The Kalana project proposes a new 1.2 Mtpa gravity and carbon-in-leach processing plant to treat saprolite and fresh rock, supported by metallurgical testwork and historical operating data from the existing 60,000 tpa plant.
Report context
The Kalana Mineral Resource Estimate and Preliminary Economic Assessment (PEA), dated 31 March 2014, includes a processing route based on metallurgical test work completed by a range of reputable laboratories, the history of gold plant operations at Kalana, and benchmarking against similar gold operations and projects in West Africa. The existing gold plant at Kalana has a capacity of 60,000 tonnes per year and uses crushing, milling and gravity concentration to recover gold from high grade quartz ores mined from underground. The existing plant is located within the footprint of the proposed open pit.
Processing route
Overview
It is proposed to construct a new process plant with a capacity of 1.2 million tonnes per year of saprolite and fresh rock to recover gold by gravity and carbon in leach (CIL) technology. The gold mineralisation is present in the weathered saprolite to a depth of about 80 m and in fresh rock. It is also proposed that the leaching and gold elution sections of the new process plant will be constructed to enable processing of the tailings resource to be completed prior to the commissioning of the crushing and milling circuits.
Crushing and ore stockpiling
It is proposed that a scrubber will be used to remove clay and fine material from saprolite ore before crushing. The primary jaw crusher will produce a product size of 100% passing 240 mm. The crushed ore stockpile would have a capacity of about 5,000 tonnes.
Milling and classification
It is currently proposed that the milling circuit will include a SAG mill, ball mill and pebble crusher; however no detailed work has been completed to design the SAG mill. The circuit is expected to produce a particle feed size to the CIL of 80% passing 75 micron. Preliminary test has not identified potential viscosity issues but more detailed test work is required. It is proposed that the gravity gold will be recovered by Knelson concentrators, which is the same process used in the existing plant.
Carbon in leach
There is no presence of preg-robbing materials. Tests have shown addition of oxygen has some benefit and it is proposed to introduce oxygen to the tanks prior to cyanide leaching. Leach tests have shown that 30 hours residence time is appropriate. The plant will require a cyanide detoxification process. No test work has been completed to assess the optimum plant.
Flotation potential
There is potential to introduce flotation into the recovery process after recovery by gravity concentration. Test work on underground mineralisation indicates that 85% of the gold in the gravity tailings can be recovered in 10% of the mass, resulting in a potential reduction in the cost of reagents and a smaller plant footprint. Further test work is required to demonstrate the viability of including flotation in the process design. A flotation circuit has not been included in the capital estimates. Test work has shown potential benefits of a flotation circuit for fresh ore and possibly oxides.
Elution and gold recovery
It is assumed that a standard AARL method will be used for elution and a kiln used for carbon regeneration. Standard electro-winning cells will be used for recovering gold from pregnant eluate. An electric furnace will be used for smelting.
Consumables and services
The main consumables are cyanide and lime. Metallurgical tests have shown consumption to be acceptable within normal gold operations. Storage will be to internationally acceptable standards. It is assumed that an oxygen plant will be required to provide the required quantity of oxygen; however the actual quantity required has not been estimated. The capital estimate allows for two compressors, one operational and one standby. Water supply to the existing gold plant is supplied from underground water pumping and it is understood that excess water will be available from the same source, with pumping from boreholes. There will be an added benefit of dewatering the pit ahead of mining. Potable water is available on site but will require purification.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Existing plant capacity | 60,000 tpa | Historical operating data |
| Existing plant gravity recovery | 80% to 90% since 2004 | Historical operating data |
| Proposed new plant capacity | 1.2 Mtpa saprolite and fresh rock | Proposed design |
| Work index, saprolite | 11 kWh/t | Metallurgical test work and historic operations |
| Work index, fresh rock | 17 kWh/t | Metallurgical test work and historic operations |
| Gravity recoverable gold, saprolite and fresh rock | 40% to 95% | Metallurgical test work |
| Gravity recovery, underground mineralisation | 80% to 92% | Operating experience |
| Leach grind size, saprolite and fresh rock | 80% passing 75 micron | Cyanide leach test work |
| Leach grind size, tailings | 80% passing 180 micron | Cyanide leach test work |
| Tailings recovery | 83% | Assumed, no milling required |
| Gold recovery, oxide and fresh mineralisation | 93% | Assumed, based on 2013 results |
| Gravity and BLEG leach recovery on gravity tailings | 94.2% | SGS testwork, 2014 |
| CIL residence time | 30 hours | Leach tests |
| Crushed ore product size | 100% passing 240 mm | Proposed design |
| Crushed ore stockpile capacity | about 5,000 tonnes | Proposed design |
| CIL feed size | 80% passing 75 micron | Expected circuit performance |
| Preg-robbing | Not present | Metallurgical tests |
| Flotation: gold recovered in gravity tailings | 85% in 10% of mass | Test work on underground mineralisation |
Project website: https://www.endeavourmining.com/our-portfolio/projects/kalana/
Technical qualifications
The process description is based on metallurgical test work, historical operating data and benchmarking, with several elements remaining at a preliminary stage. Specific limitations identified in the report include:
- No detailed work has been completed to design the SAG mill.
- More detailed test work is required to confirm the absence of viscosity issues.
- No test work has been completed to assess the optimum cyanide detoxification process.
- Further test work is required to demonstrate the viability of including flotation in the process design.
- A flotation circuit has not been included in the capital estimates.
- The actual quantity of oxygen required has not been estimated.
- The plant flow sheet and design is expected to be similar to many process plants world-wide, indicating a benchmarking approach rather than site-specific design.
Source: Avnel Gold Mining Limited, Kalana Mineral Resource Estimate and PEA, 31 March 2014, Section 17 Recovery methods.
