The occurrence of microdiamonds in Mesoproterozoic Chapada Diamantina intrusive rocks--Bahia/Brazil

The origin of diamonds from Serra do Espinhaço in Diamantina region (State of Minas Gerais) and in Chapada Diamantina, Lençóis region (State of Bahia) remains uncertain, even taking into account the ample research carried out during the last decades. The lack of typical satellite minerals in both di...

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Bibliographic Details
Published in:Anais da Academia Brasileira de Ciências 2007-06, Vol.79 (2), p.321-332
Main Authors: Battilani, Gislaine A, Gomes, Newton S, Guerra, Wilson J
Format: Article
Language:English
Subjects:
Chapada Diamantina
Formação Tombador
intrusive rocks
Mesoproterozoic
Mesoproterozóico
microdiamantes
microdiamonds
MULTIDISCIPLINARY SCIENCES
rochas intrusivas
Serra do Espinhaço
Tombador Formation
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Summary:The origin of diamonds from Serra do Espinhaço in Diamantina region (State of Minas Gerais) and in Chapada Diamantina, Lençóis region (State of Bahia) remains uncertain, even taking into account the ample research carried out during the last decades. The lack of typical satellite minerals in both districts makes a kimberlitic source for these diamonds uncertain. In mid 18th century the occurrence of a metamorphosed igneous rock composed of martite, sericite and tourmaline was described in Diamantina region and named hematitic phyllite, considered by some researchers as a possible diamond source. Similar rocks were found in Lençóis and examined petrographically and their heavy mineral concentration was investigated by means of scanning electron microscopy (SEM). Petrographic analyses indicated an igneous origin for these rocks and SEM analyses showed the discovery of microdiamonds. Geochronological studies using the Ar/Ar technique in muscovites yielded minimum ages of 1515+/-3 Ma, which may correlate with 1710+/-12 Ma from U-Pb method in igneous zircons from the hematitic phyllites. Both rock types also have the same mineral and chemical composition which leads to the conclusion that the intrusive rocks were protolith of the hematitic phyllites. This first discovery of microdiamonds in intrusive rocks opens the possibility of new investigation models for diamond mineralization in Brazilian Proterozoic terrains.
ISSN:0001-3765
1678-2690
0001-3765
1678-2690
DOI:10.1590/s0001-37652007000200013