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《Acta Geologica Sinica》 2018-06
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Geochronological and Geochemical Study of Volcanic Rocks from the Yincan Cu-Zn Deposit in North Qilian

GUO Zhouping;ZHAO Xinmin;WANG Yuxi;BAI Yun;ZHANG Jiangwei;GAO Yongwei;ZHANG Haisong;Key Laboratory for the Study of Focused Magmatism and Giant Ore Deposits,MLR,Xi'an Center of China Geological Survey;Nuclear Industry of Tibet Geology Research Institute;  
The Yincan deposit,located in the middle part of North Qilian Mountains,is a small-sized Cu-Zn ore deposit occurring in the Lenglonglin volcanic rock belt.Ore-bearing rocks consist of basalt-rhyolite association of the Yingou Group,with mineralization occurring in bimodal rhyolitic volcanic rocks.Spatially,orebodies show well developed zonation,from the lower part upward,gradual change from Zn→Cu-Zn→Cu→Fe orebody.Zircon LA-ICP-MS dating yielded concordant ages of 454.0±2.0 Ma and 417.7±1.7 Ma for basalt and rhyolite,respectively,indicating that the Yincan deposit formed in Middle Ordovician.Geochemical data show that the basalt belongs to sub-alkaline tholeiite because of low TiO_2(0.22%~0.25%),high MgO(10.83%~14.17%,Mg#=68~73),Cr(974×10~(-6)~1110×10~(-6)),Ni(219×10~(-6)~291×10~(-6)).Trace element primitive mantle-normalized spidergram shows a distinct loss of Nb,and REE chondrite-normalized diagram shows a left-dipping pattern.The rhyolite belongs to the lowK tholeiitic series and is depleted in Th,Nb,Ta,Sr and Ti,probably generated by partial melting of the crust rocks.The both volcanic rocks show characteristic of bimodal volcanic rocks and formed in the island arc rifting environment triggered by slab subduction of North Qilian ocean.Theδ34 S compositions(+4.3‰~+8.7‰)of the ore deposit show the mixing features of mantle-driven magmatic sulfur and seawater reduced sulfur.The weak water-rock reaction in the Yincan deposit led to a less amount of metal materials leached from volcanic rocks.This may be one important reason for the small size of the Yincan deposit.
【Fund】: 中国地质调查局项目(编号:DD20160012)资助成果
【CateGory Index】: P618.41;P618.43
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