The Iron Quadrangle has been the scenery of the most important gold production in Brazil. It is estimated that during the three centuries of gold mining in the Iron Quadrangle, at least 390,000 t of arsenic was discharged into the drainage system. This study presents geochemical data for the three river basins in the region, with focus on surface water and stream sediment monitoring. Samples of primary and oxidized sulfide ores as well as of tailings and groundwater from the major gold mines were also studied. The highest As concentrations in water and stream sediments occur in the vicinity of mining areas. In surface water, up to 300 lg As/l were found whereas the As contents in stream sediments were in the range of 20 to 4,000 mg/kg. The As 3+ /As 5+ concentration ratios obtained for some water samples range from 1.10 )1 to 4.10 )2 . The As mobility associated with ore-deposit weathering could be traced in some closed gold mines by observation of insitu pyrite and arsenopyrite oxida-tion, precipitation of scorodite and gippsite, As adsorption onto goethite, and final liberation of As into underground and surface waters. This process is likely to produce large volumes of mine effluents containing total As and trivalent As up to 1,960 and 60 lg/l, respectively. River sediments and tailings pile samples were submitted to a leaching procedure showing maximal arsenic release from 1 to 4% of the original total As in the samples. There are potential risks for As hazards in some areas induced by, for instance, the dispersion of old tailings by flooding, occupation of poisoned soils for settlements, and occasional consumption of contaminated surface and groundwater.
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.
No Quadrilátero Ferrífero (QF), o abastecimento público de água é feito principalmente com a captação de águas das bacias hidrográficas. Entretanto, em alguns locais, há a utilização de água subterrânea, proveniente de nascentes ou mesmo de minas abandonadas, para o abastecimento humano. As principais fontes naturais de As no QF estão relacionadas às rochas que hospedam depósitos auríferos sulfetados. As fontes antrópicas de As são as pilhas de rejeito, solos e sedimentos contaminados. Em águas coletadas em algumas minas auríferas subterrâneas e nascentes das regiões de Ouro Preto e Mariana, foram encontradas concentrações de As total variando de 2 a 2980µg/L e de As3+ de 1 até 86 µg/L. Com base nos estudos geológicos e hidrogeoquímicos da ocorrência de As, nas rochas e nas águas subterrâneas, observou-se que as maiores concentrações de As são encontradas nos aqüíferos hospedados em rochas que possuem sulfetos e carbonatos, embora as concentrações dos aqüíferos que possuem somente sulfetos também foram elevadas. O monitoramento de As na água subterrânea deve ser periódico, independentemente de sua ausência num primeiro momento, nos poços e em outras fontes de captações de águas subterrâneas atualmente em utilização no abastecimento público ou privado.
In the Iron Quadrangle region the public supply of water is done mainly by the impound of water of watersheds. However, in some places, the population use spring water or ground water from closed mines for human consumption. The main natural sources of As in the Iron Quadrangle are related to the rocks that contain lode gold deposits. The antropic sources of As are contaminated refuse piles, soil, and sediment. It was found total As concentration varying from 2 to 2,980 µg/L and As3+ from 1 to 86 µg/L in water samples collected in underground gold mines, artesian wells, and springs in Ouro Preto and Mariana counties. Based on geological and hydrogeochemical studies of the occurrence of As in rocks and groundwater, it was found that the highest As concentrations occurred in aquifers hosted in carbonate sulphide rich rocks. The As monitoring in underground water should be done periodically, independent of its absence in a first instance, in wells and other groundwater caption sources that are used nowadays for public or private suppliers
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.