Capa > v. 30, n. 3 (2000) >	BORBA
ARSENIC IN WATER AND SEDIMENT IN THE IRON QUADRANGLE, STATE OF MINAS GERAIS, BRAZIL
RICARDO PEROBELLI BORBA, BERNARDINO RIBEIRO FIGUEIREDO, BARRY RAWLINS, JORG MATSCHULLAT
Since the end of 17th century, the Iron Quadrangle in the State of Minas Gerais has been known as one of the most famous gold producing regions in Brazil. Gold was initially produced from alluvial placers and oxidation zones and, finally from primary ores in modern times. Total gold production must have exceeded 13001 in all history. Only in the very famous Morro Velho mine around 600-t gold has been produced since 1834. The gold ore is rich in arsenic with the As/Au ratios ranging from 300 to 3000 among the several deposits deposits. The arsenic in rocks and ores (pyrite, pyrrhotite and arsenopyrite) undergo oxidation during the weathering processes and part of the arsenic is naturally liberated into the environment. Since the tailings produced in the past were discharged directly into drainage until 1980, the amount of arsenic that entered the drainage systems must have exceeded 3900001 in the whole region. In the Iron Quadrangle region, the highest arsenic concentrations in water and sediment occur near the mining areas where the river sediments were contaminated by tailing discharge since colonial times. In surface drainage water, the dissolved arsenic concentration ranges from <2 to > 160 mg/L, and from <20 to >2830 mg/kg in the stream sediments. Although the present mine operations do not contribute significantly to contamination of the rivers, there are a potential risk for arsenic hazard in some areas induced by, for instance, dispersion of old tailings by flooding, occupation of polluted soils and consumption of contaminated surface and underground water.
Arsenic; Water; Groundwater; Sediment; Tailings; Contamination; Gold mining; Arsenopyrite; Iron Quadrangle; Minas Gerais; Brazil.