Metallogenic Process And Structural Driving Mechanism Of The Middle Permian Aluminum Clay Deposits In Zibo,Eastern North China

According to the type of bedrock,bauxite can be divided into karst type and laterite type.Among them,the bedrock of karst type bauxite is karst paleoweathering surface,and the material comes from the transportation in other places;the bedrock of laterite type bauxite is aluminosilicate rock,and the material comes from the weathering of floor rock.Zibo bauxite in the east of North China is a special case of bauxite.Its floor is sandstone and is in integrated contact with the ore bed,so it should be classified as laterite bauxite.However,because there is no archaic surface on the roof of bauxite,it shows that it is formed by deposition of allochthonous materials.In this study,the mineral composition and crystallinity characteristics of the samples were analyzed by microscopic observation and X-ray diffraction(XRD).The results show that the main minerals of the bauxite-clay deposit include kaolinite and anatase,as well as a small amount of boehmite and siderite.The crystallinity index hi of the bottom of the ore bed in Boshan area is 0.57,which belongs to disorder.The crystallinity index of the kaolinite in the ore bed is 1.03,which belongs to order.The crystallinity index of the bottom of the ore bed and the kaolinite in Yanggu area is1.02-1.14,which belongs to order.Disordered kaolinite is formed by terrigenous clastic weathering;ordered kaolinite is formed by colloidal chemical crystallization,which is formed by parent rock weathering and precipitated in the acidic environment of the lake and marsh,and may also be related to the oxidation and heating of organic matter in the coal seam in the later stage of sedimentation.Most of the zircons in the ore bed and roof and floor have obvious concussion ring,indicating that the bauxite mineralization is magmatic;the U-Pb age of zircons in the bauxite bed is a single peak,with a peak age of 290 Ma,while the top and floor ages show three peaks,indicating that the bauxite mineralization comes from a concentrated magmatic activity,while the top and floor materials come from three magmatic activities.The epsilon ?Hf(t)values of zircons from 300 Ma are-20.81 to-5.98.The range of ?Hf(t)of zircons in bauxite layer overlaps with that in the north margin of North China Craton,while the range of ?Hf(t)of zircons in the top and bottom layers is distributed in the north margin of North China and North Qinling orogenic belt.It shows that the bauxite minerals are derived from magmatism in the northern margin of North China,while the top and bottom materials are derived from the northern margin of North China and the North Qinling orogenic belt.