Platinum-group element remobilisation and concentration in the Cliff chromitites of the Shetland Ophiolite Complex, Scotland

Brian O'Driscoll, Russell Garwood, James M. D. Day, R A Wogelius

    Research output: Contribution to journalArticlepeer-review

    252 Downloads (Pure)

    Abstract

    The ~492 Ma Shetland Ophiolite Complex contains an extensive mantle section, within which numerous podiform chromitite bodies formed during melt percolation in a supra-subduction zone setting. One of the Shetland ophiolite chromitite localities has an unusual style of platinum-group element (PGE) mineralization. Specifically, the Cliff chromitite suite has relatively high (>250 ppm) Pt plus Pd, compared to other chromitites in the Shetland Ophiolite Complex. In this study, we apply petrographic observation, mineral chemistry and novel X-ray microtomography data to elucidate the petrogenesis of PGE-bearing phases at Cliff. The combined datasets reveal that the PGE at Cliff have probably been fractionated by an As-rich fluid, concentrating Pt and Ir into visible (0.1–1 µm) platinum-group minerals (PGM) such as sperrylite and irarsite, respectively. The high (>1 ppm) bulk-rock concentrations of the other PGE (e.g. Os) in the Cliff chromitites suggests the presence of abundant fine-grained unidentified PGM in the serpentinized groundmass. The spatial association of arsenide phases and PGM with alteration rims on Cr-spinel grains suggests that the high Pt and Pd abundances at Cliff result from a late-stage low-temperature (e.g. 200–300°C) hydrothermal event. This conclusion highlights the potential effects that secondary alteration processes can have on modifying and upgrading the tenor of PGE deposits.
    Original languageEnglish
    Pages (from-to)471-490
    JournalMineralogical Magazine
    Volume82
    Issue number3
    Early online date12 Apr 2018
    DOIs
    Publication statusPublished - Jun 2018

    Fingerprint

    Dive into the research topics of 'Platinum-group element remobilisation and concentration in the Cliff chromitites of the Shetland Ophiolite Complex, Scotland'. Together they form a unique fingerprint.

    Cite this