Study On The Genesis Of Carboniferous Karst-type Bauxite In Northern Shanxi

Shanxi Province is the largest bauxite resource province in China.The proved reserves of bauxite rank first in the country.Currently,the proved reserves are about 102.652 million tons.The bauxite deposits are widely distributed and the deposit area is about 67,000 square kilometers.Xingxian bauxite is located in the northwestern part of Shanxi Province,in the north-east direction of the Nandiwu-Duancun-Leigou ore belt,which belongs to the karst-type ore-controlling area and is a typical karst type bauxite mine.The sampling location is located in the southeast of Xing County,east of the southern section of the Xing County-Shilou south-north fold belt.The research object Xingxian bauxite occurs in the lower part of the Carboniferous Benxi Formation.It is a set of ore-bearing rock series containing "G-layer bauxite Shanxi-type iron ore",also known as the bauxite section.From the sampled borehole section,the ore-bearing rock series is divided into five main rock layers from bottom to top,which are floor limestone,iron mudstone,bauxite,clay mine and roof sand mudstone.It is in unconformity contact with the underlying Ordovician Fengfeng Formation limestone.The bauxite ore body morphology is controlled by the underlying karst ancient landform.The main output morphology is layered,layer-like and lens-like.The ore structure is mainly a massive structure,and the ore structure is mainly a detrital structure,oolitic structure,cryptocrystalline structure,and recrystallized microcrystalline structure.The minerals in the ore-bearing rock section mainly include diaspore,gibbsite,illite,pyrite,goethite,hematite,oolitic chlorite,oblique chlorite,magnesite and kaolin Stone,in addition to a small amount of rutile,anatase,calcite and quartz.Based on the analysis of geological characteristics,mineralogical characteristics and stable S isotope characteristics of bauxite deposits,combined with the research conclusions of other scholars,it is inferred that the bauxite deposits were deposited in an alkaline-weak reduction environment and are in the "shallow zone" type The transition zone from the earth mine to the "seepage zone" bauxite.The ore system has undergone oxidation ? reduction? oxidation,semi-closed ? closed sedimentary environment from bottom to top.The corresponding sedimentary facies are lagoon facies ? inland lake marsh facies.The waterbody is shallow and the salinity is brackish,which is generally consistent with the geological development history of the area.The average value of sulfur ?34S in the bauxite is approximately the same as the average value of ?34S in the Early Cambrian gypsum layer in Shanxi,which proves that the sulfur in the deposit comes from the lower Early Cambrian gypsum layer.It indicates that the deep matter may provide a part of the material source for the formation of bauxite.