Abstract
The Um Samiuki Zn–Cu–Pb–Ag mineralisation, south Eastern Desert, Egypt is hosted by felsic volcanic rocks which form part of the 712-Ma-old, east-west-trending Shadli Volcanic Belt. Two major occurrences of massive sulphides are present at the top of rhyolitic breccia in the Western and Eastern mine areas. In each occurrence, a bornite-bearing zone is overlain by a pyrite-chalcopyrite-bearing zone and underlain by a disseminated, Cu-depleted zone. In the massive sulphide ore, sphalerite, chalcopyrite, pyrite, galena, bornite and tetrahedrite–tennantite are major minerals, whereas arsenopyrite, pyrrhotite, molybdenite and magnetite are accessory phases. Covellite and digenite are common secondary minerals. Bornite, tetrahedrite–tennantite and covellite contain high amounts of silver (averages of 1.97, 1.39 and 1.82 wt% respectively). Based on mineralogical balance calculations, bornite and covellite accommodate 80% of silver in the Um Samiuki deposit. Ag was incorporated in the crystal structure of the early-crystallised copper sulphides and sulphosalts and silver minerals. The temperature, sequential precipitation of the fluids and the structure of the crystallising phases control the distribution of silver. Post-depositional deformation and metamorphic processes caused liberation, remobilisation and redeposition of silver within the massive sulphides.
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Acknowledgments
H.M. Helmy is grateful to Profs. E.F. Stumpfl, Institute of Mineralogy and Petrology, Mining University of Leoben, and G. Hoinkes, Institute of Earth Sciences (Mineralogy and Petrology), Karl-Franzens University, Graz, Austria for the analytical facilities offered. Reinhard Kaindl is thanked for reading the final version of the paper. The comments of David Huston, Ross Large, David Lentz and Bernd Lehmann greatly improved the final version of the manuscript.
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Shalaby, I.M., Stumpfl, E., Helmy, H.M. et al. Silver and silver-bearing minerals at the Um Samiuki volcanogenic massive sulphide deposit, Eastern Desert, Egypt. Miner Deposita 39, 608–621 (2004). https://doi.org/10.1007/s00126-004-0427-y
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DOI: https://doi.org/10.1007/s00126-004-0427-y