西藏扎西康锌多金属矿床地质特征及银的赋存状态研究

Geological characteristics and modes of occurrence of silver in Zhaxikang zinc polymetallic deposit

扎西康锌多金属矿床位于西藏特提斯喜马拉雅板片的"金锑多金属"成矿带东段。研究显示,矿体主要呈脉状、透镜状产于近南北向的张性断裂中。热液成矿作用主要可划分为早、晚2个成矿阶段,7个成矿亚阶段,早期以铅锌矿化为主,晚期以锑(铅)矿化为主。岩矿石镜下鉴定和电子探针分析表明,扎西康矿床矿石种类繁多,矿物组合和成矿元素均呈现明显的分带现象,由深至浅(W→E)为含锡(铁)闪锌矿+铁锰碳酸盐+少量方铅矿+少量黄铜矿(深部)→(铁)闪锌矿+铁锰碳酸盐+少量方铅矿+黄铁矿+毒砂+少量银黝铜矿+少量石英(中深部)→方铅矿+闪锌矿+脆硫锑铅矿+铁锰碳酸盐+硫锑铅矿+少量银黝铜矿+石英(中部)→辉锑矿+方铅矿+少量闪锌矿+石英+少量铁锰碳酸盐(浅部),对应的元素分带为Zn(Pb+Ag+Cu+Sn)→Zn(Pb+Ag)→Zn+Pb(Sb+Ag)→Pb+Sb+Ag+Zn。矿区银矿化主要集中在Ⅴ号矿体ZK2703-ZK2302、ZK1502-ZK1105和ZK806三个区域,与铅锑矿化关系密切。矿石中银主要以类质同象的形式存在,独立银矿物相对较少。其中,类质同象银主要赋存在方铅矿中,少量赋存在硫锑铅矿、脆硫锑铅矿、毒砂、黄铁矿等金属硫化物中;独立银矿物有少量的银黝铜矿、硫锑铅银矿、银(含银)硫铜锑矿。成矿流体中铅、锌、锑、银的运移和富集沉淀是受体系中温度、压力、浓度、pH值等多种因素综合控制的结果。

The Zhaxikang zinc polymetallic deposit is located in the east of the gold-antimony polymetallic metallogenic belt of the Tethyan-Himalayan plate bar.According to deposit geology,ore bodies are mainly distributed in the nearly NS-trending tensile fractures and assume veined and lenticular forms.The ore-forming process can be divided into 2 stages and 7 sub-stages,with the main mineralization at the early stage being lead-zinc mineralization and the main mineralization at the late stage being antimony（lead）mineralization.The microscopic appraisal and electron probe analyses suggest that there are varied sorts of ore minerals,and the distribution of mineral assemblages and elements displays obvious zonation：from the depth to the shallow part（from west to east）,there exists the zoning of tin（iron）-bearing sphalerite＋ferromagnesian carbonate＋small amounts of galena＋small amounts of chalcopyrite（in depth）sphalerite＋ferromagnesian carbonate＋small amounts of galena＋pyrite＋arsenopyrite＋small amounts of aftonite＋small amount of quartz（medium-large depth） ※galena＋sphalerite＋jamesonite＋ferromagnesian carbonate＋boulangerite＋small amounts of aftonite ＋quartz（middle part）※stibnite＋galena＋small amounts of sphalerite（shallow part）＋quartz＋small amounts of ferromagnesian carbonate,with the corresponding element zonation being Zn（Pb＋Ag＋Cu＋Sn）※ Zn（Pb＋Ag）※Zn＋Pb（Sb＋Ag）※Pb＋Sb＋Ag＋Zn.The silver mineralization is closely related to Pb-Sb mineralizationand is mainly distributed in areas of ZK2703-ZK2302,ZK1502-ZK1105 and ZK806 which are located around theⅤore body.The silver mainly exists as isomorphism in galena,with a small amount existent in boulangerite,jamesonite,arsenopyrite,pyrite and other metal sulfides.Independent silver minerals only possess a small proportion,and they are mainly aftonite,sundtite and silver-bearing wolfsbergite.The precipitation of Pb,Zn,Sb,Ag in ore fluids was controlled by such factors as temperature,pressure,density and pH.