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Permo-Triassic unconformity- related Au-Pd mineralisation, south Devon, UK : new insights and the European perspective

Shepherd, Tom J.; Bouch, Jon E.; Gunn, Andrew G.; McKervey, John A.; Naden, Jonathan; Scrivener, Richard C.; Styles, Michael T.; Large, Duncan E.. 2005 Permo-Triassic unconformity- related Au-Pd mineralisation, south Devon, UK : new insights and the European perspective. Mineralium Deposita, 40 (1). 24-44. 10.1007/s00126-004-0459-3

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Abstract/Summary

An integrated mineralogical-geochemical study of unconformity-related Au-Pd occurrences within and around the Permo–Triassic basins of southwest England, UK, has confirmed the importance of low temperature (86±13°C), hydrothermal carbonate veins as hosts for the mineralisation. Fluid inclusion data for the carbonate gangue, supported by stable isotope (13C and 18O) and radiogenic (87Sr/86Sr) data, have identified three principal fluids: (1) a reducing calcic brine [>25 wt% salinity, <0.5>2)] originating in the sub-unconformity basement and an expression of advanced mineral–fluid interaction; (2) an oxidising sodic brine [~16 wt% salinity, >0.9 NaCl/(NaCl+CaCl2)] originating in the post-unconformity red beds under evaporitic conditions, and (3) an oxygenated, low salinity groundwater (<3 wt% salinity).="" the="" sodic="" brine="" is="" reasoned="" to="" be="" the="" parent="" metalliferous="" fluid="" and="" to="" have="" acquired="" its="" enrichment="" in="" au="" and="" pd="" by="" the="" leaching="" of="" immature="" sediments="" and="" intra-rift="" volcanic="" rocks="" within="" the="" local="" permo–triassic="" basins.="" metal="" precipitation="" is="" linked="" to="" the="" destabilisation="" of="" au="" and="" pd="" chloride="" complexes="" by="" either="" mixing="" with="" calcic="" brines,="" dilution="" by="" groundwaters="" or="" interaction="" with="" reduced="" lithologies.="" this="" explains="" the="" diversity="" of="" mineralised="" settings="" below="" and="" above="" the="" unconformity="" and="" their="" affinity="" with="" red="" bed="" brines.="" the="" paucity="" of="" sulphide="" minerals,="" the="" development="" of="" selenides="" (as="" ore="" minerals="" and="" as="" mineral="" inclusion="" in="" gold="" grains),="" the="" presence="" of="" rhodochrosite="" and="" manganoan="" calcites="" (up="" to="" 2.5 wt%="" mn="" in="" calcite)="" and="" the="" co-precipitation="" of="" hematite="" and="" manganese="" oxides="" are="" consistent="" with="" the="" overall="" high="" oxidation="" state="" of="" the="" ore="" fluids.="" a="" genetic="" model="" is="" proposed="" linking="" permo–triassic="" red="" beds,="" the="" mixing="" of="" oxidising="" and="" reducing="" brines,="" and="" the="" development="" of="" unconformity-related="" precious="" metal="" mineralisation.="" comparison="" with="" other="" european="" permo–triassic="" basins="" reveals="" striking="" similarities="" in="" geological="" setting,="" mineralogy="" and="" geochemistry="" with="" au,="" au-pd="" and="" selenide="" occurrences="" in="" germany="" (tilkerode,="" korbach-goldhausen),="" poland="" (lubin)="" and="" the="" czech="" republic="" (svoboda="" nad="" úpou="" and="" stupná).="" though="" the="" known="" au-pd="" occurrences="" are="" sub-economic,="" several="" predictive="" criteria="" are="" proposed="" for="" further="">

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1007/s00126-004-0459-3
Programmes: BGS Programmes > Economic Minerals
ISSN: 0026-4598
Date made live: 13 Jul 2012 10:37
URI: http://nora.nerc.ac.uk/id/eprint/18699

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