Acid mine drainage

A severe case of acid mine drainage. The river is colored red from acidic, metal-rich water from a mine. Acid mine drainage is further discussed in lecture 5.

CHAPTER 3: MINING AND THE ENVIRONMENT

This chapter introduces different kinds of environmental impacts associated with mining and explains the implications on local communities and nature.

Mining changes the environment. Extracting minerals from the ground will change the landscape, alter water quality, change the local ecology, and change land use. To what extent the environment is impacted depends on several things.

The nature of the deposit, the method chosen for extraction, for mineral processing, for storage of mine waste and for treatment of mine water and for mine closure.

The environmental impact also depends on the location; the natural environment; sensitive biotopes; biodiversity and pre-mining land use and on long term goals of mine closure.

The people and society at the mine, before mining, during mining and after mining, will be impacted by environmental changes directly and indirectly. The impact on people will differ due to economic, cultural, and socio-economic dynamics.

The environmental impact at a mine is also very dependent on the preparedness, organisation, economy, policy, culture, experience and skills of the operator, the company, and its people at the mine.

The environmental impact from mining is also very dependent on how mining projects are reviewed, audited, permitted, and monitored by accountable representatives, government agencies, by owners and financers, by activist groups, by international organisations and by shareholders. The capability of authorities and others depend on the same conditions as for the operator.

Legislation, guidelines and policy describe how short-term and long-term goals of sustainable mineral extraction are to be reached.

In depth knowledge of all the factors above is needed within an authority charged with permitting and monitoring a mine site or mining as an activity. It is not a small task and requires several skills from a team and from a network of specialists and authorities. A person or organisation tasked with environmental management, permitting or monitoring mines, also need to understand which of the factors above can be audited and improved, with who the responsibility lies for each factor and how the factors are interdependent. A mining code and environmental legislation in its own is only a small part of ensuring the mine delivers the minerals we need and leaves the environment to support future generations.

Environmental impacts

Mining and mineral processing are important activities that have had a major contribution to human civilisation and advancement of technologies, though, both activities results also in serious environmental impact. The economic benefit if mineral extraction can only be measured by calculating long-term impacts on people and the environment. Predicting and managing environmental impacts are crucial if mining is to benefit society sustainably and protect societies and future generations from environmental and economic risk.

The world’s population continues to increase and as it does, greater demand is placed on the finite resources that the earth provides. Which environmental effects that are deemed acceptable are generally decided in a regulatory process, either in court or by a governmental agency or institution. Legislation is the result of political decisions derived from of the complex interaction of public opinion, debate, democratic process, research, and lobbying. The regulatory process differs between countries. To receive a permit for mining, the company (or governmental agency in some countries) is generally required to carry out an Environmental Impact Assessment (EIA).

The EIA process and the EIA document serves to help decision makers to understand the magnitude and extent of environment impact of a given mining project and to decide whether or not a project can proceed to a next phase, or if any actions have to be implemented before moving forward or if the project should be halted.

Environmental impacts of a mining project

The life cycle of a mining project (Fig. 1) goes through several steps, beginning from mineral ore exploration and ending with closure or post closure stage. Each phase has different type of environmental impacts.  

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Photo: Jonathan Hamisi, SGU.

Exploration drilling – Ground disturbance is limited to access road and drilling site. Photo: Jonathan Hamisi.

Exploration

Environmental impact related to the exploration phase may include clearing of  vegetation for access, housing or investigations. Vegetation is often cleared to allow the entry of heavy vehicles mounted with drilling rigs. Ideally environmental impacts are minimal during the exploration phase however many countries require a separate EIA for the exploratory phase of a mining project because the impacts of this phase can also be profound.  In many areas indirect impacts such as settlement, deforestation, poaching or informal mining commences in the wake of regulated and permitted exploration.

Environmental management and collecting of data for prediction of environmental impacts start at the earliest stages of exploration. Information from exploration about geology, the environment and people in the area is very valuable for later environmental assessments. This is when baseline studies and other important environmental work is carried out. All geological sampling part of early mineral exploration must be designed also to support environmental studies throughout the advancement of the project.

 Information, communication, stakeholder engagement and public consultation is crucial at an early stage. Protocols and guidelines for contacts with indigenous populations must  be well understood before exploration in remote areas with isolated or vulnerable populations.

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Figure 1: Life cycle of a mining project. Source: https://superfund.arizona.edu/

Development

After the exploration phase If an ore deposit proves to be large enough and of sufficient grade, then the project proponent may begin to plan for the development of the mine. This phase of the mining project has several distinct components and environmental impacts at this stage are more extensive. We will briefly present some of the steps and their associated environmental impacts.

Access road construction

Developing a mine involve amongst other supplying heavy equipment and consumable to the site and shipping out the processed ore and metals. Access roads are needed to achieve both activities. Constructing the road have commonly substantial environmental impact especially if it is done in sensitive area or near previously isolated community. The EIA must include a comprehensive study of environmental and social impact of constructing access roads.

 

Clearing and site preparation

Mining in remote and undeveloped area requires substantial amount of land clearing for construction of the mine and plant, housing for project staff, and storage for equipment and consumables. Land clearing has significant environmental impact. The size of the land to be cleared usually depend on the ore deposit size and shape and the conditions of the terranes. The EIA must have a separate assessment on the impact associated with land clearing and site preparation. 

Extraction

Once the land has been prepared the mining and plant construction may begin. Mining commonly involve extracting the ore from the mine through excavation and processing the ore to produce a concentrate of the metal and then eventually producing the metal mined. Mining project will differ considerably according to the extracting and processing method which depends on : the type of ore (sulphides, oxides a combination of both), the metal to be extracted, the depth at which the deposit is buried under the ground, and the terrane conditions. If a deposit is buried deep under the ground the volume of soil and rock also called ‘overburden or waste rock’ to be removed to access the deposit is significant. Thus, an underground mine method might be preferred over an open pit mine.

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Photo: Jonathan Hamisi, SGU.

Acid mine drainage in an abandoned copper open pit mine. Photo: Jonathan Hamisi.

Mine closure and site reclamation

At the end of mining operations, the mine and it associated facilities must be reclaimed and closed. The ultimate goal is to return the site to conditions that resembles the pre-mining status. Some of the impacts of mining can persist for decades or even centuries if they are not well managed during mine closure, therefore the EIA must be very specific about the reclamation and closure plan. Using the baseline study, the project owner need to describe in details each steps of the site restoration and provide information about how it will prevent – on the long run – after mine closure the release of toxic contaminants to the environment from various mine facilities (e.g. TSF and pits); the project owner must also describe how funds will be set aside to ensure the cost of reclamation and closure are paid for as well as monitoring post-closure.

It can be easier to get an overview of the environmental impacts by categorizing them. Below follows a short summary of common environmental impacts from mining consisting of environmental impacts on water, air, social impacts, wildlife, and climate.

Water

A significant impact from many mining activities is the impact on water quality and the availability of water. As a mine can take up a large area, it can change the way water travels within the landscape. Sometimes, rivers need to be re-routed to not flood the mine. At the same time, groundwater needs to be pumped to also not flood the mine. By disrupting the landscape and possibly building dams or re-routing rivers and groundwater, the availability of water can be impacted over long distances downstream from the mine. This can impact flora, fauna, local communities and other industries and should be addressed in the EIA.

Impacts on water quality can have possible health implications for local communities, or impact the environment, flora and fauna. The mine uses large quantities of water that is sometime released to the environment, intentionally or unintentionally, and depending on its composition it can potentially harm the environment. Water can also, in contact with waste rock, dissolve minerals and release metals and other harmful elements to the environment. What elements that can be released to the environment, and the effect, depends on the composition of the rocks. Therefore, the characterization is important to identify possible risks and prevent and mitigate accordingly. Impacts on water quality is controlled by the way mine water and mine waste is managed and is generally a very significant environmental impact from most mines. Impacts on water will be further discussed in chapter 5.

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Photo: Pontus Westrin, SGU

Water sampling close to a mine in Tanzania. Photo: Pontus Westrin.

Air

Impacts on air quality is, as water, controlled by the way the mine is managed, but also by factors such as climate, topology, availability of water and composition of rocks. Dust from mining operations or waste can contain harmful elements such as chemically or radiologically toxic metals, which can have health implications when breathed or when dust contaminates water sources. A large amount of dust, even if not containing significant amounts of toxic elements, can also be harmful.

Dust is often controlled by spraying water on haul roads, open pit walls, waste rock piles and so on. In arid climates with high winds, high temperatures and low precipitation, dust can be hard to control due to water evaporating quickly. Special liquids and solutions, which does not evaporate as quickly, can be used in these cases.

Negative impact on air quality can also come from gaseous emissions from smelters, processing plants, machinery, or power plants. These can contain heavy metals or acid solutions which can be harmful to the environment. These emissions can often be controlled by installing filters and flue gas cleaners.

Vibrations and noise are often counted among the airborne impacts. These can have negative impacts for local communities and wildlife. The mine can potentially have a large area of disturbance due to heavy transports, carrying concentrate or supplies, going to and from the mine.

Social impacts

Social impacts from mining projects are many and diverse. The impacts can differ heavily between projects, but some are general and always need to be considered such as land-use and land occupation. The social impacts of mining will be further discussed in chapter 6.

Wildlife

The impact on wildlife can be large depending on factors such as location and size of the mine, availability of water, safety measures etc. Different types of wildlife react in different ways to mining, some may be heavily impacted and some not. Wildlife documentation is important in the baseline study, and continued monitoring of certain species can give more information on how the environment is influenced by the mine than for example monitoring metal content in rivers. Protecting animals from the mine operations, for example from trucks, open pits, and shafts, can be done by installing safety measures such as fences.

Some species may be endemic and sensitive to even very little disturbance. Even though some species have a higher degree to which they can tolerate human competition, it does not mean directly that it is acceptable to invade their space without good mitigation and control measure in place.

Without prevention and mitigation measures, sensitive species and endangered species can sometime be a reason for halting a project. Criteria that are often examined at this stage are habitat loss and habitat fragmentation. During the baseline study it is critical to carry out an extensive inventory of all types of species that may be impact by the project and their habitat.

Climate

As an industry which consumes large amounts of energy, the climate impact of a mining project can be significant and should be considered in the EIA. The climate impact from mining factors from release of greenhouse gases in relation to usage of machinery, processing of ore and energy consumption, but is also impacted by the loss of carbon uptake in lost forests and vegetation.

> Chapter 4: Mining waste

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