Pump up the gold
FMR Investments was formed in 2007 when specialist hard rock underground mining services provider Barminco – founded in 1987 – divested its contracting business.
Today, the company operates three mining projects in Australia: the Eloise Copper Mine in northwest Queensland, as well as the Greenfields Mill and Gordon Sidar mine, both of which are located in WA.
The Greenfields mill is situated in the WA goldfields, three kilometres east of Coolgardie.
For more than 20 years, the site has provided first class toll milling to the local gold mining industry.
The plant has a unique set-up with three ball mills, allowing the circuit to be optimised for gold recovery depending on the needs of different clients.
In its current configuration, the plant can process up to one million tonnes per annum.
Stockpile ore delivered by FMR’s customers initially passes through a three-stage crushing circuit consisting of a primary jaw crusher followed by secondary and tertiary cone crushers.
The feed from the secondary and tertiary crushers is graded by a double deck screen that removes undersize material from the circuit.
The crushing system produces a P80 product size between 6 and 8mm which is then transferred and stored in a 1000t mill feed bin.
The mill circuit consists of 1300, 875 and 500 kW ball mills.
Classification of leach feed product is handled by 15-inch cyclones.
Free gold particles in the cyclone underflow are separated in a concentrator and sent to the gold room for direct smelting, while the remaining underflow goes back to the grinding circuit to be further reduced.
The overflow product from the cyclones is sent to a CIL (Carbon-in-Leach) circuit.
In this process, gold is dissolved from the ore in a cyanide solution in the presence of oxygen, and the resultant gold cyanide complex molecule is then absorbed onto activated carbon.
The gold is stripped from the loaded carbon, in a process known as elution.
Gold is later recovered from the pregnant strip solution by electrowinning onto steel wool, and direct smelting before shipment to an external refinery.
Mill discharge pumps
Critical to the operation of the mill-to-classification process are the plant’s mill discharge pumps.
They are responsible for transporting the milled slurry up a large vertical pipe to the classification cyclones.
The pumps process a high volume of material that is highly abrasive in nature.
This means that key wear components must be monitored regularly to ensure the pumps operate efficiently and prevent unexpected downtime.
FMR maintenance supervisor Dave Scott describes how the pump setup has been designed to ensure there is always one pump available.
“If the mill circuit is stopped, it basically costs the business about $40,000 per hour,” he said.
“That’s why we have a pair of pumps for this application. If the active ‘ duty’ pump fails or is under maintenance, there is always a standby ready to take over.”
Metso pumps cut costs
In 2014, FMR invested in two Metso HH200 pumps to replace existing units that were nearing the end of their effective life.
During routine maintenance of their original pumps, operators had to disconnect the suction and discharge spools, front casings and case liners to access critical internal components.
A mobile franna crane and a licensed operator were required to conduct the procedure.
The labour-intensive nature of the job meant that it could take up to eight hours to complete, which made it difficult to maintain the pumps on a regular basis.
The new mill discharge pumps are equipped with Metso’s unique slide-base technology.
The slide-base allows operators to open the pump without removing the suction and discharge pipework, making it extremely easy to inspect wear components and conduct routine maintenance.
The slide bases have also reduced the time required to get a blocked pump online again.
Greenfields Mill alternative registered manager Morgan Dombroski said the site’s mill discharge pumps are now checked on a weekly basis.
“Our team here have a lot of experience at this site and are good at forecasting maintenance activities,” he said.
“We monitor the pumps through weekly inspections including a ‘shimming’ process. This optimises both front and rear impeller clearances which makes the pumps operate more efficiently and extends wear life.”
FMR maintenance fitter Travis Dingle explains how shimming extends a mill discharge pump’s wear life.
“The pump operates more efficiently when the impeller is closer to the volute liner,” he said.
“If you have a wider gap between these components, larger particles get in and wear the volute down at a faster rate. Shimming ensures the gap is reduced and the pump operates effectively.”
The slide base technology helps the team to undertake this process quickly and with improved safety.
“What makes it easy with the Metso pumps, is the hydraulic slide. We simply remove the volute bolts and pull the housing back to access everything we need – without the use of a crane,” he said.
By conducting weekly inspections and shimming both mill discharge pumps, the Greenfields Mill has been able to reduce the frequency of major overhauls.
Mr Scott said this has reduced operational costs for the site.
As well, the new pumps have also created a safer working environment on site.
“The slide base allows the team to conduct routine maintenance without using a crane,” he said.
“This means there is no rigging gear for anyone to get struck by. The other factor is by not having to disassemble everything, most of the possible pinch points are removed from the process.”