得尔布干成矿带太平川铜钼矿床含CH_4流体包裹体研究

CH_4-containing fluid inclusion study of the Taipingchuan porphyry Cu-Mo deposit,Inner Mongolia

太平川斑岩铜钼矿床位于得尔布干断裂西北侧,成矿斑岩时代为200Ma左右。该斑岩铜钼矿可划分为3个成矿阶段:早阶段为辉钼矿-黄铁矿(黄铜矿)-石英组合,中阶段为黄铜矿-黄铁矿(辉钼矿)-石英组合,晚阶段以碳酸盐-黄铁矿-石英脉为特征。石英脉中可见含子晶三相、含子晶两相、CH4-H2O和NaCl-H2O四类包裹体,早阶段发育含子晶和CH4-H2O包裹体,中、晚阶段以NaCl-H2O类包裹体为主。成矿早、中、晚各阶段流体包裹体的均一温度分别分布在340～500℃、158.8～360.5℃和147.8～219.7℃,相应盐度为10.1%～55.8%NaCleqv、0.7%～10.9%NaCleqv和2.1%～10.9%NaCleqv。激光拉曼探针测试显示,早、中阶段包裹体含有CH4和H2O,晚阶段包裹体则以盐水溶液为主。早阶段多种类型包裹体共生,均一温度相近,且均一方式多样,指示早阶段流体发生过沸腾作用。本文认为早阶段成矿作用主要与高温、高盐度、含CH4流体的沸腾作用有关,中-晚阶段成矿作用显示出不同来源流体的混合作用特征。成矿构造环境可能是蒙古-鄂霍茨克洋向南俯冲所形成的陆缘弧。

The Taipingchuan porphyry Cu-Mo deposit is located in northwest of Derbugan fault,Inner Mongolia.The age of host porphyry is about 200 Ma.The mineralization of processes can be divided into early,middle and late three stages,which are characterized by assemblages of molybdenite-pyrite-quartz,chalcopyrite-pyrite-(molybdenite)-quartz,and carbonate-pyrite-quartz,respectively.Four types of fluid inclusions in quartz can be observed,i.e.,three-phase daughter crystal-containing,two-phase daughter crystal-containing,CH4-H2O,and NaCl-H2O.The former three types were developed in early stage,the latter type is major inclusions in middle and late stages.Fluid inclusions in minerals formed in early,middle and late stages yield homogeneous temperatures of 340 ～ 500℃,160 ～ 361℃ and 148 ～ 220℃,respectively,with salinities of 10.1% ～ 55.8% NaCleqv,0.7% ～ 10.9% NaCleqv and 2.1% ～ 11.9% NaCleqv.Laser Raman spectroscopy shows that the early and middle stage inclusions contain H2O and CH4,whereas late-stage inclusions only trap H2O.Some fluid inclusions with similar temperatures are homogenized to different ways,and different types inclusions coexist in same minerals,which strongly suggest that fluid-boiling had occurred in the early stages.Authors believe that the mineralization of early stage may be mainly related to high temperature,high salinity and boiling fluid inclusion with CH4,the middle-late stage mineralization mainly be resulted by the mixing of fluids from different sources.Tectonic environment maybe the continental margin arc formed by the southward subduction of Mongolia-Okhotsk Ocean.