滇西北兰坪盆地白秧坪多金属矿床成矿物质来源：C、H、O、S和Pb同位素制约

Sources of the Ore-forming Material of the Baiyangping Poly-metallic Deposit in Lanping Basin,Northwestern Yunnan:Constraints from C,H,O,S and Pb Isotope Geochemistry

白秧坪多金属矿床位于滇西兰坪中—新生代沉积盆地中北部,是在著名的三江成矿带内新近发现的重要矿床之一。为确定该矿床成矿流体特征和成矿金属元素来源,对白秧坪多金属矿床开展了系统的C、H、O、S和Pb同位素地球化学研究。白秧坪多金属矿石硫化物δ34S为-5.6‰～11.2‰,具有兰坪盆地中—新生界蒸发岩硫酸盐的热化学还原性质;矿石与盆地中—新生界沉积岩铅同位素组成相似,成矿金属源于盆地沉积地层。成矿流体中水的δDV-SMOW=-122‰～-86‰,δ18OV-SMOW=-4.52‰～-15.34‰,为大气降水补给的盆地热卤水。研究区热液成矿早阶段白云石δ13CV-PDB=-3.4‰～0.5‰,δ18OV-SMOW=4.8‰～20.3‰,晚阶段方解石δ13CV-PDB=-3.1‰～0.5‰,δ18OV-SMOW=4.1‰～18.6‰,说明成矿流体中CO2来自盆地地层中灰岩的溶解。

Baiyangping poly-metallic deposit,located in the central,slightly north of the Lanping Mesozoic-Cenozoic sedimentary basin,is one of important deposits in the famous Sanjiang metallogenic belt.C,H,O,S and Pb isotope geochemistry are discussed in this paper in order to find out sources of the ore-forming material and characteristics of ore-fluids.The δ34S value of poly-metallic ore in Baiyangping deposit is between-5.6‰ and 11.2‰,with the property of thermal-chemic reduction of Mesozoic to Cenozoic evaporite sulfate in Lanping Basin.Moreover,the composition of Pb isotope in ores and sedimentary rocks of Mesozoic to Cenozoic is also very similar,which illustrates that ore-forming metal elements derive from the sedimentary rocks of the basin.The δDV-SMOW and δ18OV-SMOW of the ore-forming fluids are between-122‰ to-86‰ and-4.52‰ to-15.34‰,respectively,showing that they come from basinal hot brine,supplied by precipitation.The δ13CV-PDB and δ18OV-SMOW value of dolomite formed in early hydrothermal ore-forming stage are between-3.4‰ to 0.5‰ and 4.8‰ to 20.3‰,respectively,while the corresponding values in late hydrothermal ore-forming stage are between-3.1‰ to 0.5‰ and 4.1‰ to 18.6‰,respectively,all of which indicate that CO2 of the ore-forming fluids derive from the solution of the limestone.