The City of Yellowknife, Canada is considering using heat extracted from a recently-closed gold mine to warm its buildings. Early in 2008, Yellowknife will formally study what could eventually become Canada's first large-scale geothermal heat plant.
The miners are already laid off; and the mine pumps are shut down, allowing the 2.5 Km deep shafts to fill with water that is consistently close to 50 degrees F. It's estimated that by pumping the naturally warm water out of the mine for distribution through a district heating network, the former Con mine could provide up to 20 megawatts of heat - enough for half the City's populationBy preliminary engineering estimates, the pay-back period for a 20 megawatt system may be under three years. The planned feasibility study in 2008 would firm up the cost effectiveness figures.
Wondering how much time after payback would be needed to equal cumulative profits taken by all previous mine owners?
For more information on district heating schemes in North America, see this earlier TH post.
See background and history at this link. (pdf file)