JOHANNESBURG (miningweekly.com) – Normal production throughput has restarted at multicommodity mining company Mwana Africa’s Freda Rebecca gold mine, in Zimbabwe, following a leach tank failure in February.

The company halted plant processing operations at the gold mine following the rupture of a leach tank and its collapse onto a second tank.

This caused structural damage to both tanks and led to the discharge of leach tank contents onto the ground surrounding the tanks beyond the bunded containment area.

Following the incident, immediate modifications were made to the processing circuit to allow limited milling and production to continue.

Normal production throughput was enabled through the use of tanks one, four and five as leach tanks, with eight absorption tanks, to ensure that minimum leach times required for full throughput were maintained. 

During March, a total of 50 000 t of ore was milled at a grade of 2.5 g/t, achieving a recovery of 80.2%. 

“Management is confident that this will work as an interim solution, at full production, with the intention of getting back to an optimal tank configuration of tanks one, two and three as leach tanks with ten absorption tanks over the next few months,” the company said in a statement.

Meanwhile, the planned rehabilitation of tanks two and three had started, with repairs to tank two progressing well and due for completion in April.

On completion of the repairs to tank two, the system configuration would be altered so that tanks one, two and four will be used as leach tanks.

Construction work to replace tank three had also started and an external contractor was on site to complete the removal of damaged tank infrastructure and begin the build.

Mwana reported that, following the clean-up of the pulp spillage in February, the Environmental Management Authority (EMA) had acknowledged the mine's compliance with the authority’s clean-up requirements.

“Freda, in conjunction with the EMA, has since continued to monitor the discharge levels in the drainage canal and these have returned to acceptable levels,” the group noted.

Moreover, the Mines Inspectorate had completed its preliminary investigation report, providing recommendations for the required structural tank repairs. 

Freda had, in addition, reviewed its internal standards for pressure and storage vessels.

As part of this review, ultrasonic thickness tests and integrity tests were carried out on nine of the 13 tanks, to date, in addition to a structural audit having been conducted across the complete plant.