The 2014 PEA for the Piskanja project assumes a conceptual processing route to produce colemanite concentrate and boric acid, based on limited testwork and no demonstrated technically feasible process route.
Report context
The preliminary economic assessment (PEA) for the Piskanja project was prepared by SRK Consulting in September 2014. The report acknowledges that no technically feasible process route has yet been demonstrated that can upgrade the Piskanja ore to what is considered a minimum marketable colemanite concentrate grade. The processing assumptions and conceptual flowsheet presented in the PEA are based on a limited amount of non-definitive metallurgical data.
Processing route
Processing assumptions
For the purpose of the PEA, SRK assumed that a process can be developed to upgrade the ore to satisfactory levels of B₂O₃ and iron. The assumed criteria are a concentrate grade of 35% B₂O₃ for the range of head grades in the proposed mine plan (24.3-32.9% B₂O₃) and a tailings grade of 7.5% B₂O₃, the figure achieved for the magnetite fraction in the SGS HIMS testwork.
Production plan
The production plan calls for the production of both colemanite concentrate and boric acid, the latter at a rate of 25 ktpa and the former at a rate of approximately 200 ktpa. SRK modelled this production scenario according to a conceptual process route shown in block form as Figure 17-1 in the report.
The mass yield and B₂O₃ recovery across the beneficiation stage are variable, a function of the variable run-of-mine grade and the fixed concentrate and tailings grades. For the boric acid plant, a fixed B₂O₃ recovery of 80% has been assumed as representing a typical industry value.
Tailings management
The quantity of beneficiation plant tailings is projected to range from 22 ktpa to 123 ktpa over the life of the project, averaging 88 ktpa. The quantity of tailings from the boric acid plant is expected to be 49 ktpa.
A desktop study was undertaken to determine the possible location for the tailings storage facility (TSF) to store 5% of 1.8 million tonnes of colemanite tailings and 5% of 1.0 million tonnes of boric acid tailings material. The amount of tailings material to be stored within the TSF totals 0.135 Mt (0.122 Mm³) at a dry density of 1.1 t/m³. The remaining 95% of boric acid and colemanite tailings will be utilised for backfill.
Site selection
The site selection study was not carried out as the client’s preferred location was the site immediately south of the proposed plant. The client stated that this site was previously used by the Ibar Mine to clarify water for the coal washing plant and was therefore considered a perfect location for the TSF.
TSF design
A conceptual TSF design has been developed by SRK to store about 150,000 m³ of tailings material that occupies an area of about 6 ha including the dam footprint area. SRK considered a downstream construction method for the proposed facility, which will require the construction of full height dam walls using suitable material for construction acquired from local borrow areas. The dam wall will have slopes of 1V:2.5H on the downstream side and 1V:3H on the upstream side and a crest width of 5 m. The maximum dam height at the lowest ground is about 4.4 m, and the crest elevation at 381 metres above sea level. A freeboard of 1 m was added to the dam height.
Tailings waste will be disposed as slurry which will be delivered via a pipeline into the facilities. SRK did not consider dry stacking at this stage as there are many unknowns regarding the final tailings product. The conceptual design includes a double 2 mm HDPE liner system with a leakage detection system between the liners and below the bottom liner.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Concentrate grade (B₂O₃) | 35% | Assumed design criterion |
| Head grade range (B₂O₃) | 24.3-32.9% | Proposed mine plan |
| Tailings grade (B₂O₃) | 7.5% | Based on SGS HIMS testwork (magnetite fraction) |
| Colemanite concentrate production | ~200 ktpa | Production plan |
| Boric acid production | 25 ktpa | Production plan |
| Boric acid plant B₂O₃ recovery | 80% | Assumed typical industry value |
| Beneficiation plant tailings (life-of-project range) | 22-123 ktpa | Projected, variable |
| Beneficiation plant tailings (average) | 88 ktpa | Projected |
| Boric acid plant tailings | 49 ktpa | Projected |
| TSF storage capacity | 150,000 m³ | Conceptual design |
| TSF storage mass | 0.135 Mt | At dry density 1.1 t/m³ |
| TSF area | ~6 ha | Including dam footprint |
| Dam slopes (downstream:upstream) | 1V:2.5H : 1V:3H | Conceptual design |
| Dam crest width | 5 m | Conceptual design |
| Maximum dam height | 4.4 m | At lowest ground |
| Dam crest elevation | 381 masl | Conceptual design |
| Freeboard | 1 m | Conceptual design |
Project website: https://www.theglobeandmail.com/investing/markets/markets-news/ACCESS%20Newswire/1076360/boron-one-holdings-inc-advances-with-potential-partner/
Technical qualifications
The report states that only a very limited amount of metallurgical testwork has been undertaken in support of the production of this PEA. This work consisted of some upgrading testwork which, while resulting in a reduction in the iron content of the product to close to the assumed target level, did not result in any significant upgrading of the boron content, at least not to the assumed minimum figure of 35% B₂O₃ for a saleable colemanite concentrate.
The metallurgical parameters developed for the PEA are therefore largely assumptions based on a limited amount of non-definitive data. Virtually no specific engineering was conducted with regard to the process plant design, and the process plant capital and operating costs subsequently generated are high level estimates based on generic databases and parallel project data.
No technically feasible process route has yet been demonstrated that can upgrade the Piskanja ore to what is considered to represent a minimum marketable colemanite concentrate grade.
Geophysical, rheological and geochemical testing on tailings material is recommended to evaluate the preferred tailings deposition method.
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*Source: Piskanja Project , 2014 PEA, U5932 Piskanja 43-101 PEA_Final.docx, September 2014, sections 17.1, 17.2, 17.3*
