闽北大药坑金矿床黄铁矿成分标型及硫、铅同位素组成研究

Study of S,Pb isotopes and composition typomorphic characteristics of pyrites in Dayaokeng gold deposit,northern Fujian Province

闽北政和-建瓯矿集区内大药坑金矿床是一个赋存于韧性剪切带中的小型矿床。在野外地质调查基础上,通过分析载金矿物黄铁矿电子探针成分和硫化物硫、铅同位素组成,探讨了大药坑金矿床的成矿作用问题。研究表明,大药坑金矿床黄铁矿的Co/Ni比值大多在1~5之间,为岩浆热液成因黄铁矿,成矿热液的温度和盐度均较高,也表现出岩浆热液的性质;金属硫化物的δ^(34) SCDT均为靠近0的较低正值(0.1‰~3.4‰),说明成矿物质为岩浆来源,硫化物的铅同位素比值以及高μ(^(238)U/^(204)Pb)和ω(^(232)Th/^(204)Pb)等特征,说明成矿物质具有壳幔混源特征。结合区域研究资料,认为大药坑金矿床形成于东南沿海区域强烈壳幔作用时期,与燕山期火山-侵入杂岩有关,矿床成因类型为岩浆期后热液型。

The Dayaokeng deposit located in the Zhenghe-Jianou ore concentration area is a small-sized gold deposit hosted by ductile shear zone.To investigate metallogenesis of the Daoyaokeng gold deposit,the authors carried out some experiments including EPMA and S-Pb isotopes.Most Co/Ni ratios of pyrites are 1 - 5 and,furthermore,the temperature and salinity of fluids are both high,suggesting magmatic hydrothermal origin.δ34SCDTvalues of pyrite,sphalerite,galenite are 2.7‰ - 3.4‰,2.2‰ and 0.1‰ - 0.5‰,respectively,which are positive values close to0‰（ δ-（34）SCDTvalue of troilite）,so it is reasonable that metal materials originated from magma.Pb isotope ratios of sulfide are 18.237 - 18.557（-（206）Pb/-（204）Pb）,15.628 - 15.799（-（207）Pb/-（204）Pb） and 38.446 - 38.988（-（208）Pb/-（204）Pb）respectively; in addition,μ（-（238）U/-（204）Pb） and ω（-（232）Th/-（204）Pb） are high,suggesting that the ore-forming materials might have resulted from mixing of ore-forming materials derived from the crust and the mantle.Combined with previous regional researches,the authors hold that the Yanshanian volcanic-intrusive complexes had a close relationship with the Dayaokeng gold deposit,the deposit was developed at the stage of strong crust-mantle interaction of southeast coast block,and the metallogenic type of the gold deposit is postmagmatic hydrothermal type.