Abstract
ABSTRACT: Magmatism associated with the Alto Paranaíba structural high comprises kimberlites, kamafugites, and alkaline complexes, forming an approximately 400 x 150 km NW-SE belt in the southern São 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 Três Ranchos and Coromandel. Six hundred and eighty (680) diamonds acquired or recovered during mineral exploration in the digging areas of Romaria, Estrela do Sul, Três 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.
Highlights
According to Barbosa (1991), Francisco Machado da Silva found the first diamond in Brazil in 1714
The objective of this work was to point out and address details observed in the studied region in Minas Gerais, to suggest local/proximal sources for the unique diamond pop‐ ulation found in the alluvial deposits of the Santo Antônio do Bonito, Santo Inácio and Douradinho rivers
With the geologist and company director, Juliano Magalhães Macedo, we examined drill core samples and visited work fronts, where material is extracted for processing and diamond recovery
Summary
According to Barbosa (1991), Francisco Machado da Silva found the first diamond in Brazil in 1714. Still in the nineteenth century, deposits were discovered in the Bagagem River, west of Coromandel It was in the alluvial deposits of this river that the 261.88‐carat South Star diamond was found in 1853, and the 119.5‐carat Dresden diamond was found four years later (Franco 1981; Machado & Figuerôa 1999). Between 1937 and 1943, diamonds over 200 carats were recovered to the east and southeast of Coromandel, more precisely in the allu‐ vial deposits of the Santo Antônio do Bonito, Santo Inácio and Douradinho rivers, including the 726‐carat Presidente Vargas, considered the largest one discovered in Brazil (Fig. 1) (Franco 1981; Barbosa 1991; Machado & Figuerôa 1999)
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