HomeBase MetalsPrieska Copper-Zinc project moves to study field trials

Prieska Copper-Zinc project moves to study field trials

JSE/ASX-listed Orion Minerals has announced that following the release of the positive BFS for the development of the Prieska Copper-Zinc Project as a long-life, high margin, base metal mine work is now underway to:

  • complete pilot-scale field trials on various aspects of mine dewatering, viewed as a critical area for project success;
  • follow-up on the optimisation opportunities identified during the BFS, including mine-to-market enterprise optimisation of the Foundation Phase mining plan;
  • formalise key supply contracts to fast-track preconstruction activities and lock-in competitive pricing of critical plant and equipment identified during BFS inquiries; and
  • expedite the granting of the various licences needed to undertake mining operations.

“We identified numerous opportunities to improve on the foundation phase mining plan at Prieska during the feasibility study process,” says Orion’s MD and CEO Errol Smart, comments.

“In our opinion, these opportunities can result in quantum improvements in the already pleasing project financial returns and risk profile.

“We are thus making use of the time, whilst securing and formalising project funding, to ensure that Prieska execution incorporates as many of these improvements as possible, further derisking the project and providing for the best commercial outcome.

The areas of focus that have been selected for priority optimisation work are chosen for their potential to make the largest positive impact on capital costs, reduce project development lead time and improve NPV at Prieska.

Pilot-scale dewatering field trials at Prieska

The BFS base case plan caters for the dewatering of approximately 8.7 million cubic metres of accumulated mine water over a 13-month period, before any mining can take place underground.

Although the mine water has been shown to have a neutral pH and has low levels of contaminants, environmental regulations require the water to be stored in lined dams.

The accumulated mine water is planned to be pumped from underground, via the existing 1 km deep Hutchings Shaft, using a cascading system of pumps into a surface, 1 million cubic metre volume, lined dam from which all the water will be evaporated, using a combination of natural and mechanically assisted evaporation.

The base case plan does not include storage in unlined dams nor the reuse of the water, both of which are opportunities to improve on estimated capital costs. The plan is also premised on zero discharge of the

Pilot-scale trials have now been commissioned to further test water qualities, refine the proposed pumping system, investigate means of cost-effective water-treatment and to confirm the size and arrangement of evaporator units to be used.

Water treatment trials are being conducted first and are due to be completed during Q3 2019.

Thereafter, evaporator field trials are planned and are due to be completed before year-end 2019.

The water treatment trials will provide engineering data to allow detailed design and costings for treating the mine water to a range of water purification specifications.

Water treatment would allow offsite discharge and other secondary uses of water to be considered and so reduce the volume of water that needs to be temporarily stored in lined environmental control dams and force-evaporated.

Reducing the footprint of the lined storage dam and the amount of forced evaporation required represents a major target for capital cost reduction. A combination of optimising placement of plant tailings as backfilling over life of mine, and a reduced requirement for sealed storage and evaporation area, could materially reduce the capital cost of the combined tailings storage facility/evaporation dams allowed for in the BFS.

A 5m3 per hour pilot water treatment plant, bespoke for the Prieska Project’s water and schedule requirements, has been constructed and commissioned.

The plant is a combination chemical treatment, precipitation, ultrafiltration and reverse osmosis (RO) purification plant, configured to allow measurement and testing of key design parameters. The water treatment flowsheet is configured as follows:

  • feed water is pumped from the mine into an aeration tank to oxidise dissolved metals and other oxidizable ions;
  • the aerated solution then passes into a clarifier whilst being dosed with cold lime to remove dissolved hardness and to coagulate solid particles suspended in the water;
  • the clarifier overflow, with reduced levels of suspended solids, hardness and dissolved oxidation load, collects in a clear well, before being pumped through an Elfi self-cleaning suction strainer. The suction strainer in use on the pilot plant, which is able to remove particles of down to 50µm in size, is the first of its kind in use in the Southern African Development Community region;
  • the screened water is then passed through a Hydranautics HYDRACap Max ultrafiltration (UF) system. The UF is the final absolute barrier for solid particles, removing solids down to 0.08µm particle size, as well as any bacteria and viruses suspended in the water;
  • thereafter the filtrate is ready for RO. The RO process uses pressure to force water molecules through a semipermeable membrane, filtering out contaminant ions as a concentrated brine solution that will reach, in the pilot setup, up to 4 times the concentration of the incoming water. The resulting permeate (treated water) can have up to 98% of ions removed and is thus purified enough for other uses such as agricultural, ore processing water and potable applications.

The pumping system, supplying the water for the treatment trials, forms part of the field trials.

On completing of the water treatment trials, pilot-scale trials of the proposed mechanically assisted evaporation assembly are planned. The BFS relied on field trials using 15kW units.

Trials using 75kW and 90kW units are planned.

Results from the trials are expected to refine the number of and improve the operating efficiency expected from the evaporation units to be installed.

Enterprise optimisation

Whittle Consulting has been engaged to undertake enterprise optimisation of the business plan that was formulated as part of the BFS.

The enterprise optimisation process is expected to significantly improve project economics whilst also mapping out key business processes to aid operational control and a better understanding of the real value drivers unique for the Prieska Project business plan.

Whittle has a demonstrated track record of having dramatically improved base case plans, with previous projects having achieved in the order of 10% – 30% improvement in net present value (NPV) from the base case.

Enterprise optimisation is a methodology for increasing the economic value of mining and mineral processing operations through better long-term planning decisions. It involves a combination of ten mechanisms, which deal with decisions at different stages of the mining value chain.

A decision made at any point in the system potentially affects the optimal decision for all other points in the value chain. The process involves the detailed and accurate mapping and linking of the whole value chain, from the Mineral Resource inventory to the marketed product.

Thereafter, critical value drivers along the value chain are simultaneously varied until optimal permutations are identified.

Fundamental parameters such as cut-off grades, mining sequence, mining rates, targeted metal recoveries, mill throughput rates, targeted grind sizes, feed blends, product specifications, product logistics routes and variances in metal prices are all considered as one integrated system to derive a series of optimal business scenarios.

Whittle has, over a 30-year period, developed sophisticated software that enables this complicated simultaneous optimisation of the whole value chain to be undertaken.

The Whittle optimisation process will be conducted along with ongoing refinements and value engineering of the individual components making up the project value chain such as optimised process plant layouts to reduce footprint, streamlined mine sequencing including backfilling, and the selection of the simplest and most cost effective route to transport the concentrates to market.

The optimisation process is expected to be completed by Q4 2019, resulting in a refined mining plan, ready for execution and that also incorporates recommendations collected from key service providers and suppliers now being engaged as part of the preparation for project execution.