Sedimentary Micro-facies And Lithofacies Paleogeography Of Dafoyan Bauxite, Chongqing

By the influence of Guangxi movement, the yangtze plate rise to land. Experienced more than100Ma’s weathering and erosion from middle permian to middle silurian. On this condition, the South Chongqing Bauxite was formed. In order to supply some basic research date for the exploration of bauxite, this paper take Dafoyan Bauxite as a representative mining area, to research its sedimentary micro-facies and lithofacies paleogeography.The regional sedimentary study found that the bauxite bearing rock series has three different profile structures. The northern part of this region shows freshening lagoon sediment, and Dafoyan Bauxite is located in the north margin of the freshening lagoon. The middle and the Northern-Eastern part shows barrier sand bar sediment. And the southern part is normal shallow sea sediment.The lithology analysis study of the bauxite bearing rock series indicate that sedimentary fabric of river, shore lake and shallow lake are formed in the rock series. The profile shows continuous change of water depth. The sporo-pollen identification reflects warm, wet and fresh water sedimentary environment. The trace elements analysis reflect it’s mainly fresh water sediment, and sometimes intruded by sea water. Synthetical judged, the sedimentary environment of Dafoyan Bauxite is freshening lagoon without doubt. On this basis, according to the lithologic features, we classified the auxite bearing rock series into seven micro-faces. Which are Muddy aluminous micro-face (MF-1), Kaolinite clay micro-face (MF-2), Chlorite clay micro-face (MF-3), Siderite micro-face (MF-4), Pisolite shape aluminous micro-face (MF-5), Oolite shape aluminous micro-face (MF-6), Clastic aluminous micro-face (MF-7). All these micro-face can be combined into Shore lagoon sub-fase, Deep lagoon and Shallow lagoon sub-fase.By collecting and studying profile datas in drill bores and trenchs, we compiled lithofacies paleogeography map of Dafoyan Bauxite. The lithofacies paleogeography map shows the terrain of Dafoyan in Liangshan period is north higher than south. The sedimentary facies belts are Spreading regularly. The sedimentary facies belts Spreading type is controlled by water depth and terrain of the area. The comparison of horizontal and vertical both indicate that the sedimentary micro-faces which belong to Shore lagoon and Shallow lagoon sub-face contain higher Al2O3than the sedimentary micro-faces which belong to Deep lagoon sub-face.Electron microprobe and energy spectrum analysis found the pisolites and false oolites in the bauxite bearing rock series have ferruginous cladding. This is a evidence of weathering process in the formation of Bauxite. But sedimentary evidence shows Dafoyan bauxite is sedimentary type bauxite. The weathering process just formed the original red-soil type bauxite. The original red-soil type bauxite was carried in the freshening lagoon by water steam.