Genesis of the Precambrian copper-rich Caraiba hypersthenite-norite complex, Brazil

Abstract

Abstract. Caraiba, the largest Brazilian copper deposit under exploitation, consists mostly of disseminated and remobilised bornite and chalcopyrite hosted in early Proterozoic norite and hypersthenite. The mafic igneous complex comprises multiple intrusions of dykes, veins and breccias of norites and hypersthenites, with minor proportions of amphibolised gabbronorite and peridotite xenoliths transported by the magma from deeper levels in the lithosphere. The country rocks are high-grade gneisses, granulites and metasediments. Compositions of plagioclase (An6o-40) and orthopyroxene (EnTo-6o) fall in a narrow range similar to the Koperberg Suite from the Okiep copper district, South Africa, and to that in many massif-type anorthosites. Whole-rock major and trace element geochemistry indicate a parental magma enriched in Fe, LREE, P, K, and Cu. Negative Nb anomalies on multi-element plots and fractionated REE patterns, along with sulphide sulphur isotopes in the range 634S = -1.495 to + 0.643%o, suggest a primary mantle lithosphere source, although a lower crustal source for the gabbronorite and peridotite xenoliths cannot be excluded. Geochronological and field evidence indicate that both norite and hypersthenite are likely to have been emplaced during a major sinistral transcurrent (partly transpressional) shearing event associated with the waning stage of evolution of the early Proterozoic Salvador-Curag~ orogen.

Mesoarchaean to Palaeoproterozoic growth of the northern segment of the Itabuna–Salvador–Curaçá orogen, São Francisco craton, Brazil

“…The São Francisco craton with location of the Itabuna-Salvador-Curaçá orogen, showing its northern (1) and southern (2) segments. Adapted from Oliveira & Tarney (1995). microcontinent, which occurred in the following sequence: 2.6-2.4 Ga, accretion of a continental arc; 2.4-2.2 Ga, intrusion of shoshonitic to alkaline monzonites and monzodiorites; 2.07 -2.08 Ga, continent-continent collision and granulite-facies metamorphism.…”

Fe–Ti–V–P ore deposits associated with Proterozoic massif-type anorthosites and related rocks

“…The Nain Plutonic Suite of Labrador, Canada (Emslie, 1978;Emslie et al, 1994;Ryan, 2000;Myers et al, 2008) has no Fe-Ti deposits but hosts the giant Ni-Cu-Co deposit of the Voisey's Bay intrusion (Li et al, 2000). Two important cupriferous deposits related to anorthosites are found in the Koperberg Suite in South Africa (Conradie and Schoch, 1986;Gibson et al, 1996;Clifford et al, 2004;Duchesne et al, 2007) and the Caraiba complex in Brazil (Oliveira and Tarney, 1995;Barnes, 1996, 1999). Magnetite-hypersthene ores have been described in these localities but Ti-resources are absent.…”

Implication of the Caraíba Deposit's Structural Controls on the Emplacement of the Cu-Bearing Hypersthenites of the Curaçá Valley, Bahia-Brazil

“…To study the Mine in the detail of a PhD thesis, Oliveira (1990) logged three bore holes and sampled two of them for mineral and chemical analyses, as well as four outcrops in the open pit of Caraíba. He interpreted the whole orebody as made up of multiple veins or dyke-like intrusions (and breccias) of hypersthenites, norites, and anorthosites, with peridotite and gabbro xenoliths (see also Oliveira & Tarney 1993). The sub-vertical dyke-swarm would have been emplaced around 1.89 Ga (whole rock Sm-Nd isochron of hypersthenite) after the main period of crustal growth.…”