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Belo Horizonte, Brazil

Detailed geological mapping of the Sopa-Brumadinho Formation (Espinhaço Supergroup) in the area of the Extração Diamondiferous Field (Diamantina, MG), identified a series of sedimentary continental deposits. These deposits indicate the transition from a quiescent tectonic regime with braided rivers to another regime controlled by rift-related faults in the basin, with the development of incised fluvial deposits and alluvial fans. By the facies analysis supported in the identification of architectural elements of this formation, were recognized seven lithofacies associations (A1 to A7) that characterize the evolution of the depositional systems of Espinhaço Supergroup in the area. Diamond occurrences that are known in the old local mines can be related to A2 Association and, probably, also to A3 Association. Source

Chaves M.L.C.,Federal University of Minas Gerais | Andrade K.W.,GEOMIL Servicos de Mineracao Ltda | Azzi A.A.,Sao Paulo State University | Silveira F.V.,Servico Geologico do Brazil Companhia de Pesquisa de Recursos Minerais

The Alfeu-01 kimberlite intrusion was discovered in 1994, and is hosted by granitoid rocks of the Pinheiro Machado Complex, of Neoproterozoic age, in the Sul-Riograndense shield. This kimberlite is melanocratic, and has an afanitic matrix where xenoliths of the host rocks as well as macrocrysts of phlogopite, rutil, garnet and, possibly diopside can be observed. The petrographic descriptions (basically phlogopite + olivine + talc + serpentine) indicate that it is an explosive breccia, probably of diatreme facies. In geochemical terms, the high contents of TiO2, MnO and K2O are characteristics, in contrast with diamondiferous intrusions of Minas Gerais. The garnets were divided into three different colors, a strong association of colors with the Fe2O3, MgO and Cr2O3contents having been observed. All garnets, identified as the pyrope type, are located in the mineral fields known as G4, G5 and G9, generally not associated to fertile intrusions. In the same way, the high oxidation grade in the Mg-ilmenite is not favorable for diamond preservation. Chromite data indicates that the mineral is out of the diamond inclusion field. Diopside of the intrusion is Cr-poor, and recognized as associated to an alkaline basalt suite. All mineralogical parameters characteristically diverge from the observed in fertile kimberlites of Minas Gerais; in this way, they strongly not encourage another prospecting works on the intrusion. © 2014 Universidade Estadual Paulista. All rights reserved. Source

da Silva M.C.R.,GEOMIL Servicos de Mineracao Ltda | Chaves M.L.S.C.,CPMTC IGC UFMG | Andrade K.W.,GEOMIL Servicos de Mineracao Ltda

At Diamantina region occur siliciclastic predominantly rocks belonging to the Espinhaço Supergroup, of Paleo to Mesoproterozoic age, that are currently admitted as members of two large distinct sedimentary cycles in the cratonic rift domain, informally designated Espinhaço I (Estaterian) and Espinhaço III (Stenian) cycles. In the lower portion of this sequence occur since thin to thick levels of polymictic conglomerates, associated to the Sopa-Brumadinho Formation, that were intensively mined due to their diamondiferous content. Such conglomerates were studied near the village of Extração in order to some sedimentological aspects especially in this paper the clasts of banded iron formation (BIF) are characteristically abundant in that locality. Geochemical analyses of this material from the most important sites of old mines (Serrinha, Boa Vista, Cafundó and Cavalo Morto) mainly identified a prominent geochemical signature of rare earths elements showing simultaneous negative anomalies of europium and cerium, that are typical of proterozoic sources. The main sources of these clasts probably is the Pedro Pereira Sequence, of supposed Paleoproterozoic age, with actual better exposures at south of Gouveia town. © 2015, Universidade Estadual Paulista. All rights reserved. Source

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