Pan African-owned Muriel Mine has turned a legacy tailings storage facility into a profitable production asset through a carefully engineered hydrosluicing and carbon-in-leach process. With the dump now in its final five months of life, the operation offers a textbook case of efficient surface mining, water recycling, and integrated processing, all while funding a major exploration drive that has extended the mine’s underground life to five years.
The following technical overview, compiled from presentations made during an Association of Mine Managers of Zimbabwe (AMMZ) technical visit, details every stage of the process. Webster Chemhuru, Senior Plant Metallurgist, led the delegation through the hydrosluicing and processing circuits, while specialised contractor BillNick Engineering provided additional insights into the hydrosluicing system and tailings management.
Water Sourcing and Storage
The hydrosluicing operation relies on a dual-source water supply. Sixty per cent of the water comes from Chawara Dam, located approximately four to five kilometres from the mine and shared with local farmers. The remaining forty per cent is recycled water drawn from the active tailings storage facility. This water is detoxified to break down residual cyanide before reuse, reducing both fresh water consumption and the operation’s environmental footprint.
Water is first stored in a 10,000-cubic-metre tank. From there, it is fed into a high-pressure system where pumps deliver water to the hydrosluicing monitor at pressures of 1,500 to 1,800 kilopascals at the nozzle.
Hydrosluicing (Hydro-Mining)
The dump, a consolidated legacy tailings deposit, is broken down using a water jet monitor. The high-pressure stream mixes with the tailings to form a slurry that is pumped to the plant. BillNick explained that the water jet mixes the tailings into a pumpable slurry, which is moved by variable-speed pumps to a trash screen that removes debris such as timber and old pipes. From there, the slurry flows into a surge tank before being fed directly into the processing plant.
Operational controls are critical for safety and efficiency. Because the dump material has been consolidated over decades, the mining angle is maintained between 27 and 33 degrees to prevent slope failure, a phenomenon known as “sloughing.” Before each shift, crews inspect the working face for any signs of instability.
The mine is also fabricating a remote-controlled monitor in-house. Once completed, it will allow operators to work away from the face edge, improving safety and enabling higher pressures of up to 2,500 kilopascals for applications requiring denser slurries.
BillNick, which specialises in hydrosluicing and tailings management, noted that it handles everything from design and construction to operation, offering the same technology to other mining operations.
Milling and Classification
After screening, the slurry is collected in a surge tank and then distributed to the milling circuit. The plant is equipped with four 8-by-16-foot open-discharge ball mills, each fed by its own buffer tank with a volume of approximately 890 cubic metres. These buffer tanks ensure a steady feed even when the hydrosluicing rate fluctuates.
Because the dump material contains fine-grained gold locked in refractory host minerals, the target grind is 90 to 95 percent passing 75 microns, significantly finer than conventional milling. This process liberates the gold particles and exposes them to the leaching solution.
After milling, the slurry is pumped to hydrocyclone classifiers. Coarse material (cyclone underflow) is returned to the mills for further grinding, while fine material (cyclone overflow) passes through a final trash screen before flowing to the thickener.
Thickening
The thickener is a 35,000-cubic-metre unit designed to dewater the slurry from about 15 to 20 percent solids to the 50 percent solids required for the carbon-in-leach (CIL) circuit. This densification reduces the volume of liquid that must be heated and agitated during leaching, lowering operating costs.
Carbon-in-Leach (CIL) Circuit
The CIL circuit comprises ten tanks, each with a capacity of 890 cubic metres. Together, they provide approximately 36 hours of residence time. Sodium cyanide is added to dissolve gold, forming a stable cyanide complex in solution. Activated carbon is introduced simultaneously so that, as gold dissolves, it is immediately adsorbed onto the carbon.
This carbon-in-leach approach maximises recovery by keeping the dissolved gold concentration low, which drives the leaching reaction forward. Carbon moves counter-current from the last tank to the first tank, and the loaded carbon is harvested from tank number one, where gold concentration is highest.
Webster Chemhuru highlighted two significant metallurgical challenges. First, some zones in the dump contain up to 0.5 percent copper, which consumes cyanide and interferes with gold dissolution. The mine manages this through selective mining and blending high-copper material with lower-grade zones.
Second, the ore contains naturally occurring carbonaceous material that can adsorb gold directly from solution, a phenomenon known as preg-robbing. This competes with the activated carbon and reduces overall recovery. As a result, recovery rates have declined from 80 per cent in 2023 to approximately 70 to 75 per cent currently, reflecting the variable nature of the remaining dump material.
Elution and Smelting
Loaded carbon is transferred to the elution section, where gold is stripped from the carbon using a Zadra elution process. The plant has two elution vessels: one with a three-tonne capacity and another with a one-and-a-half-tonne capacity, giving a combined throughput of 4.5 tonnes of carbon per day.
The Zadra system uses a hot caustic cyanide solution to desorb gold, producing a concentrated pregnant solution that is sent to electrowinning cells. Electrowinning produces a gold-rich sludge, which is dried and smelted in the on-site smelt house once per week, producing gold doré bars.
Production figures presented during the visit show that tonnage treated grew from 200,000 tonnes in 2023 to 765,000 tonnes in 2024, reaching 1,166,000 tonnes in 2025. Gold production increased from 104 kilograms in 2023 to 425 kilograms in 2024 and 630 kilograms in 2025. In early 2026, the operation is averaging approximately 45 kilograms of gold per month.
Tailings Storage Facility
Waste material from the CIL circuit, now largely depleted of gold, is pumped to the tailings storage facility, which covers approximately 40 hectares. Water that settles on the surface is decanted and pumped back to the plant, contributing to the 40 per cent recycled water used for hydrosluicing.
Standpipes are installed around the facility to monitor the phreatic water table, ensuring structural stability. Berms and spillways are designed to contain any accidental releases, meeting environmental requirements.
Operational Risks and Mitigation
BillNick identified two major operational risks. The first is slope failure, or sloughing, which is managed by maintaining mining angles between 27 and 33 degrees and conducting pre-shift inspections. The second is high-pressure pipe failure, which can cause serious injury. Pipes are inspected regularly and repaired promptly, and the water used contains few chemicals, reducing environmental risk in the event of a spill.
From Dump to Underground
The current dump being retreated has only five months of material remaining. Revenue from the dump retreatment operation, combined with a dedicated US$20 million exploration programme, has funded a major extension of the mine’s underground life.
Exploration has extended Muriel Mine’s underground life-of-mine to five years, while the nearby Aysha deposit now holds 1.3 million ounces of resources with a projected 30-year life.
However, the newly discovered underground reefs, including the South Reef and extensions in the Fortuna and Cape Gum areas, are not yet being mined. The operation is currently constructing a crusher to process the harder primary ore from these zones, ensuring a seamless transition when the dump is exhausted.
Industry Recognition
AMMZ President Gift Mapakame praised the operation’s approach, noting that retreating materials with more efficient technologies presents an opportunity for greener mining.
“There is no mobile equipment—just pumping, processing, and tailings storage,” he said.
AMMZ Vice President George Wayeni of RZM Murowa added that revenues from the dump retreatment project are funding exploration for the future.
“Lots of other operations can take a leaf from this initiative,” he said.
Conclusion
Muriel Mine’s dump retreatment process—from hydrosluicing with high-pressure water, through fine grinding, CIL leaching, elution, smelting, and responsible tailings disposal—demonstrates how legacy tailings can be transformed into a productive, self-funding operation.
With the dump now in its final months and a crusher being built for new underground ore, the operation is well positioned to sustain production growth while maintaining the cost discipline that has made it one of Zimbabwe’s leading gold producers.
