Source-to-sink system of sandstone uranium mineralization
The application of source to sink analysis method in the study of the formation of sandstone-type uranium deposits in the basins of northern China is conducive to the study and summary of the enrichment mechanism and metallogenic pattern of sandstone-type uranium deposits.The physical,chemical and biological processes of the whole uranium metallogenesis,from denudation of source material to confluence and enrichment,are considered as a complete source-to-sink system of sandstone-type uranium deposits.The source-to-sink system of sandstone uranium deposit is composed of three parts:uranium source,uranium confluence system and uranium mineralization.Uranium sources can be divided into three types:external uranium sources,internal uranium sources and uranium sources in deep basin.The external uranium source refers to the large-scale exposed rich uranium basement and rock at the edge of the uranium producing basin.The internal uranium source refers to the uranium bearing formation of the target layer itself,which is the preconcentration of uranium matter formed in the process of sedimentary diagenesis.The uranium confluence system is the transporting process of the uranium matter from the uranium source area to the sand body and migrating in the ore bearing body.Under the high temperature and pressure of hydrocarbon expulsion,uranium rich source rocks in deep basin can provide uranium sources for shallow sandstone uranium deposits through active faults.The uranium rich matter migrate to the interior of the target layers through the confluence system in the sedimentary and metallogenic periods.The uranium mineralization system is a process of reducing the uranium bearing fluid to precipitation and enrichment by reducing substances or microorganisms in sandstone.Palaeogeomorphology restoration is one of the important methods for the study of source-to-sink system of sandstone-type uranium deposits.The restoration of palaeogeomorphology in sedimentary basins is helpful to determine the distribution characteristics of favorable sedimentary facies belts,to reveal the spatial evolution characteristics of target layers,and reconstruct the spatial change of palaeogeomorphology and paleocurrent direction in different periods.The southwestern part of the Ordos basin has the characteristics of shallow infiltration and deep exudation convergence systems.Shallow layers formed interlayer oxidation zone type and sedimentary rock type uranium deposits or mineralization in the Zhiluo formation and the middle and upper parts of Huanhe formation,while deep layers formed exudative type uranium mineralization in the the Luohe Formation and Lower Huanhe formation.The superposition and transformation of infiltration and exudation convergence systems have also played an important role in uranium mineralization.
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