A Study On Pyrite Mineralogy And Geochimestry Of The Xiangtanzi Gold Deposit In Liangdang Area,Gansu Province

The Xiangtanzi deposit is a typical gold deposit in the West Qinling metallogenic belt.Based on detailed field geological survey and microscopic observation,in this paper,we analyzes the main and trace element composition of pyrite in different stages of Xiangtanzi deposit using electron probe(EMPA)and LA-ICP-MS technology,and discusses the sources of ore-forming fluids and mineralization materials and ore genesis.The pyrite in the Xiangtanzi gold deposit is divided into five generations of Py? ~ Py? based on the cross-cutting relationship,crystal morphology and mineral association.Among them,Py? is subhedral to anhedral fine-grained pyrite,which is sporadically distributed in thick quartz veins;Py? is euhedral to subhedral medium-coarse grained pyrite,and intergrown with arsenopyrite;Py? occurs as euhedral to subhedral coarse to fine grains and intergrown with sulfides such as chalcopyrite,galena,sphalerite,arsenopyrite,etc.;Py?V is anhedral fine-grained pyrite,and intergrown with sphalerite;Py? is euhedral coarse-grained pyrite,distributed in the calcite veins.EMPA and LAICP-MS analysis results show that the main element content of pyrite in different generations is similar,with the characteristics of deficient in sulfur and iron,but the trace elements are obviously different;Py?is relatively enriched in Co,Ni,poor in As and Au;Py?is enriched in Co,Ni,and As;Py? is relatively enriched in Cu,Pb,Zn,Bi,Au,Ag,and poor in Co;Py?enriches most of the elements in this analysis;Py?has relatively few other elements except As.In addition,the Co / Ni ratio of pyrite in each stage is mostly> 1,combined with the Co-Ni-As element relationship,indicating that the pyrite in the Xiangtanzi gold deposit is magmatic hydrothermal pyrite.Microscopic observation and LA-ICP-MS time-resolved depth profiles show that gold in the Xiangtanzi gold deposit exists in two forms of visible and invisible gold;among them,visible gold occurs mainly as inclusion and fracture gold in pyrite;invisible gold is present mainly as lattice gold and submicron fine-gold inclusions in pyrite.The comprehensive analysis shows that(1)temperature decreasing and fluid mixing may be the main mechanism leading to Au precipitation in the Xiangtanzi gold deposit;(2)the Xiangtanzi gold deposit is a typical magmatic hydrothermal deposit.