The Relief Canyon Gold Project is a proposed conventional heap-leach gold operation in Nevada, U.S.A., with existing infrastructure and a feasibility-level processing design.
Report context
The Relief Canyon Gold Project is described in the *Technical Report and Feasibility Study, Relief Canyon Gold Project, Nevada, U.S.A.*, dated July 6, 2018, prepared for Pershing Gold Corporation. The project is a proposed mining and heap-leach processing operation located in Nevada, U.S.A., with significant existing site infrastructure from previous operations. The report presents a feasibility-level assessment of the processing route, infrastructure, water supply, and permitting status as of the report date.
Processing route
Proposed crushing and agglomeration
Ore will be processed using a conventional heap-leach flowsheet with an ADR (Adsorption, Desorption, Recovery) circuit. The ore will first be crushed in a single-stage crushing plant to 80 percent passing 3 inches. Crushed material will then be belt agglomerated using cement, and conveyed and stacked on the heap-leach pad. The single-stage crushing plant is designed to process up to 16,700 tons daily, or a maximum of 6.0 million tons annually. Approximately 30.2 million tons of ore are planned for stacking and leaching over the proposed mine life.
Heap leaching and solution management
The stacked ore will be leached with a dilute sodium cyanide solution. The heap-leach pad, designated Pad 5, 6, 7, will include both new and existing lined pad area, for a combined total of approximately 3.3 million square feet. The existing Operating Pond East (“OPE”) and Operating Pond West (“OPW”) process ponds will be used for solution containment and management, with no additional ponds required during the first two to three years of operation. In Year 3, the leach pad is planned to be expanded by an additional 2.2 million square feet, and an additional process solution pond will be constructed for storm water management to provide additional process solution containment capacity and operational flexibility.
ADR plant and mercury control
Pregnant heap-leach solution will be processed in the ADR plant for the recovery of precious metals from solution. The gold recovery plant will process a nominal 3,000 gallons per minute of pregnant heap leach solution. The plant consists of existing carbon-in-column adsorption, pressure strip, and refining circuits, along with a new electrowinning circuit and new melt furnace. The existing plant also includes carbon acid washing and regeneration. The gold and silver sludge resulting from the ADR plant will be treated in a mercury retort and smelted to produce doré bars. The plant will be retrofitted with mercury control equipment authorized in the Mercury Operating permit, which includes a mercury retort, sulfur-impregnated carbon circuits, and baghouse for removing mercury from process equipment exhaust gases.
Site infrastructure
Significant infrastructure currently exists at the Relief Canyon site from previous operations, including site access and haul roads, ADR facility, process solution ponds, heap-leach pad, waste rock facilities, site buildings, electrical power supply, water wells, and fencing around the process facilities. The plan intends to use as much of the existing infrastructure as possible.
Power supply
Electrical power will be supplied by a combination of line power and diesel-fired generator units. Approximately 41 percent of the electrical demand will be supplied by line power to most of the existing infrastructure, including the existing administration building, mine offices, warehouse, ADR plant, and process solution management. The remaining demand for the crushing plant, overland conveyor, and heap stacking conveyor system will be met by installing local diesel generators. Mine facilities such as a truck shop, truck wash, mine office complex, and fuel station will be constructed, operated, and maintained by the mining contractor. Mining facilities will be constructed during Year 1 of operation.
Water supply
The water demands for the project include make-up water for the process facilities, fire water, crushing area dust suppression, road dust suppression, and potable water supply for the offices. Water for mining, the heap-leach facilities, fire suppression, and other uses will initially be supplied by existing production wells located west of the pit area. The total average site demand is estimated to be approximately 630 gpm in the summer months and 430 gpm in the winter months. Two new deeper wells will need to be constructed to replace the existing wells for future pit dewatering when the existing wells are ultimately mined out. Water from the production wells will be pumped to a new raw/fire water storage head tank on the western side of the pit, just south of the ROM stockpile. This tank will be sized to contain the necessary fire water and process/raw water reserves and will provide raw process water for the crushing and stacking plant, and mine facilities such as the truck shop, truck wash, and mine offices. A new water tank will be connected to the existing process plant water tank to add additional capacity.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Crushing plant capacity | 16,700 tons/day | Proposed design |
| Crushing plant capacity | 6.0 million tons/year (maximum) | Proposed design |
| Ore crush size | 80% passing 3 inches | Proposed design |
| Ore stacked for leaching (life of mine) | ~30.2 million tons | Proposed design |
| Heap-leach pad area (new + existing) | ~3.3 million square feet | Proposed design |
| Additional pad area (Year 3) | 2.2 million square feet | Proposed design |
| ADR plant feed rate | 3,000 gpm (nominal) | Proposed design |
| Mine life | 5.6 years (estimated) | Proposed design |
| Average site water demand (summer) | ~630 gpm | Estimated |
| Average site water demand (winter) | ~430 gpm | Estimated |
| Electrical demand from line power | ~41% | Proposed design |
Project website: https://americas-gold.com/operations/relief-canyon/
Technical qualifications
The report provides a feasibility-level assessment of the proposed processing route and site infrastructure. Key limitations and qualifications from the report include:
- The processing route is a proposed design; no historical operating data from the proposed plant configuration was reported in the sections reviewed.
- The report notes that the project will be developed in two phases, with Phase I permitting having been approved for re-purposing of previously approved disturbance for expanded mining.
- The mercury control equipment is described as being retrofitted to the existing plant, authorized under the Mercury Operating permit to construct.
- The estimated mine life of 5.6 years and ore tonnage of 30.2 million tons are planning figures from the feasibility study.
- The power supply arrangement includes both line power and diesel-fired generators, with the split reported as approximately 41 percent line power and the remainder from local diesel generators.
- The water demand estimates are seasonal averages, and the existing production wells are expected to be replaced by two new deeper wells when the existing wells are mined out.
Source: Technical Report and Feasibility Study, Relief Canyon Gold Project, Nevada, U.S.A., July 6, 2018, Pershing Gold Corporation, relevant sections.
