ASX- and JSE-listed Orion Minerals has completed the follow-up locked-cycle metallurgical testwork on the deeper mineralised domains at its Prieska zinc/copper project, in the Northern Cape.
The Prieska deep sulphide zone is currently the subject of a bankable feasibility study (BFS) targeted for completion in the second quarter of 2019. Initial results from the metallurgical testwork programme were reported in June, and the programme has now been completed.
Results have confirmed the metallurgical continuity of the deep sulphide zone with the up-dip area of the mineralised zone.
Recoveries of both copper and zinc into separate, high-quality concentrates have been achieved using the froth-flotation process that was used in historical operations. In addition, the use of modern metallurgical reagents is showing encouraging results, Orion said in a statement on Monday.
Meanwhile, the latest bench-scale, lock-cycle metallurgical tests have achieved targeted total metal recoveries, ranging from between 80% and 94% for zinc and between 80% to 86% for copper into separated concentrates.
The resultant concentrates had metal grades ranging between 45% and 54% for zinc, and between 20% and 26% for copper in the respective products.
Gold and silver are collected in the copper concentrates at levels that would qualify them as valuable by-products, the company said. Results, it added, are consistent with expectations for bench-scale testwork, which has limited stabilisation time and still provides an opportunity for improvement in continuous operations.
Meanwhile, detailed elemental analyses of the concentrates confirmed that several key deleterious elements are at negligible levels with arsenic, bismuth, cadmium, cobalt, tellurium, thorium and uranium, at levels well below thresholds that may attract material penalty charges from most smelters or exclude some markets.
Production scheduling using this information, Orion noted, will further optimise resultant marketable products.
Test results, to date, have generally equalled or exceeded the metal recoveries and concentrate grades achieved during historical mining operations. Orion explained that, when graphically superimposed over the historical plant performance dataset, the latest locked-cycle test results compare favourably with the historical operational performance.
The zinc and copper recovery results, meanwhile, correlate well to the average historical trend line.
The latest metallurgical testing programme validates this substantial historical dataset, which Orion says can now be applied, along with more recent testwork results to formulate base assumptions for ongoing mine feasibility studies and for concentrate marketing terms.
Additionally, the metallurgical testing of the Prieska deposit is being conducted as part of an ongoing BFS. Outcomes from the work programme now enable the next phase of the BFS to progress, which includes the final design of the metallurgical plant, derivation of metallurgical performance projections and optimization of the reagent suit to improve operating efficiency and cost control.
The mineral processing plant that is currently being designed employs a similar flowsheet to that used in historical mining operations, Orion said, albeit with the application of modern technology while reusing as much of the remaining surface infrastructure as is serviceable.
Investigations into optimising the reagent suite for the mineral processing plant are in progress with the object of, among others, substituting the use of sodium cyanide as a zinc depressant, with sodium metabisulfite (SMBS).
The removal of sodium cyanide from the reagent suite would have significant economic and safety benefits for the project, reducing the cost of production, avoiding any potential exposure to sodium cyanide and eliminating the need for a detoxification section of the plant ahead of tailings storage.
Further testwork is in progress to validate that the SMBS reagent suite performed as well as the cyanide control test observations.
Additionally, Orion is investigating the establishment of new mining operations targeting the extraction of the remaining zinc/copper mineralisation at the Prieska volcanogenic massive sulphide deposit.
Mine development studies are scheduled for completion in the first half of 2019.