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, and 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
The construction of Phase 1 at the Castle Mountain gold mine is complete and the first gold pour is expected in the fourth quarter, Equinox Gold has reported.

Equinox started preproduction mining in early June and has stacked more than 1.4-million tonnes of ore on the leach pad to date. Commissioning of the plant is in the final stages and irrigation of the leach pad has started.

Loaded carbon from Castle Mountain will be processed in the carbon stripping and smelting plant at the company's Mesquite mine, also in California.

The company is completing a feasibility study for the potential Phase 2 expansion, which is expected to average 200 000 oz/y.

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.