Gold producer Equinox Gold (TSX, NYSE: EQX) has announced the results of a feasibility study on an expansion of its 12,700 t/d Castle Mountain heap leach mine in California into an operation with a 45,350 t/d heap leach facility and a 3,200 t/d milling and leaching plant.
Based on an initial capital cost of US$510 million (which includes the purchase of a mining fleet) and a two-year construction period, the expansion would increase production to an average of 218,000 gold oz. annually at all-in sustaining costs of US$858 per oz. for 14 years, followed by rinsing of the leach pad to recover remaining gold. Based on US$1,500 per oz. gold, the after-tax net present value estimate for the expansion stands at US$640 million, at a 5% discount rate, with an 18% internal rate of return.
Castle Mountain achieved commercial production in November 2020; the operating first phase is expected to produce 30,000 to 40,000 gold oz. annually. Incorporating the latest expansion would extend the total mine life to over 20 years.
“The Castle Mountain phase 2 expansion will increase production from the mine to well over 200,000 oz. of low-cost annual gold production and generate nearly US$2 billion of net cash flow at current gold prices,” CEO Christian Milau said in a release.
The executive added that permitting for the expansion is now underway; the mine is expected to be “a long-life cornerstone asset for Equinox Gold.”
Based on the latest mine plan, the expanded heap leach would generate 2.1 million oz. with an additional 1.1 million oz. produced by the mill, for a total of 3.2 million gold oz.
The second phase of Castle Mountain would operate within the existing mine permit. However, Equinox notes that existing permits would need to be updated for the larger mine, with amendments and new permits required at the state and federal levels. The project timeline is estimated at four years from the start of permitting through to full expansion.
Equinox sees further upside potential from exploration-driven resource and reserve growth; expanding the reserve pits based on higher gold prices; and the use of solar power, among others.
The updated Castle Mountain reserve stands at 257.9 million tonnes grading 0.51 g/t gold, containing 4.2 million gold oz.
Castle Mountain produced over 1 million oz. of gold as a heap leach mine between 1992 and 2004.
Equinox operates eight gold mines in the Americas and expects to generate approximately 640,000 oz. this year.