The initial underground stope layout that was completed in 2006 was done using an 8
g/t gold undiluted grade and a 20 grammetre (grade thickness) planning filter. The
planning filter is equivalent to a diluted 6 g/t gold resource grade with a consideration
for minimum mining width from the grade-thickness parameter. The 2010 mine design
update used a 6 g/t gold diluted cutoff grade and 15 grammetre cutoff. Underground
minimum ore mining width is 2.5 m. Veins narrower than 2.0 m horizontal width must
have a gold content of 10 g/t Au to be considered for mining. Material meeting the filter
is included in the plan, and dilution and ore loss are applied. Non-economic material
such as small, isolated vein occurrences is not put in the plan. Ore loss and dilution
criteria are developed for the underground mine from geologic information and
benchmarking other similar mining operations. The plan assumes edge dilution of up
to 1.5 m per sill rib, and panel dilution is applied as a percentage of the ore removed.
Total dilution applied includes edge, interburden, and backfill/re-handling. Ore loss of
5% is applied to the panels and 0% to the sublevels.
During the 2004 drilling program, several thermistors were installed. The analysis
showed that permafrost exists to at least a depth of 250 m, well below the depth of the
feasibility mine plan. Geotechnical analysis recommended that only minimal ground
support be required in the stoping areas over spans up to 15 m. Based on the
geometry of the mineralization and the results of the geotechnical studies, longhole
stoping was the mining method chosen. The level of ground support required has been
found to be much more than originally called for in the feasibility study. Shotcreting and
reinforcing both the hanging wall and footwall with DWIDAGs and cable bolts is
required to minimize groundfalls and dilution. The mining method currently in use is the
AVOCA (Figure 18-2) mining method with the following parameters: