The unique location of Newmont Canada's Golden Giant mine between the Williams and David Bell operations resulted in the shaft being collared in the hangingwall of the orebody and with depth penetrating through the ore bearing formations into the footwall. Although the shaft did not penetrate any economic ore, ore was discovered within 9 meters of the north wall of the shaft. Initially a large 'shaft pillar' was delineated to protect the shaft from potential mine induced stress and blast damage from surrounding mining at the Golden Giant and the neighbouring David Bell mine. As the operation approached later mine life, economic analysis indicated that, with the original mine plan, a significant amount of valuable ore would be left behind. A study was then commissioned to determine whether it was feasible to mine the shaft pillar concurrently with the deep ore: i.e. while maintaining the complete shaft in full production. The study concluded that it was feasible to extract a 90 m high by 70 m wide destress slot in front of the shaft in order to stress shadow and protect it during subsequent mining of the shaft pillar ore. The study was accepted, a comprehensive instrumentation program was put in place and detailed planning for extraction of the destress slot was completed. Mining of the slot was begun in April 2002 and was successfully completed in July 2003. This paper describes the shaft performance during extraction of the destress slot.
The Golden Giant Mine is located in the Hemlo gold mining district in Northern Ontario, approximately 40 km east of the town of Marathon. Discovered in the early 1980's, Hemlo is a world class deposit [mined by three underground operations, including the Golden Giant [Figure 1]] producing over 1 million ounces of gold annually. The orebody has a tabular shape that dips steeply to the northeast at angles between 60° and 70°. The Golden Giant has a strike length of approximately 500 m, with an average thickness of about 20 m and vertical dimensions of approximately 700 m. Gold mineralization at the Golden Giant is found along the contact of a metasedimentary rock formation with felsic metavolcanic rocks.
The Golden Giant shaft is a 6 m x 4 m timber shaft with the long axis oriented east - west. The shaft pillar mining area is a zone of ore that includes all stopes from 4500 - 4700 extending west to the Q8 stope and east to the S1 stope on the David Bell boundary [Figure 2]. The zone is open above, but has been mined out below up to the 4600 elevation, except for the Q1-3 pillar east of the shaft which extends to 4500 elevation. In total, the shaft pillar mining area represents 660,000 tonnes at 12.23 g/t (104 million U.S @400/ounce). Ore widths vary from approximately 5 to 12 meters.
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Fig. 1. A schematic drawing of Golden Giant and other mines in Ontario's Hemlo region. The insert shows a map of the region. (The figure was taken from a 2002 Barrick Analyst Briefing on Hemlo operations).