西藏拿若斑岩型铜(金)矿床黄铁矿、黄铜矿原位硫同位素特征及其地质意义OA北大核心CSTPCD

The Naruo deposit is the third largest porphyry Cu(Au)deposit within the Duolong ore district in Xizang.Previous studies have extensively investigated the petrogenesis,metallogenetic geological chronology,and metallogenic geological background.However,the ore-forming mechanism,including the source of sulfur,remains unclear.This study focuses on the widespread occurrence of pyrite and chalcopyrite in the Naruo ore deposit.Through methods such as optical microscopy identification and LA-MC-ICP-MS isotopic analysis,mineralogical characteristics and isotopic geochemistry were investigated.The aim is to elucidate the in-situ sulfur isotope characteristics,reveal the ore genesis of the deposit,and provide guidance for mineral exploration.Based on microscopic observations,three types of pyrite are categorized,from earlier to later:Py-Ⅰ→Py-Ⅲ→Py-Ⅱ→Py-Ⅲ.Except for Py-Ⅰ,all others are closely associated with the occurrence of chalcopyrite.Pyrite exhibits δ34S values ranging from-4.05‰ to 3.49‰(with a mean of-0.2 ‰,n=53),while chalcopyrite demonstrates smaller δ34S values,ranging from-7.24‰ to 0.32‰(with a mean of-2.44‰,n=24).These test results closely approximate values found in other deposits within the ore cluster.The total sulfur value of the ore-forming fluid(δ34SΣ)is-3.06‰,indicating that the source of sulfur is primarily associated with magmatic sulfur.The sulfur isotope mineral pairs of pyrite-chalcopyrite indicate ore-forming temperatures ranging from 255℃to 590℃,with a central ore-forming temperature of 320℃,revealing a mesothermal ore-forming environment in the ore deposit center.The spatial distribution patterns of sulfur isotopes indicate a gradual decrease in δ34S values from the mineralization center to the periphery,which is notably different from some alkaline porphyry-type deposits.This study suggests that such variation is attributed mainly to ore formation in a mesothermal environment and the degassing of remote SO2,thus serving as crucial exploration indicators for the Naruo deposit.This study has enriched our understanding of the sources of sulfur and ore-forming temperatures,among other ore-forming mechanisms,in the Naruo ore deposit.It lays the foundation for further research in ore-forming theories and mineral exploration.