Ore-forming mechanism for the Xiaoxinancha Au-rich Cu deposit in Yanbian,Jilin Province,China: Evidence from noble gas isotope geochemistry of fluid inclusions in minerals |
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| Authors: | Sun JingGui Zhao JunKang Chen JunQiang Keisuke Nagao Hirochika Sumino Shen Kun Men LanJing Chen Lei |
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| Institution: | (1) College of Earth Sciences, Jilin University, Changchun, 130061, China;(2) Tianjin Institute of Geology and Mineral Resources, Tianjin, 300170, China;(3) Laboratory for Earthquake Chemistry, Graduate School of Science, The University of Tokyo, Tokyo 7-3-1, Japan;(4) Shandong Institute of Geological Sciences, Jinan, 250013, China |
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| Abstract: | The Xiaoxinancha Au-rich copper deposit is one of important Au-Cu deposits along the continental margin in Eastern China.
The deposit consists of two sections: the Beishan mine (North), composed of altered rocks with veinlet-dissemination sulfides
and melnicovite-dominated sulfide-quartz veins, and the Nanshan mine (South), composed of pyrrhotite-dominated sulfide-quartz
veins and pure sulfide veins. The isotope compositions of noble gases extracted from fluid inclusions in ore minerals, i.e.
ratios of 3He/4He, 20Ne/22Ne and 40Ar/36Ar are in the ranges of 4.45–0.08 Ra, 10.2–8.8 and 306–430, respectively. Fluid inclusions in minerals from the Nanshan mine
have higher 3He/4He and 20Ne/22Ne ratios whereas those from the Beishan mine have lower 3He/4He ratios. The analysis of origin, and evolution of the ore fluids and its relations with the ore-forming stages and the ages
of mineralization suggests that the initial hydrothermal fluids probably come from the melts generated by partial melting
of oceanic crust with the participation of fluids from the mantle (mantle-plume type)/aesthenosphere. This also corresponds
to the continental margin settings during the subduction of Izanagi ocaneic plate towards the palaeo-Asian continent (123–102
Ma). The veinlet-dissemination ore bodies of the Beishan mine were formed through replacement and crystallization of the mixed
fluids generated by mixing of the ascending high-temperature boiling fluid with young crustal fluid whereas the melnicovite-dominated
sulfide-quartz veins were formed subsequently by filling of the high-temperature ore fluid in fissures. Pyrrhotite-dominated
sulfide-quartz veins in the Nanshan mine were formed by filling-deposition-crystallization of the moderate-temperature ore
fluids and the pure sulfide veins were formed later by filling-deposition-crystallization of ore substance-rich fluids after
boiling of the moderate-temperature ore fluids. The metallogenic dynamic processes can be summarized as: (1) formation of
fluid- and ore substance-bearing Adakitic magma by degassing, dewatering and partial melting during subduction of the Izanagi
plate; (2) separation and formation of ore fluids from the Adakitic magma; and (3) success-sive ascending of the ore fluids
and final formation of the Au-rich Cu deposit of veinlet-dissemination and vein types by secondary boiling.
Supported by the National Natural Science Foundation of China (Grant No. 40472050) and the funds from the State Key Laboratory
for Mineral Deposits Research, Nanjing University (2003–2005) |
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| Keywords: | Au-rich Cu deposit fluid inclusion He-Ne-Ar isotopes ore-forming mechanism Xiaoxinancha Yanbian |
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