JOHANNESBURG (miningweekly.com) – An ongoing metallurgical test programme and plant design test at multicommodity explorer Premier African Minerals’ RHA tungsten project, in Zimbabwe, has produced “encouraging” results, the group said on Wednesday.

The programme consisted of investigative work on a 200 kg bulk sample, as well as a mini pilot run on a 800 kg of bulk sample, both originating from seven separate locations within the historic underground workings.

Based on the mini pilot run, which consisted of crushing, scrubbing and screening the sample to a -6 mm +1 mm and a -1 mm fraction, the test flow sheet produced concentrates of -6 mm +1 mm at 62.7% of tungsten oxide and -1 mm at 67% tungsten oxide at a cumulative recovery of 77.3%.

The process flow had not yet been optimised and the simple flow sheet provided the flexibility to potentially increase the -6 mm +1 mm fraction concentrate grade through a shallower jig cut.

In practice, Premier said it was likely that it would achieve a higher grade at this same recovery, as the full-scale process plant operation was continuous and the cuts on the spirals and tables easier to maintain.

“Determination of the concentrate grade and process recovery is a significant milestone in the development of the RHA mine. The fact that these positive results were achieved on a mini pilot scale allows us to finalise the flow sheet and plant design and proceed to order,” commented CEO George Roach.

In addition, investigative work on the 200 kg sample confirmed the ability to efficiently preconcentrate the plant feed at -25 mm +6 mm by achieving a fourfold upgrade of feed grade at a 20% mass pull.

“These results provide the ability and flexibility for the plant to accommodate significantly higher run-of-mine feed rates with the simple addition of jigging capacity upfront,” said the company.

The two grades of concentrate produced from a simple and low-cost process may, in principle, be optimised to customer specifications in terms of material sizing by staged crushing, screening and gravity concentration.

Roach said the group was advancing discussions on offtake and marketing agreements, adding that Premier would now update the economic model contained in its conceptual mining study released in September last year, based on the most recent results and the enhanced resource announced in May.