SOME GEOCHEMICAL CHARACTERISTICS OF URANIUM-BEARING COAL DEPOSITS IN CHINA

Uranium-bearing coal deposits in China occur in some Meso-Cenozoic continental sedimentary basins which mainly spread over intermontane down-faulted basins of geosynclinal folded and upwarped regions. The uranium-bearing basin basement consists of granite or acidic volcanic rocks;uranium abundance is more than 8 ppm. Underground water in uranium ore areas is characterizied by bicarbonate K-Xa, sulfates and bicarbonate Ca(K)-Na types;PH = 6-7.5;uranium abundance is n. 10^-7-n.10^-8g/l and n.10^-8-n.10^-5g/l in arid regions. This deposit, by its occurrence, can be classified into three categories: (1) ore bodies occurring above the unconformable plane of the basin basement, (2) below unconformable plane in sedimentary formation,(3)in the coal-bearing detrital formation. This paper describes some geochemical characteristics of uranium-bearing coals as follows: 1. Uranium-bearing coals are mainly lignites of low-rank metamorphism. The components of coals mostly are collinite (or telinite), interbeded with fusain fragments and mixed with stable components ( cuticle, resinite, spore, etc. ) . The coal's type bel ngs to semidurain-semiclarain, durain with clarain, claro-durain and duro-clarain. On the basis of analytical data, we may come to the conclusion that uranium content is negatively correlative with CY, HYcontents, H/C atomic ratio and Vf, and positively correlative with S. 2. In uranium-bearing coals the forms of uranium existence are complex. U-ranium is in the form of absorption monominerals and organic complexes. Monomi-nerals are pitchblende,coffinite and uranophane, sklodowskite, tyuyamunite, sch-rockingerite, autunite and torbernite. Absorbents consist of vitrain compound, clay minerals and colloidal pyrites. Organic complexes are humic uranyl complex and uraniferous bitumen. 3. Enrichment of organic materials to uranium is realized by special functions of self-decomposition and synthetic products in the diagenetic process. These functions consist of adsorption, reduction, ion exchange, complexation or chelation, etc. Adsorption and reduction are specially chief functions of enrichments to uranium in diagenetic and supergene stages. 4. Genesis of uranium-bearing coal deposits consist of the diagenetic and the epigenetic. According to the occurrence of ore bodies uranium deposits formed in the process of coal bed formation are typically diagenetic;uranium deposits occurring above or below the unconformable plane are mainly epigenetic.