川滇黔交界地区铅锌矿床含矿角砾岩特征及其构造意义

Feature of ore-bearing breccias of lead-zinc deposits in Sichuan-Yunnan-Guizhou border area and its tectonic significance

川滇黔交界地区的铅锌矿床中普遍发育含矿角砾岩。文章综述了角砾岩的成因分类,在重点矿床野外地质调查的基础之上,对川滇黔交界地区的铅锌矿床含矿角砾岩进行了详细研究。结果表明:大部分含矿角砾岩显示张性角砾岩的特点,仅个别矿床同时出现挤压角砾岩。综合区域地质构造演化特征和典型铅锌矿床的同位素测年数据,可大致推断出,从中二叠世茅口期以来该铅锌成矿区伸展构造至少有2期:一期发生在铅锌矿化之前或同时,即早二叠世/晚二叠世的升降运动(东吴运动)与晚二叠世峨眉山玄武岩喷发期间,此次伸展作用形成的角砾岩为成矿流体提供了大量的容矿空间,并最终导致成矿流体沿断裂运移并充填沉淀而形成角砾状或网脉状-脉状构造的矿石;另一期发生在铅锌矿化之后,即白垩纪—古近纪,发育一系列正断层,并有可能破坏了铅锌矿体的连续性。

Ore-bearing breccias commonly exist in lead-zinc deposits in the Sichuan-Yuanan-Guizhou border area.On the basis of a comprehensive study of the genetic classification of breccias and the field geological investigation in key deposits,the authors studied the features of ore-bearing breccias in lead-zinc deposits in the Sichuan-Yuanan-Guizhou border area.The results demonstrate that most of the ore-bearing breccias show features of extensional breccias,with compressional breccias seen in a few deposits.Through combining geological evolution of this area with the metallogenic epochs of the existing typical lead-zinc deposits based on isotope dating data,the authors roughly infer that there have existed at least two extensional tectonic events in this lead-zinc ore district since the middle Permian Maokou period： one extension occurred before or simultaneously with the mineralization,i.e.,the early Permian/late Permian uplift and subsidence movement（Dongwu movement） and the Late Permian Emeishan basalt eruption period.The breccias formed by this extension provided extensive space for ore-forming fluids,which subsequently moved along the fault,filled the space and precipitated,forming breccia or stockwork ores.The other extension occurred after the mineralization,i.e.from Cretaceous to Paleogene,during which a series of normal faults was formed,which destroyed the continuity of the lead-zinc body.