Geology and diamond provenance of the Proterozoic Banganapalle conglomerates, Kurnool Group, India

Abstract

The Banganapalle Quartzite Formation occurs in the Cuddapah Basin in India and is characterized by a basal diamond-bearing conglomerate horizon. The diamonds within this placer are generally thought to have been sourced from the erosion of kimberlites of the Wajrakurur cluster. De Beers' India's exploration efforts have resulted in the discovery of a number of dykes within the basin, with petrographical and geochemical similarities to lamproites. It is proposed that far-field stresses related to the Eastern Ghats Mobile Belt (EGMB) provided extensional sites during the time of lamproite emplacement. The dykes have not been dated. However, zircons recovered from heavy mineral stream samples in the area exhibit a number of age groupings, including one in the range of 1287–1370 Ma. This age is interpreted as the emplacement age of the dykes in this region. Kimberlitic indicator minerals (KIMs), recovered from conglomerate waste dumps, indicate the uniqueness of the garnet population relative to that of the known kimberlite clusters to the west of the basin. We propose that the emplacement of lamproites occurred as dyke–sill complexes at 1.4–1.3 Ga and that the lamproites represent the source of the diamonds in the Banganapalle conglomerates.Supplementary material:A list of the isotope ratios used in this paper is available at www.geolsoc.org.uk/18508

Emplacement of Lamproites in and around Ramadugu, Nalgonda District- ground Magnetic evidence

“…Thus, intersection of linear trends, bulging of contours, low magnetic anomalies are favorable indicators in their search (Ramachandran et al 1999) Interestingly, the magnetic anomalies in the Ramadugu region (Fig. 2d) (Joy et al 2012;Kumar et al 2013;Reddy et al 2003;.Sridhar and Raju, 2005) …”

Petrogenesis of Mesoproterozoic lamproite dykes from the Garledinne (Banganapalle) cluster, south-western Cuddapah Basin, southern India

“…In this study, we sampled a Garledinne lamproite dyke (15°18"27"N; 78°00"8"E; Fig. 1c) that trends WNW-ESE and corresponds to the 188 551/110/ 0003 lamproite recorded by Joy et al (2012). The dyke shows pinching and swelling and extends for about 30 m along strike.…”

“…Four sets of lamproite dykes, intruding the Tadpatri shales of the lower Cuddapah Supergroup, were reported by the De Beers Company in three areas near Banganapalle town: (i) in a road material quarry 4.5 km west, (ii) 1.7 km to the SW; and (iii) in a valley 24 km due west and exposed along a stream bed (Joy et al 2012) near Garledinne village. In this study, we sampled a Garledinne lamproite dyke (15°18"27"N; 78°00"8"E; Fig.…”

“…The dyke shows pinching and swelling and extends for about 30 m along strike. Based on the age grouping of 1287-1370 Ma for some of the zircons recovered from heavy mineral stream samples in the Banganapalle waste dumps, Joy et al (2012) infer the emplacement age of these lamproites to be Mesoproterozoic (1.28-1.37 Ga). We have obtained a slightly older whole-rock 40 Ar/ 39 Ar plateau age of 1433± 8 Ma (2 σ) for a sample collected from the Garledinne lamproite (written comm.…”

“…Against this backdrop, De Beers India Exploration company has discovered lamproitic dykes intruding the Tadpatri shales of the Lower Cuddapah Supergroup, located west of Banganapalle town near Garledinne (Joy et al 2012) in the south-western part of the Cuddapah Basin. Only reconnaissance petrological and geochemical information of these lamproite dykes is available and petrogenetic details are lacking.…”