Mining – how it works
The life of a mine can be divided into three main phases – exploration, production and remediation.
In addition to these three main phases, there are a lot of steps along the way. Here we explain the process very briefly.
Permit granting process
Examination of permits for mining operations is a process involving a large number of actors. From an operator declaring its intention to start exploration for ore, to the start-up of a mine requires several different permits. The examination process is different from that for other environmentally hazardous operations in that besides the Environmental Code (1998:808) it also involves examination under the Minerals Act (1991:45). The intention of the Environmental Code is to promote sustainable development, which means that present and future generations are assured a healthy and good environment, while the purpose of Sweden’s Minerals Act is to ensure that society has a supply of essential metals and minerals through the extraction of specially identified natural resources, so-called concession minerals.
The bodies that examine mining operations in Sweden are The Mining Inspectorate of Sweden (Bergsstaten), The County Administrative Board or CAB (Länsstyrelsen) and The Land and Environment Court (Mark- och miljödomstolen).
The Mining Inspectorate plays a central role in examining mining operations and hearing applications for exploration and mining permits. Another important mission is to supervise compliance with the Minerals Act (1991:45). The Mining Inspectorate also provides information about legislation and ongoing prospecting and processing for companies, interested parties, authorities, media and the public.
The Mining Inspectorate is a separate decision-making body sorting under the Geological Survey of Sweden (SGU) but has independent status in exercising authority. The Mining Inspectorate is headed by the Chief Mining Inspector who decides on issues in accordance with the Minerals Act.
The County Administrative Board plays an important role in the examination of mining operations. It participates e.g. as a referral body in examining exploration permits. For some exploration work a permit is also needed from the County Administrative Board, for example driving offroad. When examining a mining permit, consultation also takes place with the County Administrative Board. The County Administrative Board Environmental Permit Office decides on test mining permits. Consultations are also held with the County Administrative Board on a number of occasions.
Besides being an important element in examination, the County Administrative Board often also has a supervisory function in mining operations. There are 21 CABs in Sweden.
The Land and Environment Court. The environmental permit for mining operations is one of the last stages before operations can begin. The same rules in the Environmental Code apply to mines as to other operations impacting the environment. The health and environmental effects of a mine and protective measures if the mine is granted a permit are examined by the Land and Environment Court. Here decisions are also made on the conditions for operations, for example noise, damming, dumping, limiting emissions and so on.
There are five land and environment courts in Sweden. They are located in Umeå, Östersund, Växjö, Vänersborg and Nacka district courts.
An exploration permit according to the Minerals Act gives exclusive rights in relation to the landowner and other prospectors to map the bedrock geology in the relevant area with the aim of finding out if there is a deposit, how it is shaped, its size and possible breaking value. An exploration permit also gives preference to a processing concession of the possible deposit. It should be pointed out that an exploration permit, despite its name, does not give anyone the right to immediately begin exploration work. In order to carry out survey work, a valid work plan is required, and often also other permits or exemptions in accordance with other legislation, for example off-road driving permits. The permit holder must also provide financial security to the land and property owner for any damage that may occur. Survey work may not take place in certain places, including national parks.
An application for an exploration permit is made to The Mining Inspectorate (Bergsstaten). What an application for an exploration permit must contain is regulated in the Minerals Act. In cases where the application concerns oil, gaseous hydrocarbons or diamonds, the application must also be announced. If the application concerns another mineral, the property owners concerned and other known owners must be notified. Regardless of which mineral the application refers to, the County Administrative Board and the municipality shall be given an opportunity to comment and if the area applied for is used for reindeer husbandry, the Sami Parliament shall also be given the opportunity to comment.
Before exploration work begins, there must be a valid work plan. The work plan shall, among other things, contain an account of the exploration work and a timetable, but also an assessment of the extent to which the work can be assumed to affect public interests and individual law. The work plan must be adapted to the ongoing land use in the area where the exploration work is to be carried out. Exploration work must be carried out so that the slightest damage and intrusion possible is caused. The exploration work often consists of bedrock mapping, block exploration, geophysical measurements, geochemical sampling and core drilling.
The first step in a long value chain. Exploration is about gathering information by examining the bedrock. In practice, these are geophysical measurements such as electromagnetic measurements and gravimetric measurements. All to understand the geological history of the area and thus mineralogical composition. In order to meet the need for metals to cope with the climate, exploration must increase. Exploration is the first and most important step for all mining operations and the start of a long value chain. Therefore, active exploration is absolutely necessary for a continued mining and mineral industry.
Prospecting activities usually begin in an office, where all existing data on the bedrock and its chemical and physical properties are reviewed to determine whether the area is favorable to certain types of mineralization and ore. Different types of rock concentrate different metals, so that if a company is looking for gold, it looks for rock types that are favorable to gold deposits. If the company’s interest is in industrial minerals, such as calcite or dolomite, it looks for other rock types.
After the first mapping and sampling phase, which usually takes several years, all the collected data are analyzed. If nothing interesting is found, the area is abandoned. If there are signs that something interesting can be hidden in the ground, the next phase of field investigations is initiated. Based on the collected information, the investigations usually target a more limited area with high potential for discovering ore.
Out of 1,000 prospecting projects, only about one gives sufficient indications of the existence of ore in the area. The entire process from the initial field mapping stage to the start of mine planning usually takes several decades, even if there are favorable geological indications of ore in the area. Most prospecting projects fail to find ore.
At the turn of the year 2020/21, there were 550 valid exploration permits. This can be compared with 2013 when the number of valid permits was 823. The total exploration investments for companies looking for ore in Sweden was SEK 955 million in 2019. An increase of 22% from 2018. However, it is noteworthy that this mostly concerns exploration investments close to or in existing mines, i.e. not exploration on new locations.
The large companies, LKAB and Boliden, hold most exploration permits. Few of the exploration permits lead to a new mining establishment, but they all create a greater knowledge of the minerals and bedrock.
The environmental impact of exploration is usually barely noticeable, and is not very different than forestry or, for example, well drilling. On the other hand, questions may arise among the local population if the exploration is carried out within sight of buildings or communities, especially if it is in parts of the country where one is not used to this type of activity. The fact that exploration is being carried out does not mean, however, that there will be a mine at that particular location in the future. There are 12 mines throughout Sweden and the area of the country’s mines does not even amount to one per mille of the land area. Exploration, and especially not mines, is something that does not affect more than a very small proportion of the population.
Production differs greatly from mine to mine, for example depending on the ore mined, the location and the enrichment method. This review briefly and comprehensively describes the process, but does not cover all parts of a mining production. More reading is linked below.
The deposit forms the mine. Sweden’s bedrock was formed several million years ago. Different processes form different types of mineralizations and concentrations of valuable minerals. If these mineralizations are considered economically viable, they are called ore.
A number of factors come into play when calculating the deposit’s mining value. Important factors are the mining cost of the deposit, the metal content and its location. A copper ore with a content of 0.3 percent is probably not profitable to mine if it is at a depth of 1000 meters, but can be interesting if it is on the surface. This is because the mining cost is lower in an open pit, i.e. a mine on the surface, than in an underground mine. In opencast or open-pit mining, more ore can be mined with a lower content, while underground mines mean more expensive operations. If deposits with a higher concentration are found at great depths, however, underground mines can be profitable. In Sweden, there are mines that go down to a depth of more than 1,400 meters.
A crucial factor in the mine’s economy is the value of the ore, which is often given in SEK per ton. The value is determined above all by the metal content of the ore, and usually amounts to between SEK 200 and SEK 2,000 per ton. Metals of low value like iron therefore require ores with a high metal content (30-65 per cent Fe) for extraction to be economically viable. Deposits of gold and platinum which have a very high metal value on the other hand are profitable to extract even at a very low content (1 – 10 g metal/ton ore).
Ore extraction can be carried out in an open pit or underground. Ore bodies are often mined in open pits down to a depth of 300 – 400 meters, below which normal extraction changes to underground extraction. In Sweden, underground extraction is dominant, but the majority of the world’s extraction is in open pits. Extraction underground entails bigger costs and greater complexity, and there a richer deposit is required to achieve profitability. As an example where extraction takes place at deeper levels, the distance the ore needs to be transported to reach the surface gradually increases in length, and costs and energy needs thereby increase. Great depths often also mean increased rock stress, which lead to more stringent demands for rock reinforcement, which also increase costs. Great depth also means increased costs for and need of ventilation in the mine.
In underground mines the ore is accessed by driving ramps or shafts down to the level where the ore is extracted. At the extraction levels, production areas are prepared, i.e. drifts (tunnels) are driven to the ore face. A development tunnel can be up to 200 meters long. Where necessary, the walls and roof of the tunnel are reinforced with bolts, nets and shotcreting. The choice of mining method is made after consideration of a number of parameters, such as the placing of the ore body, the geology, geometry, rock mechanical conditions and the environment and surroundings.
One precondition for open pit extraction is that the ore body extends up to the surface or is not covered by an excessively thick layer of soil or rock. In most open pit mines, ore is extracted by so-called benching. The mining method is based on the ore being extracted in “benches” at successively lower levels. These benches give the open pit a characteristic stepped appearance.
Concentration. The ore extracted in the mine needs to be treated to separate economically valuable mineral from mineral with little or no economic value. This is done in a concentration plant. How large a proportion of the material extracted has commercial value varies from mine to mine, but as an example, iron mines contain around 50 per cent iron bearing mineral, while a copper mine perhaps contains only 0.5-1.5 per cent copper minerals (e.g. chalcopyrite). A goldmine can be profitable with as little as one or a few grams of gold per ton of ore, i.e. in the order of 0.0001 per cent. Whatever is not commercially valuable mineral is separated out from the process as “waste rock”. The concentration process normally begins with crushing and grinding.
The most common separation processes are based on differences in the density, magnetic or surface properties of different minerals. There are also methods based on differences in electrical conductivity or optical properties. For iron bearing minerals, the magnetic separation method is chosen, depending on the mineral type, between high- or low-magnetic methods. Magnetite ores react strongly to magnetic fields and can be separated by low magnetic methods, while hematite is magnetically weaker and therefore needs high magnetic methods.
Gravity based methods can be used when there are great differences in density between the minerals to be separated. For example, gold, tin, lead and tungsten-bearing minerals are usually heavy in relation to waste rock and can be separated using such methods. For the base metals copper and zinc, the methods used are often based on surface properties. This is done through selectively adsorbing chemicals (called collectors) on specific mineral surfaces to make them hydrophobic, or water repellent. In flotation cells, the mineral suspension is mixed with air bubbles which attach themselves to the hydrophobic particle surfaces and lift the particles up to the froth phase, while waste mineral is not lifted by the bubbles and instead sinks to the bottom of the cell. There are also processes based on so-called reverse flotation, where instead the waste mineral is floated away from the commercial mineral.
The lifetime of the mine
Mining operations are generally continued as long as extraction is profitable and there are deposits left to extract. Profitability is largely steered by raw material prices. It is common for the mining company to prospect while the mine is operational. During operations, knowledge is gathered about the geology of the area and around the deposits. It is not unusual for further information about the deposits and the immediate area to bring the discovery of more ore near the mine. The number of years the mine will be in operation is usually decided by the mine’s ore base. The ore base is the known deposits of ore, often expressed in millions of tonnes. The ore base divided by ore extracted per year gives the mine’s life at the time of calculation.
Remediation is restoring the area where the mine has been in operation so that it becomes a natural part of the surrounding landscape again. The goal is to create a long-term solution that does not harm the environment or involve safety risks for nature and people. The method used is determined by the conditions of the specific area.
The Environmental Code sets requirements for plans and finances for remediation of the mining area. The Environmental Code’s principle that the polluter is responsible applies. In 2019, approximately SEK 3.5 billion was set aside by the mining companies in Sweden for this. A company may not open a mine unless money has been set aside to finish the area when the mine is closed. Money is locked with the County Administrative Board for the company until the mine is closed and remediated.
Read more about exploration and production at some of our mining companies
Read more about some of our exploration companies
Read more about exploration, mining, land, compensation, etc.
> Bergsstaten (Mining Inspectorate of Sweden)
> Swedish Geological Survey, SGU