Chemical evolution and hydrothermal processes during the genesis of itabrite-hosted, high grade iron ore in the Quadrilatero Ferrifero, Brazil

[Truncated abstract] Banded Iron Formation (BIF)-hosted iron ore deposits represent the world’s largest iron supply and are of immense economic and scientific interest. Their mineralogy, structural control and genesis have been extensively studied and recent genetic models propose a polyphase, hypogene-supergene upgrade of BIF (~35 % Fe) to high-grade (>60 wt-% Fe) iron ore. The Quadrilátero Ferrífero (QF) at the southwestern border of the São Francisco craton in Minas Gerais, Brazil is one of the largest world-class iron ore districts comprising numerous high-grade iron ore bodies. Host rocks are quartz-, dolomite- and amphibolite-itabirites of the Neoarchean/Paleoproterozoic Cauê Formation. Two orogenies, the Transamazonian (2.1 – 1.9 Ga) and the Brasiliano (0.8 – 0.6 Ga), affected the QF resulting in a western low-strain (greenschist-facies metamorphic rocks) and eastern high-strain (amphibolite-facies metamorphic rocks) domains. In the low-strain domain, the iron is mainly massive, banded and/or brecciated, whereas schistose ore is dominant within the high-strain domain.