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The "Garimpo" Problem in the Amazon Region Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on May 16, 2016 | http://pubs.acs.org Publication Date: March 31, 1995 | doi: 10.1021/bk-1995-0588.ch021
Alexandre Pessoa, Gildo SáAlbuquerque, and Maria Laura Barreto Centra de Tecnologia Mineral, Cidade Universitária, Rua 4, Quadra D, Ilha do Fundão, CEP 21941-590 Rio de Janeiro, RJ, Brazil
This paper deals with questions relating to a controversial subject: "garimpo" in the Amazon region. Besides the general considerations on the subject, specific approaches are made on the state-of-the-art of the "garimpo", its economic and social aspects, its past and present legal concepts as well as its impact on the environment.
The number of active small-scale miners, known as "garimpeiros" in the Amazon region is not precisely known. Figures show estimates which varyfrom400,000 to 1,000,000 people who work directly with "garimpo" and it has also been estimated that each "garimpeiro" is indirectly responsible for another four tofivepeople. Another interesting fact is the estimate of machinery and equipment involved in "garimpo" work (numbers date back to mid-1980's) 25,000 items of production equipment: dredges, ferries and concentration mills; 20 helicopters, 750 aircraft of different types and sizes, 10,000 small boats or engine-driven canoes and around 1,100 items of digging and excavation equipment. "Garimpo" practice for concentrating gold bearing material uses mercury as one of its main inputs. DatafromBrazilian studies indicates an average usage of 1.3 kg of mercury for each kg of gold produced. The estimated gold production in the "garimpos"from1983 to 1990 is 80 tons average, so that 100 tons of mercury are annually discharged into the environment due to "garimpo" activities. Studies confirm that "garimpo" activities, mainly in the northern and midwestern regions of Brazil, have been responsible for more than 100 tons mercury emitted per year into the environment, 55% reaching the atmosphere as vapor and the remainder into the rivers as metallic mercury (7). These numbers match the estimates of mercury consumption by the "garimpos" based on importation figures and its usage in other activities. According to this study, in 1991, 168 tons were used by the "garimpos" for a total of 337 tons of imported mercury (2).
0097-6156/95/0588-0281$12.00A) © 1995 American Chemical Society Seidl et al.; Chemistry of the Amazon ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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Depending on how mercury is disposed of, it can spread throughout vast regions or remain practically unchanged close to the areas where it was discharged (3). Mercury finds its way into the environment mainly during amalgamation procedures, disposal of its tailings and amalgam pyrolysis. Another source of emission occurs in the urban centers at the gold buying agents, where the bullion containing approximately 5% of its weight in mercury, is purified. Besides the chemical pollution, the "garimpos" represent a serious threat to the rivers, because of the great quantity of fine particulate material (clay size) produced, which prevents the plancton photosynthesis processes, as well as reduction of the oxygen content in the river waters.The silting up conditions are visible and pervasive not only in gold "garimpos", but also in the cassiterite "garimpos" (tin "garimpos") as well as those of other economically valuable heavy minerals. Mining and Concentration Methods Used in the Various "Garimpos" in the Amazon Region There is no doubt that gold predominates in "garimpo" activities in the Amazon region and, therefore, in this paper general aspects of gold explotation are emphasized in any discussion of the impacts of "garimpos" in the Amazon region. The types of gold "garimpo" are directly related to the types of gold deposits to be worked. The gold deposits are divided into two main types: primary and secondary. "Garimpos" which work with primary gold deposits are typical of the State of Mato Grosso, mainly in the border regions of the Mato Grosso Wetlands (Pantanal), such as Poconé, Barão de Melgaço, Cangas and Nossa Senhora do Livramento. "Garimpeiros" of the Tapajos region have revealed the discovery of primary gold deposits in several places. The aim of this type of "garimpo" is to recover gold contained in rocks and soils that show a gold content which varies between 0.6 to 20g/ton. In this case, large amounts of gold rich soils and soft rocks - usually containing quartz veins - are excavated. In the secondary gold deposits the work of extracting the gold-bearing material is done directly on the active river beds or on the steep banks of the "igarapés" (small waterways) and may be subdivided into: raft "garimpos" and shallowriver"garimpos". The alluvium of the activeriverbeds is the feed used by the rafts. In the shallowrivers,the steep banks are broken down with jets of water, and are excavated from soil level to an approximate depth of five to eight meters. According to the "garimpeiros", the greatest concentration of gold occurs in the gravel layer. After the ore is broken up and pulped, it is manually separated using a pitchfork, so that the pulp is drained into a pitfromwhich it is pumped into a gravimetric concentration chute (4). The procedures used by the "garimpeiros" in mining and concentration activities in gold "garimpos" as well as cassiterite "garimpos" (second in importance economically) and also those of other heavy minerals that occur in the Amazon region can be basically classified as follows:
Seidl et al.; Chemistry of the Amazon ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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Manual. Uses primitive equipment such as hoes, shovels, pick-axes, kerosene cans (to carry the material), etc. In deeper locations, diesel oil pumps are used do dry the excavation. The work is normally done by two people who share costs and profits. It is estimated that 15% of the "garimpeiros" work this way. Due to this primitive raining process, very few tailings are discharged into therivers.The gold is recovered in small concentration boxes with crossed rifBes. Dredges. This process usesfloatingdredges with 10 in. or 12 in. hydraulically controlled suction pumps. There are several types of such equipment and the losses due to excess water can reach 50 to 60% in the case of fine gold, dropping considerably in cassiterite mining. Amalgamation is carried out directly on the dredge in the concentration equipment, which receives the pulp. Besides the limited space on the dredge, and the lack of control over the pulp flow, the amalgamation is done in a very rudimentary way and very often poorly. Consequently, the gold losses are considerable, although, even worse, the mercury losses are pulverized by intense shaking of the pulp and the ore. Rafts. This system is a similar to the dredge, altough the hydraulic control is substituted by an underwater operation, where a diver manually directs the suction process. This is extremely dangerous, and many people have lost their lives, hence its gradual disuse. The engine-driven pumps have a 5 in. or 6 in. diameter and the gold concentration also uses mercury, causing well-known environmental problems. Hydraulic Disintegration. Breaking down steep banks is done using a high pressure water jet pump. In fact two jet nozzles are used - one cutting and washing material down the steep bank and the other adjusting the pulp dilution and directing it to a suction pump which, in turn, directs it to the concentration unit. This unit can be assembled on a raft or on the ground. The water and pulp pumps are powered by diesel oil engines. In the case of cassiterite, the concentration units are three stage jigs of different types and sizes. In most cases, this equipment belongs to legally constituted mining companies which have given up work and rent it out to the "garimpeiros". This is certainly the most widely used method in the Amazon region. Concentration mills. This method is employed by small mining companies which recover gold from veins from underground rnining. The rnining uses caterpillar tractors and shovels, etc. when in an open pit, while the ore processing uses hammer mills, jigs, centrifuges, etc. In some cases, cyanide heap leaching is used. The intense mechanization in the alluvium mining systems used in the Amazon region, does not belong to the "garimpo" and/or to small companies, but is restricted to larger operations carried out by medium-size or big companies.
Seidl et al.; Chemistry of the Amazon ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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The rudimentary "garimpo" uses simple equipment such as the "lontona" or the "cobra fiimando" (cradle or rocker) for gold recovery. This equipment uses mercury and its loss to the environment has a great impact on nature.
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Environmental Impacts "Garimpo" activity causes strong physical and chemical environmental impacts. The physical impacts are more readily apparent (the most common are deforestation, silting-up, degradation of river banks, etc.), while the chemical impacts are often not perceived immediately, endangering the ecosystem and human beings as seriously or even more so. The mining and concentration procedures employed in the cassiterite "garimpos" and in those of other heavy metal minerals, cause stronger physical impacts. In the case of gold, along with these physical impacts there is the pollution by mercury, which is widely used for recovering fine gold. Amalgamation is generally employed on alluvium gravimetric concentrates or on primary ores withfreegold. Gold in contact with metallic mercury forms amalgams, the main forms being: AuHg2, Au2Hg and Au3Hg. The amalgam resulting from a gold-mercury contact is not uniform. In practice, the amalgam resulting from miningmetallurgical processes containsfrom0 to 20% gold. As seen above, regardless of the type of "garimpo", the mercury emited into the environment occurs mainly when amalgamation tailings are discarded and when the amalgam is burned. On the other hand, during amalgamation the excess mercury isfilteredand reused, although it acquires characteristics that are not suitable for efficient recovery of precious metals. Therefore it is usually discarded when it starts to "harden", and becomes another source of pollution. The main reason for mercury emission into the environment is that retorts are not used when the amalgam is burned. The "garimpeiros" burn the amalgam in open frying pans using butane/propane gas torches, at a temperature of 400 °C to 450 °C, resulting in more than 70% loss of the mercury. Hence, approximately 2025% of the mercury emitted into the environment comesfromthe final deposits of amalgam tailings, and 75-80%fromthe open air burning process (4). The emission factor (ratio of mercury used per quantity of gold produced) is approximately 1:1.35(7). Besides the losses due to the processes used by the "garimpeiros", whether in the final deposit of amalgamation tailings ("resumo"), or in the volatilization of mercury when burning the amalgam, there is also a third source of loss: gold buying agents in the towns near the "garimpo" areas. During the burning processes at the site, the "bullion" produced by the "garimpeiros" still contains some impurities which are removed by the gold buying agents. The gold produced by the first burn can still have up to 5% mercury, the impurities are removed at a high temperature using an acetylene burner and purifiers (scorifying agents). As hoods are not available to retain vapor, these gold buying agents are an important source of mercury loss (5,6).
Seidl et al.; Chemistry of the Amazon ACS Symposium Series; American Chemical Society: Washington, DC, 1995.
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Some areas are already affected by the mercury discharged into the rivers. Table I shows mercury concentration in fish of selected rivers in the Brazilian Amazon. Table L Mercury Concentration in Fish from Rivers of the Brazilian Amazon Region Area Ref. Hg (ug/g, wet weight) 7 0.07 -0.17 Madeirariverbasin (Rondônia) uncontaminated 0.21 -2.70 7 Madeirariverbasin (Rondônia) contaminated 0.32 -2.89 8 Madeira river basin (Rondônia) contaminated 0.03 -0.28 4 Teles Pires river 9 0.01 -0.68 Tapajosriverbasin 1.3-•24.8 10 Contaminatedrivers(world)
Table Π, gives an idea of the mercury concentraton in different gold "garimpo" areas, also outside the Amazon region, although the greatest concentration of gold "garimpo" is effectively in that region.
Table IL Mercury Concentration in Water and Sediments in Different Areas Contaminated by Gold "Garimpo" in Uncontaminated Tropical Areas and Global Averages Hg (sediments) Hg (water) Ref Area (ppm/dry weight) (ppb) 0.04 - 0.46 11 0.05 - 0.28 Madeirariver(Rondônia) Mutum-Paranãriver(Rondônia) 0.21-19.8 0.02 - 8.6 7 < 0.04 - 0.48 12 0.3 - 0.9 Paraiba do Sulriver(Rio de Janeiro) Jamaririver(Rondônia) uncontaminated
