Cobalto em depósitos residuais e ocorrências de manganês derivadas da alteração de gonditos da região sudeste brasileira
Cobalt in deposits and ocurrences of manganese derived from alteration of gondites in the Southeastern Region of Brazil
Abstract
The SE region of Brazil comprises a series of parallel manganese belts, trending generally NE-SW, associated with Paleoproterozoic volcano-sedimentary sequences. The main belts in this region are Itapira-Ouro Fino-Jacutinga-Congonhal-Careaçu; Ibituruna-Nazareno-São João del Rei; Conselheiro Lafaiete; Dom Silvério; Palmas-Natividade-Guaçui-Iuna; and Volta Grande-Pirapetinga-Santo Antônio de Pádua-Itaperuna. Cobalt has been detected in all of these belts, both in chemical analyses of manganese ore and protoore and in mineral inclusions (gersdophyte, pentlandite, and syegenite) contained in spessartite crystals or as individual cobaltite grains. Cobalt tends to be associated with manganese minerals from the phyllomanganate group, such as vernardite, lithophorite, and asbolane. Among the manganese minerals present in the ores of this region, lithophorite [(Al, Li)MnO2(OH)2] is described in mines in the areas of Ibituruna-Nazareno, Conselheiro Lafaiete (Morro da Mina), Itapira (Morro das Palmeiras and Córrego do Cocho), and Guaçui (Santa Marta Mine). The maximum cobalt values determined in samples from these areas are: 272ppm Co in Ibituruna-Nazareno; 546ppm Co in Congonhal; 1,000ppm Co in Guaçui; 272ppm Co in Conservatória; 399ppm Co in Natividade; and 858 ppm Co in Itaperuna. Regarding exploratory possibilities, in terms of cobalt content and measured ore reserves, more refined campaigns are indicated in the areas of Guaçui (1,000ppm Co x 1.7Mt); Congonhal, MG (average of 400ppm Co x 2.1Mt), to which can also be added the 1.2Mt from the Morro das Palmeiras mine and the 2.1 Mt from the Córrego do Cocho mine, both in Itapira, SP. Due to the usual presence of lithophorite in the composition of manganese ore in the Itapira area, the prospect for lithium in a Li-Co association also opens up.
