Oz science smorgasbord at upcoming geological convention

01 July 2002

Geoscience Australia presents some of its latest research findings at the upcoming Australian Geological Convention...

Fingerprints as clues in a geological whodunnit

Researchers at Geoscience Australia have shown that special zircons make ideal informants for pinpointing the exact age of important ore deposits, a task that was often very difficult until now.

The scientists have used advanced techniques to fingerprint these special zircons because they are distinctive chemically. They have put together a profile for the zircons, to help others track them down too.

One part of the fingerprinting process involves looking at microscopic bubbles of fluid trapped in a zircon's crystal structure while it was growing. If the trapped fluid is directly related to ore-forming events, then the zircons are too. These are the right kind of zircon to use — they were in the right place at the right time.

In the past, supersleuthing the precise ages of ore deposits has been hard, because remaining evidence is often changed or destroyed by the forces of nature, long before humans had evolved in many cases.

Luckily, the zircons are made of sturdy stuff. But not just any old zircons will do.

The age of an ore deposit is a big clue when trying to unravel the events that created the ore in the first place. Knowing how and why the ore formed is an important step in looking for similar deposits elsewhere.

South Australian Scene

How the north-west was won

New research by Geoscience Australia has shed light on the remote past of the north-west of South Australia — the subject of much excitement with its potential for new mineral discoveries, and a region which remains largely uncharted geologically.

The researchers have discovered an ancient system of geological faults which date back to a time long before the continent of Australia became recognisable as it is today.

These ancient faults represent the collision between mini-continents and help geologists to reconstruct how Australia built up, piece by piece, like an enormous jigsaw.

The scientists have measured the age of rocks formed inside the ancient faults and found that they were active between 1.6 billion and 1.4 billion years ago — a time when South Australia was linked to Antarctica as part of the ancient supercontinent called the Mawson continent (after Australia's famous Antarctic explorer and geologist, Sir Douglas Mawson).

The northern part of South Australia contains several important gold deposits, and geologists predict that there are more out there. But the first challenge in the quest for hidden gold is to unravel the long and complex geological history of the area.

In this study, researchers measure the age of a mineral — and therefore the age of its host rock — by comparing the amounts of potassium and argon inside. One type of potassium is unstable in nature and can spontaneously change to the more stable argon, releasing energy at the same time. This process happens at a precise rate: it takes 1.25 billion years for half of the original potassium to change.

Another Ernest Henry?

The potential is high in South Australia for the discovery of iron-copper-gold deposits that bear a striking resemblance to the Ernest Henry deposit near Mount Isa.

In South Australia, the Moonta Domain is situated on the eastern margin of the Gawler region.

The Domain's various traits echo those of the iron-copper-gold province of an important group of rocks in the Mount Isa Inlier — where intrusion by magma and incursions by distinctive salty fluids are strongly linked with mineralisation.

The Moonta Domain is made up of sediments and volcanics which were heated and squashed to high temperatures and pressures. Later, the rocks were intruded at depth by molten rock on a wide scale.

Tanami gold shows great diversity

Recent work at Geoscience Australia shows that the known gold deposits of the Tanami are surprisingly diverse, having formed over a range of physical and chemical conditions, and at various depths. It's a strong indication that as-yet-undiscovered gold may lurk in various places and guises in the region.

Some of the known deposits are hosted in volcanic rocks, others in banded iron formations, and some are in rocks made from sediments.

The Tanami is an rapidly growing gold province here in Australia. It already boasts a gold mine that was discovered in 1991 and is world-class — there's literally 100 tonnes or more of gold in the orebody itself (that's a lot of jewellery).

There are more than 60 gold occurrences in the region, including three established goldfields and several exciting gold prospects. The prospects are being explored by two of the world's leading gold miners and a number of small companies.

The 16th Australian Geological Convention is being held by the Geological Society of Australia at the Adelaide Convention Centre from July 1-5.

The theme of this Convention is "Geoscience 2002: Expanding Horizons" to celebrate the rapid increase in geological knowledge and to recognise the importance of looking outward to what currently remains unknown.

There are broad sub-themes covering most aspects of geoscience. Conventions are held every two years.

Topic contact: media@ga.gov.au Last updated: October 4, 2013