At Lachhri, uraniferous powdery soft calcrete having significant uranium values with high leachability (similar to 90%), is spread over an area of about 300 m x 200 m up to a depth of about 1 m from the surface. The soft calcrete occurs in a playa-lake environment in a local interdunal depression. Both groundwater and meteoric water, under the influence of the evaporite environment, were probably associated with the genesis of this calcrete and mineralization in it. Detailed study has shown a fair amount of continuity and uniformity in grade and thickness of the uranium-bearing calcrete horizon. Chemical assay of 50 grab samples of calcrete indicated total U ranging from 6 to 195 ppm with an average value of 90.66 ppm. At Lachhri, the uranium value in the groundwater sample is 333 ppb. The country rocks around Lachhri are carbon phyllite-quartzite of the Precambrian Delhi Supergroup, granites and metabasic rocks. The present study indicates that approximately 14 tonnes of U can be expected in the powdery soft calcrete. Contained U (in tonnes) is based on contained metal content and at the present stage it does not consider metallurgical, mining or economic aspects. This new find of significant uranium occurrence in calcrete of playa-lake type environment, in addition to being a low-grade uranium-bearing horizon, establishes the potentiality of similar geological set-up. It offers a type model and guide for prognostication of calcrete-hosted uranium occurrences in other areas, especially in Rajasthan, for further exploration.
