西天山达巴特斑岩型铜矿床流体地球化学特征和成矿作用

Mineralization and fluid geochemistry of Dabate prophyry copper deposit, western Tianshan in Xinjiang

本文对西天山地区达巴特斑岩铜钼矿床矿石中石英的流体包裹体进行了均一法和冷冻法测温,对相应的石英单矿物进行了氢氧同位素测定,据此判断了成矿流体的来源和成矿物理化学条件。结果表明含铜钼矿石中的流体包裹体主要为气液两相包裹体和含子矿物三相包裹体,不同样品中同类包裹体具有基本一致的均一温度、子矿物溶化温度、冰点、盐度和密度值,数据显示成矿流体均呈中温低盐度的特点。矿石氢氧同位素组成表明矿床的成矿流体属于岩浆水范畴,而且具有深部来源甚至幔源的可能性。根据矿体主要分布在火山机构南北两侧与地层的接触带及其内发育的断裂构造中这一空间关系,结合流体包裹体测温结果,推测尽管该矿床威矿流体具有深源特征,但成矿作用发生在中浅部环境,成矿与火山机构最晚期的花岗斑岩具有密切的成因关系。

In this study we carried out homogeneous temperature and salinities analyses on the fluid inclusions in quarzt from the copper-molybdenum mineralization satge of dabate deposit. Hydrogen and oxygen isotopic composition have also analysed on the corresponding samples for estimated the source and features of ore-forming fluids. The results show that the type of fluid inclusion could, P be devided into two types, i.e., the two phase and moly-phase inclusions with daughter minerals. In different quartz samples, each type of fluid inclusions has similar homogeneous temperature and salinities and density. Oxygen and hydrogen isotope studies show that the ore-forming fluids are mainly from magma and probably deep-derived or mantle-derived. The ore-forming fluid display low salinity with the values range form 1.74% to 14.46% w (NaCl) eq. with most of them between 2.9% to 7.2%. The homogeneous temperature of the gas and liquid phase range from 185 to 390 degrees C and most value between 185 to 283 degrees C. The melted temperature of inclusions with daughter minerals is between 181 to 431 degrees C. The sanility of this kind of inclusion is 30.97% similar to 50.97% w(NaCl) eq. Combining the Re-Os dating data for mineralization and SHRIMP zircon U-Pb dating on rhyolitic porphyry and granite-porphyry obtained previously, we suggest that during Late Carboniferous to Early Permian, the western Tianshan began to interplate collision and extension evolution stage. This tectonic event resulted emplacement of deep-derived porphyry magma and formed volcanic apparatus which consist of granite-porphyry, rhyolitic porphyry and rhyolitic crystal tuff lava. Considering the spatial relationship between the ore bodies and volcanic and sub-volcanic rocks, combining the geological information from isotope and fluid inclusion studies, the authors concluded that the ore-forming fluids are deep-derived but the ores are deposited at medium to hypabyssal environment. The Cu-Mo mineralization is closely related to the late phase of the volcanic apparatus.