Incipient Stage of Ore Formation Process of the Kamioka Zn-Pb Ore Deposit in the Hida Metamorphic Belt, Central Japan: Leaching and Precipitation of Clinopyroxene |
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| Authors: | Keitaro KUNUGIZA |
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| Institution: | Department of Earth Science, Faculty of Education, Toyama University, Toyama 930–8555, Japan |
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| Abstract: | Abstract: Boundaries between the cpx Zn-Pb ores of the Kamioka ore deposit and host clinopyroxene granitoid in the Hida metamorphic belt were examined to decipher the incipient stage of ore formation process. The boundaries are characterized by the compositional zoning of relic clinopyroxene with outward increase of XMg from 0. 5 to 0. 75 in the host rocks, and by the incline of XMg towards the ores, passing through the boundaries, reaching up to 0. 95. In the ores, relic clinopyroxene is rimmed by hedenbergite. Both clinopyroxenes show compositional zoning with outward decrease and increase of XMg and MnO, down to 0. 02 and to 3. 2 wt%, respectively. The presence of high magnesian clinopyroxene can be explained if hydrothermal fluid flow had leached hedenbergite component of relic clinopyroxene. The incline of XMg of clinopyroxene toward the ores was attributed to the degree of dissolution of clinopyroxene, and thus the total amounts of fluid to have passed. The outward decrease of XMg of clinopyroxenes in the ores was due to crystal-fluid fractionation during precipitation. These mineralogical changes at the boundaries indicate the time-integrated phenomena of hydrothermal ore forming process. Firstly, leaching of ore components by infiltrating fluid proceeded in host rocks, and enhanced the formation of a fluid channel. The condition of fluid changes through the fluid channel in P-T space, and hence ore forming minerals precipitate at a remote place from the leaching one. This in turn caused the physicochemical change of fluid condition anyhow, and accelerated the precipitation of the minerals. This leaching-precipitation sequence appears a basic process of hydrothermal ore-forming system, and characterizes the incipient stage of ore formation process of the Kamioka Zn-Pb ore deposit. Compositional zoning of clinopyroxenes defines Z-shaped compositional trend in the Di–Hd–Jo diagram, each arm of which corresponds to the leaching and the precipitation stages, and the secondary dissolution of precipitated clinopyroxene. |
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| Keywords: | Hida gneiss Inishi hedenbergite johannsenite allanite sphalerite hydrothermal fluid flow system skarn |
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