内蒙古额仁陶勒盖大型银矿床地质及地球化学特征

Geological and geochemical characteristics of Erentaolegai large-scale silver deposit,Inner Mongolia

内蒙古额仁陶勒盖银矿是得尔布干成矿带南西段的大型银矿床,位于蒙古-鄂霍茨克造山带和得尔布干断裂之间。该矿床热液成矿过程划分为石英-黄铁矿、石英-硫化物及石英-锰碳酸盐3个阶段。文章对不同成矿阶段的流体包裹体测温及采用氢氧同位素和硫同位素示踪成矿流体特征和来源,结果显示:前两阶段包裹体均一温度为200~423℃,盐度w(NaCl_(eq))可分为2组,一组盐度w(NaCl_(eq))为13.82%~16.05%,另一组盐度w(NaCl_(eq))为0.18%~8.14%;石英-锰碳酸盐阶段均一温度范围为124~245℃,盐度w(NaCl_(eq))为0.18%~15.42%,从早到晚阶段总体显示随温度降低、盐度降低的趋势;主成矿阶段对应成矿深度0.48~1.41 km,平均值为0.76 km;成矿流体氢、氧同位素组成(δ^(18)O_(H2O)值为-11.6‰~-3.3‰)位于原生岩浆水的左下方靠近雨水线位置,表明成矿流体可能是岩浆水与大气降水的混合流体,且成矿的中晚期以大气降水为主。硫同位素测试结果显示,δ^(34)S值皆分布于-4.0‰~+4.5‰之间,呈塔式分布,反映了硫主要来自幔源。铅同位素组成反映了成矿物质主要来自地壳深部或上地幔。综合分析认为,该矿床是一个与火山-次火山活动有关的浅成低温热液型银矿床。通过矿床地质及矿床地球化学研究,笔者进一步完善了额仁陶勒盖式浅成低温热液型矿床成矿模式,用该模式指导矿床外围新发现多个金、银、钼多金属矿(化)点。

The Erentaolegai silver deposit in Inner Mongolia is a large-scale silver deposit in the southwestern part of the Derbugan metallogenic belt,and is located between the Mongolia-Okhotsk orogenic belt and the Derbugan fault.This study shows that ore-forming process of the E'rentaolegai silver deposit can be divided into three stages,including quartz-pyrite stage(stageⅠ),quartz-sulfide stage(stageⅡ),and quartz-manganese carbonate stage(stageⅢ).Microthermometric data indicate homogenization temperatures of fluid inclusions ranging mainly from 200℃to 365℃in the first two stages with salinities of 13.82%~16.05%and 0.18%~8.14%NaCl equivalent,respecively and those of fluid inclusions ranging from 124℃to 245℃in the third stage,with salinities of 0.18%~15.42%NaCl equivalent.The temperature and salinity from early to late stage decrease gradually.The metallogenic depth of the main metallogenic stage is estimated to be about 0.48~1.41km,with an average of 0.76 km.The hydrogen(δ^(18)O_(H2O)=-11.6‰to-3.3‰)and oxygen isotopic composition is located at the lower left of range of primary magmatic water but close to that of meteoric water,indicating that the ore-forming fluid was derived originally from a mixture of primary magmatic water and meteoric water,with dominant meteoric water in later stages.Theδ^(34)S values of sulfide minerals in the deposit range from-4.0‰to 4.5‰,implying a mantle sulfur contribution.Lead isotope data of sulfide minerals indicate that the ore-forming materials derived mainly from the deep crust or upper mantle.Integrating geological and geochemical characteristics,the Erentaolegai silver deposit can be interpreted as an epithermal silver deposit related to volcanic-subvolcanic activity.Furthermore,we put forward a new genetic model for mineralization of the deposit,and discovered a number of gold,silver and molybdenum polymetallic ore(mineralization)points in the periphery of the deposit.