金沙江-哀牢山造山带南段长安金矿床成矿物质来源与金属沉淀机制OA

The Chang'an gold deposit is a typical Au deposit in the southern segment of the Jinshajiang-Ailaoshan metallogenic belt.Multiple-stage Cenozoic intrusions are exposed within the mining area,which are classified in-to altered diabase,unaltered diabase,syenite porphyry,and aplite.The ore bodies are hosted within siltstone and altered diabase.It remains obscure as to the relationship and the contribution between multi-stage intrusions and Au mineralization.In this study,we compared trace elements and S isotope of pyrites in these intrusions and silt-stone,respectively,to explore the source of ore metal and the contribution of intrusions to gold mineralization.The pyrites in the siltstone exhibit significant core(Fsy-1)and rim(Fsy-2)texture under BSE,and Fsy-2 is filled with amount of minerals such as arsenopyrite and galena,whereas,the pyrites in those intrusions show homoge-neous texture.The Co/Ni ratio and the large range of δ34S variation of Fsy-1 indicate that it is of sedimentary ori-gin.The Co/Ni ratio and the δ34S variation of other pyrites indicate magmatic hydrothermal genesis.Au occurs as primary nanoparticles in Fsy-11 and a few A-hly,while the rest exists in the form of solid solution in other py-rites.The content of Au,Cu,and As in Fsy-1 is much lower than that in Fsy-2,indicating that external deep fluids rich in Au,Cu,and As undergo strong fluid-rock reactions,metasomatizing sedimentary pyrite and causing Au precipitation.The As/Sb ratio of Fsy-2 and A-hly indicates that fluid boiling disrupts the stability of Au(HS)2 com-plex,which is also one of the factors causing Au precipitation.As pyrite is the main Au carrier mineral,N-hly,Zc-by and Xjy contains low Au content,and these intrusions also have very low Au content,indicating that they are not the main source of Au.The deep Au rich fluid metasomatized Fsy-1 and formed Fsy-2,accompanied by the precipitation of Au and other ore-forming elements.Overall,the ore metals of the Chang'an gold deposit mainly sourced from deep sources,and intense fluid-rock interaction behaves as a key factor controlling mineralization.The chemical composition of pyrite can effectively invert the mineralization process and can be used as a robust tool in mineral exploration.