Reward Feasibility Study Plans 5,479 t/d Three-Stage Crushing and Two-Stage Heap Leaching at 79% Gold Recovery

The September 2024 feasibility study for CR Reward LLC and Augusta Gold Corp. designs a crush, conveyor-stack and drip-leach operation in Nye County, Nevada, with carbon columns and an on-site Zadra plant from Year 2.

The Feasibility Technical Report on the Reward Project, Nye County, Nevada, was prepared by Kappes, Cassiday & Associates (KCA) for CR Reward LLC and Augusta Gold Corp. with an effective date of September 3, 2024 and signed on September 30, 2024. According to the report, earlier testwork showed the Reward mineral reserve is amenable to conventional heap leaching with carbon adsorption, desorption and recovery. The study plans to crush 2,000,000 tons a year to 80% passing ¼ inch, stack it on a lined pad in 30 ft lifts and leach it with dilute cyanide for an expected gold recovery of 79%.

Critical Data

Overview

Run-of-mine ore will be trucked to a feed stockpile and crushed in three stages in closed circuit, seven days a week, at an overall crusher availability of 75%. The crushed ore will be reclaimed, dosed with cement on the first lift or pebble lime on later lifts for agglomeration and pH control, and conveyor stacked by retreat stacking uphill from the toe of the heap. The report notes that testwork showed cement agglomeration is not required, and cement is added to the first lift only as a precaution to protect permeability.

The heap will be drip-irrigated with dilute cyanide. Pregnant solution drains by gravity to a pregnant solution tank and is pumped through carbon-in-column (CIC) adsorption. In Year 1 the loaded carbon goes to a toll processor. An on-site recovery plant, a modified Zadra desorption and recovery circuit, is to be built during Year 1 and run from Years 2 to 9. Precious metal sludge will be filtered, retorted to remove mercury and smelted to doré.

Key Process Stages

Crushing. A 980-type front-end loader feeds run-of-mine ore to a dump hopper and vibrating grizzly feeder, with bars about 4.25 inches apart. Oversize goes to a primary jaw crusher at a 5.5 inch closed side setting. Crushed ore is stacked on a primary stockpile of about 9,900 tons, with about 2,500 tons live, which lets the primary crusher run independently of the secondary and tertiary crushers. A triple-deck secondary screen (3, 0.75 and 0.35 inch decks) feeds a CH840i cone crusher with standard liners, and a double-deck tertiary screen closes a CH840i cone crusher with shorthead liners. Product passing 0.35 inch reports to the crushing plant product.

Reclaim and stacking. Three electromechanical feeders reclaim crushed ore to a tunnel conveyor, where cement or lime is added from a 2,800 ft³ (123 t) silo. Two overland conveyors, five ramp conveyors, fifteen grasshopper conveyors and a TeleStacker radial stacker place the ore in 30 ft lifts in prisms about 280 ft wide, at an overall heap slope of about 3H:1V. Old lifts are ripped before new ore is stacked on them.

Leach pad. The pad is designed to hold 16 Mt: 7 Mt in Phase 1, with six cells built in Year −1 over 2.275 million ft² and about three years of capacity, and 9 Mt in Phase 2, with four cells built in Year 3 over 1.435 million ft². The Phase 1 pad and ponds are already permitted. The liner system, approved by the state of Nevada, is a two-foot overliner over a 60 mil double-sided textured LLDPE geomembrane on a 1 ft low hydraulic conductivity soil layer, with leak detection.

Two-stage leaching. CIC barren solution, recharged with cyanide, irrigates the secondary-leach ore (more than 90 days under leach). The resulting lean intermediate solution goes to the process pond, is dosed with cyanide and is applied to the primary-leach ore (less than 90 days). The aim is to keep the pregnant solution grade high. Once the heap is too high for two-stage leaching, expected after Year 3, all pregnant solution will be treated through the carbon columns.

Carbon adsorption. A single train of five open up-flow columns, each holding 3 tons of carbon as an expanded bed, is operated counter-currently, with carbon advanced manually each day. A second set of columns will be built in Year 3 for Years 4 to 9.

Acid wash, elution and gold room. About every three days, a 3 t lot of loaded carbon is acid washed with dilute hydrochloric acid at pH 2, neutralized and stripped. The elution cycle is about 18.5 hours, with 12 hours of stripping at 3 bed volumes per hour using about 5 lb NaCN/t and 10 g/L NaOH at 280 to 300°F. Electrowinning cells at 3 to 4 V deposit gold sludge, which is pressure-washed off, filtered, retorted to remove mercury and smelted with fluxes into doré.

Carbon regeneration. Stripped carbon is heated to about 1,300°F for about 10 minutes in a regeneration kiln, then quenched and sized, with fines collected separately.

Additional Interesting Data and Summary

Solution is managed with a process pond (5.2 Mgal, run at 3.0 Mgal), pregnant and barren solution tanks and an 8.7 Mgal event pond, both ponds double-lined with HDPE and leak detection. The ponds are sized for the ultimate pad. In the Phase 2 design case, storms, drain-down and 24 hours of flow give 9.7 Mgal, accommodated by the event pond and spare process pond capacity. Antiscalant is added to the barren solution at about 5 ppm.

Using Beatty weather station data (5.3 inches of rain against 79.0 inches of pan evaporation a year), the water balance shows the project in deficit in average, wet and dry years. Average make-up water is 105 gpm for the process and 115 gpm for the mine, plus 1,000 gallons a day of potable water, about 221 gpm in total. Slope stability analyses gave a heap factor of safety of 1.4 static and 1.1 pseudostatic, above the Nevada minimums of 1.3 and 1.05.

In summary, the Reward feasibility study is a conventional Nevada crushed-ore heap leach at about 2 million tons a year. It uses two-stage leaching to keep pregnant solution grades up early in the mine life, toll treats its carbon for the first year, and then recovers gold on site through Zadra elution and electrowinning, at a design recovery of 79%.

Key Processes

• Three-stage closed-circuit crushing to 80% passing ¼ inch
• Cement (first lift) or pebble lime addition for agglomeration and pH control
• Conveyor stacking in 30 ft lifts on a lined, multi-lift pad
• Two-stage drip-irrigated cyanide heap leaching
• Carbon-in-column adsorption
• Toll processing of loaded carbon in Year 1
• Acid wash, Zadra elution and electrowinning from Year 2
• Mercury retorting and smelting to doré
• Kiln carbon regeneration

Source: Feasibility Technical Report on the Reward Project, Nye County, NV, USA, prepared by Kappes, Cassiday & Associates for CR Reward LLC and Augusta Gold Corp., effective date September 3, 2024.