The Kopsa preliminary economic assessment describes a proposed processing route that would treat Kopsa ore through the existing Hitura flotation mill, with copper and bulk sulphide concentrate production followed by cyanide leaching of the sulphide concentrate for gold and silver recovery.
Report context
The Kopsa PEA technical report, dated October 2013, was prepared to evaluate the potential processing of Kopsa material through the Hitura flotation mill, located approximately 19 km from the Kopsa site. The Hitura mill had until recently processed nickel sulphide ore at a nominal annual throughput rate of 600 ktpa.
Processing route
Existing Hitura plant configuration
The Hitura plant consists of a two-stage crushing circuit feeding a three-stage milling circuit comprising a rod mill and two ball mills ahead of flotation. When treating nickel sulphide ore, the flotation circuit had been configured to produce either one or two concentrate products.
Proposed Kopsa flowsheet
For treatment of Kopsa ore, the flotation circuit would be configured to produce two sulphide concentrates: a marketable copper concentrate containing some gold and silver, and a bulk sulphide concentrate for further processing on site. The stated aim of the flowsheet would be to produce a flotation tailings essentially devoid of arsenic, such that it could be stored in the existing Hitura tailings management facility.
The bulk sulphide concentrate would be cyanide leached for the recovery of gold and silver. As indicated by testwork, the concentrate would be reground ahead of cyanidation. Cyanidation would be followed by a conventional Carbon-in-Pulp (CIP) / Carbon-in-Leach (CIL) format, producing a smelted gold/silver doré. The tailings from cyanidation would be subjected to cyanide detoxification ahead of storage in a dedicated facility.
Ore sorting consideration
Ore sorting is being considered as part of a mine site facility that conceptually would reduce the amount of ore to be trucked between the Kopsa mine site and the Hitura plant site.
Design criteria basis
Process design criteria were developed based on testwork results received to date. Two options were presented: the first for as-mined material (after crushing) delivered to Hitura, and the second with the incorporation of sorting at the mine site. The throughput values in the design criteria were as specified by the project owner, with lower throughputs than the nominal Hitura plant capacity showing the size of the Kopsa deposit and the perceived harder nature of the Kopsa material.
An analysis of available grinding power in the Hitura plant suggested that, particularly at higher Bond work index figures reported for Kopsa material (20 and 23 kWh/t), the Hitura grinding circuit may not be able to process 500 ktpa of ore assuming all feed must be ground to the final grind size (80% passing 45 µm, per recent testwork). These throughput figures were to be reviewed as the project progressed, with collection of further work index data and flotation flowsheet optimisation, potentially including staged grinding so that only a small fraction of incoming plant feed (a rougher concentrate) would need to be ground to the final grind size.
The flotation criteria assumed fixed copper and gold recoveries to a fixed grade of copper concentrate, and fixed mass and gold recoveries to the sulphide concentrate. These figures were assumed to be the same for both the non-sorting and sorting cases. The figures used were based on testwork, although the report noted that the testwork had yet to definitively demonstrate the simultaneous production of a high copper, low arsenic copper concentrate and a low arsenic final tailing following production of the sulphide concentrate.
The response of Kopsa material to sorting was based on testwork conducted to date, with the 65% mass rejection based on sorting testwork results without considering the +40 mm fraction, and recovery assumptions applied to the sorting stage.
Capital cost estimates
Capital costs for conversion of the Hitura process plant to treat Kopsa material were estimated as follows:
- Hitura plant reconfiguring and general refurbishment (nominal figure): EUR 500,000
- Sulphide concentrate CIL plant and associated goldroom: EUR 3,750,000
- Sorting plant (assumes contract crushing): EUR 1,500,000
- Hitura plant expansion (to 1-1.2 Mtpa): EUR 7,500,000 (without sorting)
The figures for the Hitura plant were estimates based on an internal cost database. The sorting figure was based on a figure provided by the project owner per sorting unit (per 500,000 tpa of production capacity).
Operating cost estimates
Operating costs for processing Kopsa material through the modified Hitura plant, with inclusion of sorting, were estimated as shown in the key reported parameters table below. The costs excluding sorting and cyanidation were based on 2012 actual costs for the Hitura plant. The sorting cost was based on a figure provided by the project owner, and the cyanidation cost was an estimate by the report consultants.
Recommendations
Design engineering activities were recommended to support the next phase of project development, including engineering of the new sections of plant required as additions to the Hitura facility, principally the CIL plant and associated gold recovery processes (elution, goldroom). A detailed analysis of the existing Hitura facility would also be required to estimate process and engineering modifications required to convert the plant from its existing configuration to the configuration required for the Kopsa project. Consideration was also identified for whether parts of the plant require refurbishment to meet contemporary operating requirements. The cost for such an engineering programme was estimated at EUR 1.0-1.5 million.
Key reported parameters
The following table summarises process design criteria for both options considered, without sorting and with sorting.
| Parameter | Unit | Without Sorting | With Sorting |
|---|---|---|---|
| RoM Production | tpa | 500,000 | 1,200,000 |
| Material delivery to plant | tpa | 500,000 | 420,000 |
| Sorting loss, Cu | % | – | 25 |
| Sorting loss, Au | % | – | 10 |
| Flotation feed grade, Cu | % | 0.15 | 0.32 |
| Flotation feed grade, Au | g/t | 0.91 | 2.34 |
| Copper concentrate production | tpa | 2,700 | 4,800 |
| Copper concentrate, Cu recovery | % | 80 | 80 |
| Copper concentrate, Au recovery | % | 40 | 40 |
| Copper concentrate, Cu grade | % | 22.5 | 22.5 |
| Copper concentrate, Au grade | g/t | 75 | 82 |
| Sulphide concentrate production | tpa | 15,000 | 12,600 |
| Sulphide concentrate, Au recovery | % | 44.75 | 44.75 |
| Sulphide concentrate, Au grade | g/t | 13.5 | 35.0 |
| Cyanidation recovery, Au | % | 95 | 95 |
| Recovery to doré, Au | % | 42.5 | 42.5 |
| Overall recovery, Cu | % | 80 | 60 |
| Overall recovery, Au | % | 84.75 | 76.30 |
Project website: https://www.globenewswire.com/news-release/2013/10/02/1412135/0/en/Belvedere-Announces-Positive-PEA-on-Their-Kopsa-Gold-Copper-Project.html
| Operating Cost Item | Cost (EUR/t RoM) |
|---|---|
| Crushing (non-sorting case) | 1.00 |
| Sorting (including crushing) | 1.75 |
| Grinding | 1.90 |
| Flotation | 3.10 |
| Cyanidation | 0.75 |
| Filtration | 0.50 |
| Processing general | 0.32 |
| Maintenance | 0.32 |
Technical qualifications
The design criteria are based on a number of assumptions that carry specific technical limitations. The throughput values were specified by the project owner, and the report noted that the Hitura grinding circuit may not be able to process 500 ktpa of ore assuming all feed must be ground to the final grind size. The sorting testwork was conducted on a sample with different grade characteristics than the resource average, and the report noted the sorting recovery values could be considered somewhat optimistic. The flotation recoveries were based on testwork that had yet to definitively demonstrate the simultaneous production of a high copper, low arsenic copper concentrate and a low arsenic final tailing, and as such the recoveries and mass yield to the sulphide concentrate should be considered provisional. The cyanidation testwork was conducted under intensive cyanidation conditions, while the report's consultant believed a conventional CIP/CIL circuit would be capable of similar recovery based on experience.
Source: Kopsa PEA , 2013 Technical Report, October 2013, Section 17 Recovery Methods.
