Copper North Mining Corp. is pleased to introduce the new processing plan for leaching and recovery of copper, gold and silver at Carmacks.
The testwork program that commenced in September has indicated that the oxide mineral resources at Carmacks have very favourable leach dynamics and that the optimal leach process is an agitated tank leach for both copper and the gold and silver.
Dr. Harlan Meade, President and CEO of the Company, states "that the elimination of a heap leach pad removes many of the concerns associated with leach pads and operating under winter conditions. The agitated tank leach is a contained system, has a small footprint and provides more operational control to optimize recoveries and better manage reagent use. These changes and the ongoing re-engineering of the project provide an opportunity for a significant potential capital cost reduction; the Company has set a new initial capital cost target of US$150M for the project, an approximate 30% reduction compared to that in the July 2014 Preliminary Economic Assessment."
The New Process Plan consists of three-stage crushing to 80% passing minus 13mm, followed by rod mill grinding to 1 to 2mm. The ores are then placed in an agitated tank for leaching of copper oxides with weak sulphuric acid. Testwork has indicated 84% recovery of total copper with leach times of 16 to 18 hours; however, the addition of waste heat from the sulphuric acid plant could further reduce the leach times. The leachate is pumped to the solvent extraction electrowinning (SX/EW) plant for recovery of cathode copper. The copper cathode can be sold directly to end-users for fabrication.
Following copper leaching, the solids are rinsed to remove any remaining acid prior to being pumped directly into a second set of agitated tanks for the addition of lime and cyanide for gold and silver extraction. The testwork at ambient temperatures indicates a recovery of 80% for gold and 78% for silver over 48 hours. Higher leach temperatures (50ºC) provide potential for a significant reduction in leach time and further increases in recovery, and is under investigation. Recoveries for the agitated leach indicate a modest improvement in recoveries for both copper and gold & silver.
Leachate from the cyanide tanks is sent to a Merrill Crowe circuit to recover gold and silver as a doré bar for refining. A SART circuit is used to remove copper cyanates from leach fluids to recover cyanide and thereby manage cyanide consumption. The SART circuit will produce a small amount of copper-rich sulphide that will add slightly to the total copper recovery.
Residues from the cyanide circuit undergo cyanide destruction prior to deposition in a dry stacked waste facility. Dry stacked tails are a preferred means of storing waste as it eliminates the need for a tailings pond. This change is very attractive for environmental management at the site.
With this information, BGRIMM (Beijing General Research Institute Mining and Metallurgy: see October 14, 2014 news release) has commenced design work for the new process plan as part of a Prefeasibility Study to be completed in mid-year, before completing the Feasibility Study at year-end.
The improvement of recoveries and bringing forward revenues from operations, as compared to that of operations in the July 2014 PEA; is an important improvement in project economics.
All metallurgical testwork was carried out at the facilities of Inspectorate Metallurgical Division of Bureau Veritas Commodities Canada Ltd. in Richmond B.C. Dr. Morris Beattie, PEng. supervised the metallurgical test work in progress and has provided Copper North with results of the test work and a preliminary plan for optimizing the processing of the leaching and recovery of the oxide mineralization at Carmacks. Dr. Morris Beattie, P.Eng. is a Qualified Person under National Instrument 43-101 and is responsible for and has reviewed the technical content in this news release. Test work is continuing in efforts to refine the process plan and provide additional design information.