9.5 Environmental Impacts of Metallic Mineral Mining
Environmental issues can include erosion, formation of sinkholes, loss of biodiversity, and contamination of soil, groundwater and surface water by chemicals from mining processes. In some cases, additional forest logging is done in the vicinity of mines to create space for the storage of the created debris and soil. Contamination resulting from leakage of chemicals can also affect the health of the local population if not properly controlled. Extreme examples of pollution from mining activities include coal fires, which can last for years or even decades, producing massive amounts of environmental damage. [4]
Mining companies in most countries are required to follow stringent environmental and rehabilitation codes in order to minimize environmental impact and avoid impacting human health. These codes and regulations all require the common steps of environmental impact assessment, development of environmental management plans, mine closure planning (which must be done before the start of mining operations), and environmental monitoring during operation and after closure. However, in some areas, particularly in the developing world, government regulations may not be well enforced.[4]
Mine Waste: Tailings
To extract the ore from rock, ore mills need to crush large volumes of rock. This generates piles of non-economic material, a form of “waste” called tailings. For example, for each ton of copper, 99 tons of waste are generated, the amount of waste is larger for gold and silver.
Tailings can be toxic. Tailings are usually produced as a slurry (mixed with water) and are most commonly dumped into ponds made from naturally existing valleys. These tailing ponds are secured by impoundments (dams or embankment dams). In 2000, it was estimated that 3,500 tailings impoundments existed and that every year, 2 to 5 major failures and 35 minor failures occurred; for example, in the Marcopper mining disaster, at least 2 million tons of tailings were released into a local river.
The tailings and the waste rock at most mines are an environmental liability because they contain pyrite plus small amounts of ore minerals. Thus, besides dam failure, tailings can produce acid drainage. Tailings ponds and waste-rock storage piles must be carefully maintained to ensure their integrity and monitored to ensure that acidic and metal-rich water is not leaking out.
Acid Drainage
The primary impact of metallic mineral mining comes from the process of mining itself, including disturbance of the land surface, covering of landscapes by tailings impoundments, and increased risk of mass wasting that is accelerated by erosion in the area. In addition, many metal deposits contain pyrite, an uneconomic sulfide mineral, that when placed on waste dumps, may generate acid rock drainage.
Environmental Regulation of Copper Mining in Arizona
The main environmental protection agencies which govern a mine’s potential to contaminate the local environment include the Arizona Department of Environmental Quality (ADEQ) and the United States Environmental Protection Agency (US EPA). These two agencies, as well as county or other local agencies, ensure that operating mines, as well as mines that have been closed, do not release contaminated or hazardous materials outside of the mine site. Hazardous materials have the potential to leave a mine site through wind, which can carry dust; rain, which can flow in washes and streams; and in the groundwater, which can contaminate the local drinking water.
If hazardous materials or contaminated water were to leave a mine site, mine owners could face very large fines on a daily basis, be rejected for future permits, and even face time in jail. Mines on reservations must meet environmental quality standards set out by the respective reservations. For instance, the Navajo Nation Environmental Protection Agency (NNEPA) has well-defined water and air quality standards, which the mines must comply with. Many of the laws in NNEPA are modeled after the US EPA; companies working in such areas often follow the governing body with the strictest policies to ensure adequate environmental compliance.
If there is no formal tribal environmental protection agency, the mines will be governed by the US EPA. Typically, mining companies will have environmental engineers on staff at the site or use environmental consulting firms to interact with the regulatory agencies.
Apache Tribe Concerns with Mining
Throughout history, tribes have faced displacement, discrimination, and marginalization due to mining on their lands (Ballard, 2003). Environmental health is an important concern for communities living near mine sites. The impacts of mining on sacred and ancestral lands are of concern for tribal communities. Although U.S. laws for the most part protect sacred lands on and off tribal reservations, there are still potential risks for loss. For example, traditional livelihoods may be limited due to lack of access to land and/or destruction of important resources (e.g., mountains, vegetation, wildlife). Tribal communities often rely on natural resources found on sacred lands for cultural, medicinal, and spiritual purposes.
On the Navajo Nation in northeastern Arizona and southeastern Utah, Navajo people living in and near uranium mining areas used mill tailings, a sandy waste containing heavy metals and radium, which is radioactive, to build their traditional earthen homes (hogan), many of which remain in use today (DOE, 2013).
Another example is the nearly 100 sacred and cultural sites of the Tohono O’odham Nation, which may be impacted by the proposed development of the Rosemont Copper Mine in southern Arizona (Tohono O’odham, 2009). A final example is the Oak Flat area east of Superior, AZ, lands sacred to the San Carlos Apache tribe, where Resolution Copper is proposing to mine (Allen, 2015). Innovative mining companies implementing responsible mining have recognized the need for more respectful relationships with tribal nations to ensure that when mining is undertaken, the rights and interests of the People are considered.
Rehabilitation
After mining finishes, the mine area must undergo rehabilitation. Waste dumps are contoured to flatten them out, to further stabilize them. If the ore contains sulfides it is usually covered with a layer of clay to prevent access to rain and oxygen from the air, which can oxidize the sulfides to produce sulfuric acid, a phenomenon known as acid mine drainage. This is then generally covered with soil, and vegetation is planted to help consolidate the material. Eventually, this layer will erode, but it is generally hoped that the rate of leaching or acid will be slowed by the cover such that the environment can handle the load of acid and associated heavy metals.
There are no long-term studies on the success of these covers due to the relatively short time in which large-scale open pit mining has existed. It may take hundreds to thousands of years for some waste dumps to become “acid neutral” and stop leaching to the environment. The dumps are usually fenced off to prevent livestock from denuding them of vegetation. The open-pit is then surrounded by a fence, to prevent access, and it generally eventually fills up with groundwater. In arid areas it may not fill due to deep groundwater levels. [4]
the process in which a material is worn away by a stream of liquid (water) or air, often due to the presence of abrasive particles in the stream
FeS2
A brassy yellow metallic mineral from the sulfide class. Pyrite is also known as "Fool's Gold" for its golden color.
A mineral compound characterized by the linkage of sulfur with a metal or semi-metal such as galena, PbS, or pyrite, FeS2.
An organic or chemical sedimentary rock that is primarily composed of calcium carbonate (CaCO3). Limestone is a subgroup of rocks that includes chalk, coquina, and fossiliferous limestone.
CO3--
The anion group consisting of one carbon bonded to three oxygen atoms. Carbonate is a key ingredient in calcite, limestone, and is a solid form of carbon dioxide (CO2).
CaCO3
A carbonate mineral that strongly reacts with dilute acid. Calcite composes the sedimentary rock limestone and composes the skeletons of some ocean life.
A carbonate mineral, CaMg(CO3)2, that is more resistant to weathering by acid at room temperatures. Dolomite often composes the material of fossilized shells.
