The mining of gold is commonly perceived as ‘unsustainable’ – after all, gold is a metal with finite resources. A more comprehensive analysis of sustainability and gold mining, however, reveals that the reality is more complex – and depends on exploration, economics, technology and production, as well as a range of legal, social and environmental constraints. Ultimately, the ‘sustainability’ of gold mining depends on your perspective, but it is clear that the environmental costs are likely to gradually increase in the future – in energy, water, chemicals and greenhouse costs. This article summarizes recent research which has sought to compile long-term trends in gold mining to underpin analysis of these critical aspects of environmental and mineral resource sustainability.
Sustainability and Gold Mining : A Brief Review
The observation that mining has both positive and negative impacts is not new – with significant treatises dating back to Georgius Agricola in 1556 and earlier. Following the near-continual global mining boom since about 1960, there has been a wide-ranging debate about the sustainability of modern mining.
The most common starting point for discussing sustainability is the definition proposed by the 1987 World Commission on Environment and Development (WCED, or the ‘Brundtland Commission’), namely ‘to meet the needs of the present without compromising the ability of future generations to meet their needs’. Although this is a somewhat open definition, in the context of mining, this is generally taken to include:
- the ongoing availability of mineral resources (e.g., are minerals truly ‘finite’ ?);
- a healthy environment (e.g., any ongoing pollutant releases ?); and
- viable community (e.g., stable economy, socially vibrant).
The long-term trends in economic mineral resources are critical in sustainability, though they often are only presented as the quantity of a particular mineral or metal remaining and exclude other aspects such as ore grades, mine wastes (waste rock, tailings) and mining technique (underground, open cut, alluvial). The issue of ‘non-renewable’ mineral resources is critical in the sustainability debate as it relates to present generations meeting their needs for metals and minerals while still allowing for future generations to provide for their anticipated requirements.
The nature of environmental impacts associated with gold mining are related to mining cycle of exploration, development, operation, closure and rehabilitation. Historically, the principal concern was with gold production, and it was not until the 1970s in most industrialized countries that community expectations and legislation evolved to ensure a high standard of environmental management throughout the mining cycle.
The environmental and social health of a region and community as affected by mining – positively or negatively – remains a contentious area for the sustainability debate and the mining industry, particularly for the developing world (e.g., mercury in Africa and South America). A major challenge in this regard is the evolving environmental and social costs of extracting mineral resources – especially when compared to the equivalent costs from secondary sources and processes. This begs the question of whether future mining will cost more than at present. For gold mining this is further complicated by the intricate links between global financial systems which use gold, the widespread use of gold in jewelery and in social status.
The United Nations’ 1992 Earth Summit, held in Rio de Janeiro, represented a landmark in the sustainability debate, and was followed by the 2002 Earth Summit in Johannesburg (‘Rio+10’). During this time, the mining industry has engaged pro-actively in the debate and many mining companies have adopted policies on sustainability and release annual reports on sustainability performance alongside corporate financial performance. Mining companies are increasingly using the Global Reporting Initiative (GRI) as their basis for sustainability reporting, especially gold miners.
As part of their contribution to Rio+10, the global mining industry co-ordinated the ‘Mining, Minerals and Sustainable Development’ (MMSD) project, which critically examined the variety of complex issues and drivers for sustainability in mining.
The MMSD project articulated a pivotal change in approaching sustainability with a move away from arguing individual mines may be sustainable, to the sector as a whole contributing to sustainable development. This distinction is of fundamental and critical importance. The revised emphasis on ‘contributing to sustainable development’ allows broader consideration of a balance of social, economic and environmental facets for the industry as whole. Thus it is the sum of all individual mines over time and space and their respective resources, impacts and benefits which should be considered in ascribing sustainability to mining. While individual mine performance remains critical, a focus on the sector as a whole is necessary to assess sustainability in a proper way.
It is now possible, by combining historical reports on gold mining with annual corporate and sustainability performance reports, to begin to quantify long-term trends in gold mining and the associated environmental costs such as water, energy, greenhouse emissions, cyanide and solid wastes.
Overall, it is therefore possible to understand the current and future sustainability of gold mining with respect to long-term data on production, resources, ore grades, solid wastes and the environmental costs of gold production.
Long-Term Trends and Environmental Costs of Gold Mining
The overall trends in gold mining are summarized from the ongoing research work, and include the general relationships for the environmental costs of gold production.
Figure 2. Gold ore grades for select countries over time.
Figure 3. Energy, water and cyanide consumption per gold produced.
Figure 4. Greenhouse emissions per gold produced.
- Gold Production
Since the Californian gold rush of 1849, gold has been mined and produced on a large scale around the world. Global gold production is shown in Figure 1, showing the five major gold booms over the past 160 years.
- Gold Ore Grades
Most gold is mined from hard rock ores and processed to extract the gold. The ore grade, or amount of gold contained per tonne of rock mined, is therefore a fundamental aspect of mining as it determines the potential for a gold ore to be mined economically as well as potential environment costs. The available data for gold ore grades by country is shown in Figure 2, including an indicative general trend.
- Energy, Water and Cyanide Consumption
The general relationships for the energy, water and cyanide required to produce a kilogram of gold are shown in Figure 3, showing that the ‘environmental costs’ of gold production are sensitive to the ore grade being mined and processed.
- Greenhouse Emissions
The general relationship for greenhouse emissions, in terms of carbon dioxide equivalent (‘CO2-e’), is shown in Figure 4, showing that the ‘climate costs’ of gold production are sensitive to the ore grade being mined and processed.
- Solid Wastes – Waste Rock and Tailings
Although many mining companies report the amount of waste rock from gold mining, numerous companies do not. The available data is shown in Figure 5, showing that the solid wastes associated with gold production are increasing exponentially over time. Waste rock is critical to understand as it has the potential, if rehabilitation is poor or unsuccessful, to lead to long-term leaching of metals into adjacent surface waters or underlying groundwater resources.
- Economic Gold Resources
The known economic gold resources over time for select countries are shown in Figure 6. There appears to have been a ‘peak’ and subsequent decline in gold resources for Canada, South Africa and the United States, while conversely Australia’s gold resources have gradually increased. In global terms, the extent of gold resources is subject to ongoing economic assessments, which explains the recent declines in South Africa and the United States, but it is difficult to predict how long the historic trend of near-stable or increasing resources can be maintained.
|Table 1. Average Environmental Costs for Gold Production|
|Energy Consumption||Water Consumption||Greenhouse Emissions||Cyanide Consumption|
|143 GJ/kg Au||691,000 L/kg Au||11.5 t CO2-e/kg Au||141 kg cyanide/kg Au|
Overall, the environmental costs of gold production are summarized in Table 1.
Figure 5. Waste rock from gold mining over time by country.
Figure 6. Economic gold resources over time.
Figure 6. Economic gold resources over time.
The Environmental and Mineral Resource Sustainability of Gold Mining
Historically, the gold mining industry has clearly sustained itself with respect to production and responded to various threats and opportunities. Over the past decade gold production has reached historic levels of about 2,600 tonnes of gold per year. This has been made possible by the combination of the rise in the real price of gold since the 1970s plus the new technology for cyanide processing known as ‘carbon-in-pulp’ (CIP) milling – together these two factors facilitated the 1980s gold boom (production in 1980 was only 950 tonnes of gold). The new gold mines of the past 25 years, however, have commonly been from lower grade mineral deposits. Based on sustainability reporting, it has also been shown that the unit environmental costs of gold production increase – meaning increasing energy, water and cyanide inputs and greenhouse emission outputs. In terms of environmental and mineral resource sustainability, given the long-term decline in ore grades, this points to the environmental costs of gold production beginning to increase substantively in the near future.
Ultimately, the sustainability of gold mining depends on whether one emphasizes economic resources or the environmental costs.
- Mudd, G.M., 2007, Global Trends in Gold Mining: Towards Quantifying Environmental and Resource Sustainability? Resources Policy, 32 (1-2), pp 42-56.
- Mudd, G.M., 2007, Gold Mining in Australia: Linking Historical Trends and Environmental and Resource Sustainability. Environmental Science and Policy, 10 (1-2), pp 629–644.