Heap leaching an option at Integra’s DeLamar project

Metallurgical test work at Integra Resources’ (TSXV: ITR; US-OTC: IRRZF) DeLamar project in southwestern Idaho shows heap leaching is a viable option for a large percentage of the resource, the company says.

Results from test work at the project’s Delamar and Florida Mountain deposits show recoveries as high as 85% for gold and up to 50% for silver. Recoveries of 80–90% gold and 20–50% silver come from Florida Mountain, and 65–80% gold and 15–40% silver are from Delamar. Column test data shows that the oxide and transitional mineralization from both deposits behaves similarly, the company says.

On a tonnage basis, over 54% of the project’s modelled measured and indicated resources and 39% of its inferred are potentially amenable to low-cost heap leaching — findings that will be incorporated into the preliminary economic assessment (PEA) that the company plans to finish in September.

A drill site at Integra Resources’ DeLamar gold-silver property in southwestern Idaho. Credit: Integra Resources.

“The confirmation that a substantial component (nearly 50%) of the current 4.4 million equivalent oz. gold resource (all categories) is amenable to heap leaching, with attractive gold and silver recoveries, is a very important development ahead of the planned PEA,” Tara Hassan, an analyst at Raymond James, writes in a note to clients. “These results confirm our view that the project has significant optionality that will position Integra to consider a number of development options, with the most important being an attractively sized heap-leach project that is still of the scale that could be funded and built by Integra.”

Integra updated the project’s resource estimate in June, incorporating over 250,000 metres of historic drilling by Kinross Gold (TSX: K; NYSE: KGC) and its predecessors, and 30,000 metres (93 holes) completed by Integra since the first quarter of 2018, which is the first exploration DeLamar has seen in 25 years.

DeLamar’s resource stands at 172.4 million measured and indicated tonnes grading 0.43 gram gold per tonne and 21 grams silver per tonne, or 0.70 equivalent gram gold, for 2.38 million contained oz. gold and 116.51 million oz. silver, for 3.88 million equivalent oz. gold. Inferred resources add 28.3 million tonnes grading 0.38 gram gold and 13.5 grams silver, or 0.55 gram gold-equivalent, for 343,000 contained oz. gold and 12.24 million oz. silver, for 500,000 equivalent oz. gold.

As for the two deposits’ unoxidized mineralization, test work so far shows good recoveries on established processing options. At Florida Mountain, test work studying milling, gravity and flotation  with concentrate regrinding and cyanidation holds recoveries of 85–90% gold and 65–80% silver.

Tom Jordan, project operations manager, at Integra Resources’ DeLamar gold project in southwest Idaho. Credit: Integra Resources.

At DeLamar, 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 need more processing, such as fine grinding and leaching, or oxidative treatment, such as autoclaving.

The two deposits — situated 8.5 km apart, and connected by an all-weather haul road — are 160 km from Boise.

Kinross Gold’s historic DeLamar mine produced 1.6 million oz. gold and 100 million oz. silver before it closed in 1998, due to low metal prices.

Historic underground mining at Florida Mountain from the 1830s to the 1910s produced 133,000 oz. gold and 15.4 million oz. silver. Kinross mined the deposit via open pit in the 1990s, and produced another 124,500 oz. gold and 2.6 million oz. silver. The mine closed the same year as DeLamar, and was put on care and maintenance.

Integra’s management team is made up of former executives of Integra Gold, which was sold to Eldorado Gold (TSX: ELD; NYSE: EGO) in July 2017 for $590 million. Integra Resources’ president and CEO, George Salamis, previously served as Integra Gold’s executive chairman, while Integra Gold’s president and CEO, Stephen de Jong, is now chairman of Integra Resources.

At press time, Integra’s shares traded at $1.09 in a 52-week range of 61¢ to $1.15. The company has a $84-million market capitalization.