赣南淘锡坑石英脉型钨矿床成矿机制探讨:来自流体包裹体的证据

Mineralization mechanism of Taoxikeng quartz vein type tungsten deposit in southern Jiangxi Province: Evidence from fluid inclusions study

赣南地区淘锡坑钨矿床是典型的大型石英脉型钨锡多金属矿床。矿体赋存于震旦系浅变质砂(板)岩,并延伸至深部花岗岩内,按空间产出位置分为内带矿体和外带矿体,包括宝山、西山、烂埂子、枫岭坑4大脉组,矿体产出各不相同,矿物组合也具有明显分带特征。在详细的岩相学研究基础上,文章选择淘锡坑主成矿期石英为研究对象,并与共生黑钨矿作对比,从空间角度开展不同脉组、不同矿体或中段的流体包裹体的对比研究。根据流体包裹体岩相学,石英包裹体类型有H_2O-NaCl型包裹体(Ⅰ型)、H_2O-NaCl-CO_2型包裹体(Ⅱ型)和纯CO_2体系裹体(Ⅲ型)及少量含石盐子晶的多相包裹体,并同时捕获贫CO_2的盐水溶液包裹体和纯CO-2气相包裹体。包裹体显微测温结果显示:内、外带石英脉气液两相的包裹体均具有较宽温度和盐度范围,外带均一温度和盐度w(NaCl_(eq))分别集中于200～220℃、1%～6%,内带均一温度和盐度w(NaCleq)分别集中于100～220℃、3%～7%,流体为中-低盐度、富含CO_2的H_2O-CO_2-NaCl体系,不同脉组不同矿脉之间对比结果均显示出多期成矿的特征。在矿脉形成过程中,流体的成分和温度在内外接触带有明显变化,表明岩体与围岩接触界面是造成淘锡坑矿床内带矿体和外带矿体的成矿条件改变的转折位置,成矿流体在此附近发生CO_2逸失引起相分离的不混溶作用是成矿的主要因素。

The Taoxikeng is a large scale quartz vein type tungsten deposit in Chongyi County,southern Jiangxi Province.The quartz veins occur in shallow metasandstone of sinian system and extent to the deep granite,which respectively are outer orebody and inner orebody.The Baoshan,Xishan,Langengzi and Fenglinkeng are four vein groups.They are characterized by different occurrence and mineral assemblage.The main types of fluid inclusions:H2O-NaCl type(Ⅰtype),H2O-NaCl-CO2type(Ⅱtype),pure CO2(Ⅲtype)and minor daughter mineralbearing inclusions in all samples from quartz and intergrowth wolframite in main metallogenic period.The existence of capturing both aqueous salt inclusions with poor CO2and pure CO2inclusions is a typical feature of the Taoxikeng deposit.Experimental results show that the main homogenization temperature and salinity of inner and outer orebody are in a wide temperature range.The homogeneous temperatures and salinities w(NaCleq)of fluid inclusions in quartz of outer orebody vary from200℃to220℃and1%to6%,respectively.The homogeneous temperatures and salinities w(NaCleq)of fluid inclusions in quartz of inner orebody vary from100℃to220℃and3%~7%,respectively.According to the data above,it can be concluded that the ore-forming fluids generally belong to middle temperature,low salinity,rich CO2,H2O-CO2-NaCl system.The temperature and composition show the significant changes in inner orebody and outer orebody.It is the main reason that fluid immiscibility caused by CO2escaping happened in contact interface between granite and surrounding rock possibly led to tungsten precipitation.