Castle Mountain Expansion

Long-life low-cost gold mine in California

Castle Mountain Phase 2 operations will complement the current operation and increase production to more than 200,000 ounces of gold per year.





California, USA

Production estimate1

218,000 oz/year

Cost estimate2

<$950 per oz AISC


4,168 Koz @ 0.51 g/t gold

M&I Resources3

1,470 Koz @ 0.62 g/t gold

Mining and processing

Open-pit / small mill / heap leach

Phase 2 mine life

14 years plus residual leaching

1. Based on the 2020 feasibility study. See Cautionary Notes.
2. Based on costs outlined in the 2020 feasibility study with rough adjustments for inflation. Costs will be updated closer to the project commencing production. See Cautionary Notes.
2. M&I Mineral Resources are exclusive of Mineral Reserves. See Operations / Reserves & Resources and Cautionary Notes.


In November 2020, Equinox Gold announced commercial production for the Phase 1 heap leaching operations at Castle Mountain. The project is being developed in a phased ramp-up scenario, starting with heap leaching of stockpile material using existing operating permits, and then a Phase 2 expansion that will include milling and carbon-in-leach (CIL) processing of higher-grade ore.

On March 22, 2021, Equinox Gold released the results of a feasibility study for the planned Phase 2 expansion, which will increase production from the mine to well over 200,000 ounces of gold annually and generate nearly $2 billion of net cash flow (feasibility study estimate at $1,800/oz gold). Phase 2 will also extend the total mine life to more than 20 years.

Phase 1 operations place 12,700 tonnes of ore per day (t/d) on the heap leach pad to produce 25,000 to 30,000 ounces of gold per year. The Phase 2 expansion will include a 45,350 t/d run-of-mine heap leach facility and a new 3,200 t/d milling and leach/CIL plant for higher grade ore.

Phase 2 Highlights

  • After-tax NPV5% of $640 million at $1,500/oz gold ($1.1 billion at $1,800/oz gold)
  • After-tax IRR of 18% at $1,500/oz gold (25% at $1,800/oz gold)
  • $1.3 billion after-tax cumulative net cash flow at $1,500/oz gold ($2.0 billion at $1,800/oz gold)
    • $114.1 million average annual after-tax net cash flow at $1,500/oz gold ($161.8 million at $1,800/oz gold)
  • <$950/oz average AISC
  • 218,000 oz average annual gold production (Phase 2 life of mine)
  • 3.2 million oz total gold production at an overall average recovery of 82%
    • 1.1 million oz produced from the mill at an average recovery of 94%
    • 2.1 million oz produced from the heap leach at an average recovery of 67% (74% after final rinsing)
  • $389 million initial capital costs, excluding $121 million leased mining fleet.
    • $510 million if the fleet is purchased up front; NPV5% and IRR assume fleet is purchased up front.
  • $147 million sustaining capital costs over the Phase 2 mine life
  • 14-year Phase 2 mine life with expansion potential from exploration, plus two to three years of residual leaching and final rinsing

Initial capital costs are estimated at $389 million, excluding the mining fleet which is expected to be leased. Sustaining capital for Phase 2 is estimated at $147 million.

Phase 2 will operate within the current approved Mine Permit boundary and existing Phase 1 site infrastructure will be incorporated into the expansion, including administration buildings, haul roads, solution handling pumps and storage tanks, a carbon-in-column (CIC) cyanide receiving and storage area, a heap leach pad and event pond, a diesel power generation plant and an assay and metallurgical laboratory.

The Phase 2 heap leach facility will consist of an enlarged heap leach pad, an additional event pond, additional larger solution handling pumps and an additional CIC plant. The new CIL plant will consist of a two-stage crushing facility, conveyors, ball mill circuit, gravity concentration, leach and CIL tanks, thickeners, tailings filters and a reagent handling area. Loaded carbon will be processed in a desorption, electrowinning and refinery plant. Additional infrastructure for Phase 2 will include water supply wells, pumps and distribution systems, installation of an electrical transmission line along a previous corridor, an electrical substation, a filtered tailings storage facility, an extension of two waste rock dumps, a truck shop, and various site improvements and upgrades to meet the expanded project needs.

Leached slurry from the CIL circuit will report to a cyanide recovery thickener to recycle as much water and cyanide as possible back to the process. Flocculant will be added to aid in settling solids to produce a thickened product that will be treated in a cyanide destruction process. The final tailings will be pressure filtered and the filtered tailings will be hauled and stacked on the historical heap leach facility and abutted to the expanded heap leach facility, which allows the Company to minimize new land disturbances.

Permitting and Timeline

The overall project timeline depends largely on attaining the discretionary operating permits from the United States Bureau of Land Management (BLM) and the County of San Bernardino, and is anticipated to take approximately four years from the start of permitting to achieving full expanded operations.

Castle Mountain is located on both public and private land and historically has been permitted by co-lead agencies, the County of San Bernardino at the state level and BLM at the federal level. Castle Mountain has all permits required to conduct mining for the current Phase 1 operations and is permitted to operate within the approved Mine Permit boundary. Phase 2 will operate within the same Mine Permit boundary; however, modifications to parts of the mine and reclamation plans, including increased land disturbance, mining and water extraction rates, will require an updated environmental review and several new state and federal permits and amendments.

The Plan amendment application was submitted to the lead agencies in March 2022. The environmental review process and public scoping is expected to begin in early 2023.

Related Operating Mine

Castle Mountain is currently producing gold from Phase 1 operations.

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Growth Projects

Equinox Gold is constructing the Greenstone Mine in Canada and advancing expansion projects in Brazil and the USA.

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