Potash–rich Magmatism and Associated Gold-Copper Mineralization in the Yishu Deep Fault Zone and Its Vicinity, Eastern China |
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| Authors: | Jiansheng QIU Ching–Hua LO Brent I A MCINNES Jincheng ZHOU |
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| Institution: | Department of Earth Sciences, Nanjing University, Nanjing 210093, P R China [e-mail: ];Department of Geology, National Taiwan University, Taipei 10770, Taiwan;CSIRO Division of Exploration and Mining, PO Box 136, North Ryde, NSW 2113, Australia |
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| Abstract: | Abstract: The Mesozoic potash‐rich volcanic rocks which hosted several gold or gold (copper) deposits are widely distributed around the Yishu deep fault zone, eastern China. Lithologically, these rocks include basaltic trachyandesite, trachyandesite, latite and trachyte, of which the trachyandesite and latite are the predominant rock types. Whole‐rock Rb‐Sr isochron ages and 40Ar‐39Ar plateau dates of them are 108.2 ? 119.6 Ma and 114.7 ? 124.3 Ma, respectively. Chemically, they are characterized by high and variable Al2O3 contents, high K2O+Na2O values, and high K2O/Na2O and Fe2O3/FeO ratios. The rocks also have enriched LILE and LREE concentrations, low HFSE abundance, and display extraordinary Sr‐Nd isotope signatures (ISr = 0.7084 ? 0.7125, εNd(t) = ‐9.43 ? ?18.07). Integrated geological and geochemical data suggest that they were formed in a continental‐arc setting and most likely originated from the partial melting of enriched mantle which was induced by source contamination of subducted continental crustal materials. Gold (copper) deposits in this district are closely related to Mesozoic volcanic‐subvolcanic magmatism. They are frequently located either at the margin or adjacent to the volcanic basins. Most of them are spatially associated with maar‐diatreme systems and/or flow‐dome complexes. The formations of two gold (copper) deposits, the Qibaoshan breccia pipe‐porphyry type Au‐Cu deposit and the Guilaizhuang tellurium‐gold type epithermal Au deposit, have been proved to be in close relation with potash‐rich magmatism. The genetic relations between potash‐rich magmatism and Cu‐Au mineralization is still quite unclear. Detailed review of the previous works demonstrates that the high contents of volatiles (such as H2O, CO2, S, F and Cl, especially F and Cl) and the high oxidation state of the potash‐rich magmas may be the main favorable factors for the formation of the Cu‐Au deposits. |
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| Keywords: | potash-rich magmatism gold-copper mineralization Mesozoic Yishu deep fault zone eastern China |
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