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Diamonds from Minas Gerais, Brazil: An Update on Sources, Origin, and Production

1994; Taylor & Francis; Volume: 36; Issue: 11 Linguagem: Inglês

10.1080/00206819409465502

1938-2839

Joachim Karfunkel, Mario Luiz de Sá Carneiro Chaves, Darcy P. Svisero, Henry O. A. Meyer,

Geochemistry and Geologic Mapping

The State of Minas Gerais (MG) was the main diamond producer worldwide for almost 150 years. Today, Brazil contributes about 1.5% to the world diamond production, with 220,000 carats (ct) coming from MG; the two principal source areas are located in the Diamantina region of Espinhaco province and in western MG. Although many theories have been advanced to explain the primary source of diamonds in MG, all commercial production is from secondary deposits. This paper reviews the geology of these deposits and emphasizes the importance of the redistribution of diamonds in Cretaceous and younger sediments. The Espinhaco diamond province, with distinct diamond districts and fields, varies in average grade from 0.008 to over 0.2 ct/m3; however, immense reserves, such as the Jequitinhonha River gravels, locally can reach 400,000,000 m3 or more. However, the largest stones weigh only several tens of carats, unlike in Western MG (which supplied practically all of Brazil's large stones), where many weigh over 100 ct. This fact was and remains the main argument for controversial theories involving the origin of diamonds in MG. Attempts to resolve the problem of the primary origin of diamonds in MG may be hampered by the possible extensive erosion of primary sources. The Precambrian diamondiferous meta-conglomerates of the Diamantina region are relatively well known, but investigations of their derivatives in Phanerozoic time, especially during the Cretaceous and the Plio/Pleistocene, are rare; such studies could be of great interest, not only for reconstructions of paleogeographic environments, but also for exploration purposes. However, no Precambrian diamondiferous conglomeratic rocks similar to those of the Espinhaco Range are known in Western MG. To date, there is no firm evidence supporting a Cretaceous primary origin for those diamonds.