滇东南安那金矿床成矿流体地球化学研究

Study on the ore-forming fluid geochemistry of the Anna gold deposit in southeastern Yunnan Province,China

云南安那金矿床位于右江盆地南缘,产于二叠纪辉绿岩侵入体之中,广泛发育乳白色石英网脉,蚀变辉绿岩体即为金矿体。与右江盆地以沉积岩为容矿岩石的卡林型金矿床类似,具有硅化、粘土化、碳酸盐化和硫化物化等热液蚀变特征。本文对安那金矿床石英中的流体包裹体岩相学、显微测温学、激光拉曼光谱以及氢氧同位素组成进行了分析,发现成矿期石英中的流体包裹体主要为富含CO_2气-液两相或三相流体包裹体,其均一温度范围为208~312℃(平均254℃),盐度很低,变化范围为0~2%Na Cleqv,成矿溶液的密度为0.88~0.98g/cm^3,表明形成安那金矿床的成矿流体属于中温、低盐度、中-低密度的流体。激光拉曼光谱分析显示,石英中包裹体的气相成分富含CO_2、N_2以及微量CH_4等挥发分。成矿流体的氢氧同位素组成显示变质流体成因,结合矿石显微岩相学结构,认为流体溶蚀交代辉绿岩中的含Ti-Fe辉石或者钛铁矿,溶解Fe的硫化作用过程是含Au黄铁矿和毒砂沉淀富集的重要机制。成矿作用可能与右江盆地南缘印支期造山事件有关。

The Anna gold deposit is located at southeastern Yunnan, China, and is hosted in altered Permian diabase intrusion, with intensive milky quartz veins and vienlets. Alteration caused silicification, argillization, carbonatization and sulfidation, similar to those in the sediment-hosted Carlin-type gold deposits in the Dian-Qian-Gui ＂Golden Triangle＂ of Southwest China. Petrography, microthermometry, laser Raman spectroscopy analyses of fluid inclusions in quartz, and hydrogen and oxygen isotopic compositions of quartz are used to characterize the ore-forming fluids associated with gold mineralization in the southeastern Yunnan. The results show that the fluid inclusions in quartz are mainly two- or three-phase, aqueous-carbonic inclusions and have higher homogenization /emperatures （208 - 312℃ ） and low salinities of 0 - 2% NaCleqv, with high density of CO2 and N2 vapor. Hydrogen and oxygen isotopic compositions of ore fluids （SD = -79‰ - -47‰, 8180 = 8.9‰- 12. 7%v） indicate a metamorphic origin, possibly related to Indosinian orogeny along the southern margin of Youjiang basin during Late Permian to Early Triassic time.