Overview

An abandoned mine is a mine that is permanently closed or not operating. It may be Crown held, privately owned or have a filed closure plan.

There are over 5,700 abandoned mine sites in Ontario that have over 17,000 mine features, known as hazards. These hazards range in size from small exploration sites with open pits, trenches or exploration shafts, to large scale operations with many mine hazards.

Deaths due to mine hazards in Ontario are rare, but deaths happen in North America every year.

Mine hazard

A mine hazard is any feature of a mine, or disturbance of the ground, that has not been rehabilitated to the standards set out in Ontario Regulation 35/24, including the Mine Rehabilitation Code.

Mine hazards include, but are not limited to:

  • unprotected and concealed shafts or pits
  • deteriorating structures
  • derelict mining-related equipment
  • destabilized and collapsing underground mine workings
  • contaminated mill tailings
  • stockpiled waste rock and surface water or groundwater
  • discarded tanks or drums of chemicals
  • toxic gases
  • unstable explosives
  • dust and/or uncontrolled surface drainage causing sedimentation damages

Tailings dams

Tailings dams and other mine containment structures are built to store tailings.

Tailings are ground up rock, sand, silt and water from the milling process on an operating mine site. When rock containing ore is mined from the earth and finely ground, water and sometimes chemicals are added to the milled rock to separate the mineral from the waste. Once the mineral is extracted, the tailings that remain are in the form of a slurry. This slurry is pumped into a reservoir or dam that is designed to store them indefinitely.

We have in-house expertise, technical ability and experience to:

  • help mine site owners deal with issues related to tailings dams
  • improve response activities during an emergency
  • respond to tailings emergencies at abandoned mine sites on Crown land

Other hazards

There are other types of hazards that could cause abandoned mine hazards to further degrade or impact rehabilitation measures already in place.

Floods

Floods could washout backfill, weaken ground, or cause tailings dams to flood.

Windstorms

Windstorms can down trees which could collapse:

  • fencing around hazards
  • buildings or other structures

Power outages

Power outages can affect acid mine drainage sites where rehabilitation treatment is required.

Beavers

Beavers can plug spillways on dams. This could increase the amount of water retained in tailings areas, leading to dam overtopping, erosion or failure.

Forest fires

Forest fires can cause environmental damage if the following are stored on site:

  • hydrocarbons including fuels, solvents or lubricants
  • hazardous substances such as polychlorinated biphenyls (PCBs), cyanide or asbestos

Closure plans

A Closure Plan provides the rehabilitation measures and financial assurance to address abandoned mine hazards, protect public health and safety and protect the environment.

Before an advanced exploration or mine production project can proceed in Ontario, a certified Closure Plan along with sufficient financial assurance to rehabilitate the site must be filed with the ministry.

We may order owners of abandoned mine sites to:

  • conduct rehabilitation activities
  • submit a Closure Plan for the site

Crown held abandoned mine sites are rehabilitated through the Ontario Abandoned Mines Rehabilitation Program on a priority basis.