大兴安岭东北部多宝山矿集区二道坎银铅锌矿床有机质特征及对成矿作用的影响

Organic matter characteristics and influence on mineralization of Erdaokan Ag-Pb-Zn deposit in Duobaoshan ore-concentrated area,Northeast Great Xing'an Range

二道坎银铅锌矿床是大兴安岭多宝山成矿带内首次发现的富含有机质的大型银铅锌矿床。为确定有机质对二道坎银铅锌矿成矿作用的贡献,笔者在前人研究基础上,系统总结了矿床地质、矿石矿物及围岩蚀变等基本特征,并对矿石及围岩中有机质进行了显微特征观察和有机质组成测试。结果显示,二道坎银铅锌矿床的矿体产于NW向构造破碎带内,赋存于上志留统-中泥盆统泥鳅河组碳质泥岩和灰岩中。矿石类型为构造角砾岩,矿石矿物包括磁铁矿、黄铁矿、方铅矿,其次为闪锌矿、黝铜矿、赤铁矿和菱铁矿等,含银矿物主要为辉银矿和深红银矿。矿石中出现与矿石矿物共生的大量沥青。赋矿围岩泥鳅河组碳质泥岩和灰岩均富含有机组分,有机碳含量分别为0.77%,3.37%,为沥青的形成提供了物质保障,也为成矿过程中金属的沉淀起到促进作用。综合研究认为,在有机质参与下的硫酸盐热化学还原作用是二道坎银铅锌矿床金属沉淀的重要机制。

The Erdaokan Ag-Pb-Zn deposit is a large Ag-Pb-Zn deposit with rich organic matter discovered for the first time in the Duobaoshan metallogenic belt,Great Xing'an Range.In order to determine the contribution of organic matter to mineralization,the authors systematically summarized the basic characteristics of deposit geology,ore minerals and wall rock alteration on the basis of previous studies,and carried out the microscopic observation and organic composition analyses of organic matter in ore and wall rocks.The results show that the ore bodies of Erdaokan Ag-Pb-Zn deposit occur in the NW-trending tectonic fracture zone and are closely associated with the carbonaceous mudstone and limestone of the Upper Silurian-Middle Devonian Niqiuhe Formation.The ore is composed of structural breccia.The ore minerals mainly consist of magnetite,pyrite and galena,followed by sphalerite,tetrahedrite,hematite and siderite,etc.,and the Ag-bearing minerals are mainly argentite and pyrargyrite.A large amount of bitumen associated with ore minerals appears in the ore.The carbonaceous mudstone and limestone of Niqiuhe Formation in the host rock are equally enriched with organic carbon content of 0.77%and 3.37%,respectively,which provide material guarantee for the formation of bitumen and promote the precipitation of metals in the process of mineralization.It is concluded that the thermochemical reduction of sulfate with organic matter is an important mechanism of metal precipitation in the Erdaokan Ag-Pb-Zn deposit.