内蒙古敖汉旗金路金矿床地质特征及成矿流体研究

金路金矿床位于华北克拉通和中亚造山带的结合部位,矿体受北东向韧-脆性断裂控制,赋矿围岩为太古宇小塔子沟组变质岩和三叠纪片麻状二长花岗岩。以流体包裹体和电子探针分析为研究手段,讨论了成矿流体的特征、演化及其与金矿化的关系。其热液成矿过程可划分为乳白色石英阶段(Ⅰ阶段)、石英-黄铁矿阶段(Ⅱ阶段)、石英-多金属硫化物阶段(Ⅲ阶段)和碳酸盐阶段(Ⅳ阶段) 4个阶段,自然金主要产于Ⅲ阶段的石英和黄铁矿中,以粒间金、裂隙金和包体金的形式产出,成色较高。石英中原生包裹体主要有水溶液包裹体、含微量CO2水包裹体、含子矿物多相包裹体3种类型。Ⅰ阶段石英中以水溶液包裹体和含微量CO2水包裹体为主,均一温度较高,为365～405℃,盐度为7. 9%～11. 7%,密度为0. 61～0. 70 g/cm3;Ⅱ阶段石英中3种类型包裹体均发育,均一温度为335～390℃,盐度为4. 3%～36. 1%,密度为0. 62～0. 79 g/cm3;Ⅲ阶段(主阶段)石英中发育3种类型包裹体,均一温度为270～367℃,盐度为1. 7%～37. 8%,密度为0. 64～1. 1 g/cm3。成矿流体属H2O-Na Cl-CO2体系,成矿温度和流体盐度呈逐渐降低趋势,密度则呈现逐渐增大趋势。根据流体包裹体岩相学特征和矿床地质特征,认为流体沸腾作用和硫化作用是本矿区金沉淀成矿的主要机制。综合分析认为矿床成因类型为岩浆热液矿床。

Geological Characteristics and Ore-forming Fluids of the Jinlu Gold Deposit in Aohan Banner,Inner Mongolia

The Jinlu gold deposit is located in the convergence of North China Craton and central Asian orogenic belt. Its ore-bodies controlled by the NE trending ductile-brittle faults, are hosted in metamorphic rocks of the Archean Xiaotazigou Formation and Triassic gneissic monzonitic granite. Based on the studies of fluid inclusions and electron probe, the aim of this paper is to discuss the characteristics and evolution of ore-forming fluids and to provide an insight into the ore genesis. The ore-forming process can be divided into four metallogenic stages, respectively named the white quartz stage(Ⅰ), the quartz-pyrite stage(Ⅱ), the quartz-polymetallic sulfide stage(Ⅲ) and carbonate stage(Ⅳ). Native gold with very high fineness are mainly produced in the Ⅲ-stage quartz and pyrite in the form of intergranular gold, fissured gold and inclusion gold. Petrographic observation indicates that fluid inclusions of the deposit can be divided into three types, i.e., aqueous inclusions, CO₂-bearing aqueous inclusions and daughter mineral-bearing multiphase inclusions. The Ⅰ-stage quartz mainly contains aqueous inclusions and CO₂-bearing aqueous inclusions. The homogenization temperatures, salinities and densities are in the ranges of 365 ℃ to 405 ℃, 7.9% to 11.7% and 0.61 g/cm³ to 0.70 g/cm³. All three types of inclusions are trapped in the Ⅱ-stage quartz. The homogenization temperatures, salinities and densities vary from 335 ℃ to 390 ℃, 4.3% to 35.5% and 0.62 g/cm ³ to 0.79 g/cm³. All three types of inclusions are found in the Ⅲ-stage quartz. The homogenization temperatures, salinities and densities have a range of 270 ℃ to 367 ℃, 1.7% to 37.8% and 0.64 g/cm ³ to 1.1 g/cm³. The studies of fluid inclusions in three metallogenic stages indicate that the ore-forming fluids belong to H₂O-NaCl-CO₂ system. The metallogenetic temperatures and fluid salinities gradually decreased and the densities showed a slightly increasing trend. Based on fluid inclusions and geologic characteristics, it is suggested that fluid boiling and sulfofication may be the main mechanism for the gold precipitation and enrichment in this deposit. The genesis of the Jinlu gold deposit is a magmatic hydrothermal gold deposit.