Fluid inclusions in coexisting cassiterite and quartz from the Tongmushan tin deposit, eastern Hunan, China

Abstract

桐木山云英岩型锡矿床是湘东锡田锡多金属矿田中一个典型矿床，在详尽的野外考察、矿石结构观察以及流体包裹体岩相学研究的基础上，采用流体包裹体组合的研究方法，利用冷热台、激光拉曼等测试手段，对矿床中锡石中流体包裹体进行直接测定，同时开展与锡石共生的石英及切割矿体的后期石英脉石英中流体包裹体对比研究。结果显示，锡石中流体包裹体的组分、均一温度、盐度与共生的石英存在明显差异，表明锡石与石英形成的P-T-X条件不同。切割矿体的石英脉为成岩成矿后流体作用的产物。与锡石形成相关的流体为中高温、中低盐度的NaCl-H₂O流体体系，与石英形成相关的流体为复杂的含碳流体。流体体系的冷却作用及流体与围岩的反应可能是导致锡石沉淀的主要因素，与石英形成相关的流体在演化过程中则经历了明显的流体不混溶作用。;The Tongmushan greisen type tin deposit is an important deposit in Xitian tin polymetallic ore field at eastern Hunan. Based on detailed field investigation and experimental studies upon the ore texture and the fluid inclusion petrographic properties of the Fluid Inclusion Assemblage (FIA), we carried out microthermometric and Raman microspectroscopic studies upon fluid inclusions in cassiterite and coexisting quartz in greisen type ore samples and quartz veins cutting the orebodies. The results show that significantly differences exist on the constituents, homogenization temperatures and salinities between the cassiterite and intergrowth quartz, suggesting that the P-T-X conditions related to the formation of cassiterite and intergrowth quartz are different. Quartz veins which cut the ore bodies are the products of fluid action after magmatism and mineralization. Fluids related to tin mineralization are from a NaCl-H₂O system with medium to high temperatures and medium to low salinities, while fluids associated with the formation of quartz are from a carbon containing system. This study indicate that water rock reaction and the cooling of fluid are the main mechanisms for tin precipitation in the fluid,and the fluid immiscibility maybe led to the formation of the quartz.