Itabira, Minas Gerais, Brazili

Regional Level Types
Itabira	Municipality
Minas Gerais	State
Brazil	Country

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Portions of the Itabira area are assigned to overlapping geological provinces, the Iron Quadrangle Province (known in Brazil as the Quadrilátero Ferrífero) and the Eastern Brazilian Pegmatite Province. The Iron Quadrangle Province is named for a more-or-less rectangular region containing rich deposits of iron ore in the form of banded iron formation (BIF). Brazil has become the world’s leading exporter of iron, largely due to these BIF deposits, and they are so important to the economy of the country that this kind of ore has become known throughout Brazil as “itabirite.” The BIF occurs in folded and thrust-faulted, marine metasedimentary rocks of Mesoproterozoic age. Geological features of these rocks formed during accretion of an island arc onto a portion of the ancient supercontinent of Rodinia roughly 2.0 billion years ago–an event typically referred to as the Transamazonian Orogeny (see Brito Neves et al., 2014).

Gold, platinum, and palladium deposits also formed in the Iron Quadrangle at that time. Those deposits occur in shear-zone veins and pods characterized by specular hematite, quartz, and kaolinite, forming a distinctive ore type referred to as “jacutinga” in Brazil. The Morro Velho Mine at Nova Lima in the Iron Quadrangle is the world’s oldest continuously operating gold mine, having opened in 1725. Upon reaching a depth of 1775 meters in 1915 it became the deepest mine in the world (since exceeded by diamond mines in South Africa). By 1960 it had produced 450 tons of gold. Platinoid ores in the area include five different essential platinum-bearing minerals, for which Itabira is type locality of one. Six essential palladium-bearing minerals have been reported from Itabira, which, rather remarkably, is the type locality for four of those. More recent hydrothermal activity associated with near-surface processes may have contributed to conditions that gave rise to this degree of mineralogic novelty, but by this time the gold and platinoids were already there.

The Eastern Brazilian Pegmatite Province (EBPP) is characterized by local pegmatitic intrusions, many of which have produced colored gemstones such as aquamarine, tourmaline, and topaz. The pegmatites are related to larger granitic intrusions that invaded what is now the eastern portion of Minas Gerais and adjacent parts of Rio de Janeiro, Espírito Santo, and Bahia states. These granites are associated with a second episode of tectonic accretion known as the Brasiliano Orogeny, of late Neoproterozoic and early Paleozoic age, roughly 660-500 million years ago. This was the most recent tectonic event that contributed to the geographic and tectonic outlines of the southern portion of the supercontinent Gondwana. The granites and associated pegmatites invaded country rock typical for the Iron Quadrangle province and other geologic provinces in eastern Brazil. Deposits of the EBPP are therefore spottily overprinted on older geological features, but because the pegmatites are important economically, and all are related to that one tectonic event, they have been recognized as belonging to a geological province in their own right.

Various portions of the EBPP have been referred to as gemological districts, and Itabira is in the Gemological District of Santa Maria de Itabira. In this area, beryllium-rich pegmatites emplaced during the Brasiliano Orogeny were leached by hot aqueous solutions, carrying Be3+ into the surrounding chromium-rich metasedimentary rocks (schists). Beryl colored green by a few tenths of a percent of Cr3+ formed the beryl variety emerald that crystallized in those rocks as temperatures declined (Gemma et al., 1996). That is considered to be a metamorphic rather than igneous process. Nevertheless, emeralds would not be present near Itabira if beryllium-rich pegmatites had not been intruded previously. Thus, this area is considered to be an outlier of the EBPP, superimposed over the larger Iron Quadrangle region. Because most pegmatites are rather small and localized, they have not fostered development of world-class open-pit and underground mines, as the iron and gold deposits have.

NK, May 2018

Commodity List

This is a list of exploitable or exploited mineral commodities recorded from this region.

Mineral List

Mineral list contains entries from the region specified including sub-localities

47 valid minerals. 5 (TL) - type locality of valid minerals.

Rock Types Recorded

Rock list contains entries from the region specified including sub-localities