Geological Society of London
18508 SupPub.csv (12.56 kB)

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

Download (12.56 kB)
posted on 2016-06-21, 11:03 authored by Sojen Joy, H. A. Jelsma, R. F. Preston, S. Kota

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.