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Avaliação geoquímica da contaminação por mercúrio dos sedimentos de correntes e solos do distrito mineiro de Zaruma-Portovelo, república do Equador
(Universidade Federal do Pará, 1996-05-31) MALDONADO RAMIREZ, Roque Vicente; RAMOS, José Francisco da Fonseca; http://lattes.cnpq.br/8189651755374537
Auriferous occurrences are known in the area of Zaruma-Portovelo, Ecuador, since the pre-Columbian period, but it was only from the end of the 70's that a very intense mining activity started to be developed. Miners in the sector carry out the activities of exploration, exploitation and processing of polymetallic ore using rudimentary techniques, which causes contamination of rivers, soil and atmosphere by mercury and other heavy metals, in addition to cyanide. They still deforest the area, as they use wood in the security structures of the mineral galleries. The deposit in the mining district of Zaruma-Portovelo is of hydrothermal, polymetallic origin, occurring in a complex of andesitic volcanic rocks of the Celíca Formation. The ore is composed of the sulphides pyrite, chalcopyrite, galena, sphalerite and bornite, among others, in addition to the gangue minerals quartz and calcite. The metals Cd, Zn, Pb and Cu are released from these minerals. Mercury is of anthropogenic origin, as it is used in the extractive metallurgy of gold, as is cyanide, which is used in a second phase of the gold recovery process. The present work had as objective the identification and geochemical evaluation and the description of the activities of the sources of pollutants, especially mercury, through the collection and analysis of samples of bottom sediments, soils and mining tailings, in addition to making a brief description of the activities from the mine. A sampling campaign was carried out at the end of the dry season, having collected 26 samples of bottom sediments, 23 of soil and 4 of tailings. At 5 points soil samples were taken in profiles with intervals of 2 cm to a depth of 14 cm. A study of the distribution of metals in the different granulometric fractions of the sediments was also carried out. Samples were collected in triplicate at three points to determine the variability of the results. The concentrations of Hg(total) in soils indicate that 83% of the samples are above the background (103ppb) with minimum and maximum values of 109 and 9,546 ppb and an average of 662 ppb, with the highest concentrations occurring in samples close to the emission sources, which are the mills (processing plants). In all profiles, it was found that the highest levels occur in the upper part, gradually decreasing with depth. In the bottom sediments, in addition to Hg(total), the elements Pb, Zn, Cd and Cu were analyzed in the exchangeable fraction, observing anomalous values for all these anomalous values concentrated mainly in the drainages of the Calera and Amarillo rivers, after the junction with the Calera River, which has most of the area's processing plants on its banks. High levels of Hg, Zn, Pb, Cd and Cu were observed in the mining tailings samples, confirming that artisanal beneficiation processes, in addition to generating pollution, cause economic losses due to the low recovery of metals. Tests to verify the amounts of mercury used by miners for amalgamation show that 95 to 97% of the mercury is released into the atmosphere in the amalgam burning stage. The rest is released in liquid form in the soils and drainages of the area. This shows the importance of developing an education policy for prospectors, offering new alternatives and technologies to avoid the burning of amalgam in the open air, which would greatly contribute to the reduction of mercury contamination.