LAKEWOOD, Colo., May 12, 2014 (GLOBE NEWSWIRE) -- Pershing Gold Corporation (OTCQB:PGLC) ("Pershing Gold" or the "Company") is pleased to announce the preliminary results of column leach tests on gold-bearing samples from the Relief Canyon Mine property in Pershing County, Nevada. These results show higher gold recoveries than the previous mine operators achieved and also indicate that this mineralized material leaches quickly. A column comprised of a master composite of drill core samples that was designed to simulate the blend of the different mineralized materials to be leached in the future at Relief Canyon yielded 79.2% gold recovery in 71 days of leaching.
The Company achieved higher recoveries from columns built with limestone breccias and clay-matrix breccias, the two rock types that contain most of the gold mineralization in the Main Zone of the Relief Canyon deposit. A column of the limestone breccia yielded 85.7% gold recovery after 70 days of leaching. Two columns of the clay-matrix breccia produced excellent recoveries, with one column achieving a 91.3% gold recovery and the other reaching 78% recovery after a 70-day leaching period.
McClelland Laboratories, Inc. ("McClelland Labs") of Sparks, Nevada, one of the foremost metallurgical testing facilities in the gold mining industry, performed the heap leach cyanidation tests. They tested eight columns of drill core samples that were crushed to 80% passing -3/4" mesh sieve size. This crush size matches the capabilities of the crushing equipment in place at Relief Canyon. The crushed samples were agglomerated with cement and loaded into 8-inch diameter by 20 foot-high columns.
Experts at McClelland and Pershing Gold's technical staff designed the testing program to determine gold and silver recoveries, recovery rates, and reagent requirements as well as to provide information about the leaching characteristics of the various gold-bearing rock types at the Relief Canyon deposit,
"The results from the column leach tests are a real game changer for the Relief Canyon deposit because these recoveries are so much higher than what has been reported for the two operators that mined the deposit in the 1980s," stated Stephen Alfers, CEO and President of Pershing Gold.
As discussed in RPA's 2013 NI 43-101 Technical Report for the Relief Canyon Mine [See Press Release dated January 24, 2013], Lacana Mining Inc. reportedly realized just 45% to 48% gold recovery from its run-of-mine heap leach operation. The next operator, Pegasus Gold Corporation, achieved 65% to 70% recoveries from crushed and agglomerated ores during the 1987–1988 timeframe.
"The high gold recoveries achieved in the McClelland Labs testing program provide evidence that the Relief Canyon gold deposit is highly amenable to heap leach processing. Additionally, the column leach tests yielded another positive result; leaching occurs very quickly – in as little as 71 days, which is great news. Prior to conducting these tests, we did not have much information about leaching rates at Relief Canyon," explained Stephen Alfers.
The master composite column was constructed using composited samples of each gold-bearing rock type in the Relief Canyon deposit in amounts proportional to the distribution of these rock types in the currently defined deposit. The Company believes the 79.2% gold recovery from the master composite column can be used to estimate the average recovery that future heap leaching may achieve. Similarly, the 71-day leaching period for the master composite column can be used to assess probable leaching cycles for future heaps at Relief Canyon.
"The very favorable results from the column leach tests will certainly enhance project economics and are an important step in moving the Relief Canyon Mine forward to production," said Stephen Alfers. "We will be using the results from the finalized tests in future economic analyses."
Leaching is still underway for a column comprised of jasperoid material. The column leach test also included a column dedicated for environmental testing that is still being evaluated and a second composite column that was blended with 10% by weight of materials leached by previous operators. This column yielded 72.7% recovery after 70 days of leaching, indicating that there is minimal recoverable gold in the previously leached materials.
The eighth column tested materials that did not yield high gold recoveries in previous metallurgical tests and confirmed that this material is not amenable to heap leaching. Pershing Gold anticipates that the column leach test results will be finalized this summer and will be announced in a future news release.
Scientific and Technical Data
All scientific and technical information related to the column leach cyanidation tests for the Relief Canyon Mine has been reviewed and approved by Daniel B. Moore, Nevada Registered Professional Engineer and Vice President and General Manager of the Relief Canyon Mine. Mr. Moore is a Qualified Person under the definitions established by Canadian National Instrument 43-101.
Mr. Earl Shortridge (MS, Metallurgy, Colorado School of Mines), the Company's in-house metallurgical expert, helped design and supervise the column leach metallurgical testing program and has reviewed the tests results. McClelland Laboratories, Inc. crushed and composited the samples using drill core samples provided by Pershing Gold geologists, filled the columns, performed the column leach tests, and supervised subsequent handling and analysis of the leached materials.
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