江西中部徐山钨铜矿床单颗粒白云母Rb-Sr等时线定年及其地质意义

徐山钨铜矿位于江西省中部，是一个由石英脉型、矽卡岩型、花岗岩型3种类型"叠置"的三位一体矿床，其中石英脉型和花岗岩型矿体及其相互关系基本符合"五层楼+地下室"或者"上脉下体"型钨矿床的特征.首次利用Rb-Sr等时线法对该矿床含黑钨矿石英脉的镶边白云母进行了亚样品定年，获得其成矿年龄为147.1±3.4 Ma(MSWD=0.71).该矿床的形成年龄与江西南部的石英脉型钨矿床相似，都形成于燕山中期；而与赣东北、赣西北的铜矿床成矿时间有较明显差异.白云母的I_Sr值很高，为0.849±0.026，其原因可能是成矿花岗岩浆本身来源于演化程度和成熟度较高的壳源岩石，而成矿流体在水-岩反应的过程中又萃取了岩石中具有异常高87Sr/86Sr比值的Sr.高I_Sr值也反映了相关的花岗岩及矿床形成过程中基本上没有幔源物质的参与. 

Rb-Sr Isochron Age of Single-Grain Muscovite in the Xushan W-Cu Deposit,Central Jiangxi,and Its Geological Significance

The Xushan tungsten-copper deposit is located in the central part of Jiangxi Province. It is a trinity deposit comprising three types of ore-bodies, i.e. quartz vein type, skarn type, and granite type. Rb-Sr micro-isochron method is first applied to determining the ore-forming age by using single grain of muscovite growing at the edge of the wolframite-quartz vein type tungsten ore. Result shows that the mineralization age is 147.1±3.4 Ma, with MSWD=0.71, and the I_Sr value is 0.849±0.026. This ore-forming age is similar to those of quartz-wolframite-vein tungsten deposits in southern Jiangxi, but is much later than the ages of copper deposits in northeastern Jiangxi and slightly earlier than the ages of copper deposits in northwestern Jiangxi. The very high I_Sr value may suggest that the ore-related granite was a melting product of highly evolved and highly saturated crust material, and the ore-forming fluids have extracted the strontium of extremely high 87Sr/86Sr ratios from the granite through water-rock interaction. It also suggests that there was almost no contribution of mantle material during the formation of either ore-related granite or tungsten mineralization.