西藏厅宫斑岩铜矿Cu沉淀机制研究

Cu precipitation mechanism in porphyry copper deposits has been the research focus of the world economic geology, but it is still under debate. Cooling, fluid mixing and fluid boiling have been put forward to this problem. The Tinggong porphyry Cu deposit in Tibet is characterized by clear alteration zones and abundant quartz–(sulfide) veins, Cu mineralization in which occurs both in potassic and phyllic alteration stages. These features make Tinggong a suitable target to study the Cu precipitation mechanism. Here, we plan to investigate the structure of quartz and paragenesis in quartz–(sulfide) veins of each stage through CL petrography study. Based on the above results, fluid inclusion petrography, microthermometry, laser Raman spectroscopy and LA-ICP-MS, and in situ quartz O isotope analyses will be conducted to investigate spatial and temporal features of the ore-forming fluid and quartz O isotope, in order to reveal the precipitation mechanism of Cu in porphyry copper deposits.

斑岩铜矿床中Cu的沉淀机制是近些年来国际矿床学研究的热点，但尚存争议，存在降温作用、流体混合及流体沸腾等多种观点。位于青藏高原的厅宫斑岩铜矿具有清晰的蚀变分带特征且各蚀变阶段脉体发育，Cu矿化形成于钾化阶段和绢英岩化阶段，这为精细研究斑岩铜矿中Cu的沉淀机制提供了良好的条件。本项目拟对厅宫斑岩铜矿中各阶段脉体进行精细的CL岩相学研究，查明石英脉中石英的结构特征及其与黄铜矿的共生关系，在此基础上，对石英中流体包裹体进行岩相学观察、显微测温及成分分析，并对各阶段石英进行O同位素分析，揭示成矿过程中流体特征及O同位素时空演化规律，探讨Cu的沉淀机制。

厅宫斑岩铜矿是西藏冈底斯带重要斑岩铜矿之一，已探明铜资源储量为149万吨，铜的平均品位为0.46%，并伴生有钼。本项目以厅宫斑岩铜矿为研究对象，在野外考察基础上，详细划分厅宫斑岩铜矿蚀变和矿化分带、石英世代，并对不同世代石英进行详细的流体包裹体及O同位素研究，旨在解决斑岩铜矿Cu的沉淀机制问题。结果表明，厅宫斑岩铜矿蚀变从早到晚有钾化、青磐岩化、绢英岩化和泥化，铜矿化主要与在钾化和绢英岩化蚀变，钼矿化与钾化蚀变相关。精细的石英岩相学研究发现，钾化阶段的铜矿化晚于钾化蚀变，而是形成于绢英岩化阶段。流体包裹体、石英O同位素及蚀变绿泥石微量研究表明，铜矿化主要形成于绢英岩化阶段，温度为300-340 oC, Cu沉淀过程中，流体中与大量天水的加入。因此推断，降温及天水的加入是斑岩铜矿中Cu沉淀的主要机制。