温泉钼矿床成矿流体精细演化及其对秦岭印支期钼富集机理约束

Refined ore-forming fluid evolution constraints on the newly identified Triassic Mo mineral system is of great significance on Mo enrichment mechanism and exploration model in the Qinling Orogen. Quartz, a typically ubiquitous gangue mineral precipitated from fluids ranging widely in composition, pressure, and temperature, and entrapped fluid inclusions thus provide a window on tracking ore-forming fluid evolution and Mo enrichment directly. However, conventional methods employed on ore fluids for hydrothermal ore deposits have been proved to hardly provide accurate data that further hampered our understanding on refined fluids evolution and its constraints on ore-forming processes due to multiple overprinting during magmatic-hydrothermal processes. The phenocryst quartz and hydrothermal quartz from disseminated ores and quartz-sulfide veins of the Wenquan porphyry Mo deposit in the Qinling Orogen will be investigated in this study by cathodoluminescence (CL) microscopy to reveal textures that are unobservable using any other technique. Electronic microprobe (EMP) and laser ablation plasma mass spectrometry (LA-ICP-MS) analyses will be further integrated to reflect the composition difference between quartz of multiple generations. Detailed quantitative evaluation of minerals by Scanning electron microscopy (QEMSCAN) as well as petrography and microthermometry on fluid inclusion assemblages will be conducted aiming at relating specific generations of quartz to specific hydrothermal events and fluid inclusion populations. Laser raman and LA-ICP-MS will be employed on individual inclusion to collect accurate composition of ore fluids throughout the magmatic-hydrothermal processes. We will eventually reconstruct the refined ore-forming fluid evolution process including the changes of pressure, temperature, and major and trace element concentrations through time, and constrain Triassic Mo enrichment processes in the Qinling Orogen.

秦岭造山带印支期钼成矿系统独具特色，成矿流体精细演化是查明钼富集过程的关键手段。石英是斑岩型钼矿床中最常见的贯通性脉石矿物，其捕获的流体包裹体是成矿流体演化和金属沉淀富集过程最直接的地质记录。然而，多期次热液叠加不可避免地造成单一脉体中同时产出多次热液作用沉淀的矿物以及多期、多阶段流体信息的混合，导致传统技术难以厘定不同阶段流体的真实组成，制约了对金属富集机理的认识。因此，项目选择秦岭温泉斑岩型钼矿床浸染状矿石和石英-硫化脉的斑晶石英和热液石英开展阴极发光、电子探针和激光剥蚀等离子质谱分析，查明石英世代及其结构和成分相关性。进而通过岩相学、显微测温、激光拉曼和单个包裹体激光剥蚀等离子质谱等分析厘清不同阶段成矿流体温度、压力和成分的变化，揭示成矿流体精细演化与成矿元素富集的耦合关系，探讨秦岭造山带印支期钼富集机理。

查明温泉钼矿床成矿流体精细演化和钼富集过程是揭示秦岭造山带印支期巨量钼来源和富集机理的关键。本项目开展岩石学、彩色阴极发光和QEMSCAN岩相学、激光拉曼、显微热力学、地质年代学和地球化学分析，创新性地运用Matlab二维数据可视化、基于ImageJ平台的Weka数据挖掘系统等机器学习方法，研究构建了温泉钼矿床成岩成矿年代学格架，厘清了构造-岩浆-蚀变矿化热事件时空特征；厘定了脉石和矿石矿物共生组合时序，定量化约束了斑岩型钼矿化水岩反应过程；查明了多世代石英微区结构及其生长物理化学环境，重建了热液石英生长历史和成矿流体精细演化过程；查明了成矿流体和物质演化从静岩压力向静水压力环境转变特征，认为富集岩石圈地幔的加入诱发岩浆混合，并提高氧逸度，高氧逸度熔体将秦岭古生代富钼沉积物的钼氧化萃取，使钼与高价态硫络合，有利于钼萃取、富集，形成富钼的花岗质岩浆最终成矿。研究结果对微区结构和微束分析重建成矿流体精细演化过程、矿物扫描显微图像数据组机器学习深度挖掘刻画水岩反应过程、秦岭巨量钼源区和富集机制研究具有重要意义。