Iron Quadrangle Analysis

The headwaters of the Doce River rise in the southeast-east area (SE-E) of the Iron Quadrangle, located in south-central portion (C-S) of the state of Minas Gerais (Figure 1).
The Iron Quadrangle is historically known as a rich auri-ferriferous province and is a classic region of the world Precambrian geology (Dorr, 1959). Its designation results from the area’s planimetric features, with a surface area of around 7,000 km2, comprising the most important iron mines of Minas Gerais (Barbosa, 1968) and amongst the most important ones across Brazil.
The geology of the Iron Quadrangle comprises summarily an Achaean greenstone belt sequence, represented by the Rio das Velhas Supergroup, surrounded by Achaean granite-gneiss terrains which are overlain by a paleoproterozoic sedimentary succession, the Minas Supergroup (Dorr, 1969) – Figure 2.
The Rio das Velhas Supergroup consists of volcaniclastic, chemical and pelitic metasediments (classic greenstone belt
Costa (2007) points out that tailings from gold prospecting containing sulfide minerals (arsenopyrite, pyrite and pyrhotite) were discharged directly into one of tributaries of the Gualaxo do Norte River in the village of Antônio Pereira, municipality of Mariana, for over 200 years. Silva (2013), in turn, notes that gold exploitation from nowadays depleted Passagem Mine in Mariana was the most impactful mining activity in the Carmo Creek sub-basin: around 4 million tons of tailings containing arsenic and heavy metals were disposed directly into the river during the mine operating period (1874 – 1973) (Vial (In Shobbenhaus, 1988). The impacts of mercury used in gold amalgamation have also been discussed by a number of papers. This element was and still is used in prospecting activities in water courses, as noted by Rodrigues (2015), Windmoller et al. (2007), and Costa et al. (2003). – Figure