西藏斯弄多浅成低温热液型银铅锌矿床银的赋存状态研究

摘要

The Sinongduo Ag-Pb-Zn deposit is a medium-large sized low-sulfidation hydrothermal deposit discovered for the first time in the Linzizong volcanic rock of the Gangdise metallogenic belt. There are various mineral assemblages and structures, and this deposit has the typical characteristics of hydrothermal mineralization. The periods of the mineralization in this deposit can be mainly divided into three stages: (I) sphalerite-chalcopyrite-enargite-pyrite-quartz stage, (II) galena-sphalerite-silver mineral stage, and (III) pyrite-quartz-calcite. Through field investigation, geological logging, microscopic observation and electron microprobe analysis (EPMA), the authors studied the modes of occurrence of the silver in Sinongduo deposit. The results show that the silver primarily exists in the form of independent silver minerals, and the other sulfides such as sphalerite, galena, pyrite and chalcopyriteonly contain very little silver. The silver minerals mainly include peaceite, argentite, pyrargyrite, akanthite and native silver, which occur in the fissures of the Fe-Mn carbonates, jasper and the early sulfides. Moreover, several silver minerals exist in the form of being wrapped in the sulfide. Some invisible silver can be found in the enargite. The silver mineralization occurred at No. II metallogenic stage and the silver was carried in the form of sulfur complex migration. With the change of physical and chemical conditions of the ore-forming fluid, the silver precipitated and formed different kinds of silver minerals.%斯弄多银铅锌矿床是冈底斯成矿带林子宗群火山岩中发现的首例低硫化型浅成低温热液型中-大型多金属矿床.矿区矿物组合多样,矿石组构复杂,具有热液成矿作用的典型特征,成矿阶段可划分为(I)闪锌矿-黄铜矿-硫砷铜矿-黄铁矿-石英阶段、(II)方铅矿-闪锌矿-银矿物阶段、(III)黄铁矿-石英-方解石三个成矿阶段.通过野外调查、地质编录、显微观察和电子探针(EPMA)微区分析,本文对该矿床中银的赋存状态进行了详细的研究.结果表明,银主要以独立银矿物形式存在,方铅矿、闪锌矿、黄铁矿、黄铜矿等金属矿物中不可见银极少.银矿物种类主要为硫砷铜银矿、辉银矿、深红银矿、螺状硫银矿和自然银,呈裂隙银或粒间银形式赋存于矿区碧玉、铁锰碳酸盐和早期金属硫化物中,次以包裹银形式赋存于早期硫化物中.另,在硫砷铜矿中发育极少的类质同象不可见银.银矿化主要形成于成矿阶段II,银主要以硫的络合物形式运移,随着成矿流体物理化学条件的变化而发生沉淀,形成银矿物.