While definitions vary, abandoned mines are most consistently defined as those mine sites where the mine operator or exploration company has ceased or suspended indefinitely their activities, be that exploration, mining or mine production, without rehabilitating the site. Some parties make a distinction between abandoned mines, those being all mine sites in the condition just described, and orphaned mines, those being abandoned mines for which an owner cannot be identified.
Abandoned mines create numerous problems, including public health and safety concerns and environmental hazards. These problems stem from both the physical hazards related to abandoned mines, including open pits and shafts, trenches, dam collapses, and ground subsidence, and environmental hazards, including acid mine drainage, metal leaching, and contamination from process agents, fuel and other pollutants that have been left on site.
Mines become abandoned for a variety of reasons. There are at least 10,000 abandoned mines in Canada. Historically, mines became abandoned because there was no legislative mechanism to prevent them from becoming so, and not enough understanding of the physical and environmental hazards involved. There were no rules in place to require clean up, and, over the decades, many records were lost or destroyed that would have matched owners with sites. Through legislative and regulatory departments in the 1980's and 90's, rules were slowly developed to require companies to clean up after themselves, and to put aside funds in order to do so. Tragically, these same rules are now either being rolled back, as in Ontario, or are not fully developed and implemented, as in Manitoba and the Yukon.