This report describes the metallurgical processing design, equipment, and historical operating data for the Ity Carbon-In-Leach Plant, including testwork results for Daapleu primary ore.
Report context
This technical report, dated June 2020, addresses the recovery methods in operation at the Ity Gold Mine, including process selection, process and plant description, historical performance, and metallurgical life-of-mine planning assumptions. The report documents design criteria, testwork results, and processing trials conducted in November 2019 and February 2020.
Processing route
Design philosophy
The process plant design is based on a robust metallurgical flowsheet constructed from unit operations well proven in industry. Key criteria for equipment selection are suitability for duty and projected mine life without unnecessarily compromising reliability and ease of maintenance. The plant layout provides ease of access while maintaining a compact footprint.
The Ity Carbon-In-Leach Plant processes oxide, transition and fresh ore types. Primary ores are significantly more competent than oxide ores.
Selected process flowsheet
The treatment plant design incorporates the following unit process operations:
- Single stage primary crushing to produce a crushed product size of P80 of 129mm
- Transfer conveyor feeding a surge bin (30 minutes live capacity) reclaimed via an apron feeder, with overflow feeding a coarse ore stockpile
- Two stage SAG/ball milling in closed circuit with hydrocyclones to produce a P80 grind size of 75µm, including pebble crushing from the SAG mill
- Gravity concentration and removal of coarse gold from the milling circuit recirculating load, with treatment by intensive cyanidation and electrowinning
- Pre-leach thickener to increase slurry density to the carbon-in-leach circuit
- A CIL circuit incorporating eight CIL tanks containing carbon for gold and silver adsorption
- Eighteen-tonne capacity split Anglo elution circuit, electrowinning and gold smelting
- Tailings treatment incorporating cyanide destruction using sodium metabisulphate and oxygen, followed by arsenic precipitation and stabilisation
- Tailings pumping to the tailings storage facility
Crushing circuit
Run-of-mine ore is delivered to the ROM pad and dumped in finger stockpiles arranged by ore grade and lithology. A front-end loader reclaims ore to the ROM bin. A grizzly protects downstream equipment from oversize material, with a mobile rock breaker used for oversize rocks. ROM ore is drawn by an apron feeder discharging over a vibrating grizzly. Grizzly oversize reports to a jaw crusher (1,600mm x 1,200mm). A tramp metal magnet was ordered for installation in 2020.
Ore storage and reclaim
Crusher output feeds a 500-tonne live capacity surge bin providing 30 minutes feed to the milling circuit. The coarse ore stockpile was increased in early 2020 to 40,000-tonne capacity. Primary ore is reclaimed from the surge bin via a variable speed apron feeder. Ore can also be reclaimed via front-end loader from the coarse ore stockpile during extended crusher shutdowns. Quicklime is added directly onto the mill feed conveyor from a silo metered by a variable speed screw feeder.
Grinding and classification circuit
The grinding circuit consists of an SABC circuit with hydrocyclones. The SAG mill is 8.50m diameter x 4.35m EGL complete with a 6,000kW variable speed drive operating at up to 18% volumetric ball loading. Speed range of 60% to 80% critical speed is available. Steel ball grinding media is typically 100mm to 125mm diameter.
SAG mill product discharges into a vibrating single deck heavy duty pebble dewatering screen fitted with nominal 15mm aperture. Oversize pebbles (+15mm) are transferred to a pebble crusher feed bin ahead of a single 250kW pebble crusher. Pebbles are crushed from nominal top size of 75mm to a P80 of approximately 12mm.
The ball mill is 6.10m diameter x 9.05m EGL overflow type, complete with a 6,000kW variable speed drive operating at up to 35% volumetric loading. Product size from the grinding circuit is 80% passing 75μm on 100% primary ore.
The cyclone cluster comprises 18 x 380mm diameter hydrocyclones operating at 95kPa. Cyclone overflow at 40% w/w solids flows by gravity to the trash screen.
Gravity circuit
Feed for the gravity circuit is drawn from a portion of the combined SAG and ball mill discharge streams. Feed is pumped to gravity scalping screens to remove coarse (+2mm) material. Screen undersize gravitates to either of two 48-inch Knelson centrifugal concentrators. Concentrator tails return to the mill discharge hopper. Concentrate is processed once per day in the intensive leach reactor, a rotating drum leach vessel, for up to 18 hours.
Leach and carbon adsorption circuit
Pre-leach thickener underflow is pumped to the CIL circuit of eight tanks interconnected with launders. Based on 5Mtpa throughput, residence time is 25 hours for thickened slurry and 19 hours for unthickened slurry. Each tank is fitted with a dual impeller mechanical agitator and two mechanically swept woven wire intertank screens.
Sodium cyanide solution is metered into the CIL feed box and tanks from a ring main system. Oxygen from either of two 50-ton capacity vacuum pressure swing adsorption plants is distributed to all tanks.
Stripping plant and goldroom operations
Operations include acid washing of carbon, cold cyanide washing as required, stripping using the split AARL method, electrowinning, and smelting. The total carbon movement around the elution circuit on a daily basis is approximately 18 tonnes.
Key reported parameters
| Parameter | Units | Design | Testwork/Actual |
|---|---|---|---|
| Plant throughput (blended ore) | Mtpa | 5.2 | , |
| Blend composition | % primary / % oxide | 58 / 42 (LoM plan) | , |
| Crushing plant mechanical availability | % | 80 | , |
| Plant mechanical availability (remainder) | % | 91.3 | , |
| Primary crushed product size (P80) | mm | 129 | , |
| Grind size (P80) | µm | 75 | , |
| ROM bin capacity | t | 241 | , |
| Primary crusher dimensions | mm | 1,600 x 1,200 | , |
| Coarse ore stockpile capacity | t | 15,000 (increased to 40,000 in early 2020) | , |
| SAG mill dimensions (dia x EGL) | m | 8.50 x 4.35 | , |
| SAG mill power | kW | 6,000 | , |
| Ball mill dimensions (dia x EGL) | m | 6.10 x 9.05 | , |
| Ball mill power | kW | 6,000 | , |
| Pebble crusher capacity | tph | 100 | , |
| Pebble crusher closed side setting | mm | 11 | , |
| Gravity concentrator capacity | tph | 2 x 400 | , |
| Intensive cyanidation reactor capacity | t/d | 5 | , |
| Hydrocyclones (No. x dia) | mm | 18 x 380 | , |
| Pre-leach thickener diameter | m | 38 | , |
| CIL tanks (No. x dia) | m | 8 x 2,900 | , |
| CIL residence time (thickened) | hours | 25 | , |
| CIL residence time (unthickened) | hours | 19 | , |
| Elution circuit type | , | Split AARL | , |
| Elution circuit capacity | t | 18 | , |
| Oxygen plant capacity | tpd | 2 x 50 | , |
| Oxide ore leach extraction | % | , | 90 to 96 (actual) |
| Daapleu primary ore leach extraction (standard cyanide) | % | , | 60 to 65 (testwork) |
| Daapleu low-grade primary ore recovery (<1.2g/t) | % | , | 76 (processing trials Nov 2019 and Feb 2020) |
Project website: https://www.endeavourmining.com/our-portfolio/ity-mine/
Technical qualifications
The report states that testwork results for Daapleu primary ore containing significant arsenopyrite indicated that a standard cyanide leach will only extract 60% to 65% of contained gold across the full grade range. Processing trials conducted in November 2019 and February 2020 indicated that low grade (<1.2g/t) primary ore can achieve a recovery of 76%. The report notes that further trials and testwork was underway to determine whether increased recoveries could be achieved from the high-grade portion of the Daapleu primary ore.
The report also notes that certain ores contain significant cyanide soluble copper and silver which has influenced the design capacity of the elution circuit and goldroom and plays a key role in determination of mill feed blends.
Source: Technical Report Ity Gold Mine, June 2020, Section 17 Recovery Methods
