湘南郴县地区下二叠统当冲组硅质岩地球化学特征与成矿

GEOCHEMISTRY AND METALLIZATLON OF SILICALITE IN THE LOWER PERMIAN DANGCHONG FORMATION, CHENXIAN COUNTY, SOUTHERN HUNAN

系统地研究了湘南郴县许家洞和华塘铺下二叠统当冲组的地层层序、岩石组合和硅质岩地球化学特征,指出郴县一带当冲组的硅质岩形成于被动大陆边缘,其沉积相与沉积盆地沉陷→裂陷→充填的发展阶段对应,经历了从深水陆棚相→台间盆地相→浅水陆棚相的演化过程。探讨了当冲组硅质岩的形成和中、新生代构造对硅质岩改造及其与成矿的关系,首次提出该区当冲组底部角砾硅岩是燕山期构造活动导致栖霞灰岩与当冲组硅泥质岩之间的构造薄弱面发生空洞爆裂形成的隐爆角砾岩。由于当冲组中、下部地层中的成矿元素有向底部角砾硅岩方向聚集的特点,因此该角砾硅岩不仅是铀的重要含矿岩石,而且富含金、银、铜等金属元素。

Systematic study on outcrop sequence stratigraphy, depositional assemblages and REE geochemistry of silicalite in the lower Permian Dangchong Formation located respectively in Xujia-dong and Huatangpu area, Chenxian county, southern Hunan province, indicates that the silicalite in the Dongchong formation was deposited in a passive continent margin, and its sedimentary fa-cies corresponds to the basinal evolution process from down-warping to subsidence to infilling, belonging to deep-watet shelf, inter-platform basin and shallow-water shelf deposition, respectively. The forming process and remoulding by post-Permian tectonic activities show that the brecciated chert and crystalline quartzite in the lower part of Dangchong Formation of the study area are cryptoexplosion breccia resulted from bursting along the weak structural level between the limestone of the Qixia Formation and siliceous argillite of the Dangchong Formation. The composition gradients of Au, Ag, Cu and U in the Dangchong Formation indicate an element migration trend from the middle -upper part to the base of the Formation. The brecciated chert, therefore, is not only the host rock of uranium, but also the enrichment horizon of gold, silver and copper.