Meteorite impacts not only alter life on Earth, they alter the rocks in ways that can create valuable mining resources. Finding them could speed up the process of locating mineral wealth, says an Australian expert.
“It is not widely appreciated that an estimated 25 per cent of the world’s impact structures are associated in some way with economic or sub-economic mineral and petroleum resources,” said Peter Haines a sedimentologist with the Geological Survey of Western Australia.
“A better understanding and appreciation of impact as a geological process may accelerate the discovery of impact-related resources,” said Haines who presented his research on the phenomenon last week on the final day of the Australian Earth Sciences Convention 2008 in Perth.
Big holes hold large wealth
These resources include gold, platinum, diamond, nickel and petroleum. While many mineral deposits have been recently recognised as having their origin in meteorite or comet impacts, locating the impact first and then looking for mineral wealth could speed up the process, he said.
Many impact-related deposits are known around the world and are of substantial size. Examples include the Vredefort crater in the Free State Province of South Africa – the biggest and oldest impact crater on Earth and home of some of the world’s richest gold deposits. The Sudbury Structure in Ontario, Canada, is the world’s second-largest impact crater and hosts the world’s largest deposit of nickel-platinum ore.
Western Australia has a number of impact structures, some of them buried under other rocks, which offered a future target for mineral exploration, said Haines.
“Many geologists are not familiar with impact structures. They see impact structures as something of academic interest and of no great economic significance, but the case overseas clearly demonstrates that they can be of considerable economic importance,” said Haines.
Mineral resources can form immediately or some time after the impact, he said.
Oil, gold and diamonds
For example: a shower of comets smashing into Siberia 36 million years ago formed the Popagai crater and transformed the carbon-rich rocks into impact diamonds. Minerals can also form from melted crust; the 10-kilometre-wide meteorite that formed the Sudbury Structure in Canada created a pool of molten magma in which the heavy minerals nickel and platinum sunk and concentrated in a layer.
Fracturing in rocks from the intense shock pressure of impacts can also form a favourable environment for hydrothermal (hot-water) mineralisation, such as gold deposits. Buried impact structures, such as those found in the Gulf of Mexico, form favourable sites for oil, gas and petroleum reserves.
Rob Hough, a geochemist with CSIRO Exploration and Mining in Western Australia, has studied impact diamonds overseas. He said it was worth looking for impact mineralisation in Australia but that no exploration of this sort was currently happening. Haines’ research is a “nice piece of work,” he said, in that it brings together a lot of information on impact structure mineralisation and applies it to Australia.
“Certainly people have talked about looking for Sudbury analogues,” said Hough, who noted that Australia’s prolonged history of erosion may have removed some of the evidence of impact structures from the surface.