Before mining begins

— The following is an excerpt from Mining Explained, published by The Northern Miner.

Environmental protection begins at the earliest stages of mine exploration, long before the first ore is extracted. During this stage, companies make every effort to minimize the impact of prospecting, drilling, trenching, road building and other related activities.

Exploration activities usually affect the environment only temporarily and, with proper planning, work can be carried out with minimal disturbance to land, vegetation and wildlife habitats. Even so, companies have learned that it is important to keep local communities informed about their activities. This consultation process sets the stage for good community relations once mine planning begins.

To keep public support, mining companies must demonstrate respect for the ecosystem in which they are working and adopt a broad range of protective measures. The drilling fluids and lubricants used in diamond drilling can seep into the water used to bring cuttings to surface. This water must be properly contained and disposed of so that it does not contaminate the groundwater. Drill holes often have to be sealed with impermeable concrete or bentonite (a clay material) to ensure that the drill hole cannot act as a channelway for contaminants to reach the groundwater from surface.

Another consideration in mineral exploration is the safe handling of camp wastes. This means more than just being careful not to litter, as isolated exploration camps must ensure that they handle fuels and dispose of human wastes in ways that do not contaminate the natural environment.

In very sensitive areas, such as tundra regions, it is common for governments to require that exploration crews have permits to work, setting down limits on what the crew can do. Respect for wildlife must be shown at all times. With proper planning, forethought and good housekeeping, all of the impacts of an exploration campaign can be minimized. In recent years, a major exploration-industry association, the Prospectors and Developers Association of Canada, developed a set of practices called E3, for “Environmental Excellence in Exploration.” A distillation of the knowledge that had been built up by mineral explorers over the years, it gives explorers a blueprint for doing their work in ways that limit the effect on the environment.

Once a deposit of economic interest has been outlined, studies and sampling programs are carried out to provide data that are used to shape a project’s design. Specialists research all aspects of the environment to establish basic data, against which future test results will be compared and evaluated. A few of the many areas investigated are: soil composition; the concentrations of metals in nearby watercourses; the populations of animal and plant species that live nearby; air quality and climate; historical and cultural sites; and numerous other pieces of data that allow regulators to determine whether the mine, once in operation, is causing adverse changes to the environment.

The permitting process

Once a promising orebody has been found, most countries require a technical environmental study of the proposed development. These reviews are so detailed that they can take several years to complete. In order to get a permit for mine construction, companies must provide details of their operating plans, as well as the results of engineering, environmental and socioeconomic studies. A further step before permits are issued is often a series of public hearings that allow individuals to voice their concerns or support. Needless to say, obtaining permission to develop a new mine can be complex and time-consuming.

The permits spell out the terms under which an environmentally acceptable mine may be developed. Typically, a government agency responsible for environmental protection or mining development will inspect the study and permit or prohibit the mining operation based on the study’s findings.

One concern is the simple physical stability of the mine workings – whether the pit walls will stay up or whether mine workings will cause nearby ground to subside. The other concern is that mining may allow contaminants to enter the atmosphere, surface waters, soils or the groundwater systems. Mines, mills, smelters, tailings ponds, effluent discharges and smokestacks must be designed to keep contaminants out of the surrounding environment.

Base metal ores are usually natural compounds of a useful metal with sulphur. In the presence of oxygen and water, the sulphide minerals react to form sulphates and sulphuric acid. These compounds are not highly concentrated, but contain sufficient acid and salts of heavy metals to be harmful to aquatic life in surface watercourses. Because coals also contain iron sulphide minerals, the same chemistry happens in coal mines.

Careful control of mine waters and surface runoff allows mines to prevent or minimize the effect of acid-generating waste rock and tailings. In difficult cases, the mine may channel its runoff water to treatment plants that neutralize the acid waters before they are released to surface watercourses.

Water also leaks into mines from the surface and through the groundwater system. This water is collected and pumped to surface, and needs to be disposed of. However, it can be slightly acidic from its contact with the sulphide minerals in the mine or can carry heavy metals that it has dissolved from the mineral deposit. To keep the mine from polluting its surroundings, this water may have to be treated to remove the contaminants before it is discharged to lakes or rivers.

There are several ways to treat such waste waters. Lime or other alkaline compounds can be added to neutralize sulphuric acid, and the heavy metals can be extracted chemically. Most countries have limits on the concentration of contaminants waste waters can contain if they are to be released to surface watercourses. These waters are treated so that any contaminants are present in concentrations lower than the prescribed limits.

Mines also have to dispose of waste rock. It comes up every day of a mine’s life. Some can be used as backfill, but there is usually plenty left over when the mine is finally exhausted. Mines have to be designed with waste rock dumps that will not slide or collapse. The waste rock also may contain traces of mineralization, and the contact of rain or snow with metal sulphides can form acidic runoff that can poison nearby watercourses.

The best way to prevent acidic runoff from reaching watercourses is to prevent it from forming in the first place. This is done by diverting water away from the waste dumps and by capping the dumps with impermeable soils that prevent rain and snow from reaching the waste rock. If that solution isn’t practical, then the runoff that forms can be collected and treated to lower concentrations of contaminants to a safe level before the water is discharged.

The permitting process and hearings can take one to three years. Applicants frequently amend their project plans to reflect local concerns or take advantage of cleaner technologies. The result is an economic development without lasting environmental disruption.