Paleoproterozoic Banded Iron Formation of the Quadrilátero Ferrífero

BRAZIL

Aerial view of Pico do Itabirito formed by a compacted hematite monolith surrounded by an open pit iron ore mine in BIF.

Geological Period

Paleoproterozoic

Main geological interest

Stratigraphy and sedimentology
Geomorphology and active geological processes

Location

State of Minas Gerais, Brazil.
20°14’25.0″S, 43°52’01.0″W

Aerial view of Pico do Itabirito formed by a compacted hematite monolith surrounded by an open pit iron ore mine in BIF.

One of the most important records of Paleoproterozoic BIF on Earth and place of ferruginous caves.

The Banded Iron Formation (BIF) in the Quadrilatero Ferrifero is a Lake Superior-type iron deposit formed at the beginning of the Great Oxygenation Event. During the Cenozoic the wetter climate favored weathering that enriched iron minerals, which produced economically significant iron ore bodies. Duricrust is formed by iron oxide and hydroxide (ferricrete) close to the top of weathering profiles in the BIF. These capstone deposits, named regionally as canga, are resistant to erosion and are host to small caves that are the first to have been described in detail in ferruginous rocks (Auler et al., 2014; Simmons, 1963).

Outcrop of folded metamorphic BIF in Serra da Piedade Protected Area.

The most conspicuous Banded Iron Formation in Quadrilátero Ferrifero, together with marbles, dolomites and hematitic and dolomitic phyllites, constitute the Cauê Formation of the Supergroup Minas. These rocks are Paleoproterozoic in age, up to 350 m thick, 2.42-2.58 GA, and deposited in a shallow marine ocean (Spier et al., 2003). They are capped by dolomitic BIF and dolomites of the Gandarela Formation, which exhibit biogenetic structures such as stromatolities and algal mats. These rocks have been deformed in two Proterozoic orogenies.

The Cenozoic climate favored weathering, which leached silicious and carbonate minerals of the the BIF and enriched iron minerals. This porcess has produced bodies of iron ore thaty have up to 75% FeO. These deposits are of global significance. Iron mines in the region produced more than 3.0 billion tons of iron in the last 20 years. The weathering profile is the oldest and most continuous known (Spier et al., 2006). The leasching at the tip of the BIF produced duricrust, which is formed by iron oxide and hydroxide (ferricrete). The Duricrust prevents erosion and is regionally called canga.

The BIF oucrops were landmarks for European and African populations in the region since the 18th century, and decribed by scientists in the 19th century. These deposits have been the subject of geochemical and tectonic investigations, as well as studies on the genesis of duricrusts and related cave formation.

Reconstitution of Pico do Itabirito, drawn on current photography. Designed based on 19th century paintings and on Rosiere et al. (2009).

Auler, A. et al. (2014) ‘Hypogene Cave Patterns in Iron Ore Caves: Convergence of Forms or Processes’, in Hypogene Cave Morphologies. Alexander Klimchouk; Ira D. Sasowsky; John Mylroie; Scott A. Engel; Annette Summers Engel. Lewisburg: Karst Waters Institute, pp. 15–19.

Rosière, C. et al. (2005) ‘Pico de Itabira, MG Marco estrutural, histórico e geográfico do Quadrilátero Ferrífero’, in Sítios Geológicos e Paleontológicos do Brasil. Winge, M. et al. Brasília: CPRM, pp. 193–202.

Simmons, G.C. (1963) ‘Canga caves in the Quadrilátero Ferrífero, Minas Gerais, Brazil’, The National Speleological Society Bulletin, 25, pp. 66–92.

Spier, C.A., de Oliveira, S.M.B. and Rosière, C.A. (2003) ‘Geology and geochemistry of the Águas Claras and Pico Iron Mines, Quadrilátero Ferrífero, Minas Gerais, Brazil’, Mineralium Deposita, 38(6), pp. 751–774. Available at: https://doi.org/10.1007/s00126-003-0371-2.

Spier, C.A., Vasconcelos, P.M. and Oliviera, S.M.B. (2006) ‘40Ar/39Ar geochronological constraints on the evolution of lateritic iron deposits in the Quadrilátero Ferrífero, Minas Gerais, Brazil’, Chemical Geology, 234(1), pp. 79–104. Available at: https://doi.org/10.1016/j.chemgeo.2006.04.006.

Paulo de Tarso Amorim Castro
Professor at Universidade Federal de Ouro Preto

Úrsula Ruchkys de Azevedo
Professor at Universidade Federal de Minas Gerais

Paleoproterozoic Banded Iron Formation of the Quadrilátero Ferrífero

BRAZIL

Geological Period

Main geological interest

Location

One of the most important records of Paleoproterozoic BIF on Earth and place of ferruginous caves.

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