Monday, May 23, 2022

Modern mining in Maldon: Porcupine Flat Mill

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Modern mining
The trucks deposit the ore into the plate feeder, which is then sent through the jaw crusher and onto the radial stacker. Photo: Tarrangower Times

As you drive towards Bendigo, past Porcupine Village and the dredge, you will see a sign on the left hand side of the road; ‘Octagonal Gold Processing Plant’. This facility, referred to as “the Mill,”  is still operational and currently processing ore from Kaiser Reef A1 Gold Mine, located 23 kilometres from Jamieson.  

The processing operation at Maldon can be best described by the generic term ‘Carbon In Leach’. All gold recovered is extracted by cyanide leaching. In order to leach the contained gold satisfactorily, the ore is reduced in size in two stages. The first stage involves crushing to less than 100 millimetres, followed by grinding to less than 100 microns, about the thickness of a sheet of paper

Once gold has been leached, the tailings (remains of the ore), a grey sludgy substance, are then placed in large, highly engineered dams on site to dry. 

Tailings
Tailings (remains of the ore) in a large purpose built dam on site. Photo: Tarrangower Times.
Tailings dam
This full tailings dam sits beside Bendigo-Maldon Road. Photo: Tarrangower Times

Once the dams are full, soil is placed on top, and a process of revegetation begins. All water used in the process is collected in the tailings dam and recycled back through the mill. While being quite toxic to humans, the cyanide handling on site has very strict controls to ensure there is no risk to humans, animals or the environment.

Flow sheet
This flow sheet demonstrates the complex processes used at the Mill. Photo: Tarrangower Times

The long strip of land on Bendigo-Maldon Road, between Porcupine Village and the Mill, is a previous tailings dam site, which has been regenerated by previous mining companies. The land on the other side of the Mill, on the left hand side of the road towards Bendigo, is being utilised by Kaiser Reef for current tailings dams.

Kathy Whiteman, Kaiser Reef Health, Safety, Environment and Communities Coordinator, told the Tarrangower Times that the Mill has an environmental review committee, with community representatives, that meet quarterly to discuss issues regarding effects of ground water, dust tests etc. 

“We have also been working with MULGA (Maldon Urban Landcare Group) on another mining site to assist with weed management,” said Kathy, who has worked at the Mill since 2014. “And we provide water to the Nuggetty Water Group..”

The gold processing plant was originally commissioned and designed by E L Bateman and Co. and was constructed in late 1987 by Triad Minerals to process low grade open pit gold ore from the nearby Union Hill deposit. 

Subsequent milling campaigns included underground sulphide ore from the Eaglehawk and Linscotts reefs in 1996-97 (Alliance Resources Limited) and from the Alliance South Shoot in 2014 (Octagonal Resources Pty Ltd).

Tarrangower Times 17 December 2021

This article appeared in the Tarrangower Times, 17 December 2021.

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