石英脉型黑钨矿床热液运移模拟与黑钨矿沉淀机制

Tungsten deposits are our advantageous strategic mineral resources. Vein-type tungsten deposits are important parts of proven tungsten reserves, but the mechanisms of wolframite deposition are still enigmatic. This blocks further development of tungsten metallogenic theories and prediction for deep ore prospecting. Our goal is to explain the thermal flow and the mechanisms of wolframite precipitation at the vein-type tungsten deposits using in-situ geochemical analysis and numerical simulation. A few typical vein-type tungsten deposits will be chosen. First, cathodoluminescence textures of quartz will be used to separate quartz at different stages and trace the infilling history. Based on cathodoluminescence study, trace element, oxygen isotope, and fluid inclusion experiments will be combined to detect hydrothermal fluids at different stages and to unravel the evolution history of ore fluids. The in-situ geochemical study will be integrated to build the thermal flow model. Then, we will simulate thermal fluid flow in complex fracture systems, and investigate the relationship between fluid mixing and wolframite deposition, and evaluate the influence of heat conduction into wallrock and irreversible expansion on fluid cooling. The team will simulate hydraulic fracturing driven by high-pressure ore fluids and its relationship to quartz and wolframite deposition. We will test and correct the thermal flow model based on the above numerical experiments. Finally, the mechanisms of wolframite precipitation will be discussed based on the geochemical and numerical results.

钨矿是我国优势和战略矿产资源。在已探明的钨资源储量中，石英脉型黑钨矿床占有重要地位，但黑钨矿沉淀机制尚存争议。这阻碍了钨矿成矿理论的发展和深部找矿预测。本课题拟通过脉体微区地球化学分析和数值模拟等方法研究钨成矿流体运移过程和黑钨矿沉淀机制。选取南岭地区几个典型的石英脉型黑钨矿床，如江西大吉山、漂塘、淘锡坑等钨矿床，根据石英等矿物的阴极发光特征，研究不同期次脉体的显微结构,示踪热液充填成脉过程；对不同期次的石英，开展氧同位素、微量元素、和流体包裹体测试分析，约束成矿流体物理化学条件和演化过程，建立热液运移模型；模拟成矿流体在复杂裂隙系统的运移过程，研究流体混合与黑钨矿沉淀的关系，定量评价围岩冷却和不可逆绝热膨胀对成矿流体降温的贡献；模拟研究高压成矿流体水力致裂过程对石英和黑钨矿沉淀的影响；通过数值模拟，验证和改进热液运移模型。综合上述研究，阐明钨成矿流体运移过程和黑钨矿沉淀机制。

钨矿是我国优势和战略矿产资源。在已探明的钨资源储量中，石英脉型黑钨矿床占有重要地位，但黑钨矿沉淀机制尚存争议。本项目通过脉体微区地球化学分析和数值模拟等方法研究钨成矿流体运移过程和黑钨矿沉淀机制。依据石英阴极发光强度，在江西漂塘钨矿Ⅲ号脉带识别出早期的白色石英和晚期暗色石英。两期石英具有不同的微量元素特征和包裹体均一温度。为避免多期次石英的显微测温混合结果，有必要利用其阴极发光特征对多期次石英进行分期。.黑钨矿、黄玉等成矿早期的高温矿物中已发现含CO2的包裹体。项目组通过水力破裂耦合多组分平衡反应的数值模拟发现，水力破裂后的压力骤降可显著降低流体中CO2的溶解度，从而使得流体pH升高，至少使钨溶解度降低30%。.围岩蚀变能指示成矿作用动力学过程。钨矿脉围岩蚀变局限分布在矿脉两侧，围岩蚀变宽度通常不超过1米，且随深度递减。项目组利用有限元方法模拟热液运移和化学组分（SiO2和H+）从裂隙向邻近围岩扩散过程，发现围岩孔隙度随深度递减可能是形成石英脉型钨矿床蚀变宽度随深度减小的有效机制。前人将钨矿蚀变特征归因于岩浆热液过渡性流体不均一的物理性质，本项目为这一科学问题提供新的解释。