[meteorite-list] Quest For Space Impact Riches

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:27:53 2004
Message-ID: <200311251651.IAA21047_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/1/hi/sci/tech/3281611.stm

Quest for space impact riches
BBC News
November 25, 2003

Sites where asteroids struck the Earth millions of years ago may be the key to discoveries of new
mineral and metal deposits in the future.

Some geologists believe that sudden, catastrophic impacts could have created some of the world's
biggest deposits - in an instant.

Mineral exploitation currently occurring at impact areas includes the world's most profitable gold
mine, in South Africa, and a massive nickel and platinum deposit in Canada.

"On average I would say that one quarter of the known impact structures on the Earth have some sort
of deposit associated with them," Canada's Natural Resources Department chief scientist Richard
Grieve told BBC World Service's Science In Action programme.

"Of that quarter, maybe about half have been actually exploited, either in the past or currently so."

Increasingly, some geologists are questioning the theory that the Earth's rock record changes slowly
over time.

Many are now looking for evidence of where rocks have been "shocked" - which would indicate the
impact of an asteroid or comet.

Impact lines

"The pressures required to make the textures that we're going to look at can only be made by impact of
something like a meteoroid or an asteroid or a comet," said Dr Adrian Jones, of University College
London.

The keys to finding such sites are grains of quartz, which, under the microscope, have tell-tale
parallel lines that reveal if they were part of an "impact structure", the area where an extraterrestrial
body struck the Earth.

Dr Jones added that one recently discovered major nickel deposit in Russia - coupled with two other,
previous finds - suggested that some metals might come from the impactors themselves.

"It makes it rather interesting that two or three large impact structures are now associated with the
same association of nickel-rich metals," he stated.

"The idea from our modelling and our smaller experiments [is] that the impact crater itself may still
retain a mixture of materials, both from the melted crust and from the residue of the meteorite
impact that has been redistributed around the crater.

"That would contain a lot of nickel-rich metals and platinum-group elements."

Gas creep

Alternatively, it may be that the impact causes such massive, immediate change that minerals become
present in ways they otherwise would not have done.

The disruption caused to the Earth's underlying crust can create the ideal conditions for the deposition
of minerals and hydrocarbons, geochemist Ian MacDonald of Cardiff University told Science In
Action.

"It's the excavation of the crater - the way that the rocks have been broken up and smashed - that has
allowed oil or gas to creep into that structure and accumulate there, for us to drill into and then tap
off," he said.

"Or it's been the way that the rocks have melted at the moment of impact that has allowed important
metals like nickel or copper or platinum to concentrate or segregate at the bottom of the crater."

But the impact theory is not popular theory with everyone.

"Geologists have always viewed the rock record as something that changes very, very slowly," Dr
MacDonald said.

"These catastrophic events, for many of them, were difficult to accept, because they seem to be so at
variance with the slow change of geological time that generally happens.

"Ninety-nine percent of the time things happen very slowly."
Received on Tue 25 Nov 2003 11:51:17 AM PST