Lithofacies palaeogeography of the early Middle Permian Liangshan Formation in northern Guizhou-southern Chongqing area and its bauxite ore-forming effect

The study area is located in the Upper Yangtze region of the Yangtze block. Abundant sedimentary mineral resources are preserved in the early Middle Permian Liangshan Formation and among them bauxite deposits are of favorable prospects for exploration and exploitation. In order to reveal the relationship between the deposition and distribution of the bauxite deposits and the lithofacies paleogeography of early Middle Permian period, the authors studied the sedimentary, distribution and ore-bearing features of the Liangshan Formation, compiled a lithofacies paleogeographic map and established a metallogenic model for bauxite deposition in behind-barrier lagoon. The paleogeographic framework shows that the study area dipped southwards, the land was located in the north and the sea lay in the south, with the development of a barrier lagoon system. The lagoon depositional system was located in the north, the barrier depositional system was situated along Ludian-Weining-Guiyang-Duyun zone, and the common sea depositional system was developed in the south. Altogether 7 sedimentary subfacies have been recognized, which include uplift, coastal lake, shallow lake, semi-deep and deep lake, barrier, inner shelf sea and outer shelf sea. Almost all bauxite deposits are located in the semi-deep and deep lake region of the lagoon in the north, obviously controlled by lithofacies paleogeography.