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Trace elements and isotope data of the Um Garayat gold deposit, Wadi Allaqi district, Egypt
Stockholm University, Faculty of Science, Department of Geological Sciences.
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Number of Authors: 62019 (English)In: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 54, no 1, p. 101-116Article in journal (Refereed) Published
Abstract [en]

Trace element composition of sulfides and O, C, Sr and S isotopic data are assessed to constrain the evolution and potential fluid and metal sources of the Um Garayat gold deposit. Ore microscopy and BSE investigations of quartz veins show blocky arsenopyrite and pyrite replaced in part by pyrrhotite, chalcopyrite, sphalerite, galena, and gersdorffite. Free-milling gold occurs commonly in close association with the late sulfides, and along fractures in pyrite. On the other hand, recrystallized pyrite is disseminated in host metavolcaniclastic/metasedimentary rocks that commonly contain carbonaceous material. In situ LA-ICP-MS analysis of sulfides shows the recrystallized pyrite enriched in most trace elements, while blocky pyrite contains only some traces of arsenic. Detected concentrations of gold (up to 17ppm) were only reported in arsenopyrite disseminated in quartz veins. The S-34 values of blocky pyrite and pyrrhotite in quartz veins define a narrow range (1.6 to 3.7 parts per thousand), suggesting a homogenous sulfur source which is consistent with the dominantly mafic host rocks. The recrystallized pyrite has a distinctive sulfur isotope composition (S-34 -9.3 to -10.6 parts per thousand), which is rather comparable to diagenetic sulfides. Hydrothermal carbonate in quartz veins and wallrock have nearly constant values of O-18 (10.5 to 11.9 parts per thousand) and C-13 (-4.2 to -5.5 parts per thousand). Based on constraints from mineral assemblages and chlorite thermometry, data of six samples indicate that carbonate precipitation occurred at similar to 280 degrees C from a homogenous hydrothermal fluid with O-18(H2O) 4.4 +/- 0.7 parts per thousand and C-13 =3.7 +/- 0.8 parts per thousand. Strontium isotope values of two samples (Sr-87/Sr-86 = 0.7024 and 0.7025) are similar to the initial Sr-87/Sr-86 ratios of island arc metabasalts (similar to 710Ma) in the South Eastern Desert. The generally homogenous sulfur, C, O, Sr isotope data are suggestive of metamorphogenic fluids, likely produced from dominantly mafic volcanic rocks at the greenschist-amphibolite facies transition.

Place, publisher, year, edition, pages
2019. Vol. 54, no 1, p. 101-116
Keywords [en]
Um Garayat gold deposit, Wadi Allaqi, South Eastern Desert of Egypt, Isotope C, O and Sr data of carbonate, EPMA and LA-ICP-MS data of sulfides, Ore genesis
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-167697DOI: 10.1007/s00126-018-0807-3ISI: 000459434900008OAI: oai:DiVA.org:su-167697DiVA, id: diva2:1301379
Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-01Bibliographically approved

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