东昆仑造山带那更康切尔沟银矿床典型硫化物特征及其指示意义

Characteristics of representative sulfides from the Nagengkangqieergou silver deposit in the Eastern Kunlun Orogenic Belt and their implications

那更康切尔沟银矿床位于东昆仑造山带东段昆中断裂北侧,是青海省近年来新发现的主要受北西向断层控制的大型独立热液脉型银矿床,此文首次对其典型硫化物进行了系统的研究。显微矿相学观察和电子探针分析等研究表明,该矿床鄂拉山组地层中硫化物主要包括闪锌矿、方铅矿、黄铁矿,而金水口岩群地层中硫化物除包括上述矿物外还含较多黄铜矿、白铁矿、毒砂、黝锡矿、磁黄铁矿。其中自然银和辉银矿与闪锌矿、毒砂和黝锡矿在空间分布上关系较密切,Ag的赋存状态除以独立银矿物存在外,还以类质同像的形式赋存于方铅矿中,并且金水口岩群和鄂拉山组方铅矿Ag含量具有明显差异,含Ag平均值分别为0.33%和0.64%,其它硫化物中基本不含Ag。此外,金水口岩群和鄂拉山组闪锌矿、方铅矿、黄铁矿等成分标型特征指示那更康切尔沟银矿床成矿作用为火山成因,而两种赋矿地层中的成矿流体在温度、成分、硫逸度等方面均具有明显差异性。

The Nagengkangqieergou silver deposit, situated in north side of the Kunzhong fault in the eastern segment of the Eastern Kunlun orogenic belt, is a recently discovered large-scale independent hydrothermal vein-type deposit, whose orebodies are mainly controlled by the NW-trending faults, in Qinghai Province. This is the first time to have undertaken a systematic study on the characteristics of representative sulfides from the Nagengkangqieergou silver deposit in this paper. The results of microscopic mineralography observation and electron microprobe analysis show that sulfides of the Elashan Formation mainly include sphalerite, galena, and pyrite, while those of the Jinshuikou Group include sphalerite, galena, pyrite, chalcopyrite, marcasite, arsenopyrite, stannite, and pyrrhotite. Silver minerals including native silver and argentite are in close spatial association with the distribution of sphalerite, arsenopyrite and stannite. Besides independent silver minerals, the Ag occurred partly in galena in isomorphism forms. In addition, the contents of Ag in galena crystals from the Jinshuikou Group are obviously different to those from the Elashan Formation, with average Ag contents of 0.33% and 0.64%, respectively. There is scarcely any Ag in other sulfides. Moreover, the compositional and typomorphic characteristics of sphalerite, galena, and pyrite indicate that the mineralization of the Nagengkangqieergou silver deposit is genetically associated with volcanic activities, and the ore-forming fluids associated with the Ag mineralization in both ore-bearing strata show remarkable differences in temperature, composition, and sulfur fugacity.