| The frequent tectonic movements in South China and the widespread distribution of Garidonian and Yanshanian magmatic rocks provide a rich material basis for the weathered kaolinite deposits in the region.Most of the kaolin deposits in Jianning are mainly of the weathered residual type,but the research on kaolinite ores in this region is limited and the geological research is low,which restricts the work idea and direction of ore search.This thesis takes the Jianning Wangjia kaolinite deposit as an example,and takes the granite,which is the parent rock of the Jianning Garidonian mineralisation in the Wuyi Mountains of western Fujian,and its weathered kaolinite as the research object.Combining field geological investigation and indoor analysis means,the geological characteristics of the kaolinite deposits after granite weathering in the study area are summarised,the lithological characteristics,geochemical characteristics,chronological characteristics and petrogenetic types of the granite are elucidated,and the weathered kaolinite deposits after granite weathering are discussed.The mineral composition of kaolinite after weathering of granite was studied in detail and the following insights were obtained:(1)The geological features of the study area are simple,only the strata of the Palaeogene Tianjingping Formation are exposed,and the kaolinite deposits are mainly in granite weathering crusts,which are well preserved and rich in reserves,generally spreading along the north-west direction,with the thickness changing gradually from south east to north west.In the vertical direction,the granite weathering crust is divided into five parts: humic layer,fully weathered layer,strongly weathered layer,weakly weathered layer and bedrock.(2)The ore-forming host rocks in the study area are all medium to fine-grained granitic,massive structures,with a high K-Ca alkaline,strongly peraluminous S-type granite of late Garidonian age.The ages of the parent rocks are 429.7±4.5 Ma,428.5±2.7 Ma and 423.9±3.5 Ma respectively,which are close in age and belong to the late Silurian magmatism of the Early Paleozoic.According to the zircon saturation temperature calculations,the magma crystallization temperature of orthoclase granite is 728.56°C ～ 777.63°C and that of diorite granite is 714.32°C,while the magma crystallization temperature of black mica diorite granite is higher at about 852.14°C.(3)The kaolinite minerals in the study area are extremely similar.Based on XRD and SEM,it is concluded that they are mainly composed of quartz,plagioclase,hydromorphite and kaolinite group minerals,while infrared and thermal stability analysis experiments were conducted on this basis,and it is concluded that kaolinite group minerals in the study area are mainly kaolinite and eclogite,and kaolinite is poorly crystalline ordered.By comparing the kaolinite after weathering of pegmatite and orthoclase granite,it was determined that the former is of purer quality and is a high-quality kaolinite in the study area.(4)The type of kaolinite deposits in the study area is weathered residual kaolinite deposits,which is the result of the combined effect of the ore-forming parent rocks,tectonics,topography,hydrology and climate.The study area is located in the western part of Fujian,with fracture tectonics,magmatic development,and extensive silicaaluminium-poor iron-titanium granite host rocks,a subtropical monsoon climate,hot,humid and rainy,lush vegetation,and a medium acidic water medium all year round,good weathering conditions,and low hilly terrain. |
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