Dual-listed Orion Minerals has announced that significant progress has been made in the metallurgical test work program being undertaken as part of the Prieska Zinc-Copper Project bankable feasibility study.
The first batch of advanced-stage, laboratory-scale, locked-cycle flotation tests, assessing the efficiency of the proposed mineral processing route, have achieved up to 94% zinc and 86% copper recoveries into marketable concentrates.
The tests are being conducted on the Hypogene Zone (Deep Sulphide Zone) of the deposit.
The Deep Sulphide Zone makes up approximately 95% of the delineated Prieska Project Mineral Resources by weight and is being targeted for extraction by underground mining methods.
The latest metallurgical results compare extremely well to the historical performance achieved in past mining operations when Anglovaal processed the up dip section of the deposit over its 20-year operating history.
Anglovaal achieved over 85% average metal recoveries for both zinc and copper into
differentiated, high-quality concentrates.
Locked-cycle testing, which simulates the build-up in concentration of various reagents and other elements during continuous operation, was conducted on a composite sample representing a blended feed comprising of 50% material from the north-western area of the deposit and 50% material from the south-eastern area.
The sample tested was composited from recent drill core samples collected from
mineralised intersections of the Deep Sulphide Zone.
Further variability tests are in progress to confirm the metallurgical response of the full extent of the Prieska Deposit and to finally determine the recoveries and concentrate qualities to be targeted for optimised returns in the ongoing BFS.
When graphically superimposed over the historical plant performance dataset, the latest locked-cycle tests, compare favourably with the historical operational performance.
The copper recovery results align with the historical trend line, while the zinc recoveries are above the historical performance. This is an excellent achievement confirming Orion’s confidence in the project.
Laboratory-scale, locked-cycle tests
Earlier metallurgical test work resulted in Orion developing a mineral processing flowsheet to treat all the mineralised zones of the remaining Prieska Deposit using froth flotation and succeeded in producing differentiated zinc and copper concentrates.
The final processing flowsheet developed will incorporate improvements on the mineral processing technology and reagents to those available to historical operations and will form the basis of process design, equipment selection, equipment sizing once tested for its effectiveness in continuous operation and its applicability to the various geographic regions of the defined deposit.
Locked-cycle testing involves the preparation of samples that are representative composites from sub samples taken from different zones of the deposit and running each composite sample through a laboratory-scale setup of the flowsheet in open circuit.
The products of the open circuit test are recycled five times through the same flow sheet setup to simulate the build-up in concentration of various reagents and other elements expected under continuous froth flotation operating conditions.
The addition of further repetitive cycles or reagent addition may yet further optimise total recoveries or achieve higher concentrate grades.
Laboratory-scale, locked-cycle metallurgical variability testing on three additional variability composites is now being conducted as part of the advanced stages of the metallurgical testing program.
This phase of testing investigates expected performance for a stable reagent suite with the inclusion of recycled scalping and cleaning streams and the performance of the flow sheet for samples obtained from the different geographic locations of the deposit.
Locked-cycle test work results
Locked-cycle testing was conducted on a Deep Sulphide zone composite sample representing a blended feed comprising 50% material from the north-western extent of the Prieska Deposit and 50% material from the south-eastern extent.
This testing resulted in the total recovery of 80% to 86% copper and 91% to 94% zinc into marketable concentrates.
Copper concentrate grades ranged from 21% to 24%, whilst the zinc concentrate grades ranged from 45% to 54%.
Current indications are that zinc recoveries are unlikely to benefit further from additional cycles, while copper recoveries and qualities have further opportunity for optimisation.
The amenability of the mineralisation to produce flotation concentrates of varying grades will allow mine-to-market product optimisation to be done at the design and planning
stages of the Prieska Project BFS.
Right-sizing planned throughput
Historical mining operations at the Prieska Project treated 3 million tonnes a year of run-of-mine ore.
Some of the mine infrastructure used to support such throughput remains on the project site such as the Hutchings Shaft barrel that was used as the main hoisting shaft, access roads, power supply line and water supply pipeline.
With the recent upgrade to the global Mineral Resources to 29.4 million tonnes of Mineral Resources, mining studies are now being advanced, as part of the BFS, to right-size the planned mining operations taking into account how best to fully exploit the defined Mineral
Resources and maximise the use of existing infrastructure.
The investigations into right sizing the mine require that higher throughput mining scenarios be considered, as well as ensuring that a significant portion of the defined Mineral Resources are upgraded to Mineral Resources categories that allow them to support a BFS.
Infill drilling of the southern extent of the Prieska Deposit has commenced with fourteen rigs now mobilised, in line with the intention to incorporate as much as possible of the defined Mineral Resources into the mine schedule of the BFS.
The implications of including more of the Prieska Deposit within the mining studies is that the resource definition drilling will extend into Q4 2018 and the BFS completion is now scheduled for late 2018 or early 2019.
This timing coincides with the scheduled time for the issuance of the Mining Right in Q2 2019, which is the required statutory authorisation required before construction, de-watering and mining operations can commence.
“The locked-cycle metallurgical tests are an important step for Orion to demonstrate minimum design metal recoveries, qualities and concentrate masses to be incorporated in feasibility study work. We are now able to start trade-off assessments in capital and operating costs for optimised returns,” comments Orion’s MD and CEO, Errol Smart.