The Archaean-Proterozoic transition and iron ore genesis: the Amazon perspective from the world-class Serra Sul iron ore deposit, Carajás, Brazil

• Applicant: Dr. Alexandre Cabral
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2011 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 181205523

Banded iron formations (BIFs) and black shales record marine environmental conditions that reflect global chemical and biological features of the ocean– atmosphere system. They host mineral deposits that, in the case of BIF, account for most of the world’s mine production of iron ore. Carajás is a world-class iron ore district in the Amazon region of Brazil, where recent exploration of the Serra Sul deposit has identified a measured resource of 4 billion tonnes at >64 wt% Fe for just one of the four orebodies hitherto recognised in the currently still pristine Serra Sul area. These results place Serra Sul as one of the world’s largest iron ore deposits. Exploration also revealed that black shales occur immediately below the BIF unit at Serra Sul. Geological inference suggests that these rocks formed at about 2.7 Ga. The coexistence of black shales and BIF allows reconstructing the evolution of the ocean–atmosphere system during the deposition of the Serra Sul rock sequence, which will shed new light on the vigorous debate involving the Archaean–Proterozoic transition and the rise in atmospheric oxygen, i.e. the Great Oxidation Event. Our Amazon perspective will integrate data from bulk-rock analysis of molybdenum, sulfur, rhenium–osmium, and samarium–neodymium isotopes, as well as microanalysis of iron and oxygen isotopes on a background of detailed petrography and elemental geochemistry. In addition, we aim at identifying the post-depositional processes which led from BIF to high-grade iron ore.

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Bernd Lehmann