Se Enrichment Mechanism of the Xiaorequanzi Copper-zinc Deposit in East Tianshan,China
The Xiaorequanzi deposit is a volcanic massive sulfide(VMS)deposit that occurred in Carboniferous volcano-sedimentary sequence,which is located in the western section of Dananhu-Tousuquan arc belt,East Tianshan.Critical metals such as Se are associated with Xiaorequanzi VMS deposit.However,Se occurrence status and enrichment mechanism are ambiguous,which restricts the comprehensive utilization of Se.Based on previous research on the geological characteristics of ore deposits,the automated integrated mineral analysis and electron probe micro-analysis on sulfides in different mineralization stages of ore were used to explore Se occurrence status and enrichment mechanism in the Xiaorequanzi deposit.The results show that Se occurs as independent mineral,namely clausthalite,or exists in the lattice of sulfide.Clausthalite occurs in a subhedral to anhedral shape with particle size less than 30 μm,which is encapsulated in chalcopyrite of exhalative sedimentary period and late hydrothermal overprinting period.The Se,S,and Pb contents of clausthalite are 20.25％-23.87％,1.11％-2.61％,and 72.49％-76.57％,with an average of 22.15％,1.92％,and 74.51％.The average S/Se ratio is 0.087,and the average chemical formula of clausthalite is Pb(Se0.78 S0.17).The Se contents of pyrite,chalcopyrite,and sphalerite are 0.07％,0.15％and 0.29％,and the average S/Se ratios are 716,222 and 110.The average content of Se and S/Se ratio of sulfide in effusive deposit period are 0.20％and 212.The average content of Se and S/Se ratio of sulfide in the late hydrothermal overprinting period are 0.05％and 938,which show a decreasing trend of Se content.Combined with the results of previous fluid inclusion studies,Se enrichment mechanism in the Xiaorequanzi deposit is attributed to the magmatic fluid with higher temperature and higher oxygen fugacity,while Se mineralization weakens followed by the decreasing of oxygen fugacity and temperature.
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