Carboniferous Bauxite Ore-forming System, Western Henan

The bauxite deposits in western Hernan provience is one of the most important bauxite metallogenic region in China. This paper is focused on Carboniferous Bauxite Ore-forming System, Western Henan, based on the study of regional distribution of bauxite deposits, typical deposits, exploration works, geological survey about mining spots, mineralogy and petrology, geochemistry and comparation with foreign bauxite deposits. Study results show that the bauxite deposits was formed on the paleo-surface of North-China Plate, Karst depressions played an important role in ore-forming, the distribution of bauxite deposits around the highlands was formed by post-ore-forming tectonic movements. The western Hernan bauxite metallogenic region has a great potential depth prospecting prediction.It is a paleo-surface metallogenic system in the Carboniferous bauxite deposits in western Henan. Every Sphere of the Earth such as Lithosphere, atmosphere, hydrosphere and biosphere was involved in the system and played an important role. Main geological processes of ore-forming controlling factors included sedimentary, weathering, tectonic movements, physiognomy, climate, hydrogeologic condition, paleontology, oxidation- reduction, transgression, karstification etc.The bauxite metallogenic system was a process that the oxide of Al remained as residues forming bauxite while the other elements were eluviated and extracted out. The bauxite was derived from laterite weathering crust on the Cambrian- Ordovician carbonate in Karst depressions on the paleo-surface of North-China Plate. Karst depressions was the primary ore-forming place.The ore-forming fluid was unsaturated meteoric in mineral elements. The laterite was swashed to Karst depressions and nudergo infiltration, dissolution and eluviation by meteoric water, formed bauxite.Plants were widely distributed on the continent in Carboniferous as the biologic evolution. The previous CO2-riching atmosphere became oxygen-riching. Chemical weathering was very strong on the paleo-surface, under the combined effect of plants and oxidation. The North China plate became a carbonate peneplain after the erosion from Later-Ordovician to Early Carboniferous and located in humid tropical rain forest, karstification was well-developed. The carbonate peneplain enriched Al minerals with the mineral elements unsaturated meteoric water eluviation. Then meteoric water, laterite and organic matter accumulated in Karst depressions. The laterite was infiltrated and eluviated by meteoric water; the other elements including Si and Fe were dissolved and taken out by the Karst-drainage system, bauxite formed.The bauxite ore-forming process was different on the paleo-surface of North China plate as spatial-temporal differences. There were three profile ore zones: ferro-clay zone at the bottom, bauxite zone in the center and carbonaceous clay on the top. In the horizontal ore distribution, bauxite was instead by claystone and clay minerals.The features of bauxite ore deposits in western Henan are listed below: Ore-grades are positive related with the thicknesses of orebodies; High grade orebodies present in the bottom of Karst sink-holes, the thickness become thinner and the grade become lower outside the sink-holes; Bauxite orebodies were limited in Karst depressions; Ore chemical composition was high in Al2O3 and SiO2, low in Fe2O3; The colors of bauxite ore are mainly in different gray to black. These features indicate that the bauxite was formed in rich organic matter, reducing ore-forming system which occurred in Karst depressions.The Carboniferous bauxite ore deposits widely horizontal distributed on the paleo-surface. It was covered by Carboniferous Taiyuan Group, Permian, Lower and Middle Triassic. In Late Triassic, Yangzi plate collided with North China plate; horizontal tectonic movement was very strong in Western Henan, the bauxite ore deposits uplifted in anticline. In Cenozoic, tectonic movements was vertical, the bauxite deposits was eroded in highlands and burried in depressions. The outcorps of bauxite deposits distribution were around highlands.