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氏名 Masaya Koseki
所属 Graduate of School of International Resource Sciences Department of Geosciences, Geotechnology & Material Engineering for Resources, Akita University
研究者番号
研究分野 Economic Geology (especially, hydrothermal vein-type Cu-Pb-Zn and Au-Ag deposits by means of field survey, optical microscopy, fluid inclusions microthermometry, laman spectrometry and XRD), Igneous rock petrology (by means of XRF, SEM, EPMA including melt inclusion interpretation), Geochemistry
会議でのプレゼンテーション "Koseki M., Watanabe Y., Aoki S., Satori S., Echigo T. (June, 2022) Factors of deposit-concentrated metal elements determination in epithermal mineralization around the Kitami region, Hokkaido, Japan. On-site Oral Session, The 71st Annual Meeting of the Society of Resource Geology, Tokyo, Japan
研究テーマ名称 "Study on differentiation of epithermal precious metal mineralization
研究テーマ概要 Epithermal metal deposits are globally distributed at collision and subduction settings in volcanic arc. This style of deposits that are located in Japan is divided into Au-Ag enriched type and Base-metal enriched (especially, Cu, Pb and Zn) type. In general, Au is transported as sulfide complex and Ag, Base-metal are transported as chloride complex in hydrothermal ore-forming fluid. These deposits are hosted by or abut Miocene to Pleistocene felsic to intermediate igneous activity. One hypothesis is inspected that factor of mineralization selectivity is derived from igneous activity and from its volatile content (especially chlorine and sulfur) of magma as the example of the Kitami Cu-Pb-Zn deposit and the Kitano-o Au-Ag deposit in the Kitami region, Hokkaido, the Arakawa Cu deposit in Akita prefecture and the Hishikari Au-Ag deposit in Kagoshima prefecture. The research method is including fluid inclusion microthermometry by using transparent mineral hosted fluid inclusion, microprobe analysis of volatile elements by the target of phenocryst hosted melt inclusion and apatite in ore forming related igneous rocks, and MELTS simulation to decide crystallizing stage of each melt inclusion hosted minerals.
調査結果 The result of fluid inclusion microthermometry analysis support the previous study that report base-metal vein was formed by high salinity fluid (5.1 wt.% NaCl eq.) and Au-Ag vein was formed by low salinity fluid (1.9 wt.% NaCl eq.). As the result of XRF analysis, Kitami deposit was formed by dacitic melt (66.1 wt.% SiO2) and Kitano-o deposit was formed by rhyolitic melt (73.9 wt.% SiO2). As the result of EPMA analysis, each magmatic apatite formed by dacitic and rhyolitic melt recorded same Cl content of each melt (0.43 – 0.85 wt.%) calculated from mineral-melt partition coefficient. As the discussion, there are 2 possibilities that contribute the meneralisation selectivity: one is the value of partition coefficient of strongly pressure and SiO2 content depended on Cl is different due to the different depth of ore forming fluid separation, the other one is the Cl/S ratio in each melt is different.
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