甘肃省沃尔给花岗岩体中黑云母的成分对其岩体碱度的响应及成岩成矿意义

Chemical Composition of Biotites Responding to Basicity of Woergei Granite Intrusion in Gansu Province and Implications for Petrogenesis and Mineralization

矿床的形成与其成矿地质体的成因和岩石化学性质密切相关,因此有必要对岩体碱度与成矿关系进行深入研究。通过甘肃省沃尔给花岗岩体的采样测试,并对国内52个各类矿床中与成矿有关岩体中黑云母的主量元素化学成分进行统计和分析,进行寄主岩石碱度判别。研究结果显示:研究区与Cu、Au成矿有关的岩体位于高碱度区域内,而与Sn矿形成有关的岩体均属于低碱度岩石系列。岩浆熔体早期至岩浆后期热液阶段,氧逸度的变化由高到低,介质的碱度逐渐增强,Cu、Au矿床的形成大致经历上述的成岩成矿过程。岩浆结晶过程早期低氧逸度、高碱度有利于Sn的活化迁移,岩浆期后热液阶段的高氧逸度、低碱度有利于锡石的沉淀,但是由于锡石沉淀过程中不断消耗O_2,致使其较高的氧逸度显著降低。认为碱度与氧逸度之间相互作用、相互影响进而引起矿化的发生。

The formation of ore deposits and the geological genesis of metallogenic rock mass are closely related to the chemical characteristics of rocks. In this paper, we centred on the investigation of relationship between the alkalinity and mineralization. The sampling and measurement of the chemical compositions of biotite, from Woergei granite intrusion in Gansu Province are carried on, and the biotite data from fifty-two kinds of different deposits in China are collected. By analyzing the basicity of host rocks, we regard that the existed metallogenic granite intrusion bearing Cu and Au were located in the high basicity area. The granite intrusion was almost re-lated to the formation of Sn ore deposits belong to the low alkalinity rock. From the early to late period of mag-matic melt transformation process, the oxygen fugacity changed from high to low and medium alkalinity increased. The formation of Cu and Au deposits was also followed by the process of diagenetic mineralization. However, the low oxygen fugacity and the high basicity are advantageous to the activation and migration of element Sn in early magmatic crystallization process. The high oxygen fugacity and the lower alkalinity are ad-vantageous to the precipitation of cassiterite in magmatic hydrothermal-fluid stage. The precipitation of cassiterite constantly consumed oxygen, leading to a significant decrease of the higher oxygen fugacity than before. The interaction of the oxygen fugacity and the basicity caused mineralization.