东昆仑那更康切尔沟银矿床银矿物特征及成矿元素沉淀机制浅析

Characteristics of Silver Minerals of Nagengkangqieergou Silver Deposit in Eastern Kunlun Orogenic Belt and a Brief Analysis of the Precipitation Mechanism of Ore-forming Elements

那更康切尔沟银矿床位于东昆仑造山带东段昆中断裂北侧,是青海省近年来首次发现的主要受北西向断层控制的大型独立热液脉型银矿床。文章首次对其银矿物和成矿元素沉淀机制进行了研究,通过矿相学显微观察、电子探针和扫描电镜能谱分析以及石英流体包裹体显微测温等手段初步查明:赋存于金水口岩群地层中的银矿物种类简单,主要为自然银和辉银矿,并且与毒砂、闪锌矿、黝锡矿在空间分布上关系较密切,不含碘元素;赋存于鄂拉山组地层中的银矿物种类复杂,包括自然银、螺硫银矿、淡红银矿、火硫锑银矿、辉锑银矿、银黝铜矿、黝锑银矿、硫锑铅银矿、辉锑铅银矿、捷辉锑银铅矿等,并且普遍含碘元素;金水口岩群中矿石石英流体包裹体均一温度主要集中于275~295℃,鄂拉山组中则主要集中于155~215℃;而两者流体盐度差异性较小,前者主要集中于4.5%~6.5%,后者主要集中于5.5%~6.5%。金水口岩群和鄂拉山组地层中围岩蚀变特征、银矿物种类、化学成分特征、成矿流体温度表明两者成矿元素沉淀机制具有显著差异性,这对金水口岩群和鄂拉山组地层中的矿产勘查具有重要指导意义。

Objectives： Nagengkangqieergou silver deposit,situated in the eastern section of Eastern Kunlun orogenic belt and to the north of Kunzhong Fault,is a large-scale structurally-controlled hydrothermal vein-type deposit,newly discovered in Qinghai Province in recent years. The characteristics of silver minerals and the precipitation mechanism of ore-forming elements of Nagengkangqieergou silver deposit has been first studied in this paper.Methods： Mineragraphy observation,scanning electron microscopy-energy dispersive spectrometry analysis,electron microprobe analysis,and microthermometry of fluid inclusions trapped in quartz were carried out to investigate the characteristics of silver minerals of Nagengkangqieergou silver deposit and precipitation mechanism of ore-forming elements.Results： It is preliminarily ascertained that silver minerals,occurred in Elashan Formation,include native silver,acanthite,proustite,pyrostilpnite,miargyrite,argentian tetrahedrite,freibergite,andorite,diaphorite,teremkovite,all of which contain high content of I. By contrast,silver minerals,hosted in Jinshuikou Group,are principally composed of native silver and argentite,both of which are spatially connected closely with arsenopyrite,sphalerite,stannite and contain scarcely any I. Besides,homogenizaion temperature of quartz fluid inclusions occurred in the Jinshuikou Group are clustered in the interval of 275 ～ 295 ℃,while in the interval of 155 ～ 215 ℃for those occurred in Elashan Formation. Moreover,there is slight difference in the salinity of ore-forming fluid forboth strata. Ore-forming fluid salinity values are clustered in the interval of 4.5 ～ 6.5% for the Jinshuikou Group,while in the interval of 5.5 ～ 6.5% for the Elashan Formation.Conclusions： Precipitation mechanism of ore-forming elements in the Jinshoukou Group and that in the Elashan Formation are remarkably different,indicated by the significant difference of wall rock alteration,category and chemical composition of silver minerals as well as the ore-forming fluid temperature. Therefore,this study provides guiding significance for ore-prospecting in both strata.