| The Upper Carboniferous Benxi Formation in the North China Block developed a thick bauxite deposit,and its provenance and metallogenic processes are hot issues,but the study of provenance and aluminum enrichment needs further research.In this paper,the Benxi Formation in the southeastern part of the North China Block is the main research object.Through field outcrops and drilling core observations,systematic mineralogy,petrology,sedimentology,stratigraphy and geochemical analysis are carried out by XRD,detrital zircon LA-ICP-MS U-Pb,Hf isotope determination and other testing methods.Based on the detailed anatomy of typical areas,the material sources of the Benxi Formation in the southeastern part of the North China Block and the enrichment of the Benxi Formation were studied.The main achievements as follow were obtained:(1)The lithology of the Benxi Formation in the study area is mainly bauxitic mudstone,and some of them contain pisolitic-oolitic bauxite.The Benxi Formation has different sedimentary successions,which can be divided into: bauxitic mudstone sedimentary succession,bauxitic mudstone-pisolitic-oolitic bauxite-bauxitic mudstone sedimentary succession,bauxitic mudstone-pisolitic-oolitic bauxite with interlayer-bauxitic mudstone sedimentary succession,thick silty mudstone-pisolitic-oolitic bauxite-bauxitic mudstone sedimentary succession.(2)The mineral mainly composed of clay minerals(mainly illite,kaolinite),diaspore,anatase,siderite,calcite,pyrite,etc.mineral.The lower mudstone is mainly illite,the upper mudstone is mainly kaolinite,and the middle diaspore mineral content is high.(3)The chemical elements in the vertical direction of the Benxi Formation in the study area have obvious regularity,which is manifested by the loss of easily migrating elements(Na,Mg,K,Ca,etc.),and the enrichment of hardly migrating elements(Al,Fe,etc.).This pattern is especially obvious in the bauxite deposits in the middle of the Benxi Formation.It indicates that the karstification is strong,and the degree of leaching and hydrolysis is high,which is more conducive to the enrichment of mineralizing elements.(4)Detrital zircon of the Benxi Formation in the study area,which can be divided into: Paleozoic zircon and Precambrian zircon.The peak ages are ?310Ma,?444Ma,?990Ma,?1830Ma and ?2510Ma.The age ?444 Ma and ?990Ma detrital zircons are mainly derived from the Caledonian mid-acid granitic intrusive rocks in the southern North Qinling Orogenic Belt and the main metamorphic strata in the area that were invaded—Kuanping Group,Erlangping Group,and Qinling Group.The age ?1830 Ma and ?2510 Ma detrital zircons are provided by the basement of the North China Block.The age ?310 Ma magma zircon with the high negative value of ?Hf(t)is derived from the Inner Mongolia Uplift in the northern part of the North China Plate.In different areas,the proportion of detrital zircon from different sources is different.In the northeast,the provenance of Inner Mongolia Uplift is the main one,and in the southwest,the provenance of North Qinling Orogenic Belt is the main one.(5)The Benxi Formation in the study area underwent iron-rich aluminization and gleization,and iron-rich aluminization transformed low-priced iron-manganese into high-valent oxidation and gleization reduced high-valent iron and manganese to low-value states,forming the structures such as oolitic and laminar structures.The enrichment of aluminum stage is divided into two or three stages according to whether the surface is excavated or not: Original sedimentary deposit of the Benxi Formation before the deposition of the Taiyuan Formation,after Taiyuan Formation to the surface of Benxi Formation excavation and after denudation of the Benxi Formation.(6)The enrichment of aluminum is the result of the coupling of many factors such as tectonic,sedimentation,and karstification.The coupling result affects the intensity of weathering and the speed of mineral element migration(leaching),leading to differences in the aluminum enrichment. |
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