THE visit to Unity Mining’s Henty Gold Mine to see how cyanide is used in the processing firsthand allayed many stakeholders’ fears on Wednesday.
Subscribe now for unlimited access.
$0/
(min cost $0)
or signup to continue reading
Six community members and two media representatives, including this journalist, toured the gold mine’s processing plant.
Sodium cyanide at Dargues Gold Mine at Majors Creek, sitting at the headwaters of Eurobodalla’s water supply, would be delivered in pods in which the chemical is also processed, eliminating manual handling.
Cyanide is added twice in the processing process – a small amount to the raw ore in the grinding process, and then later in the separation process.
The cyanide is used to dissolve the gold into a liquid form to separate it from other unwanted rocks and minerals.
Carbon, made from coconut husks, is then added to the mix. The gold attaches to the carbon and the particles more or less float to the top.
The PH level of the mix is critical throughout the whole process to ensure the cyanide remains as a liquid and not a deadly gas, so lime is added at several points along the way.
Once it has done its job, the cyanide is destroyed by sodium meta bisuphate. It goes through three cyanide destruction tanks, a process which can take up to 12 hours.
The unwanted minerals and leftover water known as “tailings”, which contain minor traces of cyanide, are then pumped to an open-air tailings storage facility.
The tailings storage facility at the Majors Creek mine would be lined with 3mm-5mm thick UV-protected polyurethane.
Unity Mining must ensure its tailings include no more than 2 parts per million of cyanide when it is discharged from the plant into the tailings storage facility.
At Henty, the water is pumped through a further clarification dam, and another water storage dam, before it is pumped into the Henty hydro electricity canal to flow into local creeks and rivers.
At this point it must contain no more than 0.1 parts per million.
It is understood 50 parts per million of cyanide is harmful to birdlife.
Tasmania’s higher rainfall means releasing the water back into the system is a necessity, however no water at Dargues will be released – it will always be recycled within the processing plant itself.
Unity Mining’s managing director Andrew McIllwain said there was no viable alternative to processing gold other than cyanide use and it was universally used around Australia.
Related coverage:
- Deua dwellers ‘gravely concerned’
- Residents flown to Tassie mine
- From the editor's desk
- Deua dwellers ‘gravely concerned’