Mining and the Environment

How mining affects the environment

Most of the environmental effects of mining come from a handful of activities: clearing and digging the ground, moving water off and around the site, crushing rock and storing what is left over. The scale differs enormously between a small gold pit and a large iron ore operation, but the list of things to watch is much the same. Our longer article on the seven main environmental impacts of mining goes through each one with sources. The short version is below.

For iron ore, coal and other bulk commodities, the biggest issues tend to be the sheer area disturbed, dust and the drawdown of groundwater around deep pits. For gold, copper and zinc mines in sulfide rock, water quality usually matters most.

Acid mine drainage and mine water

Acid mine drainage starts when sulfide minerals such as pyrite, sealed underground for millions of years, are exposed to air and water in a pit wall, a waste dump or a tailings pile. They oxidize and produce sulfuric acid, and the acid dissolves metals such as iron, copper, zinc, cadmium and arsenic from the surrounding rock. The orange iron staining in streams below old mines is the visible part. The dissolved metals are the part that harms fish and makes water unsafe for irrigation or drinking.

The reason it gets so much attention is time. Once the reaction is under way it can run for decades after the mine closes, and someone has to keep treating the water. The US EPA’s page on abandoned mine drainage explains the problem from a regulator’s side. Treatment falls into two groups:

• Active treatment doses the water with lime or another alkali in a plant, so the metals settle out as sludge. It works on large flows but needs power, chemicals and staff for as long as the water runs.
• Passive treatment uses constructed wetlands, limestone drains and bioreactors that rely on chemistry and bacteria. It costs less to run but needs land and suits smaller or gentler flows.

Our guide to acid mine water treatment plants and systems compares the two in more detail. Prevention is cheaper than either: keeping reactive rock dry, covered or underwater stops most of the acid from forming in the first place.

Tailings, closure and site restoration

Tailings are the finely ground rock left after the valuable mineral has been removed, usually pumped as a slurry into a storage facility held back by a dam. Most of the worst mining accidents have been tailings dam failures. After the collapse at Brumadinho in Brazil in January 2019, the mining industry body ICMM, the UN Environment Programme and the Principles for Responsible Investment published the Global Industry Standard on Tailings Management in 2020, which sets requirements for design, independent review and emergency planning.

Restoration is planned long before a mine closes. Topsoil is stripped and stored at the start, waste dumps are shaped so they drain and can be planted, and many jurisdictions require a closure plan with money set aside as a bond. Some operators now reprocess old tailings to recover metal that earlier plants missed, which can pay for part of the cleanup. Our articles on tailings management and reprocessing and mining site restoration cover both.

IMWA and the mine water literature

Many readers reach this page looking for a specific journal article on mining impacts on water areas, or for the wording a paper used to acknowledge the International Mine Water Association. Some background helps. IMWA was founded in 1979 and brings together consultants, mining company staff, academics and regulators who work on mine water. It publishes the quarterly journal Mine Water and the Environment and holds regular symposia and congresses, whose papers are a good source on acid drainage, mine flooding and treatment. Its website is imwa.info.

An acknowledgement is simply the short section at the end of a paper that thanks people or bodies for funding, data or support. If you are citing a congress paper, cite the proceedings volume with its editors and year. Our notes on how researchers acknowledge IMWA and on Christian Wolkersdorfer’s mine water research trace the phrases people search for back to their sources.

Permits, baselines and environmental services

In most countries a mine needs an environmental impact assessment and a set of permits before construction, and the assessment depends on baseline data: water quality, flow, plants, animals, air and land use measured before anything changes. Companies that skip early baselines often struggle later to show which effects were theirs. “Mining environmental services” usually means the consultants who collect those baselines, write the assessment, design water and tailings systems, monitor during operation and plan closure. Consultation with local and Indigenous communities runs alongside, and in many places it decides whether a project goes ahead at all. Our overview of the environmental regulations mines face sets out the main rules.

Exploration has a footprint too, from access tracks to trenches and drill pads. Screening a license with satellite mineral detection before field work means the first trenches and drill holes go on ranked Exploration Targets instead of a grid across the whole license. It is an early step, ahead of a JORC or NI 43-101 resource estimate, not a replacement for one.