Sleeper Project Tests Support Economic Improvements
WINNEMUCCA, NV - Paramount Gold Nevada Corp. reported 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 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.
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.
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%.