The Castle Mountain gold mine is an open-pit gold mine located in California, US. It is owned and operated by Castle Mountain Venture (CMV), a partnership between Viceroy Gold and Telegraph Gold.
The mine initially produced more than one million ounces (Moz) of gold between 1992 and 2004, before the production was stopped due to low gold prices. The production was restarted by Equinox Gold, the parent company of Viceroy and Telegraph Gold, in a phased ramp-up scenario to access existing and potentially new resources.
The pre-feasibility study was completed in July 2018 while the first gold pour in the phase one operations took place October 2020 followed by the start of commercial operations in the next month.
Phase one has an annual production rate of 40,000 ounces (oz) which is expected to be increased to 203,000oz in phase two. A feasibility study for the phase two expansion is scheduled for completion in Q1 2021.
The Castle Mountain gold mine is expected to produce approximately 2.8Moz of gold over an estimated mine life of 16.2 years.
The Castle Mountain gold mine project is located in the Hart mining district, at the southern end of the Castle Mountains in north-eastern San Bernardino County, California, approximately 112.6km south of Las Vegas, Nevada.
The project area is in the high desert area surrounded by the Castle Mountains National Monument and Mojave National Preserve. It includes 13,276 acres of patented and unpatented lode, placer and mill site claims.
Geology, mineralisation and reserves
The Castle Mountain gold deposit contains various styles of mineralisation classified as low-sulfidation, quartz-adularia epithermal (LSE) mineralisation hosted in silicified zones, stockwork veins, tectonic and hydrothermal breccia, and disseminations.
The epithermal gold mineralisation that occurs as electrum and native gold is primarily hosted in the Castle Mountains rhyolite volcanic rocks.
The proven and probable reserves at the Castle Mountain mine were estimated to be 3.6Moz grading 0.56g/t gold as of September 2020.The measured and indicated resources were estimated to be 4.3Moz at 0.56g/t gold while the inferred resources were estimated at 2.2Moz grading 0.40g/t gold.
The phase one development includes the re-establishment of onsite operations using the current permit and the construction of a small leach pad and a gold recovery plant to process the initial mining and the run-of-mine (ROM) heap leach of the historical JSLA pit stockpile material.
In phase two, the phase one leach pad will be expanded to enable the increased throughput with milling of higher-grade ore and the ROM heap of lower-grade material.
Mining and processing
The Castle Mountain gold mine uses the conventional open-pit heap leach mining method.
Loaded carbon from the phase one operations is processed in the carbon stripping and smelting plant at nearby Equinox Gold’s Mesquite mine, approximately 200 miles south in California.
Phase one is designed to process 14,000 tonnes per day of ROM backfill material from the JSLA pit and the excavated material is loaded into 100t haul trucks and stacked in lifts.
The material will be added with quicklime for pH control before undergoing a two-stage stacking and leaching process which the use of dilute sodium cyanide solution. The gold bearing pregnant leach solution is then gravity discharged and pumped to a carbon-in-column (CIC) adsorption circuit.
Gold and silver values are loaded onto activated carbon and then periodically stripped from the carbon in a desorption circuit. The stripped gold is electrowon and smelted to form doré.
A small mill with a three-stage mobile/skid mounted crushing circuit is proposed to be built in phase two to process high-grade material and ROM leaching of lower-grade ore.
The mineral reserve estimates of the Castle Mountain gold mine were provided by Global Resource Engineering, while the mineral resource estimates were prepared by Mine Technical Service.