Genesis Of The Late Carboniferous Karstic Bauxite Deposits In Western Henan,Southern North China Craton

More than 2 billion tons of bauxite were formed during the exposure of North China Craton between middle Ordovician and late Carboniferous.Previous researchers mostly considered that it was formed through a prolong process,namely early lateritization and subsequent diagenesis.However,recent chronological study by using different methods proved that the bauxite mainly formed during late Carboniferous.Therefore,re-recognizing the genetic mechanism of karstic bauxite deposits in NCC is of great significance.This study conducted thorough geological,mineralogical,geochemical,and isotopic investigations on the bauxite deposits in Mianchi area,southern NCC for probing the genetic process of karstic bauxite deposits in NCC.The bauxite ore-bearing rock series is hosted within the Benxi Formation and commonly composed of the bottom Fe-bearing clay,middle bauxite ore,and upper bauxitic clay.The orebody is controlled by the karstic topography and varies in thickness from 0 to10 m.The bottom Fe-bearing clay is dominated by illite,hematite,and geothite in the uplift and illite,siderite,and pyrite in the depression,while diaspore,illite,pyrite,and anatase are the major minerals in the bauxite ore.The upper bauxitic clay mainly consists of illite,diaspore,anatase,and minor kaolinte.Zircon and rutile are widely spread in the ore-bearing rock series.Provenance analysis suggest that the lower Fe-bearing clay formed from the underlying carbonates,while the upper bauxite ore and bauxitic clay formed from multiple sources,mainly including the igneous rocks and metamorphic rocks from the North Qinling Orogenic Belt.Abundant weathered materials?mainly illite?were formed overlying on the NQOB and NCC from middle Ordovician to late Carboniferous,and subsequently were transported into karstic terrian with the accretion of the NQOB to the NCC in late Carboniferous.Warm and humid climate near the equator,development of microorganisms,and acid rain promoted the weathering and dissolution of the previous weathered materials.Elements,like Al³⁺,Fe²⁺,and Ti⁴⁺were transported downward and encountered a suitable karstic environment?-0.3<Eh<0 and 7<pH<9?precipitating abundant diaspore,pyrite,and anatase and further forming large scale of bauxite ore.