Features of rock-forming minerals of Yanshanian mineralized granite in the polymetallic deposit concentration zone in southern Hunan and their implications for granite generation
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    Abstract:

    Abstract:There are three types of Yanshanian mineralized granite in southern Hunan, and the chemical compositions and species of their ore-forming minerals are notably different. The characteristics of variations in chemical compositions of the minerals all indicate a mantle-crust magma mixing origin. Systematic analyses show the following:(1)Hornblendes belong to Ca-hornblende.(2)Biotites in most early-stage MC-type granite are Mg-biotite; those in late-stage CM-type granite are mainly meroxene; and biotites in C-type granite are mainly sideophyllite and meroxene, most of which zinnwaldite. The variation in biotite composition of the three types of granite shows a linear relation, implying a genetic relation.(3)Plagioclases in the three types of granite are significantly distinguished. Plagioclases are mainly andesine in MC-type granite, oligoclase in CM-type granite and albite in C-type granite. The zoning structures of plagioclases are developed to different degrees, with the zoning of plagioclases in the early-stage CM-type granite best developed.(4)Alkali plagioclases in CM-type granite and its dark micro-inclusions are mainly K-rich orthoclase, and a few grains of plagioclase in inclusions are anorthoclase, indicating higher temperatures of plagioclase crystallization. Alkali plagioclases in C-type granite are relatively K-poor microcline and Na orthoclase.(5)The characteristics of rock-forming minerals and their compositional variations indicate that the formation of mineralized granites is related to crust-mantle magma mixing. The magmatic evolution that generated MC-and CM-type early-stage granites was mainly magma mixing, while the magmatic evolution that formed CM-type late-stage granitoids and C-type granitoids might be fractional crystallization in addition magma mixing.

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WU Guang-ying, XIAO Qing-hui, CHEN Hui-ming, MA Tie-qiu, FENG Yan-fang, YAN Quan-ren. Features of rock-forming minerals of Yanshanian mineralized granite in the polymetallic deposit concentration zone in southern Hunan and their implications for granite generation[J]. Geology in China, 2008, 35(5): 888-901(in Chinese with English abstract).

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  • Online: March 22,2013
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