Integra Resources (ITR.V) has confirmed its preliminary metallurgical test results with a more comprehensive update. The updated results confirm the Florida Mountain deposit appears to be the best choice for a heap leach operation with gold recoveries between 80-90% and silver recoveries between 20% and 50%. While the DeLamar oxide and transitional zones could also be processed through a heap leach strategy, the average recovery rates are substantially lower at 65-80% for gold and 15-40% for silver.
The results that were announced also include the anticipated recovery results for a milling scenario based on the Florida Mountain rocks: using a very common gravity & flotation based flow sheet, the test work indicates between 85% and 90% of the gold could be recovered while roughly 65-80% of the silver contained in the rocks could be recovered as well. This confirms our previous interpretation that the gold-rich zones at Florida Mountain should be leached while the silver rich zones and the DeLamar mineralization would benefit from a milling strategy. Don’t get us wrong; it’s still feasible to throw the DeLamar oxide and transitional rock on a leach pad as well, but depending on when Integra plans to build the mill, it could make sense to just focus on Florida Mountain for the initial low-capex heap leach scenario to optimize the net present value and payback period of a mining scenario. The met work on the sulphide zones of DeLamar is still ongoing but as Integra can fall back on the data provided by Kinross Gold, we don’t anticipate any negative surprises.
Another advantage of the updated Florida Mountain leach test work is the relatively low cyanide consumption, which has been estimated at 170 grams of NaCN per tonne of rock. The low consumption rate will have a positive impact on the economics of the project and we expect to see a low processing cost for the heap leach operation when Integra Resources publishes the results of its Preliminary Economic Assessment next month. Just to give you an example; the cutoff grade of the resource estimate was based on a processing cost of $3.50/t, but similar heap leach operations in Nevada report a processing cost of less than $1.5/t. The low cyanide consumption levels now confirm the $3.50/t processing cost appears to be too conservative.
Integra Resources is now in the final straight line towards completing a PEA, and we will try to build our own NSR model in the next few weeks to get a better idea of what we can expect from Integra’s upcoming study.