Sealing Abandoned Mine Shafts

When the Ministry of the Environment assumed control of the site in 1979, abandoned mine shafts and other mine hazards were scattered over the site's 242 hectares, and little information was available on where they were. Few records of the actual numbers and location of the shafts existed.

Collapsing mine working were a threat to worker safety. Further environmental cleanup work could not proceed over much of the site until the mine structures were located and sealed. In 1992, in consultation with the Ontario Ministry of Northern Development and Mines, the ministry developed an engineering plan to address mine hazards.

The closure of the mine was conducted using the best engineering practices available. It was completed in three phases. Phase 1 began in July 1992, with an in-depth review and analysis of all available archival and historical information pertaining to the Deloro Mine Site. This involved consultation with the Ministry of Northern Development and Mines, review of archives from Trent University and Queen's University, a search of local libraries, discussions with local surveyors, and conservation authorities, as well as a search of the National Archives and National Library of Canada.

An extensive field survey, started in September 1992, resulted in the identification of approximately 110 "mining related features". These included abandoned shafts, stopes, adits, pits and other remnants of historical gold mining at the site. All mine related features were assigned an "ms" (mine site) number and referenced using the Universal Transverse Mercator satellite coordinate system for easy location. That information was mapped and correlated with air photos. Permanent steel location markers bearing the appropriate number for the mine feature were erected at the location of significant mine structures. Ground Penetrating Radar was used in November - December 1992 to locate suspected underground openings.

In Phase 2 of the mine closure work, 4,000 metres of rock were drilled to verify the location of any underground voids that had been found with Ground Penetrating Radar. About 500 metres of core samples were then taken using a diamond bit drill. These core samples were used to assess the stability of the ground above the old mining stopes (mined sections underground).

Phase 3 began in September-October 1993 with the construction of safe access routes. Identified shafts, pits, stopes and adits were backfilled, according to the specifications of the Ministry of Northern Development and Mines, with a free flowing, clean sandy gravel (granular "B" material).Weak crown pillars and unsafe ground were blasted and eliminated. Three engineered rock plugs were installed in narrow vein stopes. Seven significant shafts were fitted with reinforced, acid resistant concrete shaft caps, according to Ministry of Northern Development and Mines standard shaft cap design. Concrete quality was assured through a quality control testing program which was maintained throughout the shaft cap construction period.

By 1995, all mine shafts had been located and secured. With the mines sealed and marked the area was now free of physical mine hazards. The project took three years to complete at a cost of $750,000. Funding assistance was provided by the Ministry of the Environment, the Ministry of Northern Development and Mines and Environment Canada, through the National Contaminated Sites Remediation Program. The federal program provided funding on a 50/50 cost-sharing basis.