Heap Leach Gold Recovery Methods at Minera Alamos’ Pan Mine

Source: Minera Alamos Inc (2026)
Website: https://mineraalamos.com/our-assets/pan/

Critical Data

Overview

Minera Alamos Inc. operates the Pan Gold Mine, employing a heap leach recovery method to extract gold from blended hard and soft ores. The operation has been refined since 2019 with the installation of a primary crushing system, significantly improving gold recoveries. Ore is mined from several pits, crushed to -6 inches, and blended with lime at 3.5 lbs/ton to regulate pH. The material is stacked in nominal 15-foot lifts on a leach pad, where cyanide solution is applied at rates ranging from 0.0012 to 0.0026 gpm/ft² over a 90-day leach cycle. Pregnant solution is collected at approximately 3,400 gpm and processed through carbon columns using a countercurrent adsorption system. Gold is stripped from the carbon via a pressure Zadra process, electrowon onto cathodes, and refined into doré bars for sale. The mine processes about 14,000 short tons per day, with crushed ore volumes peaking at 4.7 million short tons per year. The heap leach operation achieves gold extractions of 69–75% on blended material, with hard rock recovering 62% when crushed and soft rock recovering 85% when crushed. This comprehensive recovery method ensures efficient gold extraction while maintaining environmental compliance through robust solution management systems.

Key Process Stages

• Stage 1: Ore Preparation – Ore is mined from multiple pits at a 60:40 hard-to-soft ratio and hauled to the crushing facility. Lime is added directly to trucks at 3.5 lbs/ton for pH control. Ore is crushed to -6 inches using a 36×50″ Lippman jaw crusher, stockpiled, and then loaded into trucks for transport to the leach pad. Barren solution is added at drop points to initiate wetting and leaching early.
• Stage 2: Leach Pad Stacking and Management – Crushed or ROM ore is dumped in nominal 15-foot lifts on the leach pad. Prior to each lift, the existing pad surface is ripped in two directions with a D10 dozer using 6- to 8-foot shanks to ensure permeability. Drip tubes are buried to prevent ponding and channeling. Solution application starts at 0.0012 gpm/ft² and gradually increases to 0.0026 gpm/ft² over the 90-day leach cycle, targeting a 1:1 solution-to-ore ratio. Cells are ripped again before being buried by the next lift.
• Stage 3: Solution Collection and Pond Management – Pregnant solution percolates through the heap and is collected by drain pipes beneath the pad. It flows to the pregnant solution pond, which is designed to handle meteoric water from a 25-year, 24-hour storm event. Solution is pumped from the pond to the carbon columns at a rate of about 3,400 gallons per minute. Regular samples are taken from each phase to monitor pH, alkalinity, NaCN, and gold content for process optimization.
• Stage 4: Carbon Adsorption and Gold Stripping – Pregnant solution passes through carbon columns containing 4 tons of activated carbon, which adsorbs the gold in a countercurrent flow. Loaded carbon is transferred to an acid strip vessel, where a pressure Zadra process strips the gold from the carbon. The gold is plated onto stainless steel cathodes in electrowinning cells. Stripped carbon is regenerated in a rotary kiln for reuse.
• Stage 5: Refining and Doré Production – Gold- and silver-laden sludge is washed from the cathodes periodically, filtered, and loaded into a retort furnace to remove moisture and mercury. The retorted sludge is blended with fluxing agents and melted in a furnace. The molten gold is poured into button molds, where lighter slags are separated. The resulting doré bars are shipped to a commercial refiner for final processing.

Additional Interesting Data and Summary

The Pan Mine heap leach operation integrates robust environmental controls with efficient gold recovery. The solution management system includes pregnant and barren ponds sized for a 25-year, 24-hour storm event, ensuring all process solutions and meteoric waters are contained. Regular monitoring of pH, alkalinity, NaCN, and gold content across multiple leach pad phases allows operators to optimize irrigation rates and chemical additions, maintaining permeability and preventing clay blinding. The on-site laboratory supports rapid decision-making with two atomic adsorption (AA) machines—one for fire assays and one for cyanide shake tests—plus column and bottle roll testing capabilities. Metallurgical testwork indicates that crushing improves gold recovery by 10% over run-of-mine material. Current extractions are modeled using historical data, showing that approximately 75.5% of ultimate recovery occurs in Year 1, followed by 13.1% in Year 2, 6.5% in Year 3, 3.0% in Year 4, and 1.5% in Year 5. The leach pad recoverable gold inventory was estimated at 33,000 ounces as of the report effective date, calculated using a rolling monthly model that accounts for new gold placed and ounces produced. This model has been validated against actual production and shows consistent performance. The Pan Mine’s success in blending hard and soft ores, combined with disciplined stacking and solution application practices, makes it a benchmark for heap leach operations treating variable ore types. Future outlook includes continued optimization of the blend ratio and leach cycle parameters to further improve extractions. The operation’s economic impact is significant, generating steady doré production and maintaining a stable workforce. Sustainability initiatives include water recycling through the closed-loop solution system and minimizing energy consumption by using a single stage of crushing. The facility’s ability to adapt historical operational issues—such as permeability problems from clay segregation—into a controlled, high-recovery process demonstrates Minera Alamos’ technical expertise and commitment to responsible mining.

Key Processes: Heap Leaching, Cyanidation, Crushing

Target Commodities: Gold