Mineralogy Characteristics And Genetic Model Of The Permian Bauxite Deposit In Western Guangxi

Bauxite deposits are widespread in the western Guangxi and contain two types: 1)the Mediterranean-type,which occurs on Permian paleokarst surface,and 2)Salentotype,which occurs as Quaternary re-sedimentation derived from the Permian bauxite ores.While pyrite deposits or poor-quality bauxite deposits occur in the north of the study area.Both bauxite and pyrite deposits occur on the paleokarst surface of Maokou Formation and at the base of Upper Permian Heshan Formation.During the Late Permian,the paleogeography of west Guangxi area was characterized by alternating carbonate platform and basin,and both bauxite and pyrite deposits develop on the isolated carbonate platforms.Three typical ore deposit clusters are selected from western Guangxi,including: Dongluo,Pingguo,Fengshan for mineralogical and geochemical analysis to understand the provenance and ore-forming processes,and to evaluate the resource potential of the bauxite and pyrite deposits.Optical microscope,scanning electron microscope(SEM)and X-Ray Diffraction(XRD)were used to analyze the texture and mineralogical and geochemical composition of samples.The results suggest that the main minerals of bauxite and pyrite deposits include diaspore,kaolinite,pyrite and anatase,with a small amount of illite,chamosite,and zircon.Pyrite occurs as two major types: 1)fine-grained and framboidal pyrite occurring in aggregates,and 2)coarse-grained and euhedral pyrite.The sulfur isotope(?34S)compositions of pyrite are ranging from 2.9 to-42.6‰,indicating that microbial activities were involved in the ore-forming processes.U-Pb dating of detrital zircons retrieved from a bauxite profile in Pingguo reveals a uniform pattern in the sequences of bauxite-bearing deposition,which shows a single peak age of 257.5 Ma.This age is similar to the eruption of Emeishan Large Igneous Province and volcanic island arc to the southwestern of Youjiang Basin.All of the detrital zircons have obvious oscillating bands,indicating that the source materials of bauxite derived from intermediate-acid igneous rocks.Nb/Hf-Th/U and Hf/Th-Th/Nb trace elements binary diagrams of detrital zircons show that most data fall into arc-related/orogenic zones.Combing these evidences,we infer that the source materials are of allochthonous origin,transported from the volcanic island arcs to the southwestern of Youjiang Basin,probably by aerial.