From The Australian Mining Review – June 21, 2021
The skyrocketing gold price last year caused a flurry of exploration activity, leading to the discovery of new gold deposits around the world.
But the making or breaking of a gold mining venture does not just hinge on the presence or the quantity of the precious metal in the deposit.
It comes down to the quality of gold analysis techniques to determine recoverable gold, which ultimately indicates how profitable a project is likely to be.
Mineral Process Control (MPC) is a WA-based company formed in 1995 to develop and market LeachWELL gold technology.
Having managed his own small gold mines, MPC managing director Rob Mason is acutely aware of the need for accuracy and precision when sampling ore and waste.
The fire assay technique is centuries old but is still the most common gold analysis procedure to determine the amount of gold in a sample.
While most processing plants worldwide use cyanidation to extract the precious metal, fire assay involves a different digestion technique employing fluxes, furnaces, and lead.
‘’Critically, fire assay tells you the total amount of gold, whether it is recoverable or not,’’ Rob said.
‘’Cyanide assay will tell you the recoverable gold.
‘’There’s been a lot of gold mines that have actually gone broke because they’ve employed fire assay to do their grade control or resource estimation.
‘’This is because they thought they had an ore body containing so many thousand ounces of gold when in actual fact, when they put it through the process plant, they’re only able to recover maybe half of what’s there because the mineralogy is not conducive to cyanide extraction.’’
Mineral Process Control initially marketed LeachWELL 60X, developed by David Menne, and Rob has become increasingly passionate about the usefulness of larger assays.
The leach reagent enables traditional 24-hour bottle rolls with large sample sizes to be accelerated to within one hour.
‘’This gold assay technology has been adopted by numerous mines, both in Australia and overseas, because of its simplicity, accuracy, and cost effectiveness,’’ Rob said.
‘’It has proven especially useful where there are coarse gold particles or preg-robbing ore types.
‘’The LeachWELL cyanide assays are more predictive of expected recoveries from Carbon-in-Pulp gold recovery plants, so provide a better estimate of the economics than other assay techniques.’’
Research and development of technologies for the gold processing industry have remained the focus of MPC.
By 1997, the company had developed a reagent to treat gravity concentrates; LeachWELL GC.
This has improved recovery of gold in many mines using gravity circuits such as Union Reefs, Kundana and Penjom Mines.
By August 1998, MPC had developed the AssayTabs™, which contains all the ingredients needed for a LeachWELL assay, improving the safety and convenience of the technique.
Rob said most laboratories now choose to do LeachWELL Assays using AssayTabs™.
John Cooper joined the company as General Manager in early 1999.
John draws on twenty years of experience in commercial assaying laboratories in WA and Africa and has helped develop:
- The PAL 1000 gold assay system which pulverises and leaches 52 samples in one hour, eliminating the need for full sample preparation.
- A low speed 52 sample centrifuge, which is relatively inexpensive and yet efficiently settles even very clayey samples in minutes. This machine uses disposable cups for efficiency.
- A three-tier bottle roll machine with a capacity of more than 200 x 4.5 litre jars
MPC’s PAL Machine
MPC shipped the first PAL 1000 to the Big Bell mine near Cue in WA in early 2000.
It has been popular in the mining industry worldwide, with the 63rd machine shipped to Cambodia in March.
Machine number 64 is awaiting shipping with another four in various stages of production.
John said the PAL 1000 mirrors what happens with gold analysis in a processing plant.
‘’If the PAL 1000 suggests you have got one or two grams per tonne of gold, then that’s what the normal run-of-the mill extraction plant will be able to recover,’’ he said.
‘’If they use fire assay then they will still need to do some metallurgical test work employing cyanide to see how much their plant will recover, which involves duplication.
‘’With fire assay, they have to employ a metallurgical test worker so they know how much gold they can recover but they can only do that with a limited number of samples, which means they are not totally representative of the whole ore body, and that’s where they run into trouble.
‘’Cyanide assay methods provide the full picture but while they have always been available, the critical difference with LeachWELL is its rapid turnaround gold assays, instead of a 24-hour turnaround.’’
While other techniques such as bottle rolls can also use accelerated leach, the PAL 1000—using Assay Tabs™—simultaneously leaches and pulverises the material to liberate the gold.
‘’So, it is an all-in-one and that’s why it is so much quicker,’’ John said.
Short pulverising and leach times of one hour mean assays may be reported within two hours.
The PAL1000 contains 52 sample pots, each capable of processing up to 1kg ore samples.
Once leaching is complete, the leach solution is collected and analysed for gold by Atomic Absorption Spectroscopy (AAS).
Silver and copper analysis can also be performed.
Operating parameters such as grinding media charge, reagent dose rate, sample size, run time and speed can all be varied onsite to suit sample requirements.
MPC has also developed laboratory equipment to facilitate and streamline the use of LeachWELL Assays including:
- A tumbling machine capable of processing 60 assays per hour. This compact model only uses a square metre of floor space.
- A water dispenser which measures the exact amount of water to add to an assay by a simple timing mechanism.
The recent downturn in the Gold Industry has prompted MPC to concentrate on developing more efficient and labour-saving technologies.
Several years ago, MPC also diversified into wastewater treatment and soil remediation.
A reagent known commercially as DTOX precipitates hazardous metals such as chromium, copper, mercury, nickel, arsenic, selenium and neutralises cyanide.
Mineral Process Control has agents in Australia, Africa, and North America.
In addition to local sales, MPC exports to Africa, South East Asia, Europe, New Zealand, North and South America.
MPC is based at 30 Furniss Rd in Landsdale where it has an engineering workshop for equipment fabrication, an office and a unit for equipment storage and the formulation of DTOX.
Mineral Process Control
P: +61 8 9303 2334