Name of the Project
Castle Mountain gold project.

Location
San Bernardino County, California, in the US.

Project Owner/s
Equinox Gold.

Project Description
The Castle Mountain gold mine produced more than one-million ounces of gold as an openpit heap-leach mine from 1992 to 2004, when production ceased, owing to low gold prices; the mine was substantially reclaimed.

A prefeasibility study (PFS) has determined that Castle Mountain can be developed as a low-cost heap-leach gold mine. The project has proven and probable reserves of 197.6-million tonnes grading 0.56 g/t.

The project will be developed in two phases.

The phased ramp-up approach enables Equinox to use existing permits to expedite production while completing the feasibility study and permitting for the Phase 2 expansion. While Phase 2 will operate within the existing permitted mine boundary, the increased mining and water extraction rates will require updated permitting for the project.

Under the PFS mine plan, Phase 1 of the project will produce an average of 45 000 oz/y of gold over three years. Phase 2 production is expected to average 203 000 oz/y of gold for 13 years.

Total production is estimated at 2.8-million ounces over a 16-year mine life, with expansion potential from existing near-mine mineralisation.

Phase 1 will comprise a run-of-mine (RoM) heap-leach operation processing primarily 12 700 t/d of stockpiled ore from previous operations. Phase 2 will increase throughput to 41 000 t/d of ore, of which 2 340 t/d of higher-grade ore will be processed through a milling circuit.

Phase 1 processing operations will treat the solutions from the RoM heap-leach facility operating in a new adsorption, desorption and refining (ADR) plant capable of treating 400 m³/h of pregnant solution to produce doré bars.

Phase 2 will require an expansion of the solution handling and ADR plant capacity to receive the additional flow from the increased RoM heap-leaching operations and loaded carbon from the carbon-in-leach (CIL) plant. The Phase 2 CIL circuit will comprise a three-stage crushing circuit, ball mill, gravity circuit, CIL circuit, cyanide destruction circuit and mill fines filtration circuit, as well as an Acacia high-intensity leach circuit.  The comminution circuit is designed to achieve 80% passing 150 μm. Loaded carbon from the CIL circuit will be treated in RoM desorption and recovery circuits. The expanded plant will have capacity to treat 1 900 m³/h to produce doré bars.

The heap-leach pads for both phases will be double-synthetic-lined using a 2 mm linear low-density polyethylene liner, with a leak detection and recovery system between the synthetic liners. Spent heap-leach ore from prior operations will be used to form a 600 mm drainage layer above the lining system. Ore will be stacked in 15 m lifts with no interlift liners. Heap irrigation, at a nominal rate of 10 ℓ/hr/m², will be delivered through buried drip lines to reduce evaporative losses of solution.

Potential Job Creation
Not stated.

Net Present Value/Internal Rate of Return
The project has an after-tax net present value, at a 5% discount rate, of $406-million and an after-tax internal rate of return of 20%.

Capital Expenditure
Total project capital expenditure is estimated at $347-million – Phase 1 will cost $58-million to implement and Phase 2 $295-million.

Planned Start/End Date
Phase 1 ore is targeted for the third quarter of 2020.

Latest Developments
Equinox Gold is considering a Phase 2 expansion at the Castle Mountain mine, lifting the US mine’s output to an average of 200 000 oz/y.

A feasibility study for the expansion is targeted for completion in the first quarter of 2021.

Meanwhile, Castle Mountain has achieved commercial production and the mine is expected to produce between 5 000 oz and 10 000 oz of gold this year.

The mine poured its first gold on October 15.

Key Contracts, Suppliers and Consultants
Kappes Cassiday & Associates, supported by Mine Technical Services, Global Resource Engineering, Call & Nicholas, Geo-Logic Associates and Lilburn Corporation (PFS).

Contact Details for Project Information
Equinox Gold, tel +1 604 558 0560 or email info@equinoxgold.com.