Ground Substance Area

General Overview

The management of ground subsidence areas associated with former mining operations and associated underground workings, acquired by Kinross in December 1999, was a significant part of the reclamation work required on the former Royal Oak Mines properties. The properties, which were generally abandoned included the Hollinger Mine, the McIntyre Mine, the Coniaurum Mine and the Vipond Mine. These mines were operational at various times between 1910 and 1988. The subsidence rehabilitation work was done as a cooperative effort with the Ontario Ministry of Northern Development of Mines.

Many drifts and stopes remained that were not backfilled as part of the mining operations. Historically, loose sand backfill was used in Timmins area mines. In several cases, very thin and weak crown pillars remained between the stopes and the ground surface. Historical records indicate this had been a concern in Timmins, particularly in the Schumacher area, as far back as the 1920's when large holes would appear in public areas. As the mines were abandoned and mine water levels were allowed to rise, sand backfill was washed out of several stopes, removing support that would otherwise keep the stope walls and crown pillars from collapsing. Since 1999, when water levels began approaching the ground surface, a significant number of subsidence areas became evident, often on commercial, institutional and residential properties outside of mine property boundaries. Extensive ground subsidence also occurred on the Hollinger Golf Course property, south west of the Hollinger Mine, where several parallel stopes exhibited overburden collapse into the mine workings.

Due to the sheer size of the subsidence areas and the associated stopes located underneath and nearby, Kinross was obligated under the Ministry of Northern Development and Mines agreement to secure these areas in order to prevent inadvertent access to the mine workings by the public. In 2000-2001, Kinross Gold Corporation began prioritizing subsidence areas for fencing and filling. Kinross carried out extensive back filling of open stopes at the corner of First Avenue and Hollinger Lane in Schumacher, the Hollinger Golf Course parking lot, and at locations along the Algonquin Boulevard corridor. All existing and potential ground subsidences were fenced in areas easily accessed by the public and signs were placed to prohibit unauthorized access. A program was also initiated to regularly monitor fencing conditions and carry out repairs where necessary.

Investigations were also carried out to determine the stability of other stopes where subsidence had not yet occurred. In several cases, it was determined that backfill had settled or washed out of stopes and that filling would be required to ensure stope wall and crown pillar stability. Methods are being investigated that would allow for back filling of these stopes, through crown pillars, from the surface. One such method would consist of drilling series of large diameter boreholes to allow sand fill to be poured directly into the stopes. Once the backfill reaches equilibrium and no longer settles, this would prevent peeling of the stope walls and ceilings, thus maintain-ing the integrity of the stope.

Kinross Gold Corporation continues to monitor ground subsidences associated with the former Hollinger Mine. A final closure plan for the mine will be prepared by 2005.