Evidence of young, proximal and primary (YPP) diamond source occurring in alluviums in the Santo Antônio do Bonito, Santo Inácio and Douradinho rivers in Coromandel region, Minas Gerais

Abstract

Magmatism associated with the Alto Paranaiba structural high comprises kimberlites, kamafugites, and alkaline complexes, forming an approximately 400 × 150 km NW-SE belt in the southern Sao Francisco Craton. Dating of some intrusions reveals ages between 120 and 75 Ma. Chemical analyses of garnet recovered in alluvium from traditional diamond digging areas indicate peridotitic garnet windows in Trěs Ranchos and Coromandel. Six hundred and eighty (680) diamonds acquired or recovered during mineral exploration in the digging areas of Romaria, Estrela do Sul, Trěs Ranchos and Coromandel show unique characteristics, certain populations indicating young, proximal and primary sources (YPP). Analyses of 201 stones from Santo Antônio do Bonito, Santo Inácio and Douradinho rivers alluvium, Coromandel, present no evidence of transport, characterizing a proximal source. Within these river basins, exposures of the Late Cretaceous Capacete Formation basal conglomerate contain mainly small rounded and/or angular quartzite pebbles and of basic and ultrabasic rocks, as well as kimberlite minerals (garnet, ilmenite, spinel, sometimes diamond). A magnetotelluric profile between the Paraná and Sanfranciscana basins shows that the thick underlying lithosphere in the Coromandel region coincides with the peridotitic garnet window and with a diamond population displaying proximal source characteristics. Diamond-bearing kimberlite intrusions occur in different areas of Alto Paranaíba.