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Golden Mile yields shiny new treasure

Media release

A Curtin WA School of Mines geochemist has discovered a new mineral while combing through historical ore samples dug from the Kalgoorlie Super Pit.

Ore sample showing a mix of different minerals, including kalgoorlieite (cream and light blue area). Photo: Kirsten Rempel/Curtin University

Dr Kirsten Rempel, from Curtin’s Department of Applied Geology, noticed the microscopic, silvery coloured material in January 2015 when examining samples held in the School’s museum at the University’s Kalgoorlie campus.

She subsequently undertook a year-long verification and classification process, culminating last month in the International Mineralogical Association formally declaring the material a new mineral.

“I’ve decided to name it kalgoorlieite, after the type locality – it’s about time Kalgoorlie had its own mineral!” Dr Rempel said.

The sample, although tiny, was the largest amount of the mineral found so far and provided a unique opportunity to understand the origin of high grade ores taken from an area that was now just empty space in the middle of the Kalgoorlie Super Pit.

“This mineral, while only seen in very small grains so far, can provide important information about the genesis of the giant Golden Mile gold deposit, which is widely contested,” Dr Rempel said.

The sample was collected from the former Associated Gold Mines (1000 foot level of the Tetley Lode) – one of the many underground workings that were later consolidated into the Kalgoorlie Super Pit, operated by Kalgoorlie Consolidated Gold Mines (KCGM). It sat in the museum for years, simply described as ‘gold ore showing tellurides’. The collector and date of collection is unknown.

Dr Rempel said the idea of examining the samples more closely came from former Curtin WA School of Mines lecturer Dr Phillip Stothard, who has since left the project. Dr Rempel continued on with the study herself, enlisting outside help to prove that the mineral she had noticed was new.

Curtin’s John de Laeter Centre provided high-magnification imaging, characterisation of the mineral’s crystal structure and chemical mapping; the University of Western Australia supplied an electron microprobe to obtain a highly accurate chemical composition; and Dr Chris Stanley of the Natural History Museum of London performed measurements of the amount of light reflected off the surface of the mineral – a property used to characterise and identify metallic minerals like this one.

Dr Rempel said kalgoorlieite was a telluride mineral that was chemically related to the gold and silver telluride ores in the Kalgoorlie Super Pit. It had the general formula As2Te3, with As being the chemical symbol for arsenic.

“Kalgoorlieite contains only trace amounts of gold and silver, but it is closely associated with gold-silver telluride minerals such as sylvanite,” Dr Rempel said.

“The mineral will be added to the list of 5107 known minerals.

“Due to advances in analytical technology, the rate of new mineral discoveries is increasing.

“The International Mineralogical Association receives more than 100 mineral proposals per year, with the majority of these being approved. However, most newly discovered minerals are very complex, with relatively small differences to existing minerals.

“It is very rare to find a mineral with the simplicity of kalgoorlieite these days, and I am very excited to be a part of it,” Dr Rempel said

The sample will eventually be on display in the WA Museum.