Natural gamma ray measurements using a portable device were performed at 157 sites in the area around Sirohi town and Sindreth village in Rajasthan (NW India). This region comprises sedimentary rocks, metasediments, granites and gneisses that bear characteristic GR dose values and U/Th ratios corresponding with their specific geological history. A-type Malani granites and rhyolitic derivates, also referred as high heat production granites, show distinct differences as compared to the S-type Erinpura and Balda granites, most prominent in a high Th content of the former (up to 90 ppm). Sedimentary rocks in the Sirohi and Sindreth area are variable in their signatures reflecting their variable source rocks. In the area between the Balda and Paladi villages, northeast of Sirohi, measurements in vicinity of a N–S running shear zone, have shown U enrichment up to 8 ppm. This shear zone has been synkinematically mineralized with quartz and shows evidence of fluid infiltration into the host rocks in the vicinity of the shear zone. Erinpura granites have been altered due to fluid activity and show a light depletion of K (3.96%) and Th (20.11 ppm) as compared to the unaltered rocks (K, 4.06; Th 24.46 ppm). Enrichment of U (with a mean value of 13 ppm) has also been recorded in the lower clastic unit of the Sindreth Basin, especially within gritty conglomerates wherein migration and precipitation along fault planes is proposed.
Volume 128 | Issue 8
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