Petrogenesis of Lingshan highly fractionated granites in the Southeast China: Implication for Nb-Ta mineralization |
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| Institution: | 1. CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of Chinas, Hefei 230026, China;2. CAS Center for Excellence in Comparative Planetology, Hefei 230026, China;3. Wuhan Centre of China Geological Survey, Wuhan 430205, China;4. Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, College of Earth Sciences, Guilin University of Technology, Guilin 541004, China;1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Geology Bureau for Nonferrous Metals of Guangdong Province, Guangzhou 510060, China;4. Geology Bureau for Nonferrous Metals of Guangdong Province, 931 Team, Shantou 515041, China;1. Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 100039, China |
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| Abstract: | Whole rock major and trace element and Sr-, Nd- and Hf-isotope data, together with zircon U-Pb, Hf- and O-isotope data, are reported for the Nb-Ta ore bearing granites from the Lingshan pluton in the Southeastern China, in order to trace their petrogenesis and related Nb-Ta mineralization. The Lingshan pluton contains hornblende-bearing biotite granite in the core and biotite granite, albite granite and pegmatite at the rim. In addition, numerous mafic microgranular enclaves occur in the Lingshan granites. Zircon SIMS U-Pb dating gives consistent crystallization ages of ca. 132 Ma for the Lingshan granitoids and enclaves, consistent with the Nb-Ta mineralization age of ～132 Ma, indicating that mafic and felsic magmatism and Nb-Ta mineralization are coeval. The biotite granites contain hornblende, and are metaluminous to weakly peraluminous, with high initial 87Sr/86Sr ratios of 0.7071–0.7219, negative εNd(t) value of ?5.9 to ?0.3, εHf(t) values of ?3.63 to ?0.32 for whole rocks, high δ18O values and negative εHf(t) values for zircons, and ancient Hf and Nd model ages of 1.41–0.95 Ga and 1.23–1.04 Ga, indicating that they are I-type granites and were derived from partial melting of ancient lower crustal materials. They have variable mineral components and geochemical features, corresponding extensive fractionation of hornblende, biotite and feldspar, with minor fractionation of apatite. Existence of mafic microgranular enclaves in the biotite granites suggests a magma mixing/mingling process for the origin of the Lingshan granitoids, and mantle-derived mafic magmas provided the heat for felsic magma generation. In contrast, the Nb-Ta mineralized albite granites and pegmatites have distinct mineral components and geochemical features, which show that they are highly-fractionated granites with extensive melt and F-rich fluid interaction in the generation of these rocks. The fluoride-rich fluids induce the enrichment in Nb and Ta in the highly evolved melts. Therefore, we conclude that the Nb-Ta mineralization is the result of hydrothermal process rather than crystal fractionation in the Lingshan pluton, which provides a case to identify magmatic and hydrothermal processes and evaluate their relative importance as ore-forming processes. |
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| Keywords: | Nb-Ta mineralization Highly-fractionated granite Petrogenesis Hydrothermal activity South China |
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