatively oxidized continental crust, reflecting oxic atmosphere and subduction mechanism operating, had evolved it by this time. Post-tectonic granitic plutons formed largely between circa 2900 Ma and 2700 Ma can be subdivided into low-Ca ilmenite series and high-Ca magnetite series.

DOI： 10.1016/S1342-937X(05)70630-4

Language：English   Publishing type：Research paper (scientific journal)  

ranitoid series in terms of magnetic susceptibility: A case study from the Archean Barberton Region, South Africa.

Language：English   Publishing type：Research paper (scientific journal)  

K-Ar ages of the following porphyry Cu deposits in the western Luzon arc are determined: Lobo-Boneng (10.5±0.4 Ma), Santo Niño (9.5±0.3 Ma), Black Mountain (2.1±0.1 Ma), Dizon (2.5±0.2 Ma) and Taysan (7.3±0.2 Ma). Microphenocrystic apatite in the late Cenozoic intermediate to silicic intrusions associated with porphyry Cu deposits in the western Luzon arc contains sulfur as SO₃ detectable by electron probe microanalyzer. Sulfur is supposed to have been accommodated dominantly as oxidized species in oxidizing hydrous magmas that generated porphyry Cu deposits. Likewise, such high SO₃ contents in microphenocrystic apatite are common characteristics of the intermediate to silicic magmatism of the western Luzon arc, from tonalitic rocks of the Luzon Central Cordillera of about 15 Ma to an active magmatism at Mount Pinatubo. Thus, the western Luzon arc has been generating porphyry Cu mineralization associated with oxidizing hydrous intermediate to silicic magmatism related to eastward subduction, since Miocene to the present day. Intermediate to silicic rocks since 15 Ma to present-day western Luzon arc generally show high whole-rock Sr/Y ratio ranging from 20 to 184. However, porphyry Cu deposit is not necessarily related to the rocks that show higher Sr/Y ratios compared to the other barren rocks in the western Luzon arc. The characteristics of the intermediate to silicic magma associated with porphyry Cu deposit are not attributed to the composition of the source material of the magma, but to the properties defined by the high activity of oxidized species of sulfur in the fluid phase that is encountered during the generation of intermediate to silicic magmas.

DOI： 10.1111/j.1751-3928.2002.tb00127.x

Language：Japanese   Publishing type：Research paper (scientific journal)  

Genesis of Na-series rock alteration widespread in the southeastern area of Hachimantai geothermal field: Water-rock interactions driven by descending groundwater and fossil seawater.

Language：English   Publishing type：Research paper (scientific journal)  

Further occurrence of brown ores in Kuroko-type deposits in Japan.

Language：English   Publishing type：Research paper (scientific journal)  

The occurrence of so-called brown ore from the Kuroko-type deposits in Japan was examined. Brown ore specimens from the Kannondo, Inarizawa, Matsumine, Fukazawa, Uchinotai, Kosaka (orebody unknown) and Nurukawa deposits have been found in the ore collection stored by Dowa Mining Co. Ltd. and the subsidiary companies. In addition, occurrences from the Fukazawa, Matsumine, Ezuri, Shakanai, and Ginzan deposits were previously reported. The brown ore is characterized by its color and by its higher Ag concentration (up to around 2,400 g/t) than ordinary black ores. This type of ore occurs commonly in the Kuroko-type deposits in Japan, whereas its extent is limited. The brown ore is a type of Au-rich massive sulfide ore formed in submarine hydrothermal system.

DOI： 10.1111/j.1751-3928.2001.tb00098.x

Language：English   Publishing type：Research paper (scientific journal)  

Generation and evolution of ore fluids for porphyry Cu-Au mineralization at the Santo Tomas II (Philex) deposit, Philippines.

Language：English   Publishing type：Research paper (scientific journal)  

The Santo Tomas II (Philex) deposit is a porphyry Cu-Au deposit, located in the southern part of the Baguio mineral district, Benguet Province, northern Luzon, Philippines. The Santo Tomas II deposit is associated with an intrusive complex consisting of four rock types that are distinguished based on petrography. They are 1) post-ore clinopyroxene-bearing hornblende andesite porphyry, 2) ore-generating hornblende andesite porphyry, 3) hornblende quartz diorite porphyry and 4) porphyritic hornblende quartz diorite. K-Ar age of hydrothermal biotitization was estimated to be 1.5±0.4 Ma. A number of intrusive bodies having broadly similar petrography and K-Ar age occur in the vicinity of the Santo Tomas II deposit, such as at Clifton, Ligay (Binang), Bumolo (Waterhole) and Philex Main Camp areas. The intrusions at the Santo Tomas II deposit and in the vicinity are characterized by high XMg (Mg/[Mg+Fe] atomic ratio, about 0.7 or higher) of mafic silicate phenocrysts such as hornblende, and high sulfur contents (> 0.2 wt&#37; as SO3) in accessory microphenocrystic apatite, suggesting a highly oxidizing condition. Sulfur is accommodated dominantly as oxidized species since the crystallization of phenocrysts. Sub-dendritic rim of tremolitic amphibole on hornblende phenocryst in the ore-generating andesite porphyry at the Santo Tomas II deposit suggests interaction of magma and aqueous fluid(s) exsolved due to decompression during intrusion. Dissemination of magnetite is associated with hydrothermal biotitization and is followed by sheeted and stockwork quartz veinlets having silician magnetite and rare titanohematite instead of Cu-Fe sulfides. The silician magnetite-rich quartz veinlet was formed at fO2 near the hematite-magnetite buffer at nearly magmatic temperature, where sulfur dominantly existed as oxidized species such as SO2. Chalcopyrite and bornite, which commonly exhibit micrographic texture often accompanying Pd telluride and native gold/Au-rich electrum, are associated with subsequent anhydrite (-quartz) veinlets and stringers. Both intermediate solid solution (iss) and bornite solid solution (bnss) are thought to have coprecipitated primarily at above 500°C based on fluid inclusion microthermometry and sulfur isotope thermometry applied for anhydrite and associated chalcopyrite and bornite. The initial iss is considered to have converted to chalcopyrite partly replacing bnss during cooling. The hypersaline polyphase fluid inclusions abundantly found in the sheeted and stockwork quartz as well as anhydrite veinlets with scarce gaseous inclusions suggest that they have been trapped in the two aqueous fluid immiscible region. The western Luzon arc associated with porphyry Cu mineralization is characterized by oxidized hydrous magmatism and shallow emplacement, and by the source of sulfur enriched in 34S.

DOI： 10.1111/j.1751-3928.2001.tb00083.x

Language：Others   Publishing type：Research paper (scientific journal)  

Horizontal strain rate in relation to vein formation of the Hishikari gold deposits, southern Kyushu, Japan.

Language：English   Publishing type：Research paper (scientific journal)  

The Hishikari deposits comprise the Honko (Main), Yamada, and Sanjin deposits. The horizontal strain in the direction (approx. N40°W) normal to the general NE-SW strike of the Hishikari vein system was calculated, based on the measured total vein widths to the distance along three crosscuts. Veins were assumed to accompany no significant fault displacement in the calculation. Veins in the eastern and the middle parts of the Honko-Sanjin deposits spatially occupy 3.2&#37; and 1.3&#37;, respectively, and veins in the Yamada deposit occupy 6.7&#37;. Significant local variation of strain is observed in some areas. Reported K-Ar ages on adularia-quartz veins indicate the duration of vein opening to be 2.6×105 yr in the Honko-Sanjin deposits and 5.9×105 yr in the Yamada deposit. Horizontal strain rates were calculated to be 5.0-12×10-8 yr-1 through the Hishikari deposits. The calculated strain rates at the Hishikari deposits are roughly comparable to the regional horizontal strain rate in the Recent. Widespread extensional movement in southern Kyushu seems to have been able to provide sufficient strain for the formation of the Hishikari deposits, rather than contribution of local movements.

DOI： 10.1111/j.1751-3928.2001.tb00077.x

Language：English   Publishing type：Research paper (scientific journal)  

Sulfur isotope study and re-examination of ore mineral assemblage of the Hol Kol and the Tul Mi Chung skarn-type copper-gold deposits of the Suan mining district, Korean Peninsula.

Language：English   Publishing type：Research paper (scientific journal)  

Ore specimens collected by the late Professor Takeo Watanabe from the Hol Kol and the Tul Mi Chung deposits, Suan mining district, Korean peninsula, were examined. In addition, measurements of sulfur isotopic ratio of ores and preliminary fluid inclusion microthermometry were carried out. Ores from the New orebody of the Hol Kol deposit consist mainly of bornite, wittichenite and chalcopyrite presently, which exhibit lamellae intergrowth texture, associated with native bismuth and electrum. Bismuthian bornite solid solution is considered to be a principal initial phases, while native bismuth was nucleated as molten bismuth melt initially. The occurrence of cubanite, miharaite, carrollite, siegenite, hessite and geikielite are recognized from the New orebody. Ores from the Eastern orebody of the Hol Kol deposit consist chiefly of chalcopyrite, occasionally associated with trace amounts of pyrrhotite, pyrite, bismuthinite and rare tellurobismuthite, while an ore specimen from the Western orebody consists mainly of sphalerite associated with chalcopyrite, pyrite and galena. Ores from the Tul Mi Chung deposit consist mainly of chalcopyrite and pyrite, occasionally associated with magnetite, sphalerite, galena and rare molybdenite. Some portions of magnetite are revealed to be silician magnetite. Sulfur fugacity is supposed to be below the stability field of bismuthinite in the New orebody. A reducing condition is suggested by the occurrence of geikielite without Fe3+ content. The sulfur and oxygen fugacities for the Eastern and Western orebodies of the Hol Kol deposit and for the Tul Mi Chung deposit were higher than the New orebody of the Hol Kol deposit. On the other hand, the Suan granite (porphyritic granodiorite) and the Chil Sing Dai granite (biotite granite porphyry) from the Hol Kol area can be classified as weakly magnetic magnetite-series. Polyphase fluid inclusions are observed in gangue diopside associated with Cu ore of two specimens. The dissolution temperatures of daughter crystals are 394±26°C and 442±45°C, while the disappearing temperatures of vapor bubble were 475±25°C and >500°C. Highly saline fluids were responsible for the mineralization at the Hol Kol deposit. The δ34S values of ore sulfides of the Hol Kol and the Tul Mi Chung deposit range from +11.5 ‰ to +16.1 ‰, having anomalous lower values mainly from the Tul Mi Chung deposit. Such anomalous lower δ34S values can be caused by isotopic fractionation against oxidized sulfur species. The δ34S value of bulk sulfur in the ore solutions responsible for the Hol Kol and the Tul Mi Chung deposit is estimated to be +13.5±2.5 ‰.

DOI： 10.1111/j.1751-3928.2000.tb00071.x

Language：English   Publishing type：Research paper (scientific journal)  

Geneses of high chlorine and silver-lead-zinc-mineralized granitoids in Tsushima, Japan.

Language：English   Publishing type：Research paper (scientific journal)  

The Lepanto Far Southeast porphyry Cu-Au deposit is located beneath and to the southeast of the Lepanto enargiteluzonite Cu-Au deposit in Mankayan, Benguet Province, Philippines. The principal orebody consists of potassic alteration subjected to partial retrograde chlorite alteration that rims stockwork of quartz-anhydrite veinlets. Fluid inclusions found in stockwork quartz and anhydrite in the biotitized orebody center are dominated by polyphase inclusions that homogenize at temperatures of >500°C. Sulfur isotopic thermometry applied to the sulfides-anhydrite pairs suggests around 500°C. The principal ore minerals associated with quartz-anhydrite stockworks are chalcopyrite and pyrite with minor bornite and Bi-Te-bearing tennantite, with trace of native gold. Rounded pyrite grains appear fractured and corroded and are interpreted as remnants of primary intermediate solid solution + pyrite assemblage. A breccia pipe truncates the deposit. Mineralization in the breccia pipe is brought by quartz-anhydrite veinlets and infilling in the interstices between clasts. Chalcopyrite-Au mineralization associated with molybdenite is recognized in the deeper zone in the breccia pipe. Fluid inclusion microthermometry on polyphase inclusions in veinlet quartz as well as sulfur isotope thermometry applied for the pair of anhydrite and sulfides suggests >450°C. Fluid inclusions in veinlet quartz and anhydrite in the fringe advanced argillic alteration are chiefly composed of coexisting liquid-rich inclusions and gas-rich inclusions, in addition to coexisting polyphase inclusions and gas-rich inclusions. These inclusions exhibit a wide range of homogenization temperatures, suggesting heterogeneous entrapping in the two-fluid unmixing region. Sulfur isotopes of aqueous sulfide and sulfate exhibit a general trend from the smallest fractionation pairs (about 11 ‰) in the biotitized orebody center to the largest fractionation (about 25 ‰) pairs in the fringe advanced argillic alteration, suggesting a simple evolution of hydrothermal system. The slopes of arbitrary regression lines in δ34S versus △34S[SO4=-H2S] diagram suggest that the abundance ratio of aqueous sulfate to sulfide in the hydrothermal fluid has been broadly constant at about 1:3 through temperature decrease. The intersection of these two regression lines at the δ34S axis indicates that the bulk δ34S is about +6 ‰. Thus, the Lepanto FSE deposit is a further example which confirms enrichment in 34S in the hydrous intermediate to silicic magmas and associated magmatic hydrothermal deposits in the western Luzon arc.

DOI： 10.1111/j.1751-3928.2000.tb00065.x

Language：English   Publishing type：Research paper (scientific journal)  

Miocene granitoids of the Tsushima Islands have unique characteristics that cannot be seen in other major granitic plutons in the Japanese Islands as follows: (1) They are granitic in composition but contain synplutonic mafic dikes, abundant mafic enclaves, and intermediate facies between granite and mafic enclaves. (2) They are mixture of magnetite-bearing and -free facies, but generally magnetite-free in the marginal part. (3) They are high in K₂O content (K₆₅=3.1) and intermediate in normative corundum (C₆₅=0.1) and δ¹⁸O value (+9 ‰ at SiO₂ 70 %), which may be comparable with those of the Miocene Outer Zone granitoids. (4) Yet the initial Sr ratio is low as 0.7037. (5) They are high in Cl and S, which occur in fluid inclusions and as pyrrhotite>pyrite, respectively. Two genetic models are considered for the source of the unique granitoid magmas: the continental crust or the upper mantle fertilized with Si, K and ¹⁸O. The latter may be the case for the Tsushima granitoids, because of the low initial Sr ratio. The age of the granitoids (16 Ma) indicates the magmatism related to the opening of the Sea of Japan. It is suggested that both basaltic and granitic magmas were generated in the continental lithosphere under an extensional tectonic setting; the two magmas could have been partly mingled. The mingled magma was originally an oxidized type, but reduced during the emplacement by repeated inflow of S and C-bearing gases from the pelitic wall rocks. Because of the reduction, SO₃ sulfur is almost nil in the rock-forming apatite, and most of sulfur remained in fluid phase of the magma as reduced species. Cl content was high in the original magma and concentrated in the fluid phase of the residual system which dissolved silver, lead and zinc metals. Such a fluid migrated into the Taishu fracture systems, as the magma crystallized, and formed the silver-lead-zinc deposits.

DOI： 10.1111/j.1751-3928.2000.tb00066.x

Language：English   Publishing type：Research paper (scientific journal)  

Sulfur isotopic study of the Toyoha deposits, Hokkaido, Japan -Comparison between the earlier-stage and later-stage veins-.

Language：English   Publishing type：Research paper (scientific journal)  

The Mamut deposit of Sabah, East Malaysia, is a porphyry type Cu-Au deposit genetically related to a quartz monzonite ("adamellite") porphyry stock associated with upper Miocene Mount Kinabalu plutonism. The genesis of the Mamut deposit is discussed based on petrology of the intrusives in the Mount Kinabalu area combined with ore-and alteration-petrography, fluid inclusion and sulfur isotope studies. Groundmass of the adamellite porphyry at Mamut is rich in K which suggests vapor transport of alkaline elements during the mineralizing magmatic process, while the groundmass of the post-ore "granodiorite" porphyry at Mamut contains small amounts of normative corundum suggesting depletion in alkaline elements at the root zone of the magma column. Subdendritic tremolitic amphibole rims on hornblende phenocrysts in the Mamut adamellite porphyry suggest interaction between the mineralizing magma and the exsolved fluids. Occurrences of clinopyroxene microphenocrysts and pseudomorphic aggregates of shredded biotite and clinopyroxene after hornblende phenocrysts in the barren intrusives imply lower water fugacity and decreasing in water fugacity, respectively. Compositional gap between the core of hornblende phenocrysts and the tremolitic amphibole rims and those in the groundmass of the Mamut adamellite porphyry suggests a decrease in pressure. Higher XMg (=Mg/(Mg+Fe) atomic ratio) in the tremolitic amphibole rims in the Mamut adamellite porphyry compared to those of the barren intrusions suggests high oxygen fugacity. High halogen contents of igneous hydrous minerals such as amphiboles, biotite and apatite in the Mamut adamellite porphyry suggest the existence of highly saline fluids during the intrusion and solidification of the mineralizing magma. Fluid inclusions found in quartz veinlet stockworks are characterized by abundant hypersaline polyphase inclusions associated with subordinate amounts of immiscible gaseous vapor Both Cu and Au are dispersed in disseminated and quartz stockwork ores. Chalcopyrite and pyrrhotite as well as magnetite are the principal ore minerals in the biotitized disseminated ores. Primary assemblage of intermediate solid solution (iss) and pyrrhotite converted to the present assemblage of chalcopyrite and pyrrhotite during cooling. Subsequent to biotitization, quartz veinlet stockworks formed associated with retrograde chlorite alteration. The Cu-Fe sulfides associated with stockwork quartz veinlet are chalcopyrite and pyrite. Overlapping Pb and Zn and subsequent Sb mineralizations were spatially controlled by NNE-trending fractures accompanying the phyllic and advanced argillic alteration envelope. Sulfur isotopic composition of ore sulfides are homogeneous (about +2‰) throughout the mineralization stages. These are identical to those of the magmatic sulfides of Mount Kinabalu adamellitic rocks.

DOI： 10.1111/j.1751-3928.2000.tb00052.x

Language：English   Publishing type：Research paper (scientific journal)  

The sulfur isotopic ratios (δ³⁴S) of ore minerals from the Toyoha deposit, Hokkaido, one of the largest Pb-Zn-Ag polymetallic vein-type deposits in Japan, were studied. More than 90% of the δ³⁴S values of the studied sulfide minerals collected from the Toyoha deposit range from +5 to +9‰, with an average of approximately +7‰ irrespective of the mineral species, veins, elevations, depth, mineralization stages and mineral assemblages. Relatively uniform δ³⁴S values obtained in this study suggest that the reduced aqueous sulfur species predominated over the oxidized sulfur in the ore solution throughout the mineralization stages. Thus, the source of sulfur for the ore sulfides is postulated to be magmatic. The temperature obtained from the fluid inclusion study and the temperature of the sulfur isotopic geothermometer are not consistent. This suggests that each mineral precipitated under disequilibrated conditions with respect to the sulfur isotope. The change in redox conditions presumably encountered between the mineralization stages did not account for the isotopic fluctuations since the isotopic exchanges between the oxidized and reduced aqueous sulfurs are much slower than the rate of oxidation of the ore solution.

DOI： 10.1111/j.1751-3928.2000.tb00061.x

Language：English   Publishing type：Research paper (scientific journal)  

Pyrite disease in luzonite from the Lepanto Cu-Au deposit, Mankayan, Philippines: Further example of disease texture and its origin.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/j.1751-3928.1999.tb00042.x

Language：English   Publishing type：Research paper (scientific journal)  

The Shin-Ohtoyo Cu-Au deposit is located in the Harukayama district, 20 km west of Sapporo, Hokkaido, Japan. Both acid-type disseminated and adularia-quartz-type vein Au mineralizations have been recognized within a small distance of less than 500 m in the district. Mineralogical characteristics of sulfide ores from the Shin-Ohtoyo deposit have been proved to be polymetallic. Ore minerals containing Sn, V, Bi and Te are recognized. Nine ore types are recognized in terms of characteristic mineral assemblage; (1) chalcedonic quartz veinlets in silicified zone around the deposit, (2) bismuthinite, emplectite, ±friedrichite and tetrahedrite, (3) an unnamed Cu-Sn-Fe-Zn sulfide, colusite-series minerals, ±stannoidite, emplectite and tetrahedrite, (4) bournonite, Se-bearing galena and tetrahedrite, (5) luzonite/famatinite and Ag-bearing tetrahedrite, (6) colusite-series minerals, emplectite, aikinite and tetrahedrite/goldfieldite, (7) luzonite/famatinite, colusite-series minerals, mawsonite and tetrahedrite/goldfieldite, (8) enargite, luzonite/famatinite and tetrahedrite, and (9) colusite-series minerals and tetrahedrite. The first occurrence of friedrichite and stibiocolusite from Japan are reported. The chemical formula of the unnamed phase corresponds to Cu6(Cu,Fe,Zn)Sn3S10. Sulfur isotopic ratios (δ34S) of sulfides from the stockpile range from -0.5 ‰ to + 1.9 ‰, and those from drill cores recovered by Metal Mining Agency of Japan (MMAJ) vary from -2.7 ‰ to +0.8 ‰. Sulfur isotopic ratio of barite in a cavity in the silicified tuff breccia collected from the stock pile yields +27.1 ‰, while that of barite collected from MMAJ core is +21.7 ‰. Sulfur isotopic thermometry applied for a pair of barite (+21.7 ‰) and associated pyrite (+1.8 ‰) indicates about 300°C. High-Te tetrahedrite composition from both the chalcedonic quartz vein in the silicified zone around the Shin-Ohtoyo deposit and the polymetallic sulfide ores from the adit of the deposit, suggests that the Au mineralization in the former is attributed to a hydrothermal system marginal to the polymetallic mineralization.

DOI： 10.1111/j.1751-3928.1999.tb00033.x

Language：English   Publishing type：Research paper (scientific journal)  

Manned submersible studies have delineated a large and actively growing Kuroko-type volcanogenic massive sulfide deposit 400 kilometers south of Tokyo in Myojin Knell submarine caldera, The sulfide body is Located on the caldera floor at a depth of 1210 to 1360 meters, has an area of 400 by 400 by 30 meters, and is notably rich in gold and silver. The discovery of a Large Kuroko-type polymetallic sulfide deposit in this are-front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits.

DOI： 10.1126/science.283.5404.975

Language：English   Publishing type：Research paper (scientific journal)  

Several native sulfur specimens, collected from Shiretoko-Iwozan volcano, eastern Hokkaido, Japan, exhibit spinifex texture, which appears to resemble that often observed in komatiite. The spinifex texture is exhibited by yellow-colored elongated skeletal native sulfur crystals up to 5 cm long settled in medium gray-colored fine-grained clayey matrix. One surface of a specimen is coated by layers of micro pillow lava of native sulfur. Such specimens were rarely found as clasts or fragments around the 1936 No. 1 crater that erupted native sulfur flows, together with the most common monomineralic native sulfur fragments of native sulfur flows having pahoehoe surface and of native sulfur dikes. The elongated spinifex native sulfur crystals presently consist of aggregated polygrains of orthorhombic sulfur crystals formed through crystallographic transition from the single crystal of monoclinic sulfur initially crystallized. The spinifex texture exhibited by elongated skeletal native sulfur crystals is a product of rapid cooling of sulfur melt. Many lithic fragments of altered country rocks are present in the specimens exhibiting native sulfur spinifex texture. This suggests that segregation of the sulfur melt from the mixture of lithic fragments and sulfur melt was incomplete because the mixture was chilled before the melt segregation. Elongated skeletal native sulfur crystals may have nucleated and crystallized directly from the molten sulfur liquid. Lithic fragments mixed in the melt are supposed to have acted as nuclei for the nucleation of the native sulfur crystals. On the other hand, the most of native sulfur flows consist of monomineralic massive native sulfur with very scarce lithic fragments. Such massive monomineralic native sulfur crystallized from the supercooled, solidified amorphous sulfur. Such supercooled amorphous state may have been attained due to the lack of nuclei because of the scarcity of lithic fragments. The unique structures exhibited by native sulfur lava flow, including pahoehoe surface and spinifex texture, are due to the characteristic physical property of molten sulfur liquid, that is, low viscosity.

DOI： 10.1111/j.1751-3928.1999.tb00035.x

Language：English   Publishing type：Research paper (scientific journal)  

The origin of mineralizing fluids responsible for the Hishikari vein-type epithermal Au deposits was studied on the basis of the hydrogen isotopic ratio (δD) of the inclusion fluid from vein quartz and adularia. The origin of hydrothermal fluids was estimated by combination of the present δD values and the oxygen isotopic ratios (δ18O) previously reported by Shikazono and Nagayama (1993). The water in the fluid inclusions was extracted by means of decrepitation of quartz at 500°C. Hydrogen was obtained by reduction of the collected water with Zn shot at 450°C. The δD values were determined by mass spectrometer. The δD values of inclusion fluid obtained from quartz range from -61 to -114 ‰. These are significantly lower than the δD value of the thermal water presently venting from the Hishikari deposits and that of local meteoric water. Hydrogen isotopic fractionation between water and amorphous silica, which might have initially precipitated from the hydrothermal fluids at least partly, is not a probable cause of this isotopic depletion, while some water might have been released from the initial hydrous amorphous silica during recrystallization to quartz observed presently. Thus, a part of ore fluids for the Hishikari deposits is supposed to have been originated from the water having anomalous δD values of lower than -100 ‰. Such D depletion cannot be caused by simple oxygen-shift of meteoric water or by contribution of magmatic volatiles. The δD values of water released from the shale samples of the Shimanto-Supergroup, a major host to the Hishikari veins range from -132 to -148 ‰. Therefore, the anomalous δD values of inclusion fluids from some vein quartz and adularia suggest that the water released from hydrous minerals of the sedimentary basement rocks by dehydration or the groundwater isotopically exchanged with sedimentary rocks at elevated temperatures during circulation, partly contributed to the hydrothermal fluids responsible for the Hishikari deposits.

DOI： 10.1111/j.1751-3928.1998.tb00014.x

Language：English   Publishing type：Research paper (scientific journal)  

The origin of mineralizing fluids responsible for the Hishikari vein-type epithermal Au deposits was studied on the basis of the hydrogen isotopic ratio (δD) of the inclusion fluid from vein quartz and adularia. The origin of hydrothermal fluids was estimated by combination of the present δD values and the oxygen isotopic ratios (δ¹⁸O) previously reported by Shikazono and Nagayama (1993). The water in the fluid inclusions was extracted by means of decrepitation of quartz at 500°C. Hydrogen was obtained by reduction of the collected water with Zn shot at 450°C. The δD values were determined by mass spectrometer. The δD values of inclusion fluid obtained from quartz range from -61 to -114 ‰. These are significantly lower than the δD value of the thermal water presently venting from the Hishikari deposits and that of local meteoric water. Hydrogen isotopic fractionation between water and amorphous silica, which might have initially precipitated from the hydrothermal fluids at least partly, is not a probable cause of this isotopic depletion, while some water might have been released from the initial hydrous amorphous silica during recrystallization to quartz observed presently. Thus, a part of ore fluids for the Hishikari deposits is supposed to have been originated from the water having anomalous δD values of lower than -100 ‰. Such D depletion cannot be caused by simple oxygen-shift of meteoric water or by contribution of magmatic volatiles. The δD values of water released from the shale samples of the Shimanto-Supergroup, a major host to the Hishikari veins range from -132 to -148 ‰. Therefore, the anomalous δD values of inclusion fluids from some vein quartz and adularia suggest that the water released from hydrous minerals of the sedimentary basement rocks by dehydration or the groundwater isotopically exchanged with sedimentary rocks at elevated temperatures during circulation, partly contributed to the hydrothermal fluids responsible for the Hishikari deposits.

DOI： 10.1111/j.1751-3928.1998.tb00014.x

Language：English   Publishing type：Research paper (scientific journal)  

Brown-colored sulfide ore (brown ore) occurs in the easternmost part of the Tsunokakezawa No. 1 orebody of the Fukasawa kuroko-type deposits, northern Honshu, Japan. As this type of ores also occur in the marginal or uppermost part of several other kuroko deposits in Japan, the formation of brown ore appears to be repeated in the process of kuroko formation. The brown ore is characterized by its higher Ag concentration (up to around 2000 g/t) than ordinary black ore (Zn-Pb ore) of volcanogenic massive sulfide deposits. The brown ore from the Fukasawa deposits can be divided into following three ore types based on its texture and mineral composition: pyritic brown ore, principal brown ore and "diseased" brown ore. Primary precipitation textures such as framboidal- and colloform-textures and compositional zoning within sulfide grains are significant in the brown ores. This seems to be due to lack of overprinting high temperature mineralization resulting in preservation of primary features. The Ag-Au mineralization is widely observed within the brown ores. Silver and gold are especially concentrated in the barite veinlets in the principal brown ore, which are supposed to be fillings of conduit of hydrothermal solution precipitated in the latest stage of hydrothermal activity. This mineralization seems to occur at waning stage of brown ore formation by ore solution at a lower temperature (around 250°C) than that of main part of brown ore (around 270°C). Relatively low fluid temperature and contribution of oxic ambient seawater may be responsible for the development of the Ag-Au mineralization in the brown ore. The occurrence of framboidal-rich pyritic brown ore having negative δ³⁴S values (less than -10‰) and filamentous texture of sphalerite, seeming remnant of bacteria, indicate the presence of intensive microbial activity in the hydrothermal area for brown ore formation. Formation environment of each ore type of the brown ore is supposed to be as follows: Pyritic brown ore is likely to have formed on the sea-floor around redox boundary at temperature (around 240°C) lower than ordinary black ore. Principal brown ore seems to have been formed beneath the shell of the pyritic brown ore at temperature around 270°C. Footwall of the brown ore is disseminated tuff breccia corresponding to feeder zone of hydrothermal fluid. Overprinting chalcopyrite mineralization is not observed in the brown ore except in limited part of "diseased" ore, which occurs just above the disseminated tuff breccia. Based on the features distinct from the ordinary black ore, the brown ore can be regarded as a product in the marginal part of submarine hydrothermal system, where temperature and flow rate of hydrothermal solution was relatively low and microbial activity was intensive. The brown ore seems to well preserve its primary features after its deposition and might show the initial feature of some part of the ordinary stratiform black ore.

DOI： 10.1111/j.1751-3928.1998.tb00007.x

Language：English   Publishing type：Research paper (scientific journal)  

The Bulawan deposit is located in the porphyry copper belt of southwest Negros island, Philippines. Propylitic, K-feldspar, sericitic, and carbonate alteration types can be distinguished in the deposit. Propylite alteration occurs mainly in Cretaceous-Eocene andesitic lavas and agglomerates while K-feldspar, sericite and carbonate alteration types occur mostly in the Middle Miocene dacite porphyry breccia pipes and stocks which were intruded into the andesites. K-feldspar zones occur in the inner parts of the sericitized zone. Sericite alteration overprinted the propylitized and K-feldspar alteration zones, at lower temperature than epidote and chlorite in the propylitized zone. Carbonate alteration is associated with the mineralization in the center of the breccia pipes and along faults. Mineralization consists of gold-silver telluride ores that are hosted by the carbonate- and sericite-altered dacite porphyry breccia pipes. The Bulawan ores occur mainly as disseminations, but unlike many epithermal gold deposits, lack classical epithermal colloform and crustiform quartz veins. The ore minerals are sphalerite, galena, chalcopyrite, pyrite and tetrahedite-tennantite with minor amounts of electrum, calaverite, petzite, sylvanite, hessite, tellurobismuthite, coloradoite, altaite, and rucklidgeite. Electrum and telluride minerals are associated mostly with calcite and dolomite-ankerite minerals. Fluid inclusions in quartz and calcite in clasts of propylitized andesite in the breccia pipes homogenize from about 300° to 400°C while fluid inclusions in quartz, calcite and sphalerite within the dacite porphyry breccia pipes homogenize between 300° to 310°C. The ores were formed around 300°C from hydrothermal solutions with salinity of about 6.6 wt % NaCl equivalent. The presence of sylvanite and calaverite as intergrowths with each other, and the Ag content of calaverite are consistent with the above temperature estimate. Based on paragenesis, the Bulawan deposit formed in a pyrite-stable environment, with pH between 3.4 and 5.5, f_O2 between 10^-32 to 10^-30 atm, f_S2 between 10^-9.8 to 10^-7.8 atm, f_Te2 between 10^-8.9 to 10^-6.5 atm, and total sulfur content about 10^-2.8 molal. The dominant reduced sulfur species in the ore solutions may have been H₂S_(aq), and the likely aqueous tellurium species were H₂Te(_aq) and H₂TeO_3(aq). The ore minerals in the Bulawan deposit were probably formed by mixing of slightly saline and low salinity fluids.

DOI： 10.1111/j.1751-3928.1998.tb00009.x

Language：English   Publishing type：Research paper (scientific journal)  

Systematic sulfur isotope data for whole-rock sulfides have been obtained from the chert-dominated, continuous, pelagic sedimentary sequences spanning the Permian/Triassic (P/Tr) boundary at Tenjinmaru in the Chichibu Terrane and at Sasayama in the Tanba Terrane in Japan. The P/Tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed Cretaceous/Tertiary (K/T) boundary claystone. The observed data clearly demonstrate a significant bimodalism. The S-34/S-32 ratios with respect to CDT are generally low throughout the Middle Permian (ca.-39 to -25parts per thousand) and show a remarkable increase beginning in the lower Upper Permian and persisting into the Lower Triassic (ca. -20 to -2parts per thousand), with a temporary and drastic negative shift, down to roughly the same isotopic level as in the Middle Permian, just at the suspected P/Tr boundary (ca. -41 to -23parts per thousand). Interestingly, the mode of isotopic excursion across the P/Tr boundary is in striking contrast to that across the K/T boundary which was recently described at Kawaruppu in Hokkado, Japan. The apparent extent of fractionation, with respect to contemporaneous seawater sulfate, in the high S-34/S-32 group lies within the range of -25 +/- 10parts per thousand, which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction, and that in the low S-34/S-32 group mostly exceeds this range, giving the values typically in the range of -45 +/- 10 parts per thousand, which is similar to what is generally observed in the present-day oceanic sediments. The present data would provide strong evidence for the development of a largely stagnant, anoxic, stratified ocean, which presumably began to form in the lower Upper Permian and persisted into the Lower Triassic, and for a brief episode of its temporary massive mixing just at the suspected P/Tr boundary. Such an oceanic oxic-anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal Triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal Permian mass extinction.

DOI： 10.1016/0031-0182(94)90072-8

Language：English   Publishing type：Research paper (scientific journal)  

Systematic sulfur isotope data for whole-rock sulfides have been obtained from the chert-dominated, continuous, pelagic sedimentary sequences spanning the Permian/Triassic (P/Tr) boundary at Tenjinmaru in the Chichibu Terrane and at Sasayama in the Tanba Terrane in Japan. The P/Tr boundary is characterized by the occurrence of siliceous shales in association with a carbonaceous black mudstone which is similar in appearance to the worldwide distributed Cretaceous/Tertiary (K/T) boundary claystone. The observed data clearly demonstrate a significant bimodalism. The ³⁴S/³²S ratios with respect to CDT are generally low throughout the Middle Permian (ca.-39 to -25%0) and show a remarkable increase beginning in the lower Upper Permian and persisting into the Lower Triassic (ca.-20 to -2%0), with a temporary and drastic negative shift, down to roughly the same isotopic level as in the Middle Permian, just at the suspected P/Tr boundary (ca.-41 to -23%0). Interestingly, the mode of isotopic excursion across the P/Tr boundary is in striking contrast to that across the K/T boundary which was recently described at Kawaruppu in Hokkado, Japan. The apparent extent of fractionation, with respect to contemporaneous seawater sulfate, in the high ³⁴S/³²S group lies within the range of -25 ± 10%0, which is quantitatively equivalent to the currently confirmed range of kinetic isotope effect during bacterial dissimilatory sulfate reduction, and that in the low ³⁴S/³²S group mostly exceeds this range, giving the values typically in the range of -45 ± 10%0, which is similar to what is generally observed in the present-day oceanic sediments. The present data would provide strong evidence for the development of a largely stagnant, anoxic, stratified ocean, which presumably began to form in the lower Upper Permian and persisted into the Lower Triassic, and for a brief episode of its temporary massive mixing just at the suspected P/Tr boundary. Such an oceanic oxic-anoxic history may account to some extent for the relatively high enrichments of chalcophile elements in basal Triassic sediments in the world and add a significant constraint to the current arguments on the cause and consequence of the terminal Permian mass extinction.

DOI： 10.1016/0031-0182(94)90072-8

Language：English   Publishing type：Research paper (scientific journal)  

The occurrence of sulfide globules in highly silicic rocks associated with the Mount Kinabalu quartz monzonitic complex suggests that the unmixing of sulfide liquid from a silicic melt may be an important step in the ore-generating magmatic process. -from Author

DOI： 10.2113/gsecongeo.89.1.181

Language：English   Publishing type：Research paper (scientific journal)  

The occurrence of sulfide globules in highly silicic rocks associated with the Mount Kinabalu quartz monzonitic complex suggests that the unmixing of sulfide liquid from a silicic melt may be an important step in the ore-generating magmatic process. -from Author

DOI： 10.2113/gsecongeo.89.1.181

Language：English   Publishing type：Research paper (scientific journal)  

Dacitic pumices from pyroclastic-flow deposits and air-fall tephra of the June 14-15, 1991, eruption of Mt. Pinatubo, Philippines, are characteristically rich in sulfur. The presence of microphenocrystic anhydrite suggests that sulfur existed mostly as oxidized species in the magma. This supposition is corroborated by unusually high sulfur contents (up to 0.78 wt&#37; as SO3) in apatite microphenocrysts and apatite inclusions in other phenocrystic minerals and by the highly oxidized state of the magma, near or slightly below the hematite-magnetite buffer, on the basis of extrapolation from biotite compositions and the two-oxide method. This highly oxidized state possibly caused the extraordinarily high sulfur content of Mt. Pinatubo dacite through prohibition of sulfide fractionation and because of increasing solubility of sulfur as oxidized species with increasing oxygen fugacity. Hornblende geobarometry indicates a pressure of approximately 2 kbar for phenocryst formation. Among the two pumice types, cummingtonite-rimmed hornblende phenocrysts are typically found in type 1 (white and crystal-rich) pumice, whereas rare hypersthene has been observed as discrete microphenocrysts in type 2 (tan and crystal-poor) pumice. These observations indicate conditions at least near if not at vapor saturation in type 1 magma and undersaturation in type 2 magma prior to eruption. Vapor-saturated type 1 dacitic magma probably caused the explosive June 14-15, 1991, eruption. The highly oxidized condition and magmatic water saturation are similar to those of intrusions related to porphyry copper deposits.

DOI： 10.1130/0091-7613(1993)021<0699:PASISO>2.3.CO;2

Language：English   Publishing type：Research paper (scientific journal)  

Dacitic pumices from pyroclastic-flow deposits and air-fall tephra of the June 14-15, 1991, eruption of Mt. Pinatubo, Philippines, are characteristically rich in sulfur. The presence of microphenocrystic anhydrite suggests that sulfur existed mostly as oxidized species in the magma. This supposition is corroborated by unusually high sulfur contents in apatite microphenocrysts and apatite inclusions in other phenocrystic minerals and by the highly oxidized state of the magma. This highly oxidized state possibly caused the extraordinarily high sulfur content of Mt. Pinatubo dacite through prohibition of sulfide fractionation and because of increasing solubility of sulfur as oxidized species with increasing oxygen fugacity. Among the two pumice types, cummingtonite-rimmed hornblende phenocrysts are typically found in type 1 pumice, whereas rare hypersthene has been observed as discrete microphenocrysts in type 2 pumice. These observations indicate conditions at least near if not at vapor saturation in type 1 magma and undersaturation in type 2 magma prior to eruption. -from Authors

DOI： 10.1130/0091-7613(1993)021<0699:PASISO>2.3.CO;2

Language：English   Publishing type：Research paper (scientific journal)  

A temporary and drastic decrease in ³⁴S/³²S ratio of whole rock sulfide has been recognized at the suspected Permian/Triassic (P/Tr) boundary at Tenjinmaru in the Chichibu Terrane in eastern Shikoku, Japan, which is characterized by the occurrence of a carbonaceous black mudstone. The observed isotopic profile in the P/Tr section is in striking contrast in mode of ³⁴S/³²S excursion to that at the K/T boundary at Kawaruppu in eastern Hokkaido, Japan, and adds to significant geochemical constraint to the current arguments on the palaeoenvironmental changes during the time of terminal Permian mass extinction. -from Authors

Language：English   Publishing type：Research paper (scientific journal)  

Hydrated garnetiferous peridotites form part of an ultramafic complex in the Mt Kinabalu area of Sabah, East Malaysia. Garnet peridotites are associated with abundant spinel lherzolites and rare plagioclase-bearing spinel lherzolites. The complex is in fault contact with the surrounding Tertiary strata. High-temperature peridotite mineral assemblages are overprinted by lower temperature hydrous assemblages characterized by abundant hornblende which is found filling interstices or thin veinlets. The small amounts of K, Na, Cl and F in the hornblende suggest that the metasomatic fluid may have been depleted in these elements. Carbon dioxide-rich, incompatible element-enriched, fluids are not thought to be the cause of the metasomatism since metasomatic phlogopite and carbonates, commonly reported from garnet peridotites and metasomatized alpine-type ultramafic rocks, are absent. The Mt Kinabalu garnet peridotites represent part of the sub-crustal mantle beneath Kalimantan which was metasomatized during ascent due to tectonism. The metasomatic fluid, poor in incompatible elements and H₂O-rich, may have been introduced into a sub-continental mantle wedge after dehydration of a subducted oceanic slab.

DOI： 10.1016/0743-9547(91)90086-D

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世界展開力事業　スマートマイニング特別プログラム

国際環境システム工学特別コース運営委員長

フィリピン大学での特別講議

インドネシア，ガジャマダ大学での特別講議

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