Geology and Geochemistry of Se-Bearing Formations in Central China

摘要: It is widely believed that selenium, a typical dispersed element, does not form independent deposits. However, this has been challenged recently by discoveries and investigations of Se-bearing formations in China. In paper we present our findings with systematic discussion on the genesis these formations. The typically are developed tensile tectonic settings, mainly along margins Yangtze Tarim cratons, or within craton. They mostly Cambrian, but few Permian age. Lithologically, they largely consist carbonaceous cherts shales (slates) contain abundant organic matter. general, characterized exceptional associations elements. particular, elements multiple oxidation states, such as V, U, P, Ni, Mo, etc., which for black shale series, like As, Ba, Sb, considered indicative hydrothermal sedimentation. some cases, also Au platinum-group (PGE), quite unusual ordinary depositions. Organic geochemical studies biomarker revealed Corg rocks relatively high formations, ranging from 1.3% to 17.8%. fraction soluble matter extracted samples commonly less than 50 ppm. Gas chromatographic (GC) analyses suggest saturated hydrocarbons low-carbon-number alkane, highest peak C15–C18 low ratios Pr/Ph (0.62–1.03). Using gas chromatographic–mass spectrometric (GC-MS) analyses, many biomarkers have identified, including complete series long-chain tricyclic terpanes hopanes m/z 191 mass chromatogram steroids 217 chromatogram. Evidence suggests source precursors might sort bacteria and/or algae. reducing sedimentary environments hosted algae favored growth preservation organisms. was organisms acted carrier Se, leading Se enrichment deposition. Finally, evidence indicates closely related formation sedimentation cherts.