Gekko Systems has recently designed, built and commissioned the 600,000tpa Stage 1 process plant for Ballarat Goldfields.
The plant, which can increase production significantly beyond 600,000tpa on completion of Stage 2, began commissioning in December and was ready for first gold pour prior to Christmas.
Throughput is expected to rise to a rate of 400,000tpa by the end of the calendar year, a rate achieved during plant commissioning.
Stage 1 of the plant has a number of unusual features designed to take advantage of Ballarat’s coarse gold orebody.
Plant design incorporates a conventional two-stage crushing circuit that is achieving a crush size of <25mm at a rate of 1.5Mtpa.
The crushed product is stored in an above ground bin that can hold up to 500t of feed for the tertiary circuit. Allowance is made for a second bin to accommodate daytime crushing and 24-hour running of the remaining circuit at the expanded capacity.
The final product size reduction is carried out by a Vertical Shaft Impactor (VSI), which is achieving better than design at a P80 crush of 650µm. Re-circulating loads are below design at less than 250% with lower than design operating costs seen to date.
The plant design allows for a second VSI to be added to the circuit when needed. The plant is also engineered for the inclusion of a Polysius High Pressure Grinding Rolls with trials planned for the middle of the year. The outcome of the trials may determine whether a second VSI or HPGR are fitted as part of any future expansion to the plant.
The Gekko Gravity Recovery System runs in closed circuit with the VSI and consists of rougher and scavenger InLine Pressure Jigs followed by a cleaner IPJ that produces a concentrate stream of around 4% of the mass (5% design).
Mass pull is variable depending on the sulphides loading in the circuit. A Falcon concentrator scavenges the final tail.
Gekko says final tailings gold residues to date are better than expected and well below design.
Investigation of the tailings product shows insignificant gold in the coarser fractions above 500µm, which Gekko says indicates “exceptional” liberation and recovery, and an ability to increase grind size even further.
Gravity recovery is high because of a liberation circuit that prevents over-grinding and ensures heavies are recovered from the circuit as they are liberated.
The plant control incorporates fully automated start-up and shut down with complete process control carried out by an Allen Bradley DeviceNet system. Gekko says the quick commissioning was down to the simple design of the overall circuit and the complete integration of the control system.
Work is ongoing in all areas of the plant to gain a better understanding of the metallurgy of the ore and the recovery system.
Stage 2 of the process plant is planned to incorporate an intensive cyanidation plant to maximise the recovery of gold from the sulphide concentrate stream. Significant work carried out on the actual concentrates ensures the downstream process is at least as efficient as the primary recovery circuit.
All cyanide leach residues will undergo detoxification prior to disposal.
Gekko says the development of the process plant is running to schedule and no foreseeable problems lie ahead in achieving the initial goals set at the beginning of the development.
Gekko’s technical director Sandy Gray says the success of the plant is a credit to the company’s design and production team.
As the plant is located in the equipment supplier’s home town, Gekko has provided a broader service than normal, which includes site preparation and construction management.
Gekko has also set up a subsidiary operations and project management team, Spinifex Projects, to operate the processing plant.
Spinifex mill superintendent Steve Gannon says he is delighted “all plant modules are performing well”.
Meanwhile, Ballarat Goldfields managing director Richard Laufmann praised Gekko saying that the timetable achieved was testament to the dedication of the team.
“I don’t think this could have been achieved elsewhere in the country in such a short time frame,” Laufmann says.
“The skills and facilities available through Gekko Systems in Ballarat are second to none,” he says.