贵州纳雍枝铅锌矿床成因研究:来自镉同位素和微量元素的约束

Genesis of the Nayongzhi lead-zinc deposit in Guizhou Province:constraints from Cd isotopes and trace elements

纳雍枝铅锌矿床是贵州省内发现的第一个大型铅锌矿床,前人对该矿床进行过大量地质和地球化学研究,对该矿床成因有了一定认识,但其成矿金属来源,特别是其中稀散金属(如Cd)的来源却少有涉及。本文分析了该矿床硫化物和精矿样品的微量元素及镉同位素组成,结合该区域不同地质端元的地球化学数据,来探讨以Cd为代表的稀散金属来源。结果表明,样品的Zn/Cd值变化较大(377~953),均高于川滇黔地区沉积岩的Zn/Cd比值(13~367),而更接近火成岩的Zn/Cd值(515~1319)。精矿和闪锌矿样品的镉同位素组成(δ^(114/110)Cd_(NIST-3108))变化范围极小(-0.09‰~-0.05‰),与已获得的岩浆岩数据一致(-0.22‰~0.15‰),但明显区别于该地区的碳酸盐岩地层(-0.25‰~0.82‰)。结合精矿的Zn/Cd-δ^(114/110)Cd_(NIST-3108)关系图解和前人研究成果,本文认为该矿床金属成矿物质(如镉、铅等)主要来自基底。

The Nayongzhi lead-zinc deposit is the first large-scale lead-zinc deposit discovered in Guizhou Province. With comprehensive geological and geochemical studies on the deposit, its ore genesis has been primarily constrained. However, the sources of its metal materials, especially dispersed metals(such as Cd), are still poorly understood. In this paper, combined with geochemical data of different geological endmembers in the region, Cd isotope and trace elements in sulfide minerals and concentrates of the Nayongzhi lead-zinc deposit have been analyzed to explore the source of Cd as a representative of dispersed elements of the deposit. The results show that Zn/Cd ratios of the studied samples, varying greatly from 377 to 953, are higher than those of sedimentary rocks(13~367) from the Sichuan-Yunnan-Guizhou area, but are similar to those of igneous rocks(515~1319). The Cd isotopic compositions(δ^(114/110)Cd_(NIST-3108)) of concentrates and sphalerite samples of the Nayongzhi deposit vary in a very small range(-0.09‰~-0.05‰), which is similar to that of igneous rocks(-0.22‰~0.15‰), but quite different from that of carbonate rocks(-0.25‰~0.82‰) in the area. Combined with the Zn/Cd-δ^(114/110)Cd_(NIST-3108)diagram of the concentrates and data of previous studies, we have concluded that metals(such as Cd, Pb, etc.) of the deposit were dominantly derived from the basements.