GEOLOGIA, MINERALOGIA E DIAMANTES DA INTRUSÃO SALVADOR-1 (SERRA DO ESPINHAÇO, BAHIA)

Geology, mineralogy and diamonds from the Salvador-1 Intrusion (Serra do Espinhaço, Bahia)

Abstract

ABSTRACT

In the Espinhaço Range (Minas Gerais and Bahia states), diamonds are mainly associated to proterozoic metaconglomerates placed in Tombador (BA), Grão Mogol and Sopa-Brumadinho (MG) formations, Espinhaço Supergroup. Although the occurrence of primary diamondiferous bodies throughout this region has always been controversial, a diamond-like intrusion into the Chapada Diamantina (means Diamondiferous Tableland) of Bahia, known as "Salvador-1", Barra do Mendes, has been mining on the surface by garimpeiros since the mid-nineties. The intrusion was studied in detail, being composed of a poorly foliated talc-schist and highly altered on the surface. Garnets, diopside and Mg-ilmenite, typical indicator minerals of kimberlites, are absent or very rare in the body, possibly due to the alteration processes and/or low-grade metamorphism. However, Cr- and Mg-rich chromites (up to ~65% Cr₂O₃) are abundant, comparable to chromite inclusions in diamond and characteristic of fertile intrusions. Diamonds present are corroded and of low gemological quality; the persistence of mining activity on the body is probably due to the mixing of sediments that added diamonds to the deposit from another secondary source, probably from the Tombador Conglomerate, outcropping in the vicinity of the body. The rock that constitutes the intrusion can be considered a metakimberlite.

Keywords: Diamond; Diamantina Tableland; Bahia State; Salvador-1 Intrusion.