Gold Recovery Methods at Arthur Gold Project – Milling & Heap Leach

Source: Unnamed_Company_44 (2026)
Website: https://www.anglogoldashanti.com/portfolio/americas/united-states-projects/

Critical Data

Overview

AngloGold Ashanti’s Arthur Gold Project in Nevada, USA, employs a dual processing strategy to maximize gold recovery from the Merlin and Silicon deposits. The pre-feasibility study, effective 31 December 2025, outlines two complementary recovery methods: a milling circuit with gravity concentration and carbon-in-leach (CIL) for higher-grade ore, and a heap leach operation for lower-grade material. This approach lowers the economic cut-off grade and enhances overall project profitability. The mill processes 7 million tonnes per year through three-stage crushing (gyratory, cone, HPGR) followed by a single large ball mill in closed circuit with hydrocyclones. Gravity recovery captures up to 50% of contained gold, with the balance recovered via CIL and pressure Zadra elution. The heap leach operation handles 5.5 million tonnes per year, employing similar crushing stages, agglomeration, and cyanide percolation through stacked ore, with gold recovered in vertical carbon-in-column (CIC) circuits. Both technologies are well-proven in the region and globally, with no novel processes required. The facility is designed for 24-hour operation with high availability, and tailings are filtered and dry-stacked to meet stringent environmental and safety standards.

Key Process Stages

• Stage 1: Comminution – Three-stage crushing uses a 42×65 gyratory crusher (373 kW), an MP1000 cone crusher (746 kW), and an HRC2000e HPGR (4,040 kW) to reduce feed to a P80 of 3.1 mm for the mill circuit. Coarse and fine ore stockpiles decouple crushing from grinding.
• Stage 2: Grinding and Classification – A single 8.28 m diameter × 12.8 m EGL ball mill (18,400 kW) operates in closed circuit with a 20-inch cyclone cluster (22 cyclones). The hydrocyclone overflow achieves a P80 of 106 µm and reports to the pre-leach thickener.
• Stage 3: Gravity Concentration and Intensive Leach – Fresh feed diverted to centrifugal concentrators recovers gold in semi-continuous mode. Concentrate is transferred to an intensive leach reactor (ILR) for cyanidation; pregnant solution is sent to a dedicated electrowinning cell. Gravity tails return to the grinding circuit.
• Stage 4: Carbon-in-Leach (CIL) Circuit – Thickened slurry (50% solids) feeds two parallel CIL trains (each with 8 tanks). Oxygen sparging maintains 20 ppm dissolved oxygen, milk of lime controls pH to 11, and sodium cyanide is added via a ring main. Carbon concentration is 15 g/L, and loaded carbon is advanced counter-currently.
• Stage 5: Elution, Electrowinning, and Gold Room – Loaded carbon undergoes acid wash (3% HCl) followed by Pressure Zadra elution at ≥145°C and 400 kPag. Pregnant solution feeds four electrowinning cells; gold sludge is filtered, dried, fluxed, and smelted in an electric furnace to produce doré bars. Carbon is regenerated in a rotary kiln at 700–750°C.

Additional Interesting Data and Summary

The Arthur Gold Project’s recovery methods are supported by extensive metallurgical testwork confirming high gold recoveries for both milling and heap leaching. For the mill circuit, the 18.4 MW ball mill with a 300% recirculating load ensures efficient grinding. The gravity circuit captures up to 50% of gold, reducing downstream cyanide consumption. The CIL circuit (16 tanks total in two trains) operates at 50% solids with a carbon inventory of 15 g/L. The pressure Zadra elution system processes two 12t carbon columns per batch, with a strip solution of 1.5% NaOH and 0.2% NaCN at ≥145°C. Electrowinning uses four cells in two parallel trains plus a dedicated cell for ILR pregnant solution. Gold is smelted into doré bars at five smelts per week. Tailings are filtered to 85% solids and dry-stacked in a filtered TSF with a starter dam and toe buttress designed per GISTM standards. The heap leach operation agglomerates HPGR-crushed ore with cement and barren solution before stacking via grasshoppers and a radial stacker. Barren solution (cyanide) is applied via drip emitters; pregnant solution is collected and processed through vertical CICs for gold and silver adsorption. Loaded carbon from the heap leach is transported to the shared ADR plant for elution and electrowinning. Environmental controls include a mercury scrubber on the carbon regeneration kiln, acid-proof bunds, and a comprehensive water management system. The filtered TSF features engineered drainage, seepage collection ponds, and a geotechnical investigation confirming site suitability. The project’s dual-circuit approach reduces the cut-off grade, maximizes resource utilization, and aligns with sustainability goals through dry tailings and water recycling. The pre-feasibility study anticipates a 24-hour operation with 92% mill availability and 75–88% crushing availability, ensuring robust annual throughput. Future studies will refine design criteria and optimize reagent consumptions based on pilot-scale column leach results and comminution data.

Key Processes: Flotation, CIP/CIL, Heap Leaching, Cyanidation, Gravity Separation, SAG Mill, Ball Mill, Crushing

Target Commodities: Gold, Silver, Copper, Zinc, Lead