Environmental viewpoint on small-scale copper, gold and silver mining in Chile

Environmental viewpoint on small-scale copper, gold and silver mining in Chile

Journal of Cleaner Production 11 (2003) 207–213 www.cleanerproduction.net Environmental viewpoint on small-scale copper, gold and silver mining in Ch...

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Journal of Cleaner Production 11 (2003) 207–213 www.cleanerproduction.net

Environmental viewpoint on small-scale copper, gold and silver mining in Chile Sergio H. Castro ∗, Mario Sa´nchez Departamento de Ingenierı´a Metalu´rgica, Universidad de Concepcion, Edmundo Larenas 270, Concepcion, Chile Received 21 December 2001; received in revised form 1 March 2002; accepted 4 March 2002

Abstract This paper analyses the importance and environmental impacts of metallic small-scale mining in Chile. This sector is characterized by the exploitation of primarily artisanal copper (Cu), gold (Au), and silver (Ag) deposits, which are dispersed throughout (Chilean) Regions I through VI, with heaviest concentrations in Regions III and IV. In 2000, Chilean small-scale mines employed some 1700 workers (5.1% of total mining workers), and plants with a production capacity of less than 50 tpd accounted for 0.97% (44,603 t) of Cu; 6.5% (3,484) of Au; and 1.1% (13,665 kg) of Ag output in the country. High-grade ore extraction, flotation, gravity concentration, acid leaching–cementation, and mercury amalgamation, are the main metallurgical technologies employed. Following an overview of Chilean small-scale mining, the paper examines the environmental impacts of its production processes, and discusses the legal support and regulatory framework in place for operations.  2002 Elsevier Science Ltd. All rights reserved. Keywords: Small-scale mining (SSM); Environment; Copper, gold and silver production; Mining pollution

1. Introduction Metallic small-scale mining (SSM) in Chile is devoted to mainly copper, gold and silver. Most SSM producers are concentrated within the Northern zone, which encompasses the country’s Regions I to VI (Fig. 1). Most mining activity occurs in the Atacama Desert and away from large cities and sensitive agricultural zones. The definition of SSM varies considerably from one country to another, and can even change over time. In Chile, mining operations with an extraction capacity of less than 200 tons of ores per day were originally classified as “small-scale and artisanal”. Recently, however, the SERNAGEOMIN (National Service of Geology and Mining) has begun to use the number of workers contracted per year as a basis for classification; mines having fewer than 80 workers contracted annually are now considered “small-scale”. Such operations are generally located in the remotest rural areas of Chile, are highly unsafe, feature rudimentary production and processing



Corresponding author. E-mail address: [email protected] (S.H. Castro).

techniques, and provide minimal incomes to employees (See Table 1 for a representative overview of Chilean small-scale mining operations). Before proceeding with this discussion, it is important to first explain that the most important mineral mined in Chile is copper. In fact, the country is a world leader in the production of copper, and resident large-scale mining operations now feature a wide range of modern technology. Although its workforce of 33,650 is considered low, from an economic point of view, of the US$8 billion in mineral products exported in the year 2000— some 48% of national exports—the copper industry accounted for US$ 7.25 billion, approximately 90% of the country’s mining exports [1]

2. An overview of small- and medium-scale mining in Chile 2.1. Support services for small-scale mining Technical support to Chilean small- and medium-scale mining is mainly provided by ENAMI (Empresa Nacional de Minerı´a) and SERNAGEOMIN (Servicio

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Fig. 1.

Locations of small-scale mines in Chile.

Table 1 Number of small-scale mines and processing plants in Chile [2] Region Locations

Plants

Mining operations

Total

I II III

3 11 99

27 191 641

30 202 740

139 20 1 8 281

588 95 55 29 1,626

727 115 56 37 1,907

IV V VI RM Total

Taltal Vallenar Diego de Almagro Copiapo´ Chan˜ aral OvalleAndacollo Quilpue´ Rancagua

Note: RM denotes “metropolitan region”.

Nacional de Geologı´a y Minas). Generally, the objectives of these public agencies are to provide technical assistance, credit and subsidies, purchase minerals and concentrates from miners, introduce environmental management tools at operations, and reduce environmental problems in the sector. ENAMI’s specific goal is to promote the development of small- and medium-scale mining by providing the necessary services to facilitate their access to the refined metals market under competitive

conditions. It uses three main instruments. The first, mining development, involves mining-venture financing, technical assistance for the preparation and evaluation of projects, the allocation of credit resources for the implementation of feasible undertakings, and access to the market by means of authorized ore purchases. The second is ore processing, which involves the treatment of copper sulfide and oxide ores into smelting products, concentrates and precipitates in ENAMI’s or third-party plants. The third, smelter and refinery services, helps to ensure that the products derived from the SSM sector are processed using the same technology as those employed by large-scale producers in Chile. Although ENAMI works together with the stateowned Copper Corporation (CODELCO), it does not actually own mines and is a non-profit organization. ENAMI purchases minerals and concentrates from small and mid-sized copper producers from Regions III, IV and V, and supports those companies’ mining activities during periods of low prices [1]. Collected copper ores are processed in the concentrator plants of Taltal, Salado, Manuel Antonio Matta, and Vallenar; concentrates are smelted in the Herna´ n Videla Lira (Paipote) and Ventanas smelting plants. Ventanas also has an electrolyte refinery and a precious metal plant (gold and silver). In 2000, the electro-refining plant produced 319,000 tons of electrolytic copper cathodes—some 6.93% of the national production. SERNAGEOMIN is a public agency that was created in 1980 to assist the government (Mining Ministry) with specialized geology and mining subjects, mainly in the small- and mid-sized mining sector. Regional offices from Regions I to V, and VIII are involved. Geologically, the Agency undertakes work in the area of mining exploration, environmental geology and geological risks. The mining topics cover mining property, operational risks control, environmental management, and resources protection. In 1992, the Department of Environmental Management sought to control work safety for mining, plants, tailing dams and residue disposal systems. The “Decreto Supremo” 72/Mining Ministry and article No. 71 of the “Co´ digo Sanitario” empowers SERNAGEOMIN with the authority to control the disposal of residuals, including, tailings, leaching residues, and lowgrade ores. In addition, it offers consultation services to CONAMA on environmental impact evaluation; reports to CONAMA any environmental damage or pollution detected; and supervises all tailings dams. In short, SSM activities in Chile are regulated by the government agency SERNAGEOMIN in the areas of mining property, safety and geological support, and by CONAMA, which assesses environmental impacts and problems associated with residue disposal, pollution and effluent treatment (see Fig. 2). These public agencies are both devoted to decreasing health risks in the SSM sector by encouraging the introduction of more environmen-

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Fig. 2.

209

Schematic representation of the general regulatory framework for small-scale mining in Chile.

Table 2 Copper, silver and gold production in Chile, 1996–2000 [3] Metallic production

1996

1997

1998

1999

2000

Copper, (metric ton) Silver, (kg) Gold, (kg)

3,115,800 1,147,002 53,174

3,392,000 1,091,311 49,459

3,686,900 1,340,199 44,980

4,391,200 1,380,711 48,069

4,602,000 1,242,194 54,143

tally sound processes and environmental management tools. Moreover, both are working to promote sustainable development in the sector by improving the living conditions of workers and their families, and protecting surrounding communities. 2.2. Metal production statistics Table 2 shows copper, silver and gold production in Chile from 1996–2000. Chilean production in 2000 was around 4.6 million metric tons of copper, 1.2 million kg of silver, and 54,000 kg of gold. During this period, Chilean copper production experienced a significant increase (47.7%), while gold and silver production fluctuated with minimal increases overall (1.8% and 8.3%, respectively). Due to the importance of large-scale mining, contributions from SSM in terms of total mineral production are relatively low. In 2000, large-scale mining was responsible for some 93.7% of copper; 81.5% of silver; and 50.6% of gold production (Table 3). In 2000, small-scale mines accounted for 0.97 % of

copper production, 1.1% of silver production and 6.5% of gold production. However, quantitatively, output from the sector was significant: 3,484 kg of Au, 13,665 kg of Ag and 45,000 metric tons of Cu. It is interesting to note that copper, gold and silver can also be by-products in different mining sectors. Table 4 presents gold statistics for the past 11 years, showing the different types of products produced from the Chilean small-scale gold mining sector. However, this information does not include the gold commercialized through non-official routes, which is a common practice amongst artisanal miners. This especially applies to gold obtained via mercury amalgamation. In the 1990s, the most significant producers of gold in Chile were large-scale miners and accompanying plants such as El Indio, Tambo, Choquelimpie, El Hueso, Mantos de Oro, El Bronce de Petorca and Fachinal. Unfortunately, some of these have closed because local reserves have been exhausted. It has been estimated that 1700 Chileans or 5.1% of the country’s mining workforce are currently involved in SSM, and, as Table

Table 3 Production of Cu, Mo, Au and Ag in Chile by mining sectors, year 2000 data [4] Scale mining

Copper, metric tons

Molybdenum, metric tons

Gold, Kg

Silver, Kg

Large-scale Medium-scale Small-scale Total

4,326,188 (93.7%) 247,094 (5.35%) 44,603 (0.97%) 4,617,885

33,639

27,297.6 (50.6%) 23,201.3 (43.0%) 3,483.8 (6.5%) 53,982.7

1,008,896.1 (81.5%) 216,054.5 (17.4%) 13,665.0 (1.1%) 1,238,615.6

33,639

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Table 4 Gold production in the Chilean small scale mining sector, 1990–2000 [4] Year

Dore metal Precipitates

Concentrates

Gold bars Smelting ores

Concentration ores Cyanidation

Slucing

Total

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000

– – – – – – – 1,174.0 2,802.9 1,953.5 1,897.4

– – – – – – – 893.7 773.2 826.9 517.0

1,119.0 1,092.7 629.9 313.8 252.7 78.7 369.9 25.9 20.2 48.5 67.9

392.0 471.0 564.8 503.6 467.7 350.0 453.6 377.6 210.1 168.4 227.5

21.2 40.3 26.1 12.8 – – – – – – –

4,754.3 2,323.7 1,830.2 1,824.4 3,443.5 3,429.5 3,817.2 5,481.5 4,947.2 3,673.6 2,965.9

3,064.6 526.3 440.1 846.0 2,604.9 2,906.7 2,915.7 2,927.3 1,081.1 633.6 233.5

132.1 169.1 156.1 148.2 118.2 94.1 78.0 83.0 59.7 42.7 22.6

25.4 24.3 13.2 – – – – – – – –

5 indicates, earning potential in the sector is significantly lower than that of medium- and large-scale mining. Sa´ nchez and Enrı´quez [5,6] report that in 1994, the sector was comprised of a total of 1,626 small mines and 281 small plants, with a combined extraction capacity estimated to be 5,743 tpd.

3 and 4). Cyanidation is a practice currently not common in Chile’s SSM sector.

2.3. Small scale mining technology

3.1. Environmental impact of small-scale mining in Chile

A wide variety of technical processes can be found throughout the Chilean SSM sector. Small-scale installations (usually with production capacities up to 50 tpd), featuring mineral processing activities such as, crushing, grinding and flotation, are used to produce Au–Ag, Cu, and Cu–Au–Ag concentrates. Flotation is applied to copper tailing slurries discharged from large- or mediumscale enterprises. Simple installations, where cascade flotation is coupled with conventional flotation, are employed. Additionally, sulphuric acid leaching of oxidised copper ores is carried out, and cement of copper is produced by reduction of copper ions by iron. Chilean artisanal gold mines process alluvial sands and residues from old tailing dams using gravity concentration techniques. A highly extended practice is the use of the artisanal mill called trapiche, which is employed for ore grinding and, at the same time, to amalgamate coarse gold particles with mercury. Usually, tailings of trapiche are subjected to conventional flotation (see Figs

3. Small-scale mining and the environment

The principal environmental impacts of the Chilean SSM sector include pollution by liquid effluents discharged to rivers, infiltration of soils, contamination of underground waters, residue disposal, and threats from tailings dams. Table 6 shows some selected pollutants and maximum concentrations included in the norm for contamination of superficial waters. Processed tailings dam overflow, and acid wastewaters, are some of the more common liquid industrial residues in the SSM sector [7,8]. The amalgamation process is widely employed in the artisanal and small-scale gold mining sectors. Miners typically handle mercury carelessly, and often inhale toxic mercury vapors whilst distilling gold amalgam. Some effort has been made to train miners on how to handle mercury properly. Further, certain equipment has been introduced to in an attempt to improve mercury recovery during distillation. Nevertheless, mercury tox-

Table 5 Number of workers and salaries for large, medium and small-scale copper mining in Chile in 2000 [4] Mining scale

Number of workers

Salaries (US$)

Mean monthly salary (US$)

Large-scale Medium-scale Small-scale Total

28,601 (85.0%) 3,326 (9.9%) 1.710∗ (5.1%) 33,637

837,641,643 47,660,874 8,784,791 894,087,308

2,440.6 1,194.2 428.1 –



Estimated

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Fig. 3.

211

Small-scale miners working in two trapiches for ore grinding and mercury gold amalgamation.

Fig. 4.

Flotation machine in the small-scale mining in Chile.

icity remains one of the most pervasive environmental impacts in the Chilean SSM sector. Finally, abandoned tailings dams pose another serious environmental problem in Chile’s SSM sector, because they are a contamination threat, particularly when located in close proximity to urban zones. The construction and operation of active dams poses an additional

contamination and safety risk to surrounding communities. 3.2. Regulatory and legislative initiatives for smallscale mining The most significant initiatives undertaken to date to facilitate environmental improvements in the Chilean

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Table 6 Maximum allowable pollutant concentrations for selected contaminants in Chile[2] Contaminant

Fluvial water mg/l

Fluvial water with dilution mg/l

Lacustrine water mg/l

Sea water (littoral) Sea water (non protected littoral) mg/l mg/l

Arsenic Cyanide Total copper Dissolved iron Molybdenum Mercury pH Sulphate

0.5 0.2 1 5 1 0.001 6 – 8.5 1,000

1 1 3 10 2.5 0.01 6–8.5 2,000

0.1 0.5 0.1 2 0.07 0.005 6–8.5 1,000

0.2 0.5 1 10 0.1 0.005 6–9 –

small-scale mining sector have been the formation of CONAMA (Comisio´ n Nacional del Medio Ambiente) in 1990, and the promulgation of the General Law on the Environment (No. 19,300) in 1994 [9]. This Law, combined with additional regulatory norms, established certain key control mechanisms, such as the “Evaluation of Environmental Impact”, and the “Environmental Management Plan”. CONAMA, together with the Ministries of Health, Agriculture, and Mining, and the community, have the responsibility of promoting sustainable development in the Chilean mining sector. Two other important legislative initiatives are: the non-definitive Norm 2280/year 1995, which regulates the discharge of liquid residues into superficial and underground water; and the “Decreto Ley” 2867/year 1980, which forced industry to implement technical solutions to pollution problems. It should be noted, however, that Chilean environmental legislation does not differentiate between large, medium and small-scale mining, although certain groups of regulations are only suitable for certain segments. For example, the regulation of SO2 and As emissions (“Decreto Supremo” 185/year 1991) is clearly oriented toward the copper smelters of the large- and mediumscale mining sector. However, the norms for the contamination of superficial waters, and a series of other environmental regulations are applicable to the SSM sector. To help mitigate environmental impacts in Chile’s large-scale mining sector, decontamination plans have been implemented—i.e. agreements between the company and the authorities to solve environmental problems in a given period of time. This has particularly proven effective in capturing and abating As and SO2 emissions in resident copper smelters. Implementing decontamination plans in the SSM sector, however, is more challenging, largely because of the nature of its operations (Figs. 3 and 4). However, a series of environmental initiatives are being encouraged by authorities, including, the efficient use of mercury (namely to decrease losses in wastewaters discharged from trapiches); implementation of efficient equipment for

0.5 1 3 – 0.5 0.02 5.5–9 –

mercury distillation; construction of tailing ponds; and reuse of wastewater. Training of miners in the areas of safety and environmental impact is another action being taken by authorities. 3.3. The role of international agencies, the State and local universities International agencies, particularly United Nations’ regional ECLAC office in Santiago, have been collecting information about the Chilean SSM sector, and making comparative studies with other SSM in the world [10]. The World Bank Group through the International Finance Corporation are exploring the possibility of establishing an International Consultative Group on Artisanal and Small-Scale Mining as a forum for assessing and addressing some of the sector’s problems. Its planned tasks include, developing policy guidelines, providing advise to local miners, and disseminating knowledge concerning best practices. In 1998, the State, through SERNAGEOMIN, and ENAMI, launched the ECOMIN program, the objective of which is to control and reduce the environmental impact of small and medium-scale mining, and to improve safety and hygiene in the industry. It provides training on basic environment protection issues; helps to diffuse knowledge of positive experiences of cleaner production in the sector; and has worked to incorporate the SSM sector into the national System of Environmental Impact. In Chile, there are eleven universities, based in the cities of Iquique, Antofagasta, Copiapo, La Serena, Santiago and Concepcion, which have active mining and/or metallurgy departments, which, historically, have mainly focused on large and medium-scale mining research rather than small-scale mining research. Universities have, however, been used as research centres and consulted for feedback in the area of environmental training for SSM, and in encouraging the use of effective environmental management tools, and the diffusion of more environmentally friendly techniques.

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3.4. Assessment of small-scale mining in Chile Environmental issues have only recently gained national attention in Chile. The initial legislative responses of the Government were the formation of the National Comission for Environment (CONAMA) in 1990, and the promulgation of the General Law for Environment in 1994. From this date, the State has begun to participate actively in regulating and controlling the environmental impacts of mining. During the 1990s, environmentally, the main focus in the mining industry was on large-scale mining. Primary issues examined were problems with air pollution from copper smelters (emissions of SO2, volatile As, and particulated matter); and the generation of environmental management tools (e.g. the Evaluation System of Environmental Impact). In the case of small-scale mining, the State has two different points of view: first, to support the activity for socio–economic purposes; and second, to guarantee the right of all Chileans to live in an evironment free of contamination. At the beginning, the goal was to establish a legal and fiscal framework, providing education and health care of miners and their families exposed to pollutants. Now, the challenge is to improve the living conditions of miners by introducing more environmentally responsible and safe mining, and process techniques. It must be noted that large-scale mining companies do not have any direct connection with the SSM sector. 4. Conclusions In 2000, small-scale mining in Chile was responsible for the production of some 45,000 metric tons of copper, 13,650 kg of silver, and 3,500 kg of gold, representing 0.97%, 1.1% and 6.5% of national production, respectively. The sector overall employs an estimated 1,700 workers, some 5.1% of the country’s mining labour force. The SSM sector in Chile is environmentally destructive, discharging a significant amount of wastewater into superficial and underground waters, contaminating soils, dispensing numerous solid residues, and releasing substantial quantities of mercury. Risks of health, safety and hygiene for miners and their families are also high because of toxic pollution. .

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The public agencies CONAMA and SERNAGEOMIN are responsible for regulation and control, the setting of environmental standards, and ensuring the safety for workers and surrounding communities is sufficiently adequate. The State’s approach includes education on environment protection, and the incorporation of environmental management tools.

Acknowledgements The authors would like to thank Eng. Luis Baltierra for his valuable help in the preparation of figures and tables, and to Dr Jose´ Palacios, University of Atacama– Copiapo´ , for providing the photos of the SSM sector.

References [1] Chilean Mining Compendium (Compendio de la Minerı´a Chilena), 2001, EDITEC LTDA, Santiago, Chile. [2] CONAMA. www.conama.cl. “Desarrollo de un Ana´ lisis Ambiental de la Pequen˜ a Minerı´a”. Subterra Ingenieros Limitada. [3] COCHILCO www.cochilco.cl. Statistics–Metallic Production in Chile. [4] SERNAGEOMIN. Anuario de la Minerı´a Chilena. In: Rojas J, editor. Servicio de Geologı´a y Minerı´a-Chile. 2000. [5] Sa´ nchez JM, Enrı´quez SM. Impacto Ambiental de la Pequen˜ a y Mediana Minerı´a en Chile. Documento para el Banco Mundial e International Development and Research (Canada´ ), Project: “Environmental Study of Artisanal, Small and Medium Mining in Bolivia, Chile and Peru´ ”, Dic. 1996 [6] Sa´ nchez JM, Enrı´quez SM. Environmental Impact of Medium and Small Mining in Chile. In: Figueroa E, editor. Economic Rents and Environmental Management in Mining and Natural Resources Sector. pp. 363–383, 1999. [7] Castro SH, Sa´ nchez MA, Vergara F, Oyaneder E. Water and slurry wastes assessment in the Chilean copper industry. In: Sa´ nchez MA, Vergara F, Castro SH, editors. Environment and Innovation in the Mining and Mineral Technology. Concepcio´ n, Chile: University of Concepcio´ n; 1998. p. 1005–16. [8] Castro SH, Sa´ nchez, M. An Environmental View to the Chilean Copper Industry. In: Onal G, Atak S, Guney A, Celik M and Yuce E, editors. New Development in Mineral Processing, Proceedings of the IXth Balkan Mineral Processing Congress, 11– 13 Sept., 2001, Istanbul, Turkey, pp. 559–564, 2001. [9] Lagos G. Impactos Ambientales de la Minerı´a en Chile. Minerı´a Chilena—Ambiente y Desarrollo, pp. 13–20, 1997. [10] Chaparro E. “La llamada Pequen˜ a Minerı´a: un Renovado Enfoque Empresarial”. Serie Recursos Naturales e Infraestructura. Naciones Unidas (CEPAL/ECLAC), Santiago, Chile, Julio, 2000.