青海赛什塘斑岩-矽卡岩型铜矿富CH4流体演化与成矿

CH4-rich fluids have been discovered in some porphyry (-skarn) Cu deposits. However, the sources of CH4 and its influence on the migration and precipitation processes of Cu in the ore-forming fluids remain poorly constrained. Previous studies have suggested the ore-forming fluids of the Saishitang porphyry-skarn Cu deposit in the conjunction of West Qinling and East Kunlun Orogenic Belt belong to NaCl-H2O-CH4±CO2 system, which can be served as a suitable research subject to solve the problems. This application plans to carry out detailed research on alteration zonations and mineralization characteristics and conduct in-situ LA-ICP-MS trace element analysis for single fluid inclusions in representative minerals of various mineralization stages, assisted by fluid inclusion microthermometry, Laser-Raman spectrum and H-O-C isotope analyses. In combination with previous studies, these results will be used to exactly fingerprint the P-T-X-fO2 conditions and evolution history of the ore-forming fluids, identify the sources of CH4 and reveal its influence on migration and precipitation processes of Cu in the ore-forming fluids. This study will improve our understanding of the ore-forming mechanism of CH4-rich fluids related porphyry-skarn Cu deposits and provide theoretical reference for metallogenic regularity and prospecting evaluation of the same type of deposits in the region.

部分斑岩（-矽卡岩）型铜矿中发育富CH4流体，但其中CH4的来源及其对Cu运移、沉淀过程的影响有待深入研究。已有研究证实，西秦岭与东昆仑结合部地区赛什塘斑岩-矽卡岩型铜矿成矿流体为NaCl-H2O-CH4±CO2体系，是解决上述问题的理想研究对象。本项目拟在详细的蚀变分带及矿化特征研究基础上，以各成矿阶段代表性矿物的单个流体包裹体LA-ICP-MS成分分析为主要手段，辅以流体包裹体显微测温、激光拉曼、H-O-C同位素分析等方法，充分结合已有研究资料，精细剖析成矿流体的P-T-X-fO2条件与演化过程，查明成矿流体中CH4的来源，揭示CH4对Cu运移、沉淀过程的影响。本研究将为深入理解富CH4流体相关斑岩-矽卡岩型铜矿的成矿机制提供科学依据，为秦昆结合部同类矿床的成矿规律研究及找矿评价提供理论参考。

赛什塘铜矿是东昆仑成矿带开发程度最高的代表性斑岩-矽卡岩铜矿。前期研究工作表明矿床中发育相对还原的热液蚀变矿物组合（较高的辉石/石榴子石比、矿石中含有大量的磁黄铁矿），成矿流体为富CH4的NaCl-H2O-CH4±CO2体系。本项目以赛什塘铜矿不同阶段代表性矿物中的流体包裹体为重点研究对象，开展了详细的矿化蚀变分带、流体包裹体显微测温、单个流体包裹体成分及H-O-C同位素分析工作，同时对赛什塘-铜峪沟矿田相关矿床开展了对比研究工作。结果显示，成矿流体中的CH4来源于还原性石英闪长岩杂岩体。尽管相对还原性的流体可以迁移部分Cu，但成矿的规模有限，赛什塘铜矿部分Cu来自围岩。赛什塘-铜峪沟铜矿田成矿模式可概括为两个阶段，早阶段形成中-下三叠统洪水川群弧前盆地沉积，产生含有机质的粉砂岩伴随着Cu等金属的预富集；晚阶段伸展背景下形成壳幔混合成因的石英闪长岩杂岩体，岩浆上升过程中受到围岩组分的混染，导致氧逸度降低，分异产生的岩浆热液流体进一步与洪水川群地层中的大理岩、碳质凝灰岩及中基性火山岩等发生交代作用，形成还原性的斑岩-矽卡岩型铜矿。