Greens Creek | mining
Greens Creek is an underground mine which produces approximately 2,100 to 2,300 tons of ore per day. The primary mining methods are cut and fill and longhole stoping.
The Greens Creek unit has historically been powered completely by diesel generators located on site. However, an agreement was reached during 2005 to purchase excess hydroelectric power from the local power company, Alaska Electric Light and Power Company (“AEL&P”). Installation of the necessary infrastructure was completed in 2006, and use of hydroelectric power commenced during the third quarter of 2006. This project has reduced production costs at Greens Creek to the extent power has been available. Low lake levels and increased demand in the Juneau area combined to restrict the amount of power available to Greens Creek prior to 2009. In 2009 and 2010, the mine received an increased proportion of its power needs from AEL&P. Hydroelectric power was also available during 2011, but to a lesser extent compared to the previous two years due to lower precipitation. When weather conditions are not favorable to maintain lake water levels, the mine relies on diesel-generated power.
There are three main phases to the mining process: development, production, and backfilling.
development – the tunneling or accessing phase
Using plans from the geology and engineering departments, miners drive tunnels 15ft high by 15ft wide to access the various ore zones to be mined.
production – the extraction phase
The method of extraction depends upon the geological nature of the orebody involved. Some of the smaller, more contorted orebodies are extracted using the same tunneling procedure as the development phase. In other more massive orebodies, larger scale extraction methods are used, sometimes producing voids of up to 150ft long, 25ft wide and 120ft deep.
The voids created during the production phase are filled up with a combination of mill waste (tailings) and cement. This “backfilling” process stabilizes the production voids and allows extraction of the ore beside, above, and even below the backfilled area.
