Mineral Compositions And Metallogenic Mechanism Of Important Bauxite Concentration Areas In China

The bauxites in China are distributed in the North China Craton(NCC)and South China Block(SCB)and occur in six episodes,i.e.,Early Carboniferous,Late Carboniferous,Early Permian,Middle Permian,and Late Permian,as well as Quaternary.This paper studied the metallogenic mechanism of the Carboniferous to Permian bauxite in China by microscopy,SEM-EDS,XRD,detrital zircon U-Pb dating and authigenic illite K-Ar dating.The major conclusions are as the following:The detrital zircon from the Early Carboniferous Qingzhen bauxite has a maximum U-Pb age peak of ca.800 Ma and detrital zircons from the Early Permian Wuzhengdao and Kaili bauxite show a dominate peak of 1100 Ma.The above results indicate that the Lower Carboniferous and Lower Permian bauxites are sourced from the sedimentary rocks in the western and central parts of the South China Block,respectively.This indicates that the shift from a marginal to central uplift within the paleo-island from Early Carboniferous to Early Permian has induced the transition in the provenance of the source material.The metallogenic materials of the Late Carboniferous and Middle Permian bauxite deposit came from south and north margin of North China Craton.The Late Permian deposits were derived from the felsic volcanic rocks of a Permian magmatic arc at the northern margin of the Paleo-Tethys and Emeishan Large Igneous Province.Most of the Permo-Carboniferous bauxites are karsctic type and on the carbonate unconformable surface.The bauxite-bearing rock series are devided into three sections in which the lower part consists of aluminous clay intercalated with iron concretion,the middle part consists of aluminum-containing rock series intercalated with multi-layer lenticular or earthy bauxite,and the upper part consists of carbonaceous shales and sandstones intercalatedwith coal seams.The mineral assemblages in the Early Carboniferous Qingzhen bauxite consist of diaspore,illite,anatase.This study presents the first attempt to study the genesis of bauxite with illite as its major clay minerals by age dating of authigenic illite in Qingzhen bauxite formed after post diagenetic stage.K�Ar age data indicate that the high temperature hydrothermal fluid(200-300?)and the associated illite authigenesis occurred during170-150 Ma.In Early Permian Wuzhengdao and Kaili bauxite,the minerals are diaspore,anatase,illite,clinochlore,and kaolinite.The Middle Permian Zibo bauxites are dominated by kaolinite and boehmite and the Late Permian Pingguo and Dongluo bauxite are boehmite,diaspore,siderite,kaolinite,and anatase.Different mineral assemblages indicate bauxite formed in different environment and went through different bauxitization.The late carboniferous bauxite deposits in NCC are generally located in the littoral and shallow lacustrine facies areas not far from the ancient upland.While Permo-Carboniferous bauxite in SCB deposited in a tidal flat-restricted platform.The karstic bauxite ore were formed via both ion crystallization and clastic deposition.The Early Carboniferous bauxite also influenced by the hydrothermal fluid occurred in the Middle Jurassic.The heat from the hydrothermal fluid may promote the conversion of kaolinite,gibbsite,and boehmite to diaspore.