Origin of seleniferous cherts in Yutangba Se deposit,southwest Enshi, Hubei Province

At the top of the Lower Permian Maokou Formation limestones are developed carbonaceous cherts (Plm3), which constitute the dominant seleniferous layer of the Yutangba Se deposit. The cherts contain as much Se as 1646×10-6 on average. In addition, they are rich in organic carbon, AI2O3, Si2O, but poor in S. In addition to Se, as well as Mo, Cd, V, and Co, etc are also highly enriched in the cherts. The chert samples are characterized by low ∑REE, slight LREE enrichment, relatively heavy Si isotope enrichment, and insignificant variations in δ30Si value within the range of 1.1‰-1.2‰. Generally, it can be judged from the major element, trace element and REE data and the Si isotopic characteristics that the Yutangba seleniferous cherts were formed in the shallow sea to semi-deep sea anoxic environments and their formation is controlled chiefly by bio-chemical processes.