Integra Gold Reports Up to 98% Gold Recovery from Phase 1 Metallurgical Testing at Lamaque Gold Project
VANCOUVER, BRITISH COLUMBIA -- (Marketwired) -- 05/01/13 --
-- Test work completed by ALS Metallurgy ("ALS") from Kamloops, BC
-- Initial gold recovery up to 92% for the South Cluster samples and up to
98% for the North Cluster samples
-- Phase 2 test work has now commenced and will involve the addition of
flotation to the metallurgical process to optimize gold recovery
-- Results to be incorporated into forthcoming Preliminary Economic
Assessment (PEA)
Integra Gold Corp. (TSX VENTURE: ICG) ("Integra" or the "Company") is pleased to announce it has completed Phase 1 metallurgical testing at its Lamaque Gold Project in Val d'Or, Quebec. The work has been completed by ISO 9001 compliant ALS from Kamloops, BC. Over 255 kg of core from the North and South Clusters has been used in this program. Optimized flow sheets involving gravity separation followed by direct cyanidation indicates overall gold recovery of up to 92% for the South Cluster samples and up to 98% for the North Cluster samples. A map illustrating the location of the two resource clusters is provided at the following link:
http://media3.marketwire.com/docs/icg0501.pdf
"Initial results have exceeded our expectations, not only showing high gold recovery, but also the lack of deleterious and hazardous elements in the tailings produced. Phase 1 testing clearly indicates that gold recovery can be optimized to the plus 90% level which is consistent with what was achieved for over 70 years on similar types of mineralization at the neighbouring Lamaque and Sigma mines," commented Company President and CEO, Stephen de Jong. "Following these positive results we have initiated a second phase of metallurgical testing. Phase 2 will focus on optimizing gold recovery using a combination of grind, cyanide concentration, leach time, and the addition of flotation to the flow sheet. We anticipate having this work completed towards the end of Q3 2013."
The following table gave a summary of optimized recoveries obtained for Phase 1 work.
Phase 1 - Optimized Gold Recoveries
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Maximum Gold Recoveries after
Optimization(i)
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Gravity Cyanidation Total
Recovery Recovery Recovery
Composite (%) (%) (%)
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Master Composite (4 tests) 18 - 26 63 - 70 89
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S. Cluster High Grade (4 tests) 15 - 21 64 - 74 91
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S. Cluster Average Grade (4 tests) 22 - 26 63 - 70 92
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S. Cluster Cutoff Grade (4 tests) 13 - 21 69 - 79 92
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N. Cluster High Grade (3 tests) 30 - 44 54 - 67 98
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N. Cluster Average Grade (3 tests) 30 - 43 55 - 66 98
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N. Cluster Cutoff Grade (3 tests) 28 - 39 58 - 70 98
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(i) Optimization of grind size, leach time, and cyanide concentration
Composites Characteristics
A total of 6 composites, each consisting of up to 25 individual HQ core samples, were prepared and sent to ALS Metallurgy in Kamloops, BC. Three of the composites were from the South Cluster, which includes the No. 4 Plug and Triangle Zone, and three were from the North Cluster, which includes the Forestel and Parallel Zones. No samples from the No. 5 Plug, a target within the North Cluster, were sent as no drill core was available when the tests were initiated. The weighted average grade of the three composites from each cluster examined represent, respectively, the estimated cutoff grade (3 g/t Au), the regional average deposit grade (6 g/t Au), and the higher grade mineralization (15 g/t Au).
ALS prepared a seventh sample, the Master Composite, an even weight mix of composite of the six samples. Testing was initially done on this sample to optimize the metallurgical process for the individual six samples. The head assay of the seven composites is presented in the table below.
Composites Characteristics
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Assay Results
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Fe S C As Ag Au TOC(i)
Composite (%) (%) (%) (g/t) (g/t) (g/t) (%)
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Master Composite 5.1 1.47 - 0.007 4 8.15 -
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S. Cluster High Grade 6.4 2.08 1.56 0.003 4 15.30 0.02
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S. Cluster Average
Grade 6.4 1.72 1.76 0.002 1 6.28 0.02
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S. Cluster Cutoff Grade 6.3 1.49 1.59 0.003 1 3.16 0.02
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less
than
N. Cluster High Grade 4.1 1.57 1.04 0.002 3 14.60 0.05
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less
N. Cluster Average than
Grade 4.5 1.20 1.02 0.002 2 6.14 0.02
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less
than less
N. Cluster Cutoff Grade 4.0 0.99 0.79 0.002 than 1 3.21 0.02
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(i) Total organic carbon
Iron content in the South Cluster samples measured approximately 6% of the feed and approximately 4% of the feed in North Cluster samples; most of the iron was present in non-sulfide gangue minerals. Sulfur measured about 1.5 to 2% of the feed in the South Cluster 1 and about 1 to 1.5% of the feed in North Cluster; the sulfur was present almost entirely as pyrite with trace levels of chalcopyrite. The Master Composite feed was about 5% iron and 1.5% sulfur. These statistics would identify the samples as relatively clean mineralized material. Furthermore a very low quantity of detrimental elements such as arsenic or organic carbon was detected in all samples.
Trace Mineral Searches (TMS) for gold were conducted on the high grade composites of both clusters using QEMSCAN to determine liberation and association characteristics of the gold particles within the samples and to ascertain if differences between the two samples existed. Results showed that in the South Cluster samples, a higher percentage of the gold was present in inclusions with other minerals compared with that of the North Cluster samples. Inclusions are when the gold particle is surrounded by the other minerals. This could reduce or eliminate contact between a leach solution and the gold particle, possibly inhibiting leach performance. These minerals would more likely be recoverable to a flotation concentrate. Finer grinding or increased leach times may be required to leach such gold particles, a process which will be further investigated with the Phase 2 work.
Composites from the North Cluster have a higher combined percentage of gold particles that were liberated or associated with sulfide minerals when compared to the South Cluster. They would likely have a higher specific gravity and therefore may respond better to gravity separation.
A Bond ball mill work index test was also conducted on the Master Composite. Those tests are performed to assess the energy, and therefore costs, that would be required to grind the samples. The result was a Bond ball work index of 13.8 kW-hr/tonne; this would characterize the composite as moderately soft.
Summary of Phase 1 Metallurgical Testing
Master Composite Results
On the Master Composite, a series of Knelson gravity concentrations with hand panning of the gravity concentrate were conducted with cyanide leach extractions of the gravity tailings. These were completed at four primary grind sizes: 130, 105, 79 and 56 microns at K80 (80% passing). The best combined gravity and cyanide leaching (48 hours leach) recovery obtained was about 89% at the 79 microns K80; 23% of which was by gravity separation. A grind target of 75 microns K80 was chosen for subsequent testing of the individual composites. A rougher flotation test on the Master Composite conducted at a primary grind sizing of 130 microns K80, recovered 89% of the feed gold to a rougher concentrate containing about 11% of the mass.
South Cluster Results
A series of gravity concentrations with cyanide leaches of the tailings were conducted on the individual composites from the North and South Clusters at primary grind sizing targeting 75 microns, 80% passing, with 1,000 ppm sodium cyanide ("NaCN") concentration in the leaching and 48 hour leach duration.
The South Cluster samples showed a gravity recovery of between 12 and 25% and combined recovery of approximately 79% to 84% feed gold. These samples were subsequently improved to approximately 90% by grinding the samples finer (50 microns, 80% passing), with most of the gain coming from improved gravity separation. Diagnostic leaching of leach tailings also showed potential improvement of overall recovery from the Southern Cluster samples by increasing leach intensity or duration.
Of about half the unrecovered gold from the South Cluster tests, approximately 9% of feed gold was found to be in sulfide minerals and non-recoverable through direct leaching at the current primary grind sizing. A number of cyanidation tests were therefore conducted on the South Cluster composites with attempts to improve recovery. The best combined recoveries were achieved with 96 hour leach durations and with reducing primary grind targets to 50 microns, 80% passing. This test showed improved gravity recovery, as well as improved overall recovery with about 91% to 92% percent of feed gold being recovered. Under these conditions, cyanide consumptions remained relatively low at 0.4 kg/tonne feed.
A set of rougher flotation tests were conducted on the South Cluster composites to test the viability of such a method. These tests recovered about 82% to 90% of the feed gold, at a coarser primary grinds targeting 125 microns, 80% passing. This demonstrates potential for significant improvement and future test work will be conducted investigating a flow sheet incorporating both flotation and cyanidation of the flotation products. Incorporation of a flotation extraction process could be viable if grinding economics favor coarser primary grinding.
North Cluster Results
At primary grind sizing targeting 75 microns, 80% passing, with 1,000 ppm sodium cyanide ("NaCN") concentration in the leaching and a 48 hour leach duration, the North Cluster samples showed a gravity recovery of between 28 and 38% and combined recovery of approximately 94% feed gold.
Two additional sets of gravity and cyanide leach tests were conducted on the North Cluster composites with 96 hour leach durations; these were conducted at primary grind sizing targeting 75 and 50 microns, 80% passing. At the 75 micron target, overall gold recoveries from the feed were approximately 97%. Decreasing the primary grind to 50 microns improved gravity recovery and resulted in overall gold recoveries of approximately 98% feed gold.
Commencing Phase 2 Metallurgical Testing
Following the presentation of the results of Phase 1 metallurgical testing, Integra management authorized a Phase 2 program which will focus on determining the impact on gold recoveries when flotation is included in the flow sheet, especially for the South Cluster samples. The work has started and should be completed within the next 6 to 8 weeks. Any decisions on further, larger scale test work, which may include drilling with PQ diameter core, will be made once results from Phase 2 work have been assessed by the Company.
Detailed mineralogy will also be conducted during Phase 2 testing to assess sulfide mineral liberations and associations.
Project and Company Profile
Integra's Lamaque Gold Project is located in the heart of the Val d'Or gold camp in the Province of Quebec, Canada, approximately 550 km northwest of Montreal. The Lamaque Project's primary target, the South Cluster, is 4 km from the City of Val d'Or. Quebec is rated one of the best mining jurisdictions in the world. Infrastructure, human resources and mining expertise are readily available.
The Company's primary objective is to continue to prove up additional resources while advancing the existing resource towards production. The project is split into two clusters, the North Cluster and the South Cluster, located approximate 1 km from each other.
South Cluster - No. 4 Plug and Triangle Zone
The South Cluster is the Company's top priority, and currently has a high grade gold resource of 444,962 inferred ounces grading 11.06 g/t Au in 1,263,046 tonnes, and 61,168 indicated ounces grading 13.51 g/t Au in 140,840 tonnes. Including 2013 drilling, over 34,000 meters of drilling has been completed on the South Cluster since the last resource estimate. An updated resource estimate is expected to be completed in Q2, 2013.
North Cluster - Parallel Zone, Forestel Zone and No. 5 Plug
The North Cluster hosts an NI 43-101 resource estimate of 69,981 inferred ounces grading 2.03 g/t Au in 1,072,484 tonnes, and 101,794 indicated ounces grading 4.8 g/t Au in 659,959 tonnes. An additional 8,000 meters of drilling has been completed on the North Cluster since the last resource which will also be included into the Q2, 2013 updated resource estimate.
Qualified Person
The Lamaque exploration project is under the direct supervision of Herve Thiboutot, P.Eng. and Senior Vice-President of the company, a Qualified Person ("QP") as defined by National Instrument 43-101, Alain-Jean Beauregard, P.Geo., and Daniel Gaudreault, P.Eng., Geo. of Geologica Inc., both independent QP as defined by National Instrument 43-101. The Company's QP has reviewed the technical content of this release.
Quality Assurance - Quality Control ("QA/QC")
Thorough QA/QC protocols are followed on the project including insertion of duplicate, blank and standard samples in all drill holes. The core samples are submitted directly to ALS Laboratory Group and Bourlamaque Labs in Val-d'Or for preparation and analysis. Analysis is conducted on 1 assay-ton aliquots. Analysis of Au is performed using fire assay method with atomic absorption finish, with a gravimetric finish completed for samples exceeding 5 g/t Au, or a metallic sieve assay for samples containing visible gold. When available the gravimetric or metallic sieve assay results are used for the reported composite intervals.
ON BEHALF OF THE BOARD OF DIRECTORS
Stephen de Jong, CEO & President
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Cautionary Note Regarding Forward-Looking Statements: Certain disclosure in this release constitute forward-looking statements. In making the forward-looking statements in this release, the Company has applied certain factors and assumptions that are based on the Company's current beliefs as well as assumptions made by and information currently available to the Company, including that the Company is able to obtain any government or other regulatory approvals required to complete the private placement and Company's planned exploration activities, that the Company is able to complete the private placement, that the Company is able to procure personnel, equipment and supplies required for its exploration activities in sufficient quantities and on a timely basis and that actual results of exploration activities are consistent with management's expectations. Although the Company considers these assumptions to be reasonable based on information currently available to it, they may prove to be incorrect, and the forward-looking statements in this release are subject to numerous risks, uncertainties and other factors that may cause future results to differ materially from those expressed or implied in such forward-looking statements. Such risk factors include, among others, that the private placement will not be completed, that actual results of the Company's exploration activities will be different than those expected by management and that the Company will be unable to obtain or will experience delays in obtaining any required government approvals or be unable to procure required equipment and supplies in sufficient quantities and on a timely basis. Readers are cautioned not to place undue reliance on forward-looking statements. The Company does not intend, and expressly disclaims any intention or obligation to, update or revise any forward-looking statements whether as a result of new information, future events or otherwise, except as required by law.
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 news release.
Contacts:
Integra Gold Corp.
Ariel Cobangbang
Corporate Inquiries
ariel.c@integragold.com
www.integragold.com
