Blyvoor Gold Mine — 2021 Technical Report

This report describes the processing route designed for the Blyvoor Gold Mine, including planned expansion and historic operating results.

Report context

This technical report, dated February 2021, documents the processing facilities for the Blyvoor Gold Mine project. The plant was recently constructed and was being ramped up to a total RoM feed capacity of 40 ktpm, with an expansion to 80 ktpm planned. The report presents both the current design and the modifications required for the higher throughput rate.

Processing route

Flowsheet overview

The upgraded plant follows the same process flow as the existing plant, with some circuits expanded. The flowsheet accommodates the addition of surface stockpiles directly into the crushing circuit or sluicing of fine material into the classification circuit. These sources are not planned for regular use but remain available for emergencies and are useful during start-up and commissioning. The recovery method is described as the most widely used for processing hard rock ore that does not have significant preg-robbers. The circuit is the same as the old plants that treated this ore.

Crushing circuit

The crushing circuit consists of two stages. RoM is conveyed from the shaft into the plant feed silo or added with a front-end loader via a static grizzly into the primary jaw crusher. A heavy-duty apron feeder extracts material from the silo and discharges it into a jaw crusher. The jaw crusher product is conveyed to a secondary screen, which returns oversize to a cone crusher and discharges undersize onto the product conveyor running to the crushed ore silos. The cone crusher product is also discharged onto the secondary screen feed conveyor.

The crushing circuit throughput is sufficient to accommodate higher ore throughput; it only needs to run for longer. For the planned expansion, operating hours need to increase from 12 to 18 hours per day, and the circuit should run 7 days per week instead of 5. A second RoM bin will be added to enable a larger buffer between the crushing plant and ore hoisting operations.

Milling and gravity circuit

Crushed ore is discharged into one of two crushed ore silos, each dedicated to one mill via an apron feeder and conveyor belt. The mills have a trommel discharge that removes scats and wood chips. The two mills discharge into a common sump, from where slurry is pumped to either a cyclone cluster or a Falcon Screen. The cyclone cluster returns oversize material to the mills while the Falcon screen protects the gravity concentrator from blockage by larger material. The Falcon concentrator’s tails are returned to the mill sump while the concentrate flows into the gold room for further processing. Cyclone overflow passes over a linear trash screen before being sent to the conditioning tank.

The two currently installed 900 kW mills have a specified throughput of 32.5 tph each. A third 14 ft x 21 ft mill will be added to increase milling throughput to the required 128 tph for the expansion. This mill will be fed with a new apron feeder and conveyor system. New sump pumps will pump to an existing cyclone, and another new pump will discharge onto an existing Falcon screen, with the underflow feeding the existing Falcon concentrator.

Leaching and carbon-in-pulp circuit

Ore slurry from the milling section enters a conditioning tank where lime and oxygen are added, with oxygen added via a high shear reactor. Overflow from the conditioning tank flows into the first of three leach tanks in series where cyanide is added. For the expansion to 80 ktpm, the number of conditioning and leach tanks needs to be doubled to accommodate the higher ore throughput and maintain the same residence time.

Ore slurry flows to the carbon-in-pulp carousel after the last leach tank. All tanks are filled with activated carbon, and ore slurry and carbon follow a counter-current contacting sequence. Ore slurry is periodically drained from the first tank in the sequence, and the loaded carbon is sent to elution. The second tank then becomes the first in the sequence, and the drained tank is filled with eluted carbon and becomes the last tank. No changes are planned for the CIP circuit apart from the requirement for higher gold loading on the loaded carbon.

Elution and gold room

Loaded carbon slurry from the CIP tanks is pumped via recessed impeller pumps to a horizontal vibrating carbon harvesting screen fitted above the acid wash weigh tank. Screen oversize is washed and reports into the acid wash weigh tank. Carbon is discharged into the acid wash column where it is washed and soaked in a 5% HCL solution, then rinsed until pH neutral. Carbon is then conveyed to the elution column by pressurised water.

Leach elution uses the Zadra process with a stainless-steel elution column capable of treating 6 tons of carbon at a time. Barren eluate is stored in an agitated eluate tank and pumped through a recovery heat exchanger, then heated to 125°C through a heat exchanger heated by thermal oil from an electric boiler. The heated eluant passes through the carbon in the pressurised elution column and desorbs the gold. Hot pregnant eluate is cooled through the recovery heat exchanger before flowing into the electrowinning cell feed distributor. Two electrowinning cells are used. The elution cycle is expected to take about 16 hours. No changes are planned for the elution circuit to enable the higher throughput.

The gold room houses two separate electrowinning circuits: the leach circuit and the gravity circuit, which processes pregnant solution from the ILR. During elution, pregnant gold solution from both processes is electrowon to produce gold sludge loaded cathodes. Sludge is removed by washing cathodes, passing sludge through a filter press, calcining for at least 12 hours in an electrically fired calcine furnace, and smelting in an induction furnace. The gold room is designed for two separate calcining and smelting circuits to facilitate high gold production and optimise individual accounting for leach and gravity circuits. Doré produced is transported to Rand Refinery for further processing.

Tailings detox and deposition

Cyanide content in tailings is lowered in a detox reactor employing the INCO process, using sodium metabisulphite and oxygen with copper sulphate added as a catalyst. Product from the detox reactor is sent to a tailings thickener before being pumped to the TSF. Plant tailings will be deposited on the existing No. 6 TSF. The available area on No. 6 TSF is estimated to have a capacity of up to 21 Mt, which is sufficient for the current Reserve of approximately 20.7 Mt.

Energy, water, and process materials

A power consumption rate of 45.8 kWh/t of ore was estimated for the 40 ktpm plant and 39.1 kWh/t for the 80 ktpm expansion, equating to a power draw of approximately 1,833 MWh per month and 2,778 MWh per month respectively when operating at steady state.

Maximum make-up water requirement is estimated at 0.90 m³ per RoM tonne, equating to daily consumption of 1.18 megalitres for 40 ktpm and 2.37 megalitres for 80 ktpm. Make-up water will be pumped from No. 6 Shaft or No. 5 Shaft to process water storage tanks. Potable water will be received from the Merafong local municipality.

Key reported parameters

Historic operating data (2007-2013): Blyvoor achieved recoveries of between 91% and 95.8%. Production ceased in July 2013. Lower recoveries from 2010 were attributed to co-treatment of low-grade surface material. The decrease in recovery could be attributed to poor processing efficiencies, lower grades, and toll treatment of higher-grade underground material with lower grade material at the Buffelsfontein South Plant since 2012.

Testwork basis for recovery: The expected plant feed grade of the new Blyvoor Mine will vary between 5 g/t and 10 g/t. Recovery performance is expected to be the same or better than previously. Recovery was assumed to be variable but with a fixed residue grade using the formula: R = (1 − k/F) × 100, where R is recovery in percentage, F is feed grade in g/t, and k is a constant of 0.304 g/t, which is the grade of TSF No. 6 as determined by drilling. The 0.304 g/t represents the most recent tailings reject grades from the old treatment plant.

Technical qualifications

This report presents the processing facility design and parameters as described in the technical report dated February 2021. The plant had recently been constructed and was being ramped up to 40 ktpm. The 80 ktpm expansion is planned but not yet implemented. No independent verification of the stated parameters, recovery assumptions, or consumable estimates is provided in this summary. The recovery formula uses a constant derived from drilling of TSF No. 6 and historic tailings grades. Historic operating data relates to the previous Blyvoor operation and the Buffelsfontein South Plant, which ceased operations in July 2013.

Source: An Updated NI 43-101 Technical Report on the Blyvoor Gold Mine, South Africa, February 2021, Item 17 – Recovery Methods.