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The golden ark: Arsenopyrite crystal plasticity and the retention of gold through high strain and metamorphism

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Authors
Fougerouse, Denis
Micklethwaite, S.
Halfpenny, Angela
Reddy, Steven
Cliff, J.
Martin, L.
Kilburn, M.
Guagliardo, P.
Ulrich, S.
Date
2016
Type
Journal Article

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Fougerouse, D. and Micklethwaite, S. and Halfpenny, A. and Reddy, S. and Cliff, J. and Martin, L. and Kilburn, M. et al. 2016. The golden ark: Arsenopyrite crystal plasticity and the retention of gold through high strain and metamorphism. Terra Nova. 28 (3): pp. 181-187.
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Terra Nova
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Department of Applied Geology
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This is the peer reviewed version of the following article: Fougerouse, D. and Micklethwaite, S. and Halfpenny, A. and Reddy, S. and Cliff, J. and Martin, L. and Kilburn, M. et al. 2016. The golden ark: Arsenopyrite crystal plasticity and the retention of gold through high strain and metamorphism. Terra Nova. 28 (3): pp. 181-187, which has been published in final form at http://doi.org/10.1111/ter.12206 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving at http://olabout.wiley.com/WileyCDA/Section/id-828039.html

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Abstract

Quantitative electron backscatter diffraction analysis and ion microprobe imaging of gold-rich arsenopyrites provide the first insights into the crystal plasticity and element mobility behaviour of arsenopyrites through metamorphism (340°-460° and 2 kbar). Remarkably, the gold-rich arsenopyrites remained structurally and chemically robust during high strain deformation. It was only during a superimposed lower strain deformation event, at a high angle to the preferred orientation of the arsenopyrites, that small amounts of crystal plasticity affected the arsenopyrites. During the low strain event, a dissolution-reprecipitation reaction resulted in loss of gold from the crystal lattice, facilitated by localised domains of recrystallisation, most likely due to fluid percolation along sub- and new grain boundaries. We suggest that the abundance and rheologically robust nature of gold-rich arsenopyrite in giant gold deposits, affected by greenschist-amphibolite metamorphism, is actually critical in the preservation of those deposits.