Relation between the thermal behaviour and the structure of kerogen in the Goesan uranium deposit, Korea

Abstract

The study of kerogens associated with mineralized and non or poorly mineralized samples shows that: 1. (1) The organic matter reached a high rank of evolution, namely pre-graphitic to graphitic. 2. (2) Kerogens of mineralized samples differ from those of non-mineralized samples by their behaviour under pyrolysis conditions. The kerogens associated with mineralized samples display a higher pyrolysable and oxidizable fraction under the conditions of measurement of the organic carbon content in the Rock-Eval II pyrolyser (i.e. by heating up to 600°C) than kerogens associated with non or poorly mineralized samples. 3. (3) Under Transmission Electron Microscopy, all kerogens appear to be highly coalified. They are all made of a mixture of partially graphitized shell-like sub-concentric particles (semi-graphites) and lamellae of graphite. Samples from mineralized areas (U > 100 ppm) contain relatively more, and smaller, shelly particles than samples from poorly mineralized zones (P < 100 ppm). The organization of the aromatic layers is less perfect in the shelly particles than in graphite, i.e. in lamellae. This poorer organization could have resulted from the oxidative reticulation of the carbonaceous material during uranium fixation. Their sensibility to combustion is assumed to be higher than that of lamellae displaying a higher degree of crystallinity. In conclusion, the thermal behaviour of kerogen particles up to the maximum temperature (600°C) of Rock-Eval II pyrolysis could discriminate particles associated with uranium whose crystallinity would be less perfect than that of particles of high crystallinity found in uranium-poor samples.