Cobalt Mining Legacy
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Backgrounder – Mining and the Environment
This section provides some background information on mining and how mining can affect the environment.
Mining takes place in steps, or phases: exploration, construction, operations, closure. These phases together are called the mine life-cycle.
Today, all of the mines in Cobalt are in the closure phase, though there is some exploration going on in the area, especially for diamonds. But understanding the phases of mining, and the past mining practices used in Cobalt, helps to understand how mining has affected the environment in Cobalt.
The mines in Cobalt were developed in a very different time. Today, new mines have to do environmental assessments to predict how the mines will impact the environment, and to make sure that mines are planned properly to minimize their impacts on the environment. In addition, once they start operating, mines today have many measures in place to protect the environment, such as emergency plans, water management systems, waste management systems, and systems to treat waste water. None of these things existed when the mining took place in Cobalt.
This section first briefly the main environmental concerns related to mining, and then describes each phase of the mine life cycle and how those activities can impact the environment. A resources section at the end provides links to additional sources of information on mining, and methods that can be used to protect the environment through the mining life cycle.
Environmental Concerns – Water Pollution
Mining activities can affect the environment in many ways. Some of the most significant effects of mining are water pollution caused by waste water from mines. Water pollution from mining can affect fish and other plants and animals that live in the lakes and streams near mines, and may also affect people that use the water, making it undrinkable, making the fish unsafe to eat, and making the water unsafe to use for recreation. Water pollution from older mines such as those in Cobalt can be severe, often much more severe than the water pollution from mines that are operating today.
Acidic Drainage: At many mines in Canada, including both operating mines and closed or abandoned mines, acidic drainage is a big concern, and a lot of research has been done to figure out how to prevent or control acidic drainage, to protect the environment. Acidic drainage happens when sulphide minerals are exposed to both water and air. In sulphide minerals, metals are bonded to sulphur. When they are exposed to water and air, they oxidize – rusting of steel is a kind of oxidation too, as is the tarnishing of silver. When sulphide minerals are oxidized, acid is produced. If this acid gets into lakes or streams it can have major impacts on the fish and other plants and animals that live in the water. Fortunately, in Cobalt, there are not any problems with acidic drainage, but it is a problem at many abandoned mine sites.
Metals: Waste water from mining and ore processing can contain metals that are naturally present in the rocks. The most common metals in the waste water from mining in Cobalt are arsenic, nickel and cobalt. At Cobalt, some mills used mercury to help recover the silver. As a result, there is also some mercury is some of the tailings and water around Cobalt. While some metals, such as copper and zinc, are essential elements for life, all metals can be toxic, or poisonous, if there concentration of that metal is high enough. If the concentrations of metals are high enough, then they can kills plants or animals. For example, arsenic used to be used as a poison to kills rats. But, if the metals are present at lower concentrations, they can still be harmful. Some can cause long-terms problems for fish and other animals. Some can cause cancer in people.
Cyanide: Cyanide was used at some mills in Cobalt to recover the silver. It is still used at many mills to recover gold. The waste water from mills that use cyanide contains some cyanide. Even though the last cyanide mill closed in Cobalt many years ago, there may still be some residual cyanide in some of the tailings around Cobalt, though cyanide will break down once it is exposed to sunlight. At high concentrations, cyanide can be very poisonous, and can kill fish and other plants and animals living in lakes and streams. At lower concentrations cyanide can have long-term effects.
Suspended Solids: Waste water from mining and milling can contain suspended solids, or sediment. In Cobalt, the runoff water from the clearing of rock to find silver veins caused large amounts of sediment to enter the lakes and streams, especially Cobalt Lake. Adding more sediment, or suspended solids, to lakes and streams can affects plants living there, since they get less sunlight. It can also affect fish, making it harder for them to hunt since they can’t see as well, and making it harder for their gills to work.
Environmental Concerns – Air Pollution
Mines are more commonly associated with water pollution than air pollution, but mines can also be sources of air pollution. In particular, mines can be sources of airborne particulate matter, most commonly dust. Dust can come from the many activities at operating mines sites, including drilling, blasting, and the movement of trucks on unpaved roads. However, dust can also come from mine wastes like tailings and waste rock, especially on windy days.
Dust and other particulate matter can cause breathing problems for people, especially very small dust particles. Dust can also contain metals and other contaminants which can also cause health problems. In addition to possible being a possible risk to human health, dust from mines can cause the contamination of local soils, and can affect vegetation and wildlife.
The Mine Life Cycle - Exploration
The goal of exploration is to find deposits of minerals that could be mined at a profit, in other words, to find ore. Today, exploration is a complicated and technologically advanced business that relies on many sophisticated tools, but exploration in Cobalt it was a simpler affair, especially in the early days.
Environmental Concerns - Exploration
Much of the time, exploration has relatively little impact on the environment, and those impacts that do occur are quite local. However, exploration in Cobalt had significant effects on the environment, because the unique way that exploration was done in Cobalt. The clearing of trees and the trenching and removal of soil caused considerable sedimentation in the local lakes. Some parts of Cobalt, especially the bare treeless slopes of Nip Hill on the east side of Cobalt Lake, still bear the scars of exploration.
In modern exploration programs, the risk of environmental effects often increases as exploration becomes more intensive. For example, diamond drilling is generally more extensive during advanced exploration, leading to increased risk of effects on the environment. Diamond drilling is used to get an indication of what types of rock a present at depth, rather than just at the surface. In addition, as exploration programs become more intensive, more people are involved, requiring larger camps to be built that may also affect the environment.
The Mine Life Cycle – Mine Construction
At modern mining operations, the exploration phase can last several years, and once a decision is made to open a mine, extensive planning is done. All parts of the mining operation are carefully planned. This includes planning to protect the environment. Once all of these plans are complete, and the mine owner has permission from governments to go ahead, then the construction of the mine can begin.
In the mines in Cobalt, there was little or no planning for environmental protection, and indeed, the time from exploration to mine operation was sometimes very short, with little or no long-term planning.
The most significant activity during mine construction is the establishment of mine workings. Mine construction also involves the construction of millings facilities to process the ore, waste management areas, and infrastructure. The scope and complexity of the work to be completed varies from project to project.
Establishment of Mine Workings: During mine construction underground or surface mine workings are established to provide direct access to the ore body. The mine workings are excavated by drilling and blasting. Drills are used to drill patterns in the rock that, upon blasting, will fragment the rock. To fragment the rock, explosives are injected into the drill holes and blasted. Most commonly, explosive mixtures of Ammonium Nitrate and Fuel Oil (ANFO) are pumped into the drill holes. Once the rock is fractured it is removed from the mine. During mine construction, most of the material removed is waste rock.
Construction of Mine Infrastructure: The mine and all of its on-site facilities and utilities are built during the mine construction phase. These facilities include the physical plant and the mill, as well as the administration, housing and associated facilities. Permanent transportation routes such as airstrips, roads, conveyors, railroads, pipelines, or port facilities are also constructed. Electrical power supplies are established either by construction of transmission lines from existing power generation facilities, on the construction of on-site power generation facilities.
Environmental Concerns – Mine Construction
Preparing the site for construction – removing trees and other vegetation, and leveling the site - can lead to problems with sedimentation in nearby water bodies due to releases of suspended solids in surface water run-off. In addition, sensitive plants or animals can be affected. These activities can also cause dust from the site.
At most mines today, soil that is removed is kept for later re-use in reclaiming the site, and care is taken to limits effects on the environment.
Once preparation is complete, the roads and buildings that are needed for the mine site are built. Construction activities can cause air pollution from the trucks and other equipment used in construction. Roads can affect wildlife, and lakes and streams can be affected if the roads cross streams or are built too close to shorelines.
During construction, the mine workings are also established. This pre-mining type of work would not have been needed in Cobalt, since the silver veins were often at the surface, or accessed from existing underground mine workings.
The main environmental concerns related to the establishment of mine workings are the disposal of waste rock and mine water. Mine water is groundwater that seeps into mine workings, and has to be pumped out to prevent flooding of the mine. Mine water can contain metals and be acidic, depending of the type of rock. Unless it is properly collected and treated before disposal, the pumping of mine water from mine workings can cause water pollution.
During mine construction, facilities for the disposal of waste rock, tailings, and other mine wastes are also built. At the mines in Cobalt, these facilities were rudimentary at best – perhaps a just a simple wooden dam structure to contain the tailings. At modern mines these facilities are carefully designed and constructed to prevent or minimize water pollution from these mine wastes.
The Mine Life Cycle – Mine Operations
Mines can be either open pit or surface mines, or underground mines. In Cobalt, most of the mines were underground mines. Some veins were worked from the surface, but the narrow trenches left by these operations are quite unlike modern open pit mines.
In underground mines the ore is extracted using vertical shafts and horizontal drifts and adits. Miners are selective about the rock that is removed, taking as little waste rock as possible to be able to extract the ore. Some the mine workings in Cobalt were very narrow since the veins were narrow. Ore and waste rock were removed using a hoist in the mine shaft, and ore was sent to mills for processing, and waste rock was dumped, frequently along a small rail line the extended outwards from the headframes.
Sometimes, ore is also recovered from the mine wastes of older mines, especially mine tailings. This was common in Cobalt, and many tailings in the area have been reprocessed in the past to try and remove more of the silver or cobalt from the tailings.
Once ore is extracted from a mine it is processed to recover the valuable minerals. Ore is normally a mixture of a small amount of valuable minerals with much larger amounts of waste minerals of no value (gangue). Some ore at Cobalt was an exception to this – so rich that there was more silver than gangue. But even that ore needed to be processed to recover the silver.
At mills the valuable ore minerals like silver are separated from the gangue, to produce an ore concentrate which can then be processed more, usually in a smelter or refinery, to obtain pure metal.
Before ore can be processed the rock needs to be crushed and ground up. Ore separation processes work best when the ore is ground so that it is like fine sand, or even finer than that, depending on the process. Rock is first crushed, then ground. In Cobalt most of the ore was crushed using stamp mills, in which steel drums pound the ore repeatedly against a steel plate. Stamp mills were replaced by grinding drums, which tumbled the rock, like clothes in a giant dryer. Steel balls or some other hard material was added to the drums to help grind the ore.
Once the ore is ground fine enough ore separation can begin. Several different methods were used in Cobalt. Most of these methods are still used, though the details of how ore separation is done have changed a lot. Sometimes these methods are used on their own and sometimes they are used in combination.
Gravity Separation: Some minerals are more dense than others. Gravity separation allows minerals to be separated because of the differences in density. In Cobalt, the silver in the ore was more dense than the gangue minerals.
Flotation Separation: Flotation is used for the separation of a wide variety of minerals on the basis of differences in surface energy of various minerals in contact with air and water. It is the main process for the recovery of sulphide ores including those of copper, nickel, lead and zinc. It is also used for recovery of gold associated with sulphide minerals. Flotation was used in Cobalt to produce silver concentrates. To separate minerals using flotation fine air bubbles are introduced into mixture of ground ore in water. In this mixture minerals in the ore collide with air bubbles. Some minerals favour contact with the air, and will attach to air bubbles and float to the surface of the flotation cell. As air bubbles accumulate at the surface a froth forms and eventually overflows as the ore concentrate. Minerals that favour contact with water remain in the mixture and sink to the bottom of the flotation cells. To help the flotation process, a number of chemicals may be added to the ground ore and water mixture.
Cyanidation: The main method for recovery of gold or silver is the use of cyanide to dissolve the metal. This process is known as cyanidation. In this process a solution of calcium or sodium cyanide is used to dissolve precious metals. The metals are then recovered from this solution by one of two methods: absorption directly from the solution onto particles of activated carbon addition of powdered zinc or aluminium to the solution, causing the precious metals to precipitate from the solution. This was the method most commonly used in Cobalt.
A by-product from all of these types of ore processing is a mixture of ground rock and water known as tailings. The ground rock is what remains after the minerals of value, such as silver, have been removed. Tailings may also contain leftover chemicals from the ore processing, such as cyanide. Tailings are a waste product, and are disposed of near the mill.
Environmental Concerns - Mine Operations
The main environmental concern associated with ore extraction activities is the release of mine water. Ore extraction activities can also affect the environment as a result dust, noise and vibration.
Ore extraction also results in waste rock. If waste rock is not disposed of properly it can also be a source of water pollution, depending on the type of rock.
The main waste from ore processing is tailings. Like waste rock, the minerals contained in tailings can be a source of metals and acidic, which can lead to water pollution. The water portion of the tailings can also contain cyanide or other chemicals that could also cause water pollution.
Like waste rock, tailings need to be carefully disposed of to prevent water pollution. At modern mining operations, many methods are used prevent or minimize water pollution from tailings.
Tailings can also be a source of dust, which can affect nearby plants and animals, as well as people.
The Mine Life Cycle – Mine Closure
Mines are closed when there ore is all gone, or when the mining company can no longer make any money operating the mine. Today, mine closure involved many steps intended to ensure that the site is safe, and to prevent or limit any long-term environmental problems such as water pollution. For most of the mines in Cobalt, owners simply walked away when the mines stopped operating. Many mills burned down, as did some headframes. Some headframes have survived, others have fallen or been demolished. The present owners of these sites are left with this legacy of the past, and a now responsible for closing the sites in an acceptable way.
A key concern in the closing of mines is public safety. All openings to underground mines are sealed to prevent unauthorized access. Open pits may be fenced to prevent access. Buildings are secured or removed.
An additional concern with the closing of underground mines is land subsidence. This may occur if there are any collapses in the underground workings. This could lead to unstable conditions at the surface and in some cases, collapses of material into the workings. This can be particularly hazardous in populated areas or in cases where the collapses affect roads or railways. The primary measure used to prevent subsidence is the backfilling of underground spaces, which is best done during while the mine is operating.
Where to Find out More
For those interesting in learning more about the mining and the environment, there are many excellent resources available. Just a few of these resources are listed below. Internet searches will identify many more from government, industry, international organizations such as the United Nations, and from non-governmental organizations.
Mining has changed considerably in the last century since the first silver mines opened in Cobalt. There is much greater recognition of the need to protect the environment and tremendous progress has been made in the development of measures to protect the environment through the mining life cycle. There is still work to be done to further protect the environment from the impacts of mining activity, but as these resources indicate, there is a great deal that can be done, and is being done, the limit the impacts of mining on the environment, and prevent the type of environmental legacy that was left behind in Cobalt.
Metal Mining Effluent Regulations (MMER)
The Metal Mining Effluent Regulations (MMER) are Federal regulations under Canada’s Fisheries Act that regulate the quality of effluent from metal mines operating in Canada. The MMER apply to all Canadian metal mines that exceed an effluent flow rate of 50 cubic metres per day and deposit effluent into fisheries waters. The MMER include limits for arsenic, copper, cyanide, lead, nickel, zinc, total suspended solids (TSS), radium-226, and pH in mine effluent. The MMER also include a requirement that effluent be non-acutely lethal. Mines under the MMER are also required to conduct Environmental Effects Monitoring (EEM) programs. The objective of EEM is to evaluate the effects of mining effluent on the aquatic environment.
The MMER do not apply to the closed mines in the Cobalt area, though they do apply to the McAlpine Mill on Giroux Lake, operated by SMC Canada.
Ontario Mining Act
The Ontario Mining Act regulated various aspects of the mining sector in Ontario, from exploration to mine closure. Of particular significant to Cobalt is Part VII of the Mining Act which deals with the rehabilitation of mines and mining lands. The Act requires companies to file closure plans, including financial assurance, to indicate the method, schedule and cost of all rehabilitation to be conducted on the site once closure commences.
Published by The Northern Miner, “Mining Explained” provides a good overview of the mining industry for the layperson. Topics covered in the book include:
- mining and ore processing methods
- mining and the environment
- the business of mining
- investing in the mining industry
The book is not available electronically, but can be ordered from the following website:
Environmental Excellence in Exploration (E3)
E3, developed by the Prospectors and Developers Association of Canada, seeks to support environmental stewardship in the exploration stage of global mineral development by encouraging the implementation of sound environmental management practices by the exploration community, its contractors and subcontractors, and by promoting the awareness of all stakeholders.
The E3 program includes comprehensive guidance on a wide range of environmental concerns related to mining. This guidance is available at:
Best Practice Environmental Management in Mining
The Australian Government has produced an excellent series of booklets on best practice environmental management in mining. These booklets cover a broad range of topics, including:
- Community Consultation and Involvement
- Contaminated Sites
- Cyanide Management
- Dust Control
- Environmental Management Systems
- Environmental Monitoring and Performance
- Environmental Risk Management
- Mine Decommissioning
- Tailings Containment
- Water Management
All booklets in this series are available at:
This website provides background information on various issues related to tailings disposal, including disposal and storage methods, and information on tailings safety.
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