Atacama Pacific Announces Continued Positive Metallurgical Results from Cerro Maricunga Oxide Gold Project
TORONTO, ONTARIO -- (Marketwired) -- 05/09/13 -- Editors Note: There is a photo associated with this press release.
Atacama Pacific Gold Corporation (TSX VENTURE: ATM) ("Atacama Pacific") is pleased to report that column percolation leach tests from the Cerro Maricunga Oxide Gold Project continue to achieve consistent positive gold recoveries. The test work was completed on gold mineralization taken from across the Cerro Maricunga deposit with the goal of determining the impact of gold grade, agglomeration and crush size (25, 50 and 150 mm) on gold recoveries. Table 1 summarizes the results of the completed metallurgical tests. Unless otherwise noted, all crush sizes reference 100% passing (P100) through a screen of the noted crush size. Highlights from the current test work include:
-- Average gold recoveries of 81.5% for non-agglomerated, 25 mm crushed
mineralization
-- Majority of leachable gold extracted in the first twenty days at a 25 mm
crush
-- Gold recoveries of 78% and 80% at a 50 mm crush
-- No significant variation in gold recoveries between the three main zones
-- No significant difference in recoveries between average grade and low
grade mineralization
Table 1 - Summary of Column Percolation Leach Test Results
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Gold
Test Head Grad Recovery Crush Size NaCN
# Zone (g/t Au) (%) (P100 = mm) (kg/t) Note
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60071 Crux Zone 0.48 80 25 0.75
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60074 0.24 80 25 0.62
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60077 Lynx Zone 0.49 82 25 0.75
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60080 0.24 80 25 0.82
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60083 Phoenix Zone 0.45 80 25 0.96
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60086 0.24 82 25 0.85
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65814 Composite of 3
zones; 1 :1 :1
ratio 0.49 85 25 0.78 Non-agglomerated
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65817 0.45 80 25 0.37 Agglomerated
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65828 Phoenix -
Surface trench 0.53 84 25 1.05 Non-agglomerated
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65831 0.53 82 25 0.48 Agglomerated
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65822 Phoenix -
Surface trench 0.50 80 50 0.91 Non-agglomerated
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65825 0.50 78 50 0.40 Agglomerated
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65842 Composite of 3
zones 0.35 85 9(i) 0.72 HPGR
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Notes: Gold recoveries based upon activated carbon assays; column tests run
for 98 to 127 days; non-agglomerated columns were prepared with approx. 5
kg/t of lime and agglomerated columns were prepared using approx. 12.5 kg/t
cement. (i) crushed to P80 = 9 mm
Gold recoveries from non-agglomerated mineralization crushed to 25 mm (approximately P80 = 19 mm) ranged from 80% to 85%, averaging 81.5%, slightly higher than the average gold recovery of 79.5% used in the Cerro Maricunga Preliminary Economic Assessment ("PEA") press released on January 28, 2013. The PEA envisioned a 3 stage crushing system to achieve a P80 = 19 mm crush. Leach kinetics, time versus cumulative gold recoveries, were fast (see figure 1) with the majority of the recoverable gold extracted within the first twenty days.
To view the figure associated with this press release, please visit the following link: http://media3.marketwire.com/docs/Test_Leach.jpg.
Agglomeration Comparison Column Tests
Three pairs of column tests (six columns) were undertaken to determine the impact of agglomeration on gold recoveries. Each test pair, performed on subsets of the same sample material, consisted of one non-agglomerated column and one column using 12.5 kg/t of cement to agglomerate the crushed mineralization. The tests confirmed that gold recoveries from Cerro Maricunga mineralization do not benefit from agglomeration with those tests consistently attaining lower recoveries in comparison to the non-agglomerated columns. The lower recoveries are likely due to reduced permeability caused by agglomeration.
50 mm Crush Column Tests
Two column tests were completed on mineralization crushed to 50 mm. Gold recoveries of 80% for the non-agglomerated test and 78% for the agglomerated test were achieved. The results are similar to the 78% gold recovery achieved in an earlier column tests on 50 mm crushed material (see January 10, 2012 press release) and only slightly lower than the recoveries attained from the 25 mm crush columns.
150 mm Crush Column Tests
Two column tests are underway on Cerro Maricunga gold mineralization crushed to 150 mm. After 80 days, gold recoveries are around 60% and are continuing to rise. Previously, the coarsest crushed mineralization tested was P80 = 100 mm which realized gold recoveries of 77%. Crushing to 150 mm may eliminate the requirement for secondary and tertiary crushing circuits, however, the potential benefit of reduced capital costs associated with eliminating the two crushing circuits must be weighed against the lower gold recoveries obtained from leaching coarse material. As the initial sample was composed of only +150 mm material with no natural fines, a portion of the sample was crushed and finer (-150 mm) crushed material was added to the column to achieve a P80 = 130 mm.
HPGR Column Test
One column test was completed on mineralization crushed with high pressure grinding rolls ("HPGR") to P80 = 9 mm. Gold recoveries of 85% were attained with recoveries of over 80% within the first 10 days. The HPGR option is being reviewed as it may represent a lower cost option for the tertiary crushing circuit considered in the PEA.
Metallurgical Test Details
The column tests, conducted by Kappes, Cassidy and Associates, Reno, Nevada, were run for 98 to 127 days which included a two week rest period followed by a further four days of leaching. The 25 mm crush size columns were conducted on 50 kg of mineralized material placed in a 150 mm diameter column. The 50 mm crushed material was undertaken on 200 kg of sample material placed in 240 mm columns. The 150 mm sample charges weigh 700 kg and are still undergoing leaching in 440 mm columns.
The column tests were not optimized to minimize sodium cyanide ("NaCN") consumption; however, NaCN consumption was low to moderate. The initial leach solution for each column contained 1.0 g NaCN/l of solution and during the test, the continued solution strength was maintained at a target level of 0.5 g NaCN/l. NaCN consumption is projected to be low, in the order of 0.25 kg/t.
The tests were not optimized to minimize the amount of lime or cement necessary to control solution alkalinity. Approximately 5 kg of lime was added to the non-agglomerated samples to maintain at a pH level of 9 to 11. No additional lime or cement was required during the testing.
Column test extraction results were based upon granular activated carbon assays vs. the calculated head grade (carbon assays plus tail assays).
About Atacama Pacific Gold Corporation
Atacama Pacific's primary mineral property is the Cerro Maricunga oxide-associated, breccia-hosted gold project, located in Region III, 140 kilometres by road northeast of the city of Copiapo. In Atacama Pacific's January 2013 PEA envisions a large open pit operation mining 80,000 tonne per day with a conventional heap leach processing facility producing 2.7 million ounces of gold over a 10 year mine life with cash costs of $652 per ounce. The Cerro Maricunga property hosts a pit confined resource estimate of 2.46 million ounces of gold (185.8 million tonnes grading 0.41 g/t gold) in the measured and indicated category with a further 0.94 million ounces (75.4 million tonnes grading 0.39 g/t gold) in the inferred category. The resource estimate is based upon a cut-off grade varying from 0.15 to 0.18 g/t gold.
National Instrument 43-101
Michael Easdon, a professional geologist registered with the American Institute of Professional Geologists, is the independent qualified person for the current exploration program and has reviewed, approved and verified the content of this press release. Carlos Guzman, a mining engineer, Fellow of the Australasian Institute of Mining and Metallurgy and a registered member of the Chilean Mining Commission, is the independent qualified person as defined by National Instrument 43-101 for the Preliminary Economic Assessment for the Cerro Maricunga project. Mr. Guzman is a Principal and Project Director with NCL Ingeneiria y Construccion Ltda., Santiago, Chile.
Visit Atacama Pacific's website at www.atacamapacific.com.
FORWARD-LOOKING STATEMENTS
This news release contains forward-looking statements, including predictions, projections and forecasts. Forward-looking statements include, but are not limited to statements with respect to the results of preliminary economic assessment, statements regarding the expectation and projections of gold recoveries, statements regarding expectations for receipt of permits and environmental approvals, exploration results (including with respect to water resources), the success of exploration activities generally, mine development prospects, and potential future gold production. Often, but not always, forward-looking statements can be identified by the use of words such as "plans", "planning", "expects" or "does not expect", "continues", "scheduled", "estimates", "forecasts", "intends", "potential", "anticipates", "does not anticipate", or "belief", or describes a "goal", or variation of such words and phrases or state that certain actions, events or results "may", "could", "would", "might" or "will" be taken, occur or be achieved.
Forward-looking statements involve known and unknown risks, future events, conditions, uncertainties and other factors which may cause the actual results, performance or achievements to be materially different from any future results, prediction, projection, forecast, performance or achievements expressed or implied by the forward-looking statements. Such factors include, among others, the results of due diligence activities, changes in economic parameters and assumptions, the interpretation and actual results of current exploration activities; changes in project parameters as plans continue to be refined; the results of regulatory and permitting processes; future prices of gold; possible variations in grade or recovery rates; failure of equipment or processes to operate as anticipated; labour disputes and other risks of the mining industry; the results of further economic and technical studies, delays in obtaining governmental approvals or financing or in the completion of exploration, as well as those factors disclosed in Atacama Pacific's publicly filed documents.
Although Atacama Pacific has attempted to identify important factors that could cause actual actions, events or results to differ materially from those described in forward-looking statements, there may be other factors that cause actions, events or results not to be as anticipated, estimated or intended. There can be no assurance that forward-looking statements will prove to be accurate, as actual results and future events could differ materially from those anticipated in such statements. Accordingly, readers should not place undue reliance on forward-looking statements.
Neither the TSX Venture Exchange nor its Regulation Services Provider (as that term is defined in the policies of the TSX Venture Exchange) accepts responsibility for the adequacy or accuracy of this release.
Contacts:
Atacama Pacific Gold Corporation
Carl B. Hansen
President and CEO
416 861 8267
info@atacamapacific.com
www.atacamapacific.com