Technical Report for the Fort Knox Mine - Kinross Gold

Fort Knox Mine Technical Report• All designs utilized toe and crest contours.The ultimate pit was designed from a US $525 per ounce pit optimization, which waslimited by practical pushback size limitations on the south side.On the south wall, the zone of alteration 2-3 benches above and below the schist-granitecontact has been identified as a zone that requires more conservative slopes. In theseareas, design includes slope angles as low as 32°, as well as 90 ft stepout berms up to130 ft above the contact. General design guidelines were documented by geotechnicalconsultants Call & Nicholas (“CNI”) in October 2006, and FGMI technical staff haveworked closely with CNI in areas that require local design exceptions.23.1.3 Other ConsiderationsIn 1996, a 1.3 million short ton slope failure developed in the central south wall abovethe granite-schist contact. The slide was stabilized with mining set backs at the toe of thefailure. Golder Associates Inc. was not able to develop a predictive slope stability model,because of the complex structure in the area, so a range of potential slopes wasrecommended. At a design angle of 28 o Golder predicted little chance of failure and, at adesign angle 35 o , a high chance of failure was predicted. In 2005 Call and Nicholas Inc.was retained to develop a recommendation for the slope failure area, with continuingwork resulting in design parameters described briefly in the section above. Ground waterwas believed to be a contributing factor to the failure, and a dewatering program is inplace.The dewatering department drilled two dewatering wells in 2007. The wells target waterin advancing areas of mining. There are a total of twenty-one groundwater dewateringwells, with a potential pumping capacity of 1,470 gallons per minute (gpm). Eighteen ofthe wells were active in and around the pit, as well as one well north of the pit, near thecauseway. The average annual pumping rate for wells in the pit area was 355 gpm, withan additional 650 gpm from the well north of the pit, for a total average dewatering rateof approximately 1005 gpm for 2007. The total pumping rate shows a 35% decrease in75