Environmental Code of Practice for metal mines: chapter 3

3.1 Exploration and Feasibility

Environmental concerns which may arise during the exploration and feasibility phase are summarized in Table 3.1. Most initial exploration activities are relatively non-intrusive and have limited, short-term impacts on the environment, particularly when compared to impacts associated with other phases of the mine life cycle. Access during initial exploration is seldom intensive and work camps are normally tent based, supporting a few people for short periods of time. In most areas, the main environmental effect associated with initial exploration is noise from aircraft during airborne surveys, which can affect wildlife. Line cutting for geophysical surveys results in environmental effects of varying magnitude, depending on the width of the lines that are cut and the number of lines in a given area.

Diamond drilling can also have effects. For example, access roads may be required. Drilling also requires the preparation of drill sites; the transportation, storage and handling of fuel; and the establishment of campsites for drilling and geological crews, facilities to deal with drilling waste, and an infrastructure to manage and supply the camp. All of these activities have the potential to affect the environment.

The risk of environmental effects increases as exploration becomes more intensive. Diamond drilling is generally more extensive during advanced exploration, leading to increased risk of effects on the environment. In addition, the collection of bulk samples may result in the release of contaminants to water and air, as well as noise and vibrations that may affect wildlife. The accommodation and infrastructure requirements of advanced exploration programs can also have effects. Though bulk sampling is an advanced exploration activity, it has the potential to generate environmental effects similar to those of the mine operations phase, albeit on a smaller scale.

Activities related to feasibility studies are an extension of advanced exploration activities, and the related environmental concerns are similar.

Table 3.1: Potential Environmental Concerns Associated with the Exploration and Feasibility Phase
Activity Potential Environmental Concerns
Access/Line Cutting
  • Possible concerns with terrestrial/wildlife habitat and stream crossings
Geophysical Surveys
  • Possible impacts on wildlife from airborne surveys
Field Camps
  • Sewage and garbage disposal, water supply, fuel storage
  • Impacts on terrestrial/wildlife habitat, access to remote areas
  • Physical scarring/land disturbance
  • Acid generation from exposed sulphide minerals
  • Metal leaching
  • Sediment erosion
  • Impacts on wildlife of blasting
  • Water supply, drilling fluid disposal, fuel storage/risk of spills, groundwater contamination
  • Physical scarring/land disturbance
  • Acid generation from exposed sulphide minerals
  • Release of metal-bearing groundwater
Bulk Sampling
  • All of the above but potentially greater impacts are possible, and reclamation needs to be considered
  • Dewatering of historic mine workings may have impacts on receiving water quality
Exploratory Mining
  • Potential impacts can occur that are similar to those during full-scale mining operations, albeit on a smaller scale

3.2 Planning and Construction

3.2.1 Planning

The planning phase is very important from an environmental perspective. All required environmental assessments must be conducted and all relevant environmental permits must be obtained before the project can proceed. In addition, during this phase, a broad range of plans are developed covering all aspects of environmental operations at a site.

3.2.2 Construction

Site Preparation and Construction of Mine Infrastructure

Site preparation (clearing, stripping and grading) and construction of infrastructure can have potentially important environmental implications, as identified in Table 3.2. Potential concerns are related to impacts on air quality, water quality, aquatic ecosystems, soil quality and terrestrial ecosystems.

Table 3.2: Potential Environmental Concerns During Site Preparation and the Construction of Mine Infrastructure
Potential Sources of Concern Nature of Potential Concern
Air Quality
Operation and maintenance of vehicles and any on-site power generation facilities
  • Potential releases of particulate matter, carbon monoxide, oxides of nitrogen, sulphur dioxide, and volatile organic compounds
Fuel and chemical transportation, handling and storage
  • Potential releases of volatile organic compounds and other harmful substances
Site preparation and construction activities
  • Potential releases of particulate matter
Water Quality and Aquatic Ecosystems
Operation and maintenance of vehicles and any on-site power generation facilities
  • Potential releases of substances such as suspended solids, trace metals, oil, degreasers, and detergents and other harmful substances that could affect water quality and aquatic ecosystems
Fuel and chemical transportation, handling and storage
  • In the event of spills, potential releases of petroleum products or chemicals that could affect surface waters or groundwater as well as aquatic ecosystems
Site preparation and construction activities
  • Potential release of sediments, increasing concentrations of total suspended solids in receiving waters
Sewage and wastewater disposal
  • Potential releases of nutrients and other contaminants
Construction of site access roads and power lines
  • Potential release of sediments along the routes, increasing total suspended solids in receiving waters
  • Potential for acidic drainage if sulphide-bearing minerals are exposed during construction
  • Stream crossings for access roads may affect aquatic ecosystems, particularly those of migratory or spawning fish
  • Increased road access in remote areas may lead to increased fishing, stressing fish populations
Soil Quality and Terrestrial Ecosystems
Fuel and chemical transportation, handling and storage
  • In the event of spills, potential releases of petroleum products or chemicals that could affect soils, vegetation and wildlife
Operation of vehicles
  • Vehicle operations may result in collisions with wildlife
  • Low altitude aircraft operations could disrupt wildlife
Site preparation and construction activities
  • Clearing of vegetation on site may have impacts on biodiversity, particularly if any rare, threatened or keystone species are present
  • Activities on site may disrupt and dislocate local wildlife and any migratory wildlife in the area
  • Some animals may be drawn to the site as a result of improper waste disposal or kitchen odours, which could lead to potential hazards for both workers and the animals
Construction of site access roads and power lines
  • Construction activities may disrupt and dislocate wildlife and any migratory wildlife in the area
  • Increased road access in remote areas may lead to increased hunting, stressing wildlife populations
  • Vehicle operations may result in collisions with wildlife
Noise from exploration activities, including vehicle operations, drilling, and blasting
  • Noise may affect local wildlife populations, and well as people living in communities near the exploration activity

Establishment of Mine Workings

The principal concerns related to the establishment of mine workings during the mine construction phase are the management of waste rock and mine water. These concerns are further discussed in Section 3.3. The establishment of mine workings can also affect the environment as a result of dust, noise and vibration, which are mainly the result of drilling and blasting activities.

3.3 Mine Operations

3.3.1 Ore Extraction

The primary environmental concerns associated with ore extraction activities are the disposal of waste rock and the release of mine water. Waste rock disposal and water management and treatment are further discussed below. Ore extraction activities can also affect the environment as a result of dust, noise and vibration, which are mainly the result of drilling and blasting, but may also be associated with transportation activities.

There are significant differences between open pit mines and underground mines in terms of implications for environmental management (see Table 3.3). One of the most significant differences is that open pit mines result in a larger area of surface disruption and tend to produce much larger volumes of waste rock than underground mines.

Table 3.3: Comparison of Open Pit and Underground Mines, Highlighting Differences in Environmental Management Concerns
Environmental Aspect Open Pit Mine Underground Mine
Land Disturbance Relatively large area Smaller disturbed area than for open pit mines
Waste Rock Disposal Can require large area; involves trucking, runoff and leachate management, dusting and aesthetic considerations Less waste rock than open pit mines, but may involve similar management considerations
Tailings Tailings volumes generally larger due to large volume of ore processed Tailings volumes generally smaller
Acid Drainage May be associated with both mine and waste rock areas May be associated with both mine and waste rock areas
Reclamation Both mine and waste rock area can represent major concerns due to the extent of the waste rock and pit Waste rock can be a concern, as can seepage or overflow of water from the mine workings
Land Subsidence Not a concern Can be a concern
Truck Noise Truck traffic between pit and waste rock dumps and mill can be a serious noise problem Normally not a concern
Vent Fan Noise Not a concern Requires careful consideration/mitigation
Blasting Effects Noise and vibration can be a concern requiring careful management Noise and vibration could also be a concern at underground mines, particularly when the mine workings are relatively shallow
Dust Can be a concern due to pit operations, haulage roads and waste rock piles Can be a concern due to haulage roads and waste rock piles
Mine Water Mine water volume influenced by precipitation, surface and groundwater ingress. Elevated ammonium levels from blasting can be a concern. High sediment loadings are common. Mine water may contain metals and may have a low pH. Mine water volume normally quite stable. Elevated ammonium levels from blasting can be a concern. High sediment loadings are common. Mine water may contain metals, and may have a low pH.

3.3.2 Ore Processing

The primary environmental concerns associated with ore processing relate to the disposal of tailings and the management and treatment of wastewater. Tailings disposal is further discussed below. There are also concerns associated with the risk of spills and accidents, which could result in the release of contaminants such as chemical reagents used in ore processing.

3.3.3 Potential Sources of Contamination in Wastewater

Acidic Drainage: Sulphide minerals are ore minerals for many base metals, such as copper, lead and zinc, and are ubiquitous in ore deposits. Sulphides may also occur in host rock for ore deposits, and as a result they are common in waste rock. Sulphides are important from an environmental perspective because, in the presence of water and oxygen, they can oxidize to create sulphuric acid, a process commonly known as acidic drainage and also known as acid mine drainage or acid rock drainage. The result is the generation of metal-laden effluents of low pH. Acidic drainage can have very significant impacts on aquatic ecosystems unless it is carefully managed, and it can lead to long-term liability and effluent treatment costs for the mine owner/operator.

Alkaline Effluents: Many ore separation processes, particularly flotation separation, are most efficient at an alkaline pH, and chemical additives are used to ensure an alkaline pH, sometimes as high as 10 or 11, during processing. As a result, effluents from ore processing facilities are frequently alkaline, even at the point of final effluent discharge. At some sites, pH adjustment is required to lower the effluent pH prior to discharge.

Metal Leaching: Wastewater from mining and ore processing facilities can contain metals that naturally occur in the rock. Most metals are more soluble in water at low pH, so the concentrations of metals are frequently elevated in acidic drainage. However, metal leaching can also occur in cases where acidic drainage is not a concern.

Cyanide: Cyanide is used in the recovery of gold in many facilities that process gold ore. Some cyanide is reused in processing but some is discarded in tailings. As a result, wastewater from facilities using cyanide mills may contain cyanide and a number of cyanide compounds.

Cyanide is also used in small amounts in some flotation separation circuits. Thus, cyanide compounds may also occur in wastewater from tailings from some base metal flotation mills.

Ammonia: Ammonia may be present in wastewater from mining operations as a result of the use of ammonium nitrate and fuel oil (ANFO) as a blasting agent. Any ammonium nitrate spilled in preparation for blasting or left over after a blast may contribute to increased ammonia concentrations in wastewater. In addition, ammonia may occur as a decomposition product from cyanide wastes.

Suspended Solids: Wastewater may contain suspended solids ranging from colloidal (non-settleable) to settleable materials. The discharge of effluents with high levels of suspended solids can cause a range of problems in aquatic environments that include impeded oxygen intake by fish and reduced light availability for aquatic plants. Depending on the composition of the solids in suspension, the settling of these sediments can also result in the contamination of sediments, particularly with metals.

Thiosalts: Thiosalts are sulphur oxide compounds, including thiosulphate (S2O32-) and polythionates (SxO62-), that are formed when partial oxidation occurs during the milling, grinding and floatation of some sulphide ores under alkaline conditions.Thiosalts are a concern because they can oxidize in water to form sulphuric acid, which lowers the pH of the receiving water and affect metal mobility. Both of these aspects could have significant effects on resident aquatic organisms.

3.3.4 Mine Waste Disposal

In planning the disposal of waste rock and tailings, the risks of metal leaching and acidic drainage can be predicted and the results considered in the design of waste rock piles and tailings management facilities.

If there is a risk of acidic drainage, there are several methods that may be used to prevent or control it. MEND1 concluded that the most effective method of preventing acidic drainage is subaqueous disposal. Disposal of waste rock or tailings under water significantly reduces the exposure of the material to oxygen. The avoidance of oxidation reactions results in substantial reduction in the risk of acidic drainage and the associated metal leaching problem.

If prevention of acidic drainage is not possible, several methods may be used, alone or in combination, to control or limit it, including:

  • dry covers consisting of alternating layers of material of different porosity to limit water infiltration;
  • dry covers using innovative materials such as sewage sludge stabilized by lime or sludge from pulp and paper mills;
  • impermeable geomembrane liners to prevent infiltration of acidic drainage into underlying materials;
  • waste rock or tailings maintained in a frozen state (in permafrost areas);
  • direct addition of lime or other alkaline substances;
  • raising of the water table to inhibit acid generation of materials disposed of below the water table; and
  • use of tailings as mine backfill, or disposing of tailings in mined-out open pits.
Waste Rock and Tailings Disposal

The production of both waste rock and tailings continues throughout the mine operations phase, and effluents originate from both. Effluent from waste rock is often sent to the tailings disposal area for treatment prior to final discharge, but it may also be directed to a separate treatment facility.

The key concern in the management of mine waste is the prevention or control of the release of contaminants that could have significant environmental impacts. Groundwater seepage is also a concern for both waste rock piles and tailings management facilities, in that seepage into the groundwater could result in the release of contaminants through a permeable foundation layer or other instability.

Failure of dams or other containment structures for tailings management facilities can lead to severe environmental impacts and significant risks to human health.

Treatment Sludge Disposal

Acidic drainage from mines is commonly treated with lime. A by-product of this treatment is sludge. The composition of sludge varies, and sludge may contain a wide range of metals. The volumes of sludge produced are large, and in some cases they may exceed the volume of tailings produced over the life of an operation. Sludge is generally disposed of on site, but it may also be sent to smelters for recycling.

There are uncertainties about the long-term chemical stability of many sludges, and there are risks that sludge could become an additional source of releases of metals.

3.3.5 Water Management

Water and wastewater management constitute the primary environmental concern at most metal mines in Canada. An effective water management program can incorporate measures to:

  • segregate clean and contaminated water flows in order to help reduce the requirement for the treatment of effluent;
  • control and address seepage losses from tailings containment structures;
  • reduce water usage;
  • recycle water for further process use; and
  • reduce impacts on the groundwater regime.

Measures that can be used in water management include drainage ditches to divert off-site water and drainage ditches and diversions to control the flow of on-site water and prevent contamination in order to prevent contaminated waters from leaving the site before treatment.

3.3.6 Concerns Related to Air Quality

Air quality impacts from mining are mainly associated with the releases of airborne particulate matter. Operation of vehicles and generators can also lead to releases of greenhouse gases and various air contaminants, including sulphur oxides, nitrogen oxides, carbon monoxide and particulate matter.

Releases of airborne particulate matter can result from various activities, including blasting, crushing, loading, hauling, and transferring by conveyor. Open pits, waste rock piles, tailings management facilities, and stockpiles are potential sources of wind-blown particulate matter.

Common methods to minimize releases of airborne particulate matter include:

  • spraying water to maintain sufficient surface moisture;
  • using environmentally acceptable chemical sprays to stabilize the surface;
  • revegetating the parts of the mine site that will not be disturbed in the future;
  • controlling dumping or transfer rates of materials;
  • covering dump trucks or rail cars to minimize releases during the transportation of material;
  • establishing speed limits on unpaved surfaces that are low enough to minimize dust from vehicle operations, considering local weather conditions;
  • storing ore or concentrate in storage bins, hoppers or other buildings to eliminate dusting concerns and position the material for loading or transfer;
  • covering or enclosing conveyor lines;
  • using baghouses or precipitators for point sources of releases such as stacks from ore concentrate driers;
  • covering stockpiles or other material that may be a source of releases; and
  • temporarily ceasing operations if weather conditions are such that the risks of significant releases of airborne particulate matter are unacceptably high.

3.3.7 Concerns Related to the Terrestrial Environment

Effects on Plants

The stripping of outcrops during exploration and the clearing of sites for mine construction can have significant local effects on resident plant communities. These communities also represent wildlife habitat, and destroying habitat can lead to the loss of local breeding grounds and wildlife movement corridors or other locally important features. Mining activity may also contaminate terrestrial plants. Metals may be transported into terrestrial ecosystems adjacent to mine sites as a result of releases of airborne particulate matter and seepage of groundwater or surface water.

In some cases, the uptake of contaminants from the soil in mining areas can lead to stressed vegetation. In such cases, the vegetation could be stunted or dwarfed.

Effects on Wildlife

Mining activity can affect wildlife as a result of habitat loss and habitat degradation. For example, mining activity may affect migration routes, breeding grounds, or nesting areas. Mining activity may also affect species that carry special cultural significance to local communities. As a minimum, most large mammals are dislocated from mine sites and associated facilities. Some large species may not be affected in the long term by such dislocation, but dislocation could affect others, depending on the species and the significance to that species of the lost habitat.

Conversely, some wildlife species may be attracted to mine sites, particularly if food wastes and other wastes that may attract wildlife are not properly managed. This may lead to increased interactions between humans and wildlife, and it could result in animals that pose a risk to persons on site having to be relocated or destroyed.

Terrestrial wildlife, like plants, may also be affected by contamination associated with mining activity. In particular, food sources for animals may become contaminated, and some contaminants, particularly metals, can magnify up the food chain.

3.3.8 Progressive Mine Closure Activities during Mine Operations

Large areas of land may be disturbed through ore extraction and other mining activities. Disturbed areas that are not stabilized can be susceptible to erosion caused by both wind and water; erosion can lead to problems with dust as well as water quality problems related to sedimentation.

During the mine operations phase, landscape rehabilitation may include the reshaping and restructuring of the landscape and erosion control measures. In addition to reshaping or recontouring, landscape restructuring activities can include the use of stockpiled soils to reconstruct soil structure in preparation for revegetation.

3.4 Mine Closure

The objectives of mine closure are:

  • to ensure public and wildlife safety by capping shafts and preventing inadvertent access to mine openings and other infrastructure;
  • to provide for the stable, long-term storage of waste rock and tailings;
  • to ensure that the site is self-sustaining and to prevent or minimize environmental impacts; and
  • to rehabilitate disturbed areas for a specified land use (e.g., return of disturbed areas to a natural state or other acceptable land use).

Many of the environmental considerations during the mine closure phase are common to all types of metal mines. However, there are additional concerns unique to some sites, such as the reclamation of radioactive wastes at uranium mines. A summary of components to be addressed in the mine closure phase is provided in Table 3.4.

Table 3.4: Mine Components to be Addressed in the Closure Plan
Components Aspects to be Addressed
Underground Mines
  • Sealing of shafts, inclines and declines, or ventilation raises to prevent unauthorized access
  • Effects of seepage from backfill
  • Mine water drainage
  • Formation of potentially unstable ice plugs
Open Pit Mines
  • Slope and bench stability
  • Groundwater and rainwater management
  • Security and unauthorized access
  • Wildlife entrapment
  • Effects of drainage into and from the pit
Ore Processing Facilities
  • Removal of buildings and foundations
  • Clean-up of workshops, fuel and reagent
  • Disposal of scrap and waste materials
  • Re-profiling and revegetation of site
Waste Rock Piles
  • Slope stability
  • Effects of leaching and seepage on surface and groundwater
  • Dust generation
  • Visual impact
  • Special considerations for some types of mines such as uranium mines
Tailings Management Facilities
  • Dam stability
  • Changes in tailings geochemistry
  • Effects of seepage past the dam and from the base of the facility
  • Surface water management and discharge
  • Dust generation
  • Access and security
  • Wildlife entrapment
  • Special considerations for some types of mines such as uranium mines
Water Management Facilities
  • Restoration or removal of dams, reservoirs, settling ponds, culverts, pipelines, spillways or culverts which are no longer needed
  • Surface drainage of the site and discharge of drainage waters
  • Maintenance of water management facilities
Landfill/Waste Disposal Facilities
  • Disposal or removal from site of hazardous wastes
  • Disposal and stability of treatment sludge
  • Removal of sewage treatment plant
  • Prevention of groundwater contamination
  • Prevention of illegal dumping
  • Security and unauthorized access
  • Removal of power and water supply
  • Removal of haul and access roads
  • Reuse of transportation and supply depots

1 MEND Manual Volume 4 - Prevention and Control, February 2001. MEND5.4.2d

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