Jun 25 2015
Paramount Gold Nevada Corp. ("Paramount") announced today that a final report from its metallurgical consultants confirms the potential for substantially higher gold recoveries from Paramount's 100%-owned Sleeper Gold Project in Nevada. The new metallurgical program, conducted by McClelland Laboratories of Reno, Nevada (www.mettest.com), culminates a multi-year series of met tests designed to improve the economics of the Sleeper Gold Project.
The met test program addressed two main objectives: 1) To optimize heap leach recoveries from oxide and mixed oxide-sulfide material from all the project's resource areas; 2) To find a viable recovery process for higher grade sulfide material from the West Wood, Wood and Sleeper zones. In situ oxide material accounts for about 12 % of resource tonnes and about 11% of gold resource ounces. Mixed material represents approximately 16% of resource tonnage and 15% of gold resource ounces. Sulfide material totals around 72% of resource tonnes and 74% of gold resource ounces, reflecting its significant potential value to the project.
Oxide and Mixed Material: Heap Leach Recoveries Improve at Relatively Coarse Grind
Optimization of the oxide and mixed material involved acquiring additional representative material from each of the different resource areas and testing coarser crush sizes in order to reduce the already low projected crushing costs for heap leaching. A total of four column tests were performed on oxide material and five on mixed material. For the oxide material, the most efficient recovery option was for 80% passing (P80) a 3/4 inch crush size with an overall average gold recovery of 80%. The 80% recovery average was obtained in 67 to 139 days of leaching using moderate lime consumption and moderate to high cyanide consumption, however, according to the McClelland report, "sodium cyanide (NaCN) consumption should be substantially lower during a commercial heap leach operation." Bill Pennstrom (senior metallurgist and QP on this release) added that "Typical cyanide consumption in production heaps is less than half of the cyanide consumption observed in column tests."
Gold recoveries for mixed material now average 77.5 % at the same P80 3/4 inch crush size. Time and reagent requirements for the mixed material were only slightly higher than for oxide. Facility zone recovery reached 77.1% for mixed material at a coarser crush size of 1.5 inch and it is expected that recovery at this 1.5 inch crush size will be successful for oxide material, which implies the potential for cost reductions for both initial capital and crushing operations.
Sulfide Material: Simple, Proven Partial Oxidation Processes Provide Three Options for Substantial Recoveries
In 2012, West Wood sulfide material generated poor gold recoveries when leached and this resource was therefore left out of the 2012 PEA mine plan, which employed a heap leach scenario. In its new program, McClelland performed tests to evaluate the impact on recoveries of a standard, low cost oxidation treatment on this material prior to cyanidation using three different scenarios: Heap Leaching; Stirred Tank processing and Pressure Oxidation. All three generated excellent recoveries.
For the Heap Leach scenario, column tests were performed on sulfide material from West Wood, Wood, and Facilities areas at 1/2 inch and 1/4 inch crush sizes after undergoing an initial bio-oxidation process inside the column lasting approximately 240 days. Optimum recoveries were reached after 155 days of oxidation time. Gold recoveries for these columns averaged 69 % for 1/2 inch crush size and 76 % for 1/4 inch crush size after 85 to 112 days of leaching and rinsing. In this scenario, sulfide material would be placed on a bio-oxidation pad for a number of months and then re-handled to be placed on the oxide and mixed material heap leach pads for cyanide leaching. For the Stirred Tank scenario, gold recoveries reached 92.6% after 21 days of bio-oxidation at a fine grind of 80% passing 45 microns. The same sized material subjected to Pressure Oxidation obtained average gold recoveries of 89.5%.
Each sulfide recovery scenario would require a substantially different project design with widely divergent capital, operating and cut-off grade parameters. Metal Mining Consultants of Denver, Colorado (www.metalminingconsultants.com) is evaluating the economics of these scenarios in a new Preliminary Economic Assessment (PEA) now in progress. This PEA will incorporate the new met results as well as the updated resource estimate announced on May 5, 2015.
Commenting on the report, Paramount President and CEO Glen van Treek said: "Sleeper has the advantages of a large, near surface, bulk mineable resource with excellent infrastructure. Our objective at Paramount is to improve the economics of this project in the current metal price environment. The original Sleeper mine left behind important oxide and mixed mineralized resources and did not exploit sulfide material. The sulfide material represents an excellent opportunity to increase the mine production schedules and the overall gold grade. These new tests show that excellent recoveries can be obtained from this material using oxidative treatments to partially oxidize pyrite prior to conventional cyanidation. The next step is to assess the impact on project economics."
For complete details on all met test reports visit Paramount's website.
As announced on May 5, 2015 (see news release), SRK Consulting (www.srk.com) has estimated Sleeper's total measured and indicated mineralized material at 294 million tonnes grading 0.36 Au g/T and 3.25 Ag g/T containing 3.42 million ounces of gold and 30.8 million ounces of silver. Additionally, inferred mineralized material was estimated at 241.8 million tonnes grading 0.32 Au g/T and 1.93 Ag g/T containing 2.47 million ounces of gold and 15.0 million ounces of silver. All resources were estimated at a gold cut-off grade of 0.15 Au g/T which SRK considers reasonable for large, near surface, bulk-minable deposits in Nevada at current metal prices. Please note that mineral resources that are not mineral reserves do not have demonstrated economic viability. The quantity and grade of reported Inferred resources are uncertain in nature and there has been insufficient exploration to classify these Inferred resources as Measured or Indicated, and it is uncertain if further exploration will result in upgrading them to an Indicated or Measured confidence level.
NI 43-101 Disclosure
William J. Pennstrom, Senior Metallurgist from Pennstrom Consulting Inc., and sub-contracted to Metal Mining Consultant is a Qualified Person under National Instrument 43-101, has reviewed and approved this news release.
Source: http://www.paramountnevada.com/