鄂西神农架地区铜矿床地质地球化学特征

GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF THE COPPER DEPOSITS IN THE SHENNONGJIA REGION, WEST HUBEI PROVINCE

神农架地区神农架群内的铜矿受地层控制明显,多赋存在不纯的海相白云岩地层内。主要含矿地层为乱石沟组和石槽河组。铜矿化以层状和脉状两种形式产出。层状矿体产状稳定,规模较大,脉状矿体规模较小。矿石矿物简单,以黄铜矿为主。流体的H、O同位素组成分别为δDSMOW-85‰～-62.20‰、δ18OSMOW+12.59‰～+16.64‰。含矿白云岩的C、O同位素组成为δ13CPDB-1.42‰～+1.3‰、δ18OSMOW+18.22‰～+25.53‰,具有海相蒸发白云岩的特征。黄铜矿的δ34S值为+1.74‰～+29.47‰,与含矿地层的硫同位素组成几乎一致。黄铜矿物Pb同位素特征反映矿石铅为混合铅,具有多阶段演化的复杂历史。铜矿形成分初始富集(沉积成矿)和构造改造成矿。该区的铜矿属层控热液矿床,为沉积改造型。

The copper deposits in the Shennongjia region of western Hubei province are confined in the strata of the Middle Proterozoic Shennongjia group. The hosted rocks are mainly impure marine dolomite of Luanshigou formation and Shicaohe formation. The copper ore bodies occurred in vein and layer. The occurrence of the layered ore bodies is stable with large scale and low copper content, whereas vein ore bodies are in small scale with high-grade copper content. Hydrogen and oxygen isotope of the fluid are -85‰～-62.20‰ and +12.59‰～+16.64‰, respectively, showing that the ore-forming fluid has the attribute of thermal brine. Carbon and oxygen isotope of ore-bearing dolomite are -1.42‰～+1.3‰ and +18.22‰～(+25.53‰,) respectively, presenting character of marine evaporate dolomite. The δ^(34)S value of chalcopyrite is +1.74‰～+29.47‰, accords nearly with that of the strata which hosted the deposits. The Pb isotope of chalcopyrite is representative of mixing genesis of ore lead with a complex history of multiple stage evolution. The copper deposits in the area belong to the type of strata-bound mesothermal deposit. Two subdivisions, sedimentary reformed deposit and hydrothermal infilling deposit, can be defined.