Nov 24, 2020

Rare earths in the spotlight as study probes copper-gold links

Rare earths in the spotlight as study probes copper-gold links

The Mount Isa region is well positioned to ride the surge in rare earth interest, hosting both light and heavy rare earths associated with different types of mineralisation common to the area, a researcher says.

PhD student Ross Chandler is part of a team investigating why some copper-gold deposits in Mount Isa Inlier host rare earths while others do not in an Australian National University and Geological Survey of Queensland collaboration.

“It is something that really hasn’t received a lot of attention – yet,” Mr Chandler said.

“We are trying to tackle a number of the copper-gold deposits in the area that do show that anomalous rare earth enrichment to see if we can figure out the exact relationship to the copper-gold mineralisation and the relative timing of the two types (rare earth element and copper-gold) of mineralisation.”

Mr Chandler is due to present preliminary findings from that work to a Mount Isa technical workshop hosted by the Geological Survey of Queensland this week.

Early work shows rare earths seem to correlate with two distinct styles of copper-gold deposit in the region.

One type is the classic fluorine and barium-rich IOCG ( iron oxide copper-gold) deposit like Ernest Henry, Monakoff and E1. The other style is copper-gold-uranium and rare earth skarns like Mary Kathleen, Swan, Koppany and Elaine Dorothy.

Meanwhile ISCG-style (iron sulphide copper-gold) deposits and fluorine and barium-poor IOCG deposits don’t seem to show significant enrichment with rare earths.

“There is something about the genesis of these deposits where one ends up having quite a lot of rare earths and the other does not,” Mr Chandler said.

The North West Minerals Province hosts not only light rare earths -occurring in the copper-gold-uranium systems under study – but also heavy rare earths linked to the large phosphate deposits in the region.

“This could potentially be an area where you have one deposit type that could be exploited for light rare earths alongside the copper and gold, while just to the south in the Georgina Basin heavy rare earths can be extracted alongside phosphate,” Mr Chandler said.

“The best kind of rare earth deposit is one that is de-risked by having other commodities, where you are producing rare earth as a by-product.

“The North West Minerals Province really has the perfect mix of a common mineralisation style with light (rare earths) and one with heavy.”

Now increasingly sought after as ‘new economy’ minerals, rare earths were not on the radar as many of the deposits being studied in the ANU and GSQ project were explored over the years.

“Most of the rare earth enrichments were discovered by accident by explorers following up on copper or gold or uranium enrichments,” Mr Chandler said.

“Take Mary Kathleen, for example, – when they mined that site they took all of the uranium out because that’s what they were after and all the rare earths have ended up in the waste stockpiles and in the tailings.

“The waste stockpiles are probably amongst the largest rare earth deposits in the country, they just weren’t interested in rare earths at the time.

“Now that people are starting to get a bit more interested in the rare earths it really represents a big opportunity for companies and people who want to get involved.

“It’s a resource that very few have really looked at seriously yet and could potentially be quite significant.”

The collaborative work with GSQ is expected to finish in mid-2021 and Mr Chandler said the next step would be to dive deep into geochronology.

“By constraining certain periods of hydrothermal activity in the (Mount Isa) Inlier that are distinctly associated with rare earth mineralisation we’ll both gain a better understanding of the hydrothermal evolution of the Inlier as a whole as well as the relationship of the copper-gold and rare earth mineralisation,” he said.

A sample of massive actinolite and calcite near the historical Mary Kathleen uranium mine.