Friday, 20 November 2009

Researchers at The University of Western Australia have discovered how ancient ore deposits hold the key to the Earth's evolution as well as helping pinpoint concentrations of metals important for the State's economic development.

The research, to be published today in the prestigious international journal Science , is a joint collaboration between UWA's Winthrop Professor Mark Barley, Dr Marco Fiorentini and Research Professor Stephen Beresford, and researchers at the Carnegie Institution of Washington and Wood's Hole Oceanographic Institution in Massachusetts.

Professor Barley said the work, carried out at UWA's Centre for Exploration Targeting, could not have been done in Australia up until five years ago.

"World-class analytical facilities have allowed us to understand how our important ore deposits formed and the Earth's tectonics, atmosphere and oceans evolved," he said.

"Some of Earth's largest and most important nickel sulfide ore deposits formed during the Archean and early Proterozoic, between 2,900 and 1,800 million years ago.

"Establishing the origin of the metals and sulfur in these deposits is critical for understanding how these important deposits formed (to help mineral exploration and the Australian economy) and their relationship to the evolution of our planet and its environment."

Professor Barley said komatiites were submarine volcanic rocks formed by very hot volcanic eruptions of magma from deep in the Earth's mantle at a time when the Earth's oceans were relatively sulfur poor.

"Understanding the source of the sulfur is very important for resolving how these deposits formed as sufficiently high concentrations of nickel in ores could only be created if the lavas became sulfur-saturated," he said.

"It was originally thought that the sulfur came from deep in the mantle with the magma, but analytical work shows that the original magmas contained very little sulfur, so it was then thought that the lavas assimilated sulfur from adjacent sediments when they reached the sea floor.

"However, because, prior to the Earth's great oxidation event 2,400 million years ago the Earth's sulfur flux to the oceans was much lower than now and the variation of the most abundant sulfur isotopes was not sufficient to unambiguously indicate where the sulfur in these deposits came from, this debate has continued for a long time.

"Then in the last decade it became possible for analyses of the less abundant sulfur isotopes to be undertaken and it was discovered that the strongest record of variation caused by photochemical reactions of UV light with sulfur from volcanic gasses in the atmosphere was recycled to the ocean and preserved in sedimentary sulfides and hydrothermal sulfides in rocks before the great oxidation event.  Our new data has proved that this was the major source of the sulfur in the komatiite-hosted nickel deposits."

Professor Barley said the multiple sulfur isotope record was one of the most important areas of geochemical research for resolving important questions in the evolution of the early Earth's environment and its mineral deposits.

Media references

Winthrop Professor Mark Barley (+61 8)  6488 7322 / (+61 4) 19 942 108
Dr Marco Fiorentini (+61 8)  6488 3465 / (+61 4) 09 254 445
Janine MacDonald (UWA Public Affairs)  (+61 8)  6488 5563 / (+61 4) 32 637 716


Media Statements — Research — University News
Energy and Minerals Institute — The Centre for Exploration Targeting