Sherwood Reports Geotech Program Results in Improved Pit Slopes at Minto Mine
Tuesday, July 17th, 2007
Sherwood Copper Corporation announce results of an independent geotechnical investigation of the pit slopes at its high grade Minto copper-gold mine in the Yukon. The result is a recommendation to increase pit slopes by an average of more than five degrees on the north, west and east side of the pits, which should result in reduced waste stripping and costs versus the estimates used in the 2006 feasibility study. The southern pit slope is subject to further investigation in the future, but since it lies between the main Minto deposit and Area 2, it is expected that most of the material forming the south wall of the main Minto pit will be mined, regardless of the slope, in order to access the Area 2 resources.
â€œThe increased recommended slope angles in the open pit, that resulted from the SRK geotechnical evaluation at the main Minto deposit, represents one of a number of post-feasibility optimizations being evaluated by the Company as part of our â€˜relentless pursuit of valueâ€™ strategy,â€ said Stephen Quin President and CEO of Sherwood. â€œThese geotechnical results should lead to reduced waste stripping and operating costs both in the short term and over the life of the high grade Minto open pit.â€ The results of these geotechnical investigations will be incorporated in the expanded pre-feasibility study currently in progress.
Following one of the recommendations in the Definitive Feasibility Study, the results of which were announced August 28, 2006, Sherwood retained SRK (Canada) Inc. to conduct a comprehensive investigation of the geotechnical characteristics of the rocks in and around the main Minto copper-gold deposit. This work included a review of all prior geotechnical investigations, re-logging of the four geotechnical drill holes completed by Sherwood in 2005, field and laboratory strength testing on rocks, geologic structure mapping and the drilling of five new geotechnical drill holes in 2007. The results of all this work was put into a comprehensive geotechnical model for the Minto pit. The results of the data collection programs indicated that rock strength and geologic structure are highly variable at the main Minto pit location. SRK determined that a probability based evaluation would result in better optimization of pit slope angles, because it would take full account of the variability in rock strength and rock structure orientation. Based on all of the detail collected, the following recommendations were made as compared to the previous recommendations used in the feasibility pit design.
West Pit Wall, Previous Recommended Interramp Slope Angle 38 to 46 degrees, Current Recommended Interramp Slope Angle 52 to 57 degrees
North Pit Wall, Previous Recommended Interramp Slope Angle 46 to 51 degrees, Current Recommended Interramp Slope Angle 52 to 55 degrees
East Pit Wall, Previous Recommended Interramp Slope Angle 38 to 46 degrees, Current Recommended Interramp Slope Angle 53 to 55 degrees
Sherwood is now working with SRK to incorporate these changes to the pit slope angles into its open pit design for the main Minto pit, which should result in a significant reduction in the overall quantity of waste stripping. For example, the August 2006 feasibility study estimated that a 5 degree increase in pit slopes would reduce the waste stripping by approximately 4.5 million tonnes.
A similar program of geotechnical work is nearing completion for Area 2, which information will be used in the design of an integrated pit encompassing both the main Minto deposit and the Area 2 deposit defined in 2006.
Sherwood has made considerable progress in commissioning the mill. Over the past 10 days, the mill is averaging approximately 900 tonnes per day of throughput (or about 60% of capacity) and has achieved over 1,100 tonnes on successive days. Copper recoveries have been averaging approximately 85% and concentrate grades over 40% copper, which is higher than expected at this stage of commissioning. Mill throughput and copper recoveries have been affected by some performance issues with the rougher (first stage) flotation cells and by commissioning of the tailings filters. The balance of the plant has been performing well. These equipment performance issues are believed to be temporary and are being addressed with equipment providers and should be resolved shortly.
The Minto Mine is a high-grade copper-gold deposit located in the Yukon Territory of Canada. The mill is currently undergoing commissioning and is expected to ramp up to full production during the third quarter of 2007.