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  • Boskabadi, ArmanStockholms universitet,Institutionen för geologiska vetenskaper,University of Texas at Dallas, USA (author)

Carbonate alteration of ophiolitic rocks in the Arabian-Nubian Shield of Egypt : sources and compositions of the carbonating fluid and implications for the formation of Au deposits

  • Article/chapterEnglish2017

Publisher, publication year, extent ...

  • 2016-09-26
  • TAYLOR & FRANCIS INC,2017
  • printrdacarrier

Numbers

  • LIBRIS-ID:oai:DiVA.org:uu-321062
  • https://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-321062URI
  • https://doi.org/10.1080/00206814.2016.1227281DOI
  • https://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-142706URI

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  • Language:English
  • Summary in:English

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  • Subject category:ref swepub-contenttype
  • Subject category:for swepub-publicationtype

Notes

  • Ultramafic portions of ophiolitic fragments in the Arabian-Nubian Shield (ANS) show pervasive carbonate alteration forming various degrees of carbonated serpentinites and listvenitic rocks. Notwithstanding the extent of the alteration, little is known about the processes that caused it, the source of the CO2 or the conditions of alteration. This study investigates the mineralogy, stable (O, C) and radiogenic (Sr) isotope composition, and geochemistry of suites of variably carbonate altered ultramafics from the Meatiq area of the Central Eastern Desert (CED) of Egypt. The samples investigated include least-altered lizardite (Lz) serpentinites, antigorite (Atg) serpentinites and listvenitic rocks with associated carbonate and quartz veins. The C, O and Sr isotopes of the vein samples cluster between -8.1 parts per thousand and -6.8 parts per thousand for delta C-13, +6.4 parts per thousand and +10.5 parts per thousand for delta O-18, and Sr-87/Sr-86 of 0.7028-0.70344, and plot within the depleted mantle compositional field. The serpentinites isotopic compositions plot on a mixing trend between the depleted-mantle and sedimentary carbonate fields. The carbonate veins contain abundant carbonic (CO2 +/- CH4 +/- N-2) and aqueous-carbonic (H2O-NaCl-CO2 +/- CH4 +/- N-2) low salinity fluid, with trapping conditions of 270-300 degrees C and 0.7-1.1kbar. The serpentinites are enriched in Au, As, S and other fluid-mobile elements relative to primitive and depleted mantle. The extensively carbonated Atg-serpentinites contain significantly lower concentrations of these elements than the Lz-serpentinites suggesting that they were depleted during carbonate alteration. Fluid inclusion and stable isotope compositions of Au deposits in the CED are similar to those from the carbonate veins investigated in the study and we suggest that carbonation of ANS ophiolitic rocks due to influx of mantle-derived CO2-bearing fluids caused break down of Au-bearing minerals such as pentlandite, releasing Au and S to the hydrothermal fluids that later formed the Au-deposits. This is the first time that gold has been observed to be remobilized from rocks during the lizardite-antigorite transition.

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  • Pitcairn, Iain K.Stockholms universitet,Institutionen för geologiska vetenskaper(Swepub:su)ipitc (author)
  • Broman, CurtStockholms universitet,Institutionen för geologiska vetenskaper(Swepub:su)broma (author)
  • Boyce, AdrianScottish Univ Environm Res Ctr, E Kilbride, Lanark, Scotland. (author)
  • Teagle, Damon A. H.Univ Southampton, Natl Oceanog Ctr Southampton, Southampton, Hants, England. (author)
  • Cooper, Matthew J.Univ Southampton, Natl Oceanog Ctr Southampton, Southampton, Hants, England. (author)
  • Azer, Mokhles K.Natl Res Ctr, Dept Geol, Cairo, Egypt. (author)
  • Stern, Robert J.Univ Texas Dallas, Dept Geosci, ROC 21,800 West Campbell Rd, Richardson, TX 75080 USA. (author)
  • Mohamed, Fathy H.Univ Alexandria, Dept Geol, Fac Sci, Alexandria, Egypt. (author)
  • Majka, JaroslawUppsala universitet,Mineralogi, petrologi och tektonik,AGH Univ Sci & Technol, Fac Geol Geophys & Environm Protect, Krakow, Poland.(Swepub:uu)jarma730 (author)
  • Stockholms universitetInstitutionen för geologiska vetenskaper (creator_code:org_t)

Related titles

  • In:International Geology Review: TAYLOR & FRANCIS INC59:4, s. 391-4190020-68141938-2839

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