The cutoff grade used for determining the economics of the open pit was 3.0 g/t gold
using $350 and $5.50 per ounce for gold and silver, respectively. The cutoff grade was
determined from estimated mining costs for open pit mining. For trade-off comparison,
the costs for mining the ore from underground were compared to open pit costs. The
pit optimization and detailed planning (using MINESIGHT® software) assumed a
minimum mining width of 2 m carrying a grade of 3.5 g/t gold. Veins narrower than 2 m
had to have a minimum grade of 10 g/t gold to be included in the mine plan. The pit
bottom was designed for a minimum width of 25 m, essential for safe operation of
equipment. Optimized pit selection and final design were driven by consideration of
several other factors:
• Remote location;
• Availability and capacity of existing construction fleet;
• Severe weather;
• Desire to leave level pit bottom for underground mining interface;
• Selective mining methods and grade control.
A relatively shallow pit and low production rate provides the best practical fit with the
factors and constraints in the list above. The Kupol open pit is an elongated design pit
that selectively mines the Kupol vein system with a waste-to-ore ratio of 12:1
(calculated during the feasibility study stage) (Figure 18-1). The ultimate pit depth in
the Big Bend area will reach approximately 100 m and the pit depth in the majority of
the Central and North zone areas will be approximately 45 to 50 m. Thermistor data
demonstrate that the entire pit is within permafrost, thus the pit design does not include
any measures for groundwater influences in the pit slope design. A final bench
geometry of 24 m bench height (70º bench face angle) with a minimum bench width of
10 m can be successfully and safely mined. The average overall slope angle of the pit
varies depending on geotechnical parameters but averages 49