Genesis Of Bauxite Deposit In Ningwu Region,Northern Shanxi Province

Shanxi Province is one of the most important bauxite resource bases in China.At present,the proven bauxite resource reserves rank the first in China,and the bauxite resources are widely distributed with an area of 67,000 km~2.Shanxi bauxite is a typical karst type bauxite deposit.The bauxite ore body occurs in Benxi Formation of Carboniferous system and covers the karst surface of Ordovician carbonate rocks.It belongs to the sedimentary stratum on the paleo-weathering erosion surface,and has parallel unconformity contact with the underlying Cambrian and Ordovician limestone.The bauxite deposit in Ningwu County is located in the north of Shanxi Province and in the Ningwu-Jingle Basin.The ore bodies are layered/bedlike,chicken-nested and funnel-shaped.The bauxite series consists of floor limestone,iron clay rock,bauxite clay rock,massive/clastic/oolitic bauxite and bauxite clay rock from bottom to top.Ore structures mainly include massive and clastic sedimentary structures.The main structures are cryptocrystalline structure,clastic structure and oolitic structure.Previous studies on bauxite deposits in this area mainly focused on mineral composition,metallogenic age and metallogenic environment.However,the mineralogical origin of bauxite deposits in Shanxi Province has been less studied,and the metallogenic environment and material sources have been controversial.In this study,through detailed microscopic observation,X-ray diffraction(XRD),and electron probe(EMPA)analysis showed that the minerals in the ore mainly include diaspore,kaolinite,chlorite,illite,and sharp.Titanium ore,containing a small amount of zircon,calcite,goethite,hematite and so on.The main elements of the whole rock are Al,Si,Fe and Ti,followed by Mg,K and Ca.The mineral assemblage and occurrence state reveal that diaspore is mainly of simple crystallization origin;kaolinite is mainly formed in the weathering process of terrigenous stage,and a small amount may be formed in the later stage of diaspore silicification;illite is mainly formed by mica weathering,and a small amount is produced by diaspore transformation in the later stage of mineralization;hematite and goethite are mainly formed in the latter stage of iron-bearing fluid crystallization,partly pyrite;Zircon and rutile are mainly relic minerals,sources of terrigenous debris.The analysis of correlation diagrams of Nb/Ta and Zr/Hf,REE composition,Cr/Zr,Th/U ratio,Nb-Cr discriminant diagrams of clastic rutile and Zr content thermometer shows that the ore-forming material is a mixed source of floor carbonate rocks and surrounding ancient roads,mainly floor carbonate rocks,heavy minerals such as detrital rutile and zircon mainly come from Luliang orogenic belt and Wutai-Fuping orogenic belt.The analysis of Ba/Sr and B/Ga ratios shows that bauxite formation has undergone a cycle of transgressive to regressive sedimentary environments.The La/Y ratios show that bauxite is mainly formed in a weak alkaline environment.It is concluded that bauxite has undergone lateritic clastic sedimentation and ion crystallization based on the genetic mechanism of minerals and the geochemical characteristics of the whole rock.