Uranium concentration in altered brown coals located under burnt rocks from the Kansk-Achinsk Basin, West Siberia

West Siberian brown coals from the Kansk-Achinsk basin and their combustion products are generally characterized by a low uranium content. In some pla ces where brown coal has been altered (losing density, becoming cracked or friable), the uranium content has increased by concentrations ranging from 100-1000 mug g(-1). At these locations distinct signs of underground fires are visible. The uranium distribution patterns suggest that the burnt organ ic matter was a source of uranium and altered varieties of coal serve as a geochemical barrier to uranium transport.