JOHANNESBURG (miningweekly.com) – Construction of a pilot plant at Aim-listed Mwana Africa’s Freda Rebecca gold mine, in Zimbabwe, has started, while good progress has been made on the evaluation of the economic potential of the tailings storage facilities at the project.

The pilot plant would be used to gather representative data and conduct variability testwork, which would determine optimum operating conditions and design parameters for a potential future larger-scale facility. Commissioning was planned for the third quarter of this year.

Since production at Freda Rebecca started in 1988, significant tailings had been deposited over three main storage facilities in the mine lease area. A noncompliant estimate of the available tonnage contained within the targeted North and South tailings facilities was estimated at 13.5-million tons.

During 2012, project work was initiated to evaluate the economic potential of the tailings dumps. An internal augering programme was carried out over the old North and South dumps. Assay results, together with basic bottle roll testwork delivered sufficiently encouraging results to embark on a full metallurgical test programme.

The testwork was divided into two phases. The aim of the first phase was to identify the most promising process route for the treatment of the tailings material, while the second phase was aimed at optimising process parameters on the process route selected.

Johannesburg-based engineering and project-management company Senet was appointed to oversee the testwork and Australia’s ALS Ammtec wastasked with conducting the metallurgical testwork. A lab-scale tailings sample was composed from the internal augering programme and shipped to Australia and test work started in May 2012.

Phase 1 of the testwork revealed that gold grades on the samples ranged between 0.40 g/t and 0.83 g/t, while conventional cyanidation, based on a carbon-in-leach (CIL) process, revealed high metallurgical recoveries.

The second phase confirmed the CIL process route and preliminary recoveries and also revealed a cyanide and lime consumption moderate at 1.8 kg/t and 1.83 kg/t, respectively, as well as 64.3% gold recovery.

"The initial results from the testwork on the tailings at Freda Rebecca are encouraging. Should the results from the pilot plant prove that retreatment of the tailings is viable, a full-scale tailings retreatment plant has the potential to contribute significantly to yearly gold production at Freda Rebecca," Mwana CEO Kalaa Mpinga said in a statement.