岩体引发流体压力时空变化及其成矿响应的计算模拟

In this program, the descriptive research and geodynamic computational modeling are used to probe the intrusion-triggered geodynamic processes of dynamic variation of fluid pressure and related rock fracturing and ore deposition in the shallow intrusion-centred hydrothermal mineralization systems，through researching the ore fields of Shizishan and Tongguanshan in the Tongling district, and the Gupao ore field in the Dayaoshan Au belt. The morphologic and scale measuring and fractal statistics analyzing of rock cracks and breccias, and micro-detecting and fluid-pressure estimation of fluid inclusions are planned to carry out for describing the patterns and digging the causes of the intrusion-triggered variation of fluid pressure and its association with mineralization. Based on the detail geological study of the deposits, the soft codes of GOCAD, FLAC and 3DMIS etc are used to construct the 3D dynamic models of the researched mineralization systems, including the fine models of 3 researched ore fields and two general characteristic models that consist of the essential constituents respectively of the skarn deposits and porphyry deposits. These models are computed numerically to simulate the geodynamic processes of coupled deformation (fracturing), heat transporting, fluid flow and chemical reaction. The results of descriptive research are used to verify modeling results and to modify the models. By comprehensive summary and comparative analysis of the verified modeling results, we would discuss and discover the dynamic mechanism for the magmatic intrusion-triggered variation of fluid pressure and its constraints on mineralization,and construct a conceptual model about it. It can facilitate understanding and exploration of the shallow intrusion-related ore deposits.

选择铜陵地区的狮子山和铜官山矿田以及大瑶山地区的古袍矿田中以岩体为中心的成矿系统为对象，以描述性研究和动力学计算模拟相结合的方法探求岩体引发流体压力的动态变化及相关的岩石的破裂和矿石沉淀的动力学过程和控制因素。通过对含矿裂隙和角砾岩的几何测量与分形统计、流体包裹体的显微测试与捕获时流体压力的估算，为描述岩体引发流体压力变化及其与成矿的关系的规律并分析其原因提供证据。在矿床地质详细研究的基础上,利用GOCAD、FLAC和3DIMS等构建成矿系统的三维动力学模型，包括三个研究矿田实际成矿系统的精确模型和概括了矽卡岩矿床与斑岩矿床的本质特征的特征模型，对这些模型进行一系列的变形-传热-流体流动-化学反应耦合动力学的计算模拟实验。利用描述性研究成果来校验模型,确保模拟结果的有效性。通过模拟结果的对比，分析浅成岩体引发流压力变化的动力学机制及其对成矿控制，建立理论模式，促进浅成岩体成矿研究和勘查。

与岩体相关的斑岩型和矽卡型矿床是铜、金等金属的重要矿床类型，其成矿过程中流体压力的变化及其作用一直不受重视。本项目以计算模拟为主要手段研究铜陵、大姚山和车户沟等地区的与岩体相关的重要斑岩和矽卡岩型矿床的成矿作用时空结构和动力学过程，重点研究成矿流体压力的时空变化规律及其对矿体空间定位的制约。角砾岩的特征及其与矿体空间关系以及动力学计算模拟结果都表明这些矿床在成矿过程中都存在流体演化由超压到泄压的过程。但这种流体压力升降变化的型式与构造环境密切相关，挤压环境中是由大幅度的减容升压到大幅度的扩容降压，引张环境中则是由小幅度的扩容增压到大幅度的扩容降压。矿体定位的部位就是发生了大幅度泄压的扩容部位，而且这种部位在空间上的不均匀分布是与岩体的形态密切相关的。地质调查和钻探显示，铜陵地区控矿的晚古生代以碳酸盐岩为主的富含有机质的地层在晚三叠世的印支运动发生了非常强的逆冲推覆褶皱，表明控矿地层在成矿前就具有了超压流体。我们通过分子动力学和量子化学计算模拟揭示：在低温高压的流体中，草酸根离子（CH3COO−）较氯离子更容易与Cu络合，铜-草酸根络合物[(CH3COO)2Cu−和Cu(CH3COO)(H2O)]的稳定性随压力升高而升高，但随温度升高而快速降低直到分解。这意味着地层中以草酸络合物溶解和运移的Cu会因岩体的侵位而在岩体附近沉淀。这非常有助于解释铜陵地区矽卡岩铜矿床的层控和层状特性。这些成果不仅深化了对斑岩和矽卡岩矿床矿体定位机制的认识，也能为预测矿体位置提供信息，具有重要的科学意义和实用价值。