Orion Minerals Ltd (ASX:ORN) is making positive progress with value engineering and optimisation work being carried out on the bankable feasibility study (BFS) for the Prieska Copper-Zinc Project in South Africa.
There have been positive results from water treatment trials for the shaft water to be purified for all off-site discharge, thereby allowing increased pumping rates which will accelerate planned project development timelines.
Semi-autogenous milling test work that is being undertaken has indicated reduced processing plant capital and operating costs.
The mine-to-market optimisation studies are on track to deliver results by the end of this year.
Completed “before the end of the year”
Managing director and CEO Errol Smart said: “We continue to progress a number of significant optimisation opportunities identified during the preparation of the Foundation Phase Bankable Feasibility Study (BFS) for the Prieska project.
“Our aim is to complete these studies before the end of the year and have an improved and simple-to-execute project plan with both capex and opex benefits ready for execution next year.
“Dewatering the mine is a significant workstream and is the critical path activity where the greatest impact may be achieved on development timelines and capital costs.
“Positive results from water treatment trials mean that we now have more options for dewatering and can improve on what we see as an already very robust plan.”
The historic Prieska mine is flooded to within 320 metres of the surface and requires dewatering.
Orion's current BFS plan assumes an 18-month timeline to set up and empty the mine of the accumulated water, which would be pumped into a surface dam with a designed maximum capacity of 1 million cubic metres.
A bank of evaporators will supplement natural evaporation to ensure that evaporation matches the 1,200 cubic metres per hour average dewatering rate that is planned.
Due to the high capital costs for a lined dam, the rate at which the stored water can be evaporated is the limiting factor as to how quickly mine dewatering can take place.
If water treatment trials confirm that water can be discharged offsite after treatment, the project economics could be significantly improved by increasing the pumping rates to dewater the mine, thereby reducing development timelines and costs.
The trials are being undertaken at a feed rate of 5 cubic metres per hour, compared with the full-scale operating throughput which will average more than 1,200 cubic metres per hour.
Three-phase pilot tests
The pilot tests are being undertaken in three phases and are due for completion before year-end.
- Phase I aims to confirm the technical feasibility of treating shaft water through a combination of chemical treatment, precipitation, filtration and reverse osmosis to generate water permitted for agricultural use;
- Phase II aims to determine the range of water qualities that can viably be produced; and
- Phase III involves completing the trade-off studies on the various available options, considering comparative project economics, environmental impact and regulations.
A water treatment plant, designed specifically for the intended water treatment trials, has been constructed and established on-site.
Value engineering process
Since completion of the BFS in June 2019, value engineering of the ore processing design has been in progress.
The value engineering exercise is:
- Assessing semi-autogenous grinding (SAG) in the milling section as an alternative to ball milling;
- Investigating improved plant layouts;
- Rationalising the sizes, placement and uses of various plant buildings; and
- Re-estimating efficient surge capacity allowances in line with the proposed refinements.
The use of SAG milling rather than conventional ball milling as presently incorporated into the BFS, could simplify plant operability and significantly reduce upfront capital expenditure.
This would also remove the need for multi-stage crushing and screening of the rock ahead of milling.
The plant and equipment comprising the current multi-stage crushing section of the plant contributes approximately A$11 million to the total plant capital cost of A$109 million.
This represents a significant target for reducing capital expenditure without compromising overall plant recovery performance, while the streamlined layout increases the plant’s mechanical availability and reduces maintenance effort.