ICMGP - Conference Presentation

Abstract Information :

This study presents a picture of Artisanal and Small Scale Gold Mining (ASGM) in Brazil and perspective numbers on emissions and releases of mercury, in 2016, when the country declared 25 t of gold from ASGM, representing 27% of the annual Brazilian legal gold production. When it comes to mercury losses to the environment in the country, it is also necessary to consider the production and processes of ASGM illegal mines. The methodology included spatial data of legal ASGM in the country, stakeholders identification and meetings, mercury metallurgic-balance performed in several ASGM areas, quantitative measurement of mercury in atmosphere and other quantitative and qualitative data. The average ratio of Hgused:Auproduced varied according to the ore. The secondary ore concentrate is the most frequent type of gold ore of ASGM in Brazil. The amalgam filtering technique is routine, where 50% of the initial Hg mass is recovered. Most part of legal ASGM areas visited have tailing dams, which prevent direct releases but it is a potential source of Hg re-emission. Mercury emissions depend on the presence of environmental control systems which was assumed to be close to 80% of gold production and should be well-used to attain good efficiency, which, in general terms, were assumed to be close to 70%. The percentage of their use decreases as illegal activities increase. Mercury levels in the atmosphere were measured throughout the amalgamation and thermal decomposition of the amalgam in the studied areas, as well as in some urban gold shops. Illegal ASGM production has been estimated varying from 10% to 8 times higher than the legal one. The proposed scenarios resulted in increasing mercury releases and emissions far more than an order of magnitude than that related to the legal gold mines and they can be used as a framework for future studies.