四川丹巴伟晶岩型白云母矿床是我国第二大白云母产地,但其研究程度很低,形成机理的研究停留在定性推断的水平上,本文拟从流体的角度来研究其形成机理。丹巴北部的布衣沟位于白云母矿区的中心地带,自西向东穿过混合岩化变质带→部分混合岩化变质带→夕石化变质带,分布有蒋家→下蒋家→水大→二道桥等伟晶岩矿脉,其流体包裹体的均一温度峰值依次降低,CO2-H2O包裹体的数量逐渐减少,盐度有增高的趋势。碳、氢、氧同位素示踪出成岩成矿流体主要由携带深源碳的岩浆热液、建造水及脱碳反应产生的CO2组成。从蒋家→下蒋家→水大→二道桥伟晶岩脉,流体中的CO2/CH4和CO2/N2呈降低。这些特征显示出成岩成矿流体的演化过程:携带深源碳的岩浆热液自春牛场穹隆体的深部向外迁移,在部分混合岩化带与脱碳反应产生的CO2混合,在夕石带与建造水混合而稀释。因此丹巴白云母矿床属于“岩浆+变质”混合成因。
Danba muscovite pegmatite-type deposit in western Sichuan province is the second largest muscovite producing area. But the mineralizing mechanism is still stays in debate. Located at the the center part of the muscovite deposit in the northern Danba area, Buyigou gradually transfers from west to east migmatized metamorphic zone, partially-migmatized metamorphic zone to sillimazitized zone, along which Jiangiia, Xiajiangjia, Shuida and Erdaoqiao pegmatite mineralized veins are distributed. The peaking values of homogeneous temperature of fluid inclusions from these pegmatite veins along the WE-trending belt decrease; CO2-H2O inclusions decrease, but their salinity increases gradually. C, O and H isotopic analyses suggest that metallogenic fluid mainly consists of magmatic hydrothemal fluid with deep-sourced carbon, formation water, and CO2 from decarburization. The ratios of CO2/CH4 and CO2/N2 from the above-mentioned veins from inward to outward are also decreasing. All these features indicate an evolution process of metallogenic fluid: magmatic hydrothermal fluid carrying carbon from deep mantle immigrated outward from the deep Chunmiuchang dome, mixed with CO2 from decarburization at the partially-migmatized metamorphic zone, further was diluted by formation water at the sillimazitized zone: Therefore, the Danba muscovite deposit belongs to mixed genesis of magma and metamorphism.