Application of 2D Resistivity Modelling to Delineate Lamproites in Parts of North‑Eastern Dharwar Craton

Geophysical methods have extensively been used in exploration of Lamproite bodies. Lamproites are significant source rocks of primary diamond deposits other than Kimberlites. The Eastern Dharwar Craton is unique in the way that it hosts numerous Precambrian Lamproites confined to the crescent-shaped Paleo-Mesoproterozoic Cuddapah Basin and its north-western and north-eastern margins. In the present study electrical method was used as a tool for delineation of Lamproite bodies in contrast with country rocks in Gundrapally, Vattikode and Marepally regions in parts of the North Eastern Dharwar Craton in Telangana State, India. The electrical profiling method was conducted in different direction to identify the variation of the lithology of the area due to the anisotropic nature and smaller size of the 2-D intrusive bodies adopting the Wenner electrode configuration. The electrical properties of the Lamproites tended to change with their composition due to weathering and the presence of Olivine and K-Al rich composition. The electrical response on the Lamproite pipes is shows a decrease in resistivity concerning the country-rock in the area.

Heavy metal pollution assessment and its indexing approach for drinking water around inactive mine sites, Southwestern region of Cuddapah Basin, South India.

Hazardous compounds in aquifers, especially potentially toxic heavy metals, are a major environmental and socioeconomic problem around the world. Hence, the study is intense to quantify, for the first time, the pollution status and ecological risk of heavy metals around inactive mining sites in the Southwestern (SW) region of Cuddapah Basin. Ten heavy metals, including arsenic (As), cobalt (Co), cadmium (Cd), iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), lead (Pb), zinc (Zn) and strontium (Sr) were investigated for a total of 50 groundwater samples of this study. The findings of the study revealed that arsenic (0-60.5 and o.56.3 µg/L), cadmium (0-28.1 and 0.31.1 µg/L), nickel (0-110.2 and 0–99 µg/L)), lead (0-175.6 and 0-92.3), Strontium (0-1150 and 0-1440 µg/L) concentrations are above the acceptable levels in both pre and post – monsoon seasons. The Heavy Metal Pollution Index (HPI), Heavy Metal Evolution Index (HEI) and Degree of contamination (DOC) are applied to assess hazardous metal pollution in drinking water of this area. According to HPI values 17.5 % and 10% of samples fall under high pollution index; as per the classes of HEI, 95 % and 100% of samples fall under low pollution class during the pre and post-monsoon season. According to DOC, all groundwater samples fall in a low zone. As per ecological risk classification, 90% of the samples cause extreme high ecological risk in pre & post-monsoon season in the study area.

Mesoproterozoic 40Ar–39Ar ages of some lamproites from the Cuddapah Basin and Eastern Dharwar Craton, southern India: implications for diamond provenance of the Banganapalle Conglomerates, age of the Kurnool Group and Columbia tectonics

We report Mesoproterozoic 40Ar–39Ar (whole-rock) ages of lamproites from (i) the Ramadugu field (R4 dyke : 1434 ± 19 Ma and R5 dyke: 1334 ± 12 Ma) and the Krishna field (Pochampalle dyke: 1439 ± 3 Ma and Tirumalgiri dyke: 1256 ± 12 Ma) from the Eastern Dharwar Craton (EDC) and (ii) the Garledinne (1433 ± 8 Ma) and the Chelima (1373 ± 6 Ma) dykes from within the Paleo-Mesoproterozoic Cuddapah Basin, southern India. The ages reported for the Ramadugu and Tirumalgiri lamproites constitute their first radiometric dates. Ages of the Pochampalle and the Chelima lamproites from this study are broadly comparable to their previously reported 40Ar–39Ar (phlogopite) ages of c. 1500 Ma and 1418 ± 8 Ma, respectively. The ages of all these lamproites are much older than those of the (i) c. 1.1 Ga kimberlites from the Wajrakarur and Narayanpet fields of the EDC and (ii) c. 1.09 Ga lamproitic dykes at Zangamarajupalle which intrude the Cumbum Formation of the Cuddapah Basin. However, the age of the Tirumalgiri lamproite (c. 1256 Ma) is similar to that of the Ramannapeta lamproite (c. 1224 Ma) within the Krishna field. Our study provides evidence for protracted ultrapotassic (lamproitic) magmatism from c. 1.43 to 1.1 Ga over a widespread area (c. 2500 km2) in and around the Cuddapah Basin and the EDC. Implications of the obtained new ages for the diamond provenance of the Banganapalle Conglomerates, the age of the Kurnool Group and for the timing of break-up of the Paleo-Mesoproterozoic supercontinent of Columbia/Nuna are explored.

Paleoproterozoic metaluminous syenites synchronous with the c. 2.21 Ga mafic dyke swarms from the Eastern Dharwar Craton, India: implications for alkaline magmatism associated with the breakup of supercraton Superia

The Eastern Dharwar Craton (EDC) hosts numerous Late Neoarchean to Paleoproterozoic syenites whose genesis remains unclear. Here, we present a petrological and geochemical study on the syenites from Peddavaduguru, Danduvaripalle and Vannedoddi, towards the western margin of the Paleo-Mesoproterozoic Cuddapah Basin in the EDC. These syenite bodies constitute a part of the Paleoproterozoic (2210±110 Ma) Dancherla alkaline complex and are contemporaneous with a mafic dyke swarm emplacement in the EDC. The Danduvaripalle and Vannedoddi syenites display geochemical affinities to adakites. The Peddavaduguru syenite shows a negative Eu anomaly and relatively gentle chondrite-normalized REE pattern, suggesting an origin by a different process. The initial ɛNd values range between 0.5 and 0.8 for the Peddavaduguru syenite, −5.2 and −4.2 for the Danduvaripalle syenite, and −6.0 and −1.0 for the Vannedoddi syenite. In tectonic discrimination diagrams, the Peddavaduguru syenite shows affinities to within-plate granitoids similar to syenites from the Deccan large igneous province whereas the others show geochemical similarities to arc-related alkaline rocks and volcanic arc granitoids. The adakitic syenites show deficiency of MgO, Ni, Cr and Sc, highly fractionated REE patterns and negative Nb-Ta-Ti anomalies along with low Nb/U and high Th/U ratios. These geochemical traits are compatible with their origin by the partial melting of a mafic crustal source that subsequently underwent fractionation of amphibole and garnet responsible to impart an adakitic character. We suggest that the crustal source of these syenites underwent partial melting by heat from the rising plume during the Paleoproterozoic extension of the Superia supercraton. The non-adakitic Peddavaduguru syenite, on the other hand, is suggested to have originated from direct fractionation of mafic magma.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5276675