四川甲基卡伟晶岩型锂多金属矿床成矿流体来源研究

The source of ore-forming fluid in Jiajika pegmatite type lithium polymetallic deposit, Sichuan Province

四川康定甲基卡锂矿是我国规模最大的伟晶岩型锂矿床,目前对其成矿流体来源的研究很少。本文对400多个原生流体包裹体进行了测温实验,结果表明:CO2_NaCl_H2O包裹体和盐水溶液包裹体的均一温度和相对数量呈渐变关系;在均一温度<300℃时,CO2_NaCl_H2O流体的盐度低于盐水溶液的盐度,前者的压力均值高于后者。这说明随着温度和压力的降低,CO2_NaCl_H2O流体逐步向盐水溶液演化,该过程与岩浆分异成因的阿尔泰可可托海及加拿大Tanco伟晶岩的成矿流体的演化过程相似。CO2_NaCl_H2O流体包裹体的拉曼光谱分析表明流体的主要成分是CO2和H2O,未测试出烃类物质,这与成矿流体属于深源流体、与岩浆活动有关相吻合;流体的氢氧同位素组成与岩浆水接近,碳同位素组成为-3.4‰～-7.3‰。此外,伟晶岩脉的形成稍晚于二云母花岗岩体。根据这些特征可推断出成矿流体源于花岗岩浆的结晶分异,晚期有少量建造水混入。

The Jiajika pegmatite type lithium deposit in Kangdi of Sichuan Province is the largest lithium deposit in China. Nevertheless, researches are very insufficient on the source of its ore-forming fluid. More than 400 primary inclusions in the Jiajika deposit were analyzed by the authors. The results show that the homogenization temperatures of CO2-NaCl-H2O inclusions and brine inclusions change gradually into each other. When the homogenization temperatures are lower than 300℃, the salinity of CO2-NaCl-H20 fluid is lower than that of NaCl- H2O fluid. The capturing pressure of CO2-NaCl-H20 fluid is larger than that of NaCl-H20 fluid. These data show that the ore-forming fluid evolved from CO2-NaCl-H20 to NaCl-H20 with the falling temperature and pressure, which is similar to the fluid evolution of the Keketuohai pegmatite deposit in Altay and the Tanco deposit in Canada. The laser Raman test shows that the main compositions of CO2-NaCl-H2O fluid inclusions are CO2 and H20, with no hydrocarbon detected, which is consistent with characteristics of the fluid derived from the mantle and related to magmatism. The composition of O and H isotopes is located in the area of magma wa- ter in diagram, and the δ^13Cv-PDB‰ values are - 3.4‰～- 7.3‰. The formation time of pegmatite dikes is later than that of the granite body. These characteristics indicate that the ore-forming fluid resulted from fractional crystallization of magma, with the participation of some connate water at the late stage.