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Positive Heap Leach Recoveries At The DeLamar Deposit In Idaho

VANCOUVER, BC - George Salamis, President and CEO of Integra Resources Corp, said, “Since the acquisition of this Project less than 24 months ago, Integra has been committed to demonstrating a mine development vision for DeLamar. Multiple gold-silver processing options are being evaluated, including the low-cost heap leaching. These results clearly demonstrate that heap leaching is a viable option for a large percentage of the recently updated resource at the DeLamar Project. Building upon recent test-work conducted on oxide and transitional mineralized material from the Delamar and Florida Mountain Deposits in Idaho, we are excited to report that future heap leaching of this mineralization is likely viable for the Project, with test-work indicating heap leach recoveries as high as 85% for gold and up to 50% for silver. Current indications are that on a tonnage basis, over 54% of the Measured and Indicated (“M&I”) resources, and 39% of the Inferred resources modelled at the DeLamar Project are potentially amenable to low cost heap leaching. The amount of potentially heap leachable gold-silver mineralization at DeLamar is significant and will be outlined as a mainstay of future modelled gold-silver production in the upcoming PEA expected to be completed in September 2019.
Test-work is ongoing for the unoxidized mineralization processing options, and while not yet complete, the Company is very encouraged by the results received to date. At Florida Mountain, in view of test-work studying milling, gravity and flotation with concentrate regrinding and cyanidation, results have demonstrated excellent recoveries of up to 90% gold and 80% silver. At the DeLamar Deposit, tests have demonstrated that unoxidized mineralization responds well to upgrading by gravity and flotation processing, with over 90% of the gold and silver in the mineralization reporting to a sulphide concentrate that will require further processing such as fine grinding and leaching or oxidative treatment such as autoclaving. In summary, the oxide and transitional mineralization at DeLamar and Florida Mountain is amenable to heap leaching with low to normal reagent consumption and excellent recoveries. Test-work to date has also confirmed the potential for established processing options with very good recoveries on unoxidized mineralization at the Project. Integra is now rapidly proceeding towards the maiden PEA with excellent metallurgical data and a significantly de-risked 90% M&I resource in hand, and we expect robust economics to be outlined in the PEA with multiple development and production scenarios.”
The DeLamar Project produced gold and silver from 1977 to 1992 utilizing crushing, grinding, and agitated cyanide leaching, followed by precipitation with zinc dust and in-house refining of the precipitate to produce silver-gold doré, which at the time was a common industry processing method for the type of mineralization found at DeLamar. Recoveries of oxide, transitional and some portions of the unoxidized mineralization at the property achieved average recoveries of 96.2% for gold and 79.5% for silver in the first 15 years of mining operations.
As a result of test work conducted by Integra over the last 12 months, the DeLamar Project area now has many more options for processing than just agitated leaching. The key to processing options at the DeLamar Project relates to the oxidation states of the mineralized material, and where the material is situated within both the DeLamar and Florida Mountain gold-silver Deposits.
Beginning in 2018, Integra initiated a detailed metallurgical test-work program which is still ongoing. Samples used for testing include a total of 153 drill-core composites and four bulk samples. Drill-core composites were prepared from a total of 31 drill holes (23 holes from DeLamar and 8 holes from Florida Mountain). Composites were prepared considering area, oxidation, depth, lithology, alteration, grade and grade continuity. The scope of testing conducted on individual samples generally depended on the oxidation classification (oxide, transitional, or unoxidized). Testing has included evaluation of cyanide heap leaching, grind – agitated leaching, gravity concentration, flotation, and flotation concentrate regrind with agitated leaching.
Available test data indicates that the oxide and transitional materials from both the DeLamar and Florida Mountain Deposits behave reasonably similarly and are amenable to processing by low-cost heap leach cyanidation methods. Clay contents at the Florida Mountain Deposit are regarded as low and thus agglomeration may not be required. Higher clay contents exist at the DeLamar Deposit, thus some zones at DeLamar may require agglomeration pretreatment. Low to moderate cyanide consumptions are indicated for heap leaching of the oxide and transitional material types for both deposits. Lime or cement demand is expected to be variable.
A total of 45 drill-hole composites were prepared from 7 drill holes for metallurgical testing of the Florida Mountain Deposit. Metallurgical test work conducted on Florida Mountain oxide and transitional sample composites indicates preliminary recoveries of between 80% to 90% gold and 20% to 50% silver, on samples crushed to 50 mm. The average of the column leach tests resulted in over 71% of the total gold being recovered within 10 days.
A total of 80 drill-hole composites were created from a range of different zones within the DeLamar Deposit. Preliminary metallurgical test work conducted on DeLamar Deposit oxide and transitional sample composites, assuming a 13 mm crush size, yields an expected range of recoveries of between 65% to 80% gold and 15% to 40% silver.
In the case of unoxidized material from the Florida Mountain Deposit, testing in 2018-2019 has shown that the material is amenable to grinding followed by agitated cyanide leaching. However, this material type responds very well to upgrading by gravity and flotation processing. Testing has shown that the highest gold and silver recoveries were obtained by gravity concentration, followed by flotation of the gravity tails, with regrinding and agitated cyanide leaching of the flotation concentrate. Preliminary test work on Florida Mountain unoxidized composites indicate gold and silver recoveries in the range of 85% to 90% and 65% to 80% respectively, with a relatively course grind size of 212µm.
The DeLamar Project unoxidized material types, preliminary testing has generally shown that flotation gold and silver recoveries of approximately 90% can be achieved with mass pulls of approximately 10% to 15%. For unoxidized material from the DeLamar Deposit’s Glen Silver area, flotation gold recoveries (70% - 90%) and silver recoveries (75% - 90%) have tended to be somewhat lower. Testing to evaluate further processing of the DeLamar flotation concentrates for recovery of gold and silver is planned. Possible processing options for gold and silver recovery from the concentrate include shipment off site for toll processing; regrinding followed by agitated cyanidation; or on-site oxidative treatment (such as pressure oxidation, roasting, or bio-oxidation), followed by agitated cyanidation of the oxidized concentrate. Further testing will be required for the evaluation of these processing options.
The ongoing metallurgical testing will be continued, with a focus on defining the metallurgical characteristics and potential extraction parameters of oxide, transitional, and unoxidized materials for each of the DeLamar and Florida Mountain resources. Processing alternatives involving both heap leaching and various milling scenarios will continue to be examined.
The results of the 2018-2019 DeLamar Project Metallurgical test-work study will be outlined in much greater detail in the upcoming PEA, scheduled for September of this year.
The company’s address is 400 Burrard Street, Suite 1050, Vancouver, BC V6C 3A6, (604) 416-0576, www.integraresources.com.