Copper North Mining Corp. ("Copper North" or the "Company") is pleased to update investors on metallurgical work at Carmacks for copper, gold and silver (see January 21, 2015 news release).
Dr. Harlan Meade, President and CEO of the Company, states "the metallurgical test results have been very instructive; a finer crush on leach materials coupled with increased temperatures in the leach circuit, results in much improved leach kinetics. Leach times are very fast. The test work has yielded much improved leach efficiency and reduction of operational and environmental risks."
Leach and Recovery Plan
The new processing plan consists of crushing to minus 19mm, followed by rod mill grinding to minus 1mm then acid leaching copper in an agitated leach tank, followed by gold and silver leaching in similar tanks, and cyanide destruction for final waste materials. The copper leachate is to be processed in a standard solvent extraction electro-winning (SXEW) plant to produce cathode copper sheets, and gold and silver will be recovered using Merrill Crowe to produce doré bars.
Test work indicates that raising the temperature of the acid leach for copper improves the overall recovery and significantly shortens the leach time. With a grind size of minus 1mm and a leach temperature of 40 degrees Celsius, recoveries of 88% were achieved within 4 to 6 hours, less than half the time for a coarser grind of 2mm at ambient temperature. Waste heat from the manufacturing of sulphuric acid will be used to heat the leach tanks.
The residue in the copper circuit is washed to remove residual acid and the slurry is pumped into the gold-silver circuit for cyanidation; also an agitated tank leach. Optimal leach time for a two stage cyanidation circuit is approximately 12 hours with recoveries of approximately 80% gold and 62% for 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 to the total copper recovery.
Batch test work, including locked cycle tests, is in progress to confirm the very favourable leach dynamics and define recoveries, reagent consumption and optimal equipment requirements. Similarly, test work continues to evaluate the operational application of the SART circuit in the gold-silver recovery circuit. The final steps in the test work are to determine the preferred procedure for filtration of the waste materials in preparation for waste disposal utilizing the "dry-stacked tailings" method.
Project Engineering and Costing
Application of agitated tank leaching results in the elimination of the expensive large, lined leach pads that formed the basis of the October 2012 Feasibility Study and the July 2014 Preliminary Economic Assessment. Results of the recent metallurgical test work for the agitated tank leach facility enables engineering, design and cost estimation of the processing facility. Detailed design and costing of the leach tank circuits, acid plant, SXEW and Merrill Crowe facilities by BGRIMM (Beijing General Research Institute Mining and Metallurgy) can now progress (see October 14, 2014 news release). Earlier evaluation of capital equipment requirements has indicated that there are considerable savings by sourcing detailed engineering and procurement of equipment in China.
With this new information, BGRIMM can now resume design work for the new process plan as part of a new Preliminary Economic Assessment. The improvements based on the new metallurgical test results should lead to a reduction of equipment size in the leach circuit as compared to the previous studies.
Copper North 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 improvement of recoveries and reduced leach times are expected to have a significant positive impact on project economics. The project economics based on the June 2014 PEA are now quite out of date and do not properly represent the leach plan and associated project economics. The Company is considering that it will update the June 2014 PEA with the new leach plan and other aspects of the project to produce a new enhanced PEA.
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, P.Eng. supervised the metallurgical test work 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. Mr. Joe Ringwald P.Eng. is a Qualified Person, responsible for preparation of this news release. Test work is continuing in efforts to refine the process plan and provide additional design information.
On behalf of the Board of Directors:
Dr. Harlan Meade, President, CEO and Director