四川雪宝顶钨锡铍矿床流体包裹体研究及其意义

Fluid inclusion study and its geological significance on Xuebaoding W-Sn-Be deposit, Sichuan

四川雪宝顶钨锡铍矿床产于花岗岩体与三叠系地层大理岩的接触带,赋矿石英脉受大理岩中的劈理破碎带控制。绿柱石与白钨矿中的包裹体可分为熔融包裹体、流体熔融包裹体和流体包裹体3类。流体包裹体又可分为H2O包裹体、CO2包裹体和CO2-H2O包裹体,其中,绿柱石中以富含CO2-H2O包裹体为显著特征。加热时,富H2O相CO2-H2O包裹体完全均一至H2O相,富CO2相CO2-H2O包裹体完全均一至CO2相,而二者的完全均一温度和均一压力一致,表明它们是同期捕获的CO2-低盐水不混溶包裹体组合。与绿柱石相比,白钨矿中CO2-H2O包裹体数量明显减少,H2O包裹体数量增多,成矿压力与成矿温度均有所降低。含CO2流体在花岗岩体与大理岩接触带附近发生流体不混溶和相分离,CO2的出溶使成矿流体中pH值升高,f(O2)降低,导致钨的溶解度降低而沉淀,这是形成白钨矿的主要原因。

Xuebaoding W-Sn-Be deposit of Sichuan is hosted in granite body and Triassic marble contact zone. Orebearing quartz veins are controlled by the fracture zone in the marble. The inclusions in beryl and scheelite can be divided into three categories： melt inclusions, fluid-melt inclusions and fluid inclusions. The fluid inclusions can also be divided into three kinds： H2O inclusions, CO2 inclusions and CO2-H2O inclusions. The CO2-H2O in- clusion is the main type among the beryl. When heated, the H2O-rich inclusions were homogenized into the H2O phase, and the CO2-rich CO2-H2O inclusions were homogenized into the CO2 phase. Moreover, they have the same homogenization temperature and pressure. This indicates that they are inclusion assemblage which were caught in the CO2 and low-salt water immiscible fluid at the same time. The CO2-H2O inclusions in the scheelite are more than the beryl and the H2O inclusions are less than the beryl. The scheelite＇ s formation temperature and pressure is lower than the beryl. The immiscibility effect and the phase separation of the rich CO2 fluid oc-curred in the granite body and surrounding rock contact zone. Then a lot mount of CO2 overflowed, the fugacity of O2 decreased, and the pH increased. It led to the reduction of the solubility of tungsten in ore-forming hydrothermal fluid , to the formation of the scheelite.