新疆包古图金矿四矿区L7号脉中的特殊矿物组合及其成矿意义

Special mineral assemblage in L7 vein of No.4 ore district within Baogutu gold deposit of Xinjiang and its ore-forming significance

包古图金矿四矿区L7号脉由浅部的自然砷-石英脉型矿石和深部的辉锑矿-石英脉型矿石组成。矿脉中含罕见的As、Sb矿物,如paakkonenite(Sb2AsS2)、自然砷、自然锑、方锑金矿、硫锑金银矿(Au3Ag4Sb10S12)等。热液过程划分为5个阶段:黄铁矿-毒砂阶段(Ⅰ),围岩中形成大量的毒砂和黄铁矿并伴随较强硅化;粗粒石英阶段(Ⅱ),形成沿围岩壁或围岩角砾的梳状石英;Au-As-Sb矿化阶段(Ⅲ),形成辉锑矿-自然锑-自然砷-paakkonenite-银金矿-自然金-方锑金矿-硫锑金银矿-辉锑银矿-银锌黝铜矿-斜方砷铁矿-硫铜锑矿-石英;晚期Sb矿化阶段(Ⅳ),形成与粒状方解石共生的辉锑矿、自然锑和paakkonenite;方解石阶段(Ⅴ),形成穿切矿体和围岩的方解石(-石英)细脉。辉锑矿和斜方砷铁矿交代毒砂,自然金、方锑金矿、paakkonenite和自然砷交代辉锑矿。辉锑矿的结晶主要受温度和还原S含量的控制,自然砷、自然锑的结晶主要受氧逸度和温度控制。As、Sb分别以自然砷、辉锑矿和自然锑形式存在,同时消耗大量H2S,流体进入张性空间后也释放H2S,导致硫逸度急剧降低,含Au络合物失稳而成矿。

The L7 vein in No. 4 ore district of the Baogutu gold deposit is composed of stibnite quartz-type ore body and native arsenic quartz-type ore body and contains some rare minerals, such as paakkonenite （Sb2AsS2）, native arsenic, native antimony, aurostibite and Au3Ag4Sb10S12. Based on petrographic observation, the authors identified five ore-forming hydrothermal stages. Pyrite -arsenopyrite stage （Ⅰ） consisted of massive arsenopyrites and pyrites with intense silicification. Coarse quartz stage （Ⅱ） formed comb or coarse quartz along the host rock and breccias. Au-As-Sb mineralization stage （Ⅲ） was composed of stibnite, native antimony, native arsenic, paakkonenite, electrum, native gold, aurostibite, Au3Ag4Sb10S12, miargyrite, tetrahedrite, lollingite, chalcostibite and quartz. Late Sb mineralization stage （Ⅳ） formed stibnite associated with calcite, native antimony and paakkonenite. Calcite stage （Ⅴ） formed only a few calcite （-quartz） veins, which ended the hydrothermal activity. The ore-forming fluid of stage Ⅲ greatly reformed the earlier-formed minerals, with arsenopyrite replaced by stibnite and lollingite, and stibnite by native gold, aurostibite, paakkonenite and native arsenic. The crystallization of stibnite was controlled by temperature and the quantity of reduced S species, while native antimony and native arsenic by fO2 and temperature. Arsenic and antimony were deposited as native arsenic, native antimony and stibnite, which consumed H2S. The open space also caused the escape of H2S. The loss of H2S destabilized the Au-sulfide complexes and finally caused gold deposition.