Articles


DIAMONDS AND THEIR DEPOSITS

Peter G. Chirico, Francis Barthélémy, and François A. Ngbokoto, Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic. U.S. Geological Survey Scientific Investigations Report 2010–5043, 22 pp. Available at http://pubs.usgs.gov/sir/2010/5043/ or just click here.

Mario Luiz de Sá C. Chaves & Luís Chambel, Diamantes do médio rio Jequitinhonha, Minas Gerais: qualificação gemológica e análise granulométrica. REM: R. Esc. Minas, Ouro Preto, 57(4): 267-275, out. dez. 2004. Available here.

Abstract: The Jequitinhonha River basin alluvial deposits, in Minas Gerais, were the source of most of the Brazilian diamond production since 1714 until the last middle eighties. This historical and economical importance is in itself a reason to publish grain-size and gemological quality data concerning the diamonds of the Tejucana and Rio Novo mining companies concession areas. In addition, extensive sampling (186,052 stones or 17,689 ct) on 14 locations along the river can contribute to create an important database to identify the origin of different diamond populations. Among other observations, the high proportion (82,2%) of gem diamonds should be stressed.

Mario Luiz de Sá Carneiro Chaves , Mauro César Geraldes , Yuji Sano & Luis Chambel. Primeiros resultados da datação Pb-Pb em diamantes carbonados da Chapada Diamantina (BA) e rio Jequitinhonha (MG), Serra do Espinhaço. Revista Brasileira de Geociências, 35(3):419-422, setembro de 2005. Available here.

Abstract: FIRST Pb-Pb DATING RESULTS FROM CARBONADO DIAMONDS FROM CHAPADA DIAMANTINA (BA) AND JEQUITINHONHA RIVER (MG), ESPINHAÇO RANGE. Most carbonados found in Brazil occur along the Espinhaço Range, associated to conglomeratic rocks of the Espinhaço Supergroup. This paper presents Pb-Pb radiometric ages on mineral inclusions (quartz, rutile and clay) and matrix of carbonados from the Andaraí and Jequitinhonha River areas. Even with a large experimental error, the results obtained of 3,8±1,8Ga and 3,3±0,7Ga respectively, are of regional geologic interest. The minimum carbonado formation age (ca.2,5Ga) is older than the Espinhaço Supergroup deposition age (»1,7Ga). Other evidences suggest that this minimum age corresponds to the seed aggregation phase; the crustal inclusions being aggregated in an environment rich in high-energy radioactive particles.

L. Chambel, Margarida. G. M. S. Cardoso, and A. Pinto. DIAMOND POPULATION SIGNATURES AND ORIGIN TRACING. Available here.

M.L.S.C. Chaves, L. Benitez & L. Chambel. Análise comparativa dos aspectos superficiais de populações de diamantes nas províncias da serra do espinhaço e do Alto Paranaíba (MG). Available here.

Abstract. The Espinhaço Range and the Alto Paranaíba are the two most important diamond metallogenic provinces in Minas Gerais state (Brazil). Diamond populations from these two provinces are analyzed. In particular, special attention is given to the analysis of diamond surface features acquired either during diamond formation and ascent processes or due to Earth surface (mostly water transport) processes, aiming to relate them with other diamond properties (weight, crystal morphology, and quality (gemological versus industrial qualities). A comparative analysis of the diamond populations properties shows that: (1) Average weight is much lower in the Espinhaço stones than in the Alto Paranaíba stones; (2) Primary crystal forms, such as rombododecahedra and octahedra are predominant in the Espinhaço Range diamonds, in sharp contrast with the Alto Paranaíba diamonds, where irregular forms are very abundant; (3) There is a high grade of dissolution/corrosion in the crystals of the Alto Paranaíba region in relation to the observed in the Espinhaço Range populations. In what concerns secondary diamond surface features: (1) There is an abundance of broken crystals broken in the Alto Paranaíba stones; (2) Crystals showing impact marks are very common in the Espinhaço stones, such features being rarely observed in the Alto Paranaíba stones; (3) The frequency of gemological crystals is very high in the Espinhaço Range, again in sharp contrast with the Alto Paranaíba region. The joint analysis of the mentioned parameters has an extreme importance to understand diamond and diamond deposits genetic processes, suggesting e.g. that Alto Paranaíba diamonds are much closer to their primary sources than the populations of the Espinhaço Range province.

Mario Luiz de Sá C. Chaves, Adolfo Baeta de Medeiros, & Luís Chambel. DIAMANTES “GIGANTES” DO RIO SANTO ANTÔNIO DO BONITO (COROMANDEL, MG): ORIGEM PRÓXIMA OU DISTANTE ? XII Simpósio de Geologia de Minas Gerais, SBG Núcleo Minas Gerais – novembro 2003, pp 52. Available here.

 

 

 

 

 

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