Oct 06, 2020

Peculiar plants at the root of copper study

Peculiar plants at the root of copper study Polycarpaea spirostylis - the 'copper flower' - following along strike of mineralised copper ground.

If you are seeking copper in North-West Queensland, an orderly row of Polycarpaea spirostylis may be a great guide.

The flowering plant is among four copper metallophytes in the Roseby Corridor near Cloncurry at the centre of a biogeochemical study.

These plants thrive in areas with high copper concentrations in surface soils where other species struggle, according to University of Queensland PhD researcher Roger Tang.

The in-depth study is expected to be useful not only in identifying copper targets but in the rehabilitation of mined areas.

Mr Tang said the significance of such plants was being increasingly acknowledged in the geology and mining sector.

“I guess in the past looking at the plants wasn’t necessarily seen as a hard science compared to classical geology, but nowadays it’s becoming more common,” he said.

Mr Tang said the Roseby area was chosen as report co-author – geologist Richard Lilly – had noted the growth of particular plants in the area, prompting the efforts to delve deeper into their biogeochemistry.

The study focuses specifically on the historical copper prospect locations of Turkey Creek and Green Hills, which are extensions of the Little Eva copper deposit.

Unlike the eucalypts at the centre of studies in Western Australia for their habit of drawing up gold and accumulating it in their leaves, the plants Mr Tang is studying are known as ‘excluders’ in terms of their response to high metal concentrations in the soil.

The excluder species deal with the high copper content around them by resisting metal absorption into the roots, or by restricting transportation to the shoots.

The metallophytes identified within the Roseby corridor include native perennial grass, Eriachne mucronata, a sedge, Bulbostylis barbata, a shrub called Tephrosia virens, and the flowering plant Polycarpaea spirostylis.

One of the species –Polycarpaea spirostylis, the ‘copper flower’ – has been used in the past to prospect for copper, but Mr Tang said interest in its biogeochemistry had grown considerably in the last 20 years.

The species studied are (a) Polycarpaea spirostylis (Caryophyllaceae); (b) Bulbostylis barbata (Cyperaceae); (c) Tephrosia virens (Fabaceae); (d) Eriachne mucronata (Poaceae).

“These plants are quite widespread, they don’t only grow in areas where there is a lot of copper,” Mr Tang said. “But you can see variations in plant species distribution.”

They may appear in a clearly defined strip due to the soil chemistry in the area, for example.

The main site visit was conducted about three years ago, but experiments and the analysis of the samples continues.

Three plant species (P. spirostylis, B. barbata and T. virens) were found on both Turkey Creek and Green Hills, whilst E. mucronata was only found on Green Hills.

That site has higher concentrations of bioavailable copper, which would indicate that E. mucronata has higher tolerance towards and a potential preference towards bioavailable copper.

Along with Dr Lilly, the metallophytes study also involves Peter Erskine and Anthony van der Ent from the Centre for Mined Land Rehabilitation, Sustainable Minerals Institute, The University of Queensland.

  • For a link to a recent paper on this work click HERE