西藏冈底斯斑岩铜矿带成矿流体的扫描电镜(能谱)约束——以驱龙和厅宫矿床为例

SEM/EDS constraints on nature of ore-forming fluids in Gangdese porphyry copper belt: Case studies of Qulong and Tinggong deposits

文章通过对碰撞造山型斑岩铜矿床———冈底斯斑岩铜矿带中的2个典型矿床(驱龙和厅宫)早期钾化石英脉中多相包裹体的扫描电镜/能谱研究,有效地弥补了以往研究中遗漏的成矿流体中有用组分信息,对成矿流体性质及成矿过程有了更为清晰的认识。扫描电镜/能谱研究表明,驱龙、厅宫矿床中多相包裹体中的子矿物,除常见的石盐及钾盐外,还含有重晶石、方解石、黄铜矿、钛铁矿及其他以Fe、Cu_Fe为主要元素的未知矿物。这些结果表明,成矿流体为富含Cu、Fe、Ti、Mn、S等成矿元素的高氧化态岩浆热液;黄铜矿、钛铁矿、重晶石等子矿物与石盐、钾盐子矿物共同产出,暗示直接从斑岩岩浆中出溶的高盐度流体是成矿物质组分搬运的主要载体。

Most porphyry copper deposits （PCDs） generally occur in island arcs and continental marginal arcs along convergent plate boundaries. It has been recently recognized that the continent-collision zone is also important for PCDs, as can be seen in the study of the Gangdese PCDs belt. In order to understand characteristics and evolutionary processes of the ore-forming fluids, the authors chose early quartz from Qulong and Tinggong, two most important PCD deposits in Gangdese belt, for SEM/EDS analysis. Besides common halite and sylvite, some other kinds of daughter minerals, such as barite, calcite, chalcopyrite, ilmenite and a few unidentified minerals containing mainly Fe, Cu-Fe were identified during the analysis. It is thus concluded that the primary solution in the Gangdese PCDs belt is a kind of highly oxidized magma fluids enriched in copper, iron, titanium,manganese and sulfur. Based on the coexistence of chalcopyrite, ilmenite, barite, halite and sylvite in the multiphase inclusions, the authors also hold that hypersaline liquid （or brine） exsolved directly from porphyry magma might have been the main carrier in the transport of ore-forming materials.