In situ gamma radiation measurements in the Neoproterozoic rocks of Sirohi region, NW India

Abstract

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.

Differences in natural gamma radiation characteristics of Erinpura and Malani granites in NW India

“…This is because U is far more mobile because of its increased solubility at higher oxidation states, whereas Th has only one valence state and remains inside the lattice sites of the minerals. Secondary U mobilisation along localised fault zones has been reported for the Sindreth setting as part of the MIS (Scharfenberg et al 2015).…”

“…A regional study on MIS has categorised the volcano-plutonic rocks as high heat-producing with high radiogenic element concentration (Singh and Vallinayagam 2012). A preliminary study on rock types in the region of Sindreth (figure 1) reports some data on Erinpura granites and the MIS Mirpur intrusion (Scharfenberg et al 2015). In this study, we provide for the first time, a statistically significant database on radioelement concentration in felsic rocks of NW India in order to show that in-situ GR measurements are valuable data sets for evaluating regional variations in granitic terrains.…”

Radiogenic heat production of Variscan granites from the Western Bohemian Massif, Germany

“…A-type granites (Loiselle and Wones 1979;Eby 1992) are typical of intra-plate, often anorogenic settings. They are the most abundant in Proterozoic terranes, such as the Malani Igneous suite in NW India (Eby and Kochhar 1990;de Wall et al 2018), and are characterized by generally high radioelement concentrations (Scharfenberg et al 2015(Scharfenberg et al , 2019 resulting in higher RHP (Singh and Vallinayagam 2012). Therefore A-type granites commonly rank to high-heat-producing granites (HHP granites).…”