Genesis And Metallogenic Regularity Of Late Permian Sedimentary Bauxite Deposit, Southeast Yunnan

The bauxite deposits are mainly distributed in the southeast of Yunnan province,regarded as one of the most predominant ore types in this area. Through analyses ofstratigraphy, petrography and geochemistry, a systematic research has been conductedon the sedimentary paleogeographic environment in the major mineralizationperiod—the Late Permian early Wujiaping period, and its associates to the bauxitemineralization, the characteristics of ore-bearing rock series, the geochemical featuresand the ore-controlling factors of the sedimentary bauxite deposits in southeastYunnan. The ore-forming materials, metallogenic regularity, prospecting criteria,genesis, metallogenic prospect areas are discussed and summarized.The sedimentary bauxite deposit in the study area is dominated by diasporicbauxite and its ore-bearing rock series are developed in the lower member of UpperPermian Wujiaping Stage. Diaspore is the main mineral, followed by kaolinite,anatase, goethite, etc., presenting a diversity of crystalline morphologies and modes ofoccurrence. Five main dissemination characteristics of diaspore are observed: a)unevenly disseminated in gangue minerals with euhedral or subhedral granulartextures ; b) in pisolitic, potato-shaped or oolitic forms; c) as aphanitic crystalline ormicrocrystalline aggregates or with irregular granular or microgranular texture; d) asveins, skeletal crystals; e) as aggregates of diaspore, alumina gel or gangue mineralsassuming zonal patterns or concentric circles.The bauxite deposits in the southeast of Yunnan province may form in thelow-energy gulf environment from the intertidal zone to shallow sea, and the subtidalzone is favourable to mineralization. The iron, iron-mud and iron-aluminum rocks areformed during the early stage of transgression, and the bauxite rock followed byduring the maximum transgression period. The formation of bauxite deposits, in turn,experienced the paleo-weathering crust development stage, the sedimentary-diagene-tic stage and the supergene secondary-leaching stage.Through analyzing the ratios of stable elements (Sc, V, Nb, Ta), and the ratiosbetween stable elements and Al₂O₃, combining with the regional and mining areageological background, Al₂O₃/TiO₂, REE characteristic parameters and distributionpatterns of the bauxite and the content estimation of the metallogenic material-Alfrom different sources, the results show that there is a multi-source characteristic ofthe bauxite deposits in this area. The basalt is the main source of the bauxite, and the Pre-Carboniferous sediments of the ancient land (Pingma-Yuebei ancient land andKangdian ancient land), and the carbonate rocks occurred in the Middle-UpperPermian are all likely to perform as the material sources for ore-forming. The amountof material source provided by carbonate rocks would increase gradually fromsouthwest to northeast nearer to the shallow sea.The major ore-controlling factors of sedimentary bauxite deposit in the southeastof Yunnan province occurred in the Late Permian Wujiaping period are horizon(strata-bound), sedimentary facies (facies control), material sources (source control)and paleotectonic environment. Five metallogenic prospect areas have been predictedbased on the systematic research.