新疆东准噶尔老鸦泉富碱花岗岩型锡矿床地质及成矿流体

Study on the geology and ore-fluids of the tin deposits in Laoyaquan alkaline granites in eastern Junggar,Xinjiang

老鸦泉碱性花岗岩位于新疆北部东准噶尔地区。老鸦泉碱性花岗岩体及其内卡姆斯特、干梁子锡矿床的矿石和岩石的岩矿鉴定、稀土元素以及流体包裹体的系统研究表明,老鸦泉碱性花岗岩及其内的花岗斑岩及含矿石英岩、云英岩化锡矿体、石英脉锡矿体,实际上是富碱花岗质岩浆逐渐分异演化的同源和最终产物,锡成矿流体为中-高温、低盐度。碱性岩浆晚期分异的大量气水热液富锡、富硅、富碱、富含F、Cl、SO24离子及离子团,其氧逸度高、酸度高、温度高,这种热液引起花岗岩体的硅化、云英岩化等自变质作用,在该作用中随温度、压力的降低及CH4等还原性气体及CO2气体的逃逸,改变了成矿流体的氧化-还原环境,流体向相对还原及碱性条件转化,在新的氧化还原、酸碱度界面条件下,其携带的锡的络合物不稳定而分解,锡沉淀成矿。

Laoyaquan alkaline granite is located in eastern Junggar area,northern Xinjiang.Identification of the rock and minerals in Laoyaquan alkaline granite body and the Kamusite tin deposit and Ganliangzi tin deposit,and the REE geochemical and fluid inclusions studies indicate that all of the granite porphyry,ore-bearing quartzite,greisen body-type tin ore body,and quartz vein-type ore body were the products derived from the same alkali-rich granitic magma.The ore-forming fluid from the Kamusite sin deposit has characteristics of middle-high temperature,low salinity.Large gas-water hydrothermal which was formed in the later evolution stage of alkaline magma were Sn-Si-alkali-F-Cl-SO24 rich and oxygen fugacity-acidity/alkalinity-temperature high.And the hydrothermal lead to auto-metamorphism of the granite,such as silicification,greisen-type alteration,etc.During auto-metamorphism the reduction-oxidation state of ore forming fluid had changed with the dropping of the temperature and pressure,and the escaping of CH4 and CO2.The fluid transformed into relatively high reduction state and strong alkaline environment.Under the new conditions of reduction-oxidation state and acidity-alkalinity,the tin-complex taken by the fluid was decompounded because of its unstabilizing,which lead the tin element to be deposited and form the ore.