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Sunday, October 01, 2006

World's deepest Diamond bearing rocks found under Malaita Island: 2000 Report by Australian and American researchers

Greetings folks,

This piece of information is reported by the BBC News on Science and Technology, and the ABC Science Online in May 2000. Eventhough it may be quite old with regards to the date of publication, it is quite interesting to read as it may hold some grounds on the recent belief by some Malaitans that Diamond bearing rocks have been discovered under the island of Malaita.

A gem from the deep - garnet knobs in mantle rock on Malaita Island

New research by Australian and American geologists has got diamond prospecting companies around the world licking their lips, with the surprise discovery of diamond bearing rocks deep under an island.

Professor Ken Collerson and colleagues from the University of Queensland and the University of California Santa Cruz report in Science their discovery of the world's deepest rocks, originating up to 670km below the Earth's surface.
The rocks came to the surface inside kimberlite on Malaita Island

The discovery was made on the small island of Malaita, in the Solomon Islands group.

The find, said Professor Collerson, as well as being scientifically fascinating, will "change the paradigm for diamond exploration".

"I guess this is the first time that diamond-bearing rocks have been found in oceanic environments. Previously, they have always come from the oldest (central) parts of continents," he said.

The rocks formed in an area about 10 per cent of the way to the centre of the earth, where the pressure is 250,000 times what it is at the surface. This is about twice as deep as anything studied before.

The rocks contain micro-diamonds, and also harbour a variety of high-pressure minerals, including majorite, a silica-rich form of the mineral garnet. This mineral is the "smoking gun", only stable at ultra-high pressure, which tells geologists that the rocks could only have come from deep within the earth's mantle.

Researchers also hope that study of the deep-crust minerals will reveal new information about large-scale movement of material passing through this transition zone between the lower and upper mantle.

Up until now, this knowledge has only been based on seismic imaging, various studies of diamond microstructure, and experimental simulation.
Samples contained micro-diamond (Scale bar: 10 microns)

"It's a bit like the Hubble Space Telescope when it was out of focus," Professor Collerson told the BBC. "We now have a means of getting a much clearer image of the tomography of the lower mantle because we'll have physical properties to put in our equations."
Prof Collerson (seated), and colleagues, report their findings in Science

He suspects that diamonds were formed when the plateau on which Malaita island is located was pierced, millions of years ago, by pipes of lava coming from deep within the crust. These pipes are similar to the kimberlite pipes of South Africa and elsewhere, which commonly carry diamonds from deep within the earth's mantle.

Meanwhile, results of further detailed study and analysis of the crystal structure of the unique minerals carried out with a number of international collaborators and with members of the university's Centre for Microscopy and Microanalysis over the last years is still not known.

Sources: ABC Science Online & BBC News on Science and Technology

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