陕西略阳张家山金矿成矿作用及Au-Se矿物形成物理化学条件研究

Ore-forming processes and physicochemical conditions of Zhangjiashan gold deposit,Lueyang,Shaanxi Province

陕西略阳煎茶岭金矿矿集区中的张家山金矿主要由破碎蚀变岩型、角砾岩型和含金石英黄铁矿脉型矿石组成。含金石英-黄铁矿脉型矿石产于断层下盘的石英菱镁岩中。黄铁矿发育富As黄铁矿边,环边受As含量的变化呈现一定的韵律变化,自然金赋存在富As黄铁矿中。在断裂发育形成断层角砾岩的过程中,流体充填破碎石英菱镁岩的裂隙中形成热液矿物,包括硫化物、硒化物以及自然金。石英菱镁岩发生破碎形成的网状裂隙被含金石英-方解石-黄铁矿脉充填。破碎蚀变岩型矿石中,自然金主要分布在含金石英-黄铁矿脉的石英之中或靠近热液脉的菱镁矿或石英间隙。随着大量方解石脉沿裂隙贯入,进一步促进石英菱镁岩的破碎及岩石角砾的分离,形成由石英菱镁岩碎屑、石英和褐铁矿组成的复成分角砾岩,自然金和硒化物呈浸染状分布在角砾岩中。笔者在角砾岩型矿石中发现了灰硒汞矿、直硒镍矿、硒铅矿等硒化物,这些硒化物往往与自然金密切共生。结合矿物组合以及相关化学反应关系,通过热力学计算,构建了该矿床在不同温度条件下的热力学相平衡关系图,限定了硒化物与其他相关矿物稳定存在的物理化学条件。硒化物一般与自然金和石英共生,高的f(Se2)值和f(Se2)/f(S2)比值是控制硒化物形成的关键因素。

The Zhangjiashan gold deposit,located in the Jianchaling gold concentration area of Shaanxi Province, mainlyconsistsofalteration-type, breccia-type, andauriferousquartz-pyriteveintypeorebodies.Fluidfilledfractures in broken listwaenite formed hydrothermal minerals comprising sulfides,selenides and native gold in breccias. The native gold-quartz-calcite-pyrite veins filled the mesh cracks of broken listwaenite and dissolved the broken rocks to further promote fractures,and finally formed the alteration-type ore. Native gold in alteration-type ore primarily occurs in the quartz of the Au-bearing quartz-calcite-pyrite veins or exists in the gaps of quartz and limonite adjacent to hydrothermal veins. Listwaenite broke further and breccias rocks were separated,which formed the compound breccias composed of listwaenite clastic rocks,quartz and limonite with calcite veins. Breccias-type ore is composed of complex breccias and calcite,in which native gold generally occurs in the boundary between quartz and limonite. The auriferous quartz-pyrite vein type ore is hosted in the listwaenite of footwall fault. The pyrite in this type ore develops As-rich pyrite rim that shows a rhythm change controlled by the As content. Native gold in auriferous quartz-pyrite vein type ore completely occurs in the As-rich pyrite rim. The authors have found some selenides（tiemannite,kullerudite,clausthlite） in breccia-type ore coexisting with native gold. Physicochemical phase diagrams were established according to mineral assemblages and relative reaction relationships,in which physicochemical conditions for the formation of selenides and other minerals are restricted. High f（Se2） values and f（Se2）/f（S2） ratios are the key factors controlling precipitation of selenides.