This report presents the proposed processing design for an 11,000 tpd heap leach gold operation in Turkey, based on metallurgical testwork and process design criteria.
Report context
The Öksüt Gold Project technical report, dated September 3, 2015, describes a proposed gold mining operation in Turkey. The flowsheet was derived from metallurgical testwork primarily performed by Kappes, Cassiday & Associates (KCA), with results and interpretation described in Section 13 of the report. The processing concepts and data presented are taken from the Process Flowsheets and Process Design Criteria developed for the Project. No historical operating data or actual performance results are included in this report, as the project was in the design phase at the time of writing.
Processing route
Primary Crushing
Run-of-mine ore will be delivered by 36-tonne haul trucks to the primary crusher. The ore will be dumped on a stationary grizzly installed over an 80-tonne truck dump hopper. Oversize rocks will be handled by a rock breaker. The ore will be withdrawn from the dump hopper via a 2.0 m wide x 4.5 m long grizzly feeder. The grizzly oversize will feed a 1.5 m x 2.0 m jaw crusher that will reduce the rock size to minus 150 mm prior to being conveyed by a 1.4 m wide x 95.5 m long belt conveyor to the secondary crushing circuit, along with the grizzly feeder undersize. A self-cleaning belt magnet will be installed over the conveyor belt feeding the secondary crusher building. A metal detector installed after the belt magnet will identify any remaining piece of metal and the conveyor will be stopped to allow manual removal by an operator.
Secondary Crushing
The product from the primary crushing circuit will feed a 2.4 m wide x 6.1 m long double-deck screen. The screen oversize will feed a 600 kW cone crusher while the screen undersize will report with the cone crusher product and will be transported by a 1.1 m wide x 50.7 m long belt conveyor to a radial stacker after quicklime has been added to the crushing circuit product. A 10,000 t capacity stockpile will be formed by the 1.1 m wide x 39 m long stacker installation. Dust collection units will be provided at the crushers' discharge and transfer points in both crushing buildings and a dry fog system will be installed at the truck dump. A compressor will provide compressed air for process and instrumentation application.
Heap Stacking
The crushed ore will be trucked from the crushing facility to the heap leach pad (HLP). The leach pad will be developed in three phases with an ultimate ore capacity of 40 Mt. Ore will be stacked in 10 m thick lifts.
Heap Leaching
The heap will be irrigated with a diluted cyanide solution recirculated from the ADR plant, via a network of piping covering the surface area under leach. The barren leach solution will be pumped from the barren tank at the ADR plant to the area under heap leach. The cyanide concentration will be adjusted and the pH will be controlled so that HCN gas formation is inhibited. The solution will be filtered to remove carbon fines prior to distribution over the area under heap leach to minimize emitter plugging. It will be pumped by means of two centrifugal pumps installed in series. The first pump will cover operation for the first three years of operation (end of Phase 1), while the second pump will be required from year four and beyond.
The irrigation distribution piping will consist of a 300 mm diameter main header made of carbon steel from the barren pumps discharge to the heap perimeter followed by HDPE ending at the ore panels to be irrigated. Drip emitters will be used to provide irrigation. A typical panel piping arrangement will include a 300 mm diameter HDPE header starting from the main header and running for 190 m along the 250 m side of the panel. Four lateral pipes spaced at every 62.5 m will be branched from the header. Each lateral pipe will include a 150 mm butterfly valve, a pressure gauge, and 75 m of a 150 mm diameter HDPE pipe followed by 75 m of a 100 mm diameter HDPE pipe. Emitter lines will be branched at every 500 mm on the pipes and emitters will be spaced at every 762 mm on the emitter lines.
The pregnant leach solution (PLS) will flow by gravity through a network of collection pipes at the base of the heap to the PLS pond prior to being pumped to the ADR plant for precious metals recovery.
Adsorption
The PLS will be reclaimed from the pregnant solution pond by a submersible pump at a rate varying between 300 and 500 m³/h. The PLS will be sampled and will pass through a trash screen prior to being distributed to the carbon-in-column (CIC) circuit. The solution will flow by gravity from the first to the fifth contactor of each line. Discharge from the last contactor will report to the carbon safety screen and will be sampled again prior to being pumped to the barren solution tank for recirculation on the heap.
Each contactor will hold three tonnes of carbon. Periodically, based on the precious metals loading, carbon from the first contactor will be transferred to the elution circuit using the carbon transfer pump, prior to the content of the following contactors being pumped upstream to the previous unit. It is planned to transfer three tonnes of carbon on a daily basis, alternating between both lines.
Acid Wash
Carbon transferred from the first contactor of each adsorption line will be pumped to the acid wash vessel where, under contact with hydrochloric acid, scale build-up will be removed. The acid wash vessel will have a 3-tonne capacity and will be constructed of fiberglass reinforced plastic (FRP).
Desorption and Electrowinning
Once the acid wash step has been completed, carbon will be transferred to the elution column where it will be stripped from its precious metals content using the pressure Zadra process. The circuit comprises a 3-tonne capacity carbon elution column and a barren strip solution tank with pumps. The solution exiting the elution column is pumped to electrowinning. Barren solution from electrowinning will be returned to the barren strip solution tank for recycle to the elution column. The electrowinning circuit will include two electrowinning cells.
Carbon Regeneration
Once the elution cycle is complete, carbon will be pumped to the stripped carbon dewatering screen located in the carbon reactivation circuit. The screen undersize will flow by gravity to the carbon fines collection tank while the screen oversize will report to the reactivation kiln feed hopper. From there, the carbon will be fed by a screw feeder to the reactivation kiln. Reactivated carbon will leave the kiln and will be quenched using fresh water prior to being pumped to the reactivated carbon sizing screen. Screen oversize will be returned to carbon contactors No. 5 or 10, while screen undersize will report to the carbon fines collection tank.
Refining
Precious metals will be washed from the cathodes and the resulting sludge pumped to the gold sludge filter. The filter cake will be dried in an oven prior to being mixed with fluxes. The mixture will then be processed in the gold melting furnace, which will produce liquid metal and liquid slag; the liquid metal will be poured into doré bars while the solidified slag will be collected and shipped off-site for subsequent treatment.
Heap Leach Facilities
The leach pad will be constructed in three phases with approximate areas of 578,000 m², 212,000 m² and 155,000 m² for Phases 1, 2 and 3, respectively. The total cumulative pad area including Phases 1 through 3 will be 945,000 m². The leach pad will have a composite liner system consisting of a 2 mm smooth LLDPE geomembrane underlain by a 0.5 m thick (minimum) compacted low-permeability soil layer with a maximum permeability of 1 x 10⁻⁹ m/s. The fully stacked leach pad (end of Phase 3) will have a nominal ore capacity of 40 Mt and a nominal maximum heap height of 80 m above the liner.
The PLS pond and PLS overflow pond will be double-lined, with a primary liner consisting of a 1.5 mm thick single sided textured HDPE geomembrane, and a secondary composite liner consisting of a 1.5 mm thick smooth HDPE geomembrane overlying a 500 mm thick low permeability soil layer. The make-up water pond will be single composite lined with a 1.5 mm thick single sided textured HDPE geomembrane overlying a 500 mm thick low permeability soil layer.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Throughput (average) | tpd | 11,000 | Design |
| Crushing circuit availability | % | 75 | Design |
| Primary crusher type | – | Jaw | Design |
| Primary crusher size | m x m | 1.5 x 2.0 | Design |
| Primary crusher F80 | mm | 392 | Design |
| Primary crusher CSS | mm | 175 | Design |
| Primary crusher P80 | mm | 137 | Design |
| Secondary crusher type | – | Cone | Design |
| Secondary crusher motor size | kW | 600 | Design |
| Secondary crusher CSS | mm | 45 | Design |
| Secondary crusher P80 | mm | 38 | Design |
| Heap lift height | m | 10 | Design |
| Ore under leach (per lift) | t | 547,945 | Design |
| Ore density | t/m³ | 1.45 | Design |
| Area under leach | m² | 37,790 | Design |
| Irrigation method | – | Drip emitters | Design |
| Solution application rate | L/h/m² | 12 | Design |
| Irrigation rate | m³/h | 453 | Design |
| Primary leach cycle | days | 50 | Design |
| Total leach cycle | days | 151 | Design |
| Irrigation solution pH | – | 10.5 – 11.0 | Design |
| Irrigation solution concentration | mg NaCN/L | 500 | Design |
| PLS grade – Au (average) | g/t Au | 0.79 | Design |
| PLS grade – Ag (average) | g/t Ag | 0.36 | Design |
| Recovery (life-of-mine) – Au | % | 77 | Design |
| Recovery (life-of-mine) – Ag | % | 14.0 | Design |
| Number of adsorption lines | Qty | 2 | Design |
| Number of contactors per line | Qty | 5 | Design |
| Adsorption flow rate (design) | m³/h | 500 | Design |
| Carbon hold-up per column | t | 3 | Design |
| Carbon loading – Au (average) | g Au/t | 2,400 | Design |
| Carbon loading – Ag (average) | g Ag/t | 640 | Design |
| Acid wash vessel capacity | t | 3 | Design |
| Acid wash cycle duration | h | 3 – 4 | Design |
| Strip vessel capacity | t | 3 | Design |
| Strip cycle duration | h | 8 – 12 | Design |
| Carbon kiln type | – | Horizontal, Electric | Design |
| Carbon kiln capacity | kg/h | 125 | Design |
| Number of electrowinning cells | Qty | 2 | Design |
| Furnace capacity | L | 57 | Design |
| Production – Au (maximum) | oz Au/day | 485 | Design |
| Production – Au (average) | oz Au/day | 233 | Design |
| Production – Ag (average) | oz Ag/day | 97 | Design |
| Quicklime consumption | t/a | 7,600 | Design |
| Cyanide consumption | t/a | 1,600 | Design |
| Hydrated lime consumption | t/a | 1,000 | Design |
| Carbon consumption | t/a | 80 | Design |
| Sodium hydroxide consumption | t/a | 430 | Design |
| Hydrochloric acid consumption | t/a | 440 | Design |
| Anti-scalant consumption | t/a | 60 | Design |
| Refining fluxes consumption | t/a | 1.6 | Design |
| Total connected load | MW | 7.84 | Design |
| Average power draw | MW | 4.73 | Design |
| Ore permeability (Ksat, lab test) | cm/s | 8.0 | Testwork |
| Ore permeability (Ksat, estimated range) | cm/s | 0.5 – 1.0 | Testwork |
| Static factor of safety (preferred liner) | – | 1.6 | Design |
| Pseudo-static FOS (OBE, preferred liner) | – | 1.0 | Design |
| MDE displacement (preferred liner) | cm | 24 | Design |
Project website: https://www.centerragold.com/operations/oksut/default.aspx
Technical qualifications
The technical report explicitly notes that the flowsheet for the Öksüt Project was derived from metallurgical testwork primarily performed by Kappes, Cassiday & Associates (KCA), with testwork results and interpretation described in Section 13 of the report. The concepts and data presented in the recovery methods section are taken from the Process Flowsheets and Process Design Criteria developed for the Project, indicating these are design parameters rather than operational results. The report does not include historical operating data, as the project had not yet commenced operations at the time of writing. The water balance model applied three scenarios based on varying hydraulic conductivity values of the ore, with laboratory testing indicating a permeability of 8.0 cm/s, though Golder noted that a more representative field value may be within a range of 0.5 cm/s to 1.0 cm/s, acknowledging potential factors that may lower effective vertical hydraulic conductivity.
Source: Centerra Gold Inc. – Öks
