RARE-EARTH ELEMENT TRENDS AND CERIUM-URANIUM-MANGANESE ASSOCIATIONS IN WEATHERED ROCK FROM KOONGARRA, NORTHERN-TERRITORY, AUSTRALIA

At Koongarra, Australia, three drill cores from the Cahill Schist Form ation containing U-ore, and regolith above it containing secondary U-o re, were studied to ascertain the distribution of rare earth elements (REEs) and U. The unaltered schist has a REE trend similar to the Post Archaean Australian Shale (PAAS), which is, therefore, used as a norm alising standard. Unweathered rock from the zone of primary U minerali sation contained strong enrichment of the heavy REEs, and this pattern is retained during most of the weathering. Strongly bleached and very weathered shallow samples from this zone do not show enrichment of HR EEs. In general, however, weathering appears to have little effect on the pattern of REEs in the bulk rock at this site. Zones rich in Mn ox y-hydroxides, occurring as coatings on fissure surfaces, contain large concentrations of Ce and U, with a clear Ce anomaly (Ce/Ce = 3.8). T he Ce and U apparently occur together as microcrystalline oxides withi n (1-2 mu m diameter) globules on mineral surfaces in the Mn-rich zone s.