Abstract
Abstract The Chapada Diamantina, located in the central region of the State of Bahia, is of important historical significance due to its diamond occurrences. Discovered in the nineteenth century, comprehensive research about the regional diamonds and their origins are still limited, demanding more investigation in the matter. Looking for insights about their genesis, mineral inclusions in 23 alluvial diamonds from 4 garimpos located in the Chapada Diamantina were analyzed through the use of Raman micro spectroscopy. Additionally, the characteristics of nitrogen aggregation of the host diamonds were measured using Fourier-transform infrared spectroscopy (FTIR). The diamonds from Chapada Diamantina consist mainly of well-formed crystals, with dominant dodecahedral habits, characterized by faint to very light yellow body colors, typically with green and brown radiation spots on their surface. The main surface textures observed are related to processes that took place in the late stage resorption and during the residence of the diamonds in placer environments. The diamonds are predominantly type IaAB, with a significant occurrence of poorly aggregated nitrogen (Type IaA diamond). The main mineral assemblages of the studied peridotitic inclusions refer to a harzburgitic paragenesis.
Highlights
The discovery of diamonds in the State of Bahia occurred in the Chapada Diamantina region, in 1821, nearly a century after the first finds in Brazil, which took place in the State of Minas Gerais (Leonardos, 1937)
Understanding about diamond genesis, The oldest known primary source of and is the only means to determine the diamonds in the São Francisco craton is process of diamond formation (Stachel the Neoproterozoic kimberlites of Brauna and Harris, 2008)
The concentration and aggregation state of nitrogen impurities in the diamonds were determined by Fourier transform infrared (FTIR) spectroscopy, using a Perkin-Elmer Spectrum 400 instrument, equipped with a 5x beam condenser, from the Gemological Research Laboratory of the Center for Mineral Technology (CETEM)
Summary
The discovery of diamonds in the State of Bahia occurred in the Chapada Diamantina region, in 1821, nearly a century after the first finds in Brazil, which took place in the State of Minas Gerais (Leonardos, 1937). The mining regions around the municipalities of Lençóis, Andaraí and Mucugê, within the surroundings of the established National Park of Chapada Diamantina boundaries, produced the greatest economic impact on Bahia’s diamond production (Sampaio, 1994). The exploration of diamonds occurs mainly in alluvial deposits of the Paraguaçu, Santo Antônio and São José rivers, in which the diamonds are considered a product of disintegration and reworking of the Mesoproterozoic Tombador Formation conglomerates (Bonfim and Pedreira, 1990). The primary source of such diamonds is unknown; due to the present in the Tombador Formation absence of typical satellite minerals, the conglomerates (Pereira and Fuck, 2005; diamond’s genesis in Chapada Diaman- Pereira, 2007).
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