A Non-Destructive Raman Test for Recognition of Subduction Diamond

Authors / CoAuthors

Barron, L.M. | Mernagh, T.P. | Barron, B.J.

Abstract

Two million alluvial macrodiamonds recovered from Tertiary deep leads in the Copeton/Bingara (C/B) area of New England (NSW) formed by ultrahigh pressure metamorphism during Phanerozoic subduction - based on unique isotopic composition (?13C>0), unique inclusions and high pressures on inclusions. The techniques used were either destructive or only succeeded on 3% of 200 stones tested with inclusions. Some researchers have suggested that UHP microdiamond (e.g. from Kochetav) lacks the 2nd order Raman spectral pattern (2200-2700cm-1) that is prominent in cratonic diamond. Our work on African cratonic macrodiamond shows this peak is suppressed if the stone is UV fluorescent, but is strong at 15-75Ã— (signal to noise ratio S/N) for a low background (?1100 counts per second). For NSW macrodiamond with a low background, this peak is greatly reduced at 2-14Ã— S/N for C/B (45 stones), Mt Airly (4), Walcha (2), Frenchmans (1 ) and Wenona Diatreme (1), calibrating the test. This new combined technique (UV lamp, 2nd order Raman) is much faster and works on a larger fraction of stones (including those without inclusions; 13% of C/B stones are low background). Strong brittle/plastic deformation during growth of C/B diamond is confirmed by growth textures and Laue Xray photography, indicating growth during subduction - promoting strong nitrogen aggregation, and suppressing the 2nd order Raman spectral signal. This Raman test should apply to all subduction diamond, including superdeep diamond.

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nonGeographicDataset

eCat Id

73300

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MNHD

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Commonwealth of Australia (Geoscience Australia)
Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
ACT
2601
Australia

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( Theme )

mineralogy

Australian and New Zealand Standard Research Classification (ANZSRC)

Earth Sciences

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2012-01-01T00:00:00

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