Ore Controls and Metallogenesis of Au-Ag Deposits at Atalla Mine, Central Eastern Desert of Egypt
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This study was conducted as part of a post-doctoral fellowship scheme granted by the Erasmus Mundus program (EMMAG scholarship). The author deeply thanks Prof. Marek Slobodník (Head of the Fluid Inclusion Lab.) at the Department of Geological Sciences, Masaryk University, Brno, Czech Republic; who granted permission for the use of the analytical facilities of the Fluid Inclusions and EMPA labs. Special thanks go to Prof. J. Brendan Murphy (Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia, Canada) for his English polishing and proofreading of the manuscript. I also want to express my gratitude to constructive remarks and suggestions by the Editor and two anonymous reviewers that significantly helped in improving an early version of this manuscript.

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    Abstract:

    Gold-silver deposits in the Atalla area occur as hydrothermal quartz veins in NE–SW pre-existing fractures within the Atalla granitic pluton. The orientation of such quartz veins has been attributed to extensional behavior related to the Atalla Shear Zone (ASZ). The Atalla area is covered by a variety of lithologies that are (from oldest to youngest): metasedimentary rocks, metavolcanic rocks, ophiolite assemblage (serpentinites/talc-carbonates), Atalla granite and Dokhan volcanic rocks. Microscopically, Atalla granite ranges in composition from granodiorite to monzogranite. Whole-rock geochemistry constrains the calc-alkaine affinity of the Atalla granite that was intruded within an orogenic (syn-collision) tectonic regime. The ore minerals are represented by gold/silver (electrum), pyrite (Py1 & Py2), arsenopyrite, pyrrhotite, sphalerite, chalcopyrite, galena, covellite and goethite. The temperature of ore formation ranges from 240 to 285°C and the estimated fluid pressure is in the range of 20–100 MPa. Based on the geological setting, ore textures and fluid characteristics; the Atalla Au-Ag deposits are considered to be orogenic in nature, formed from a continental collision (~653-590 Ma), synchronous with the emplacement of calc-alkaline magmatism during the evolutionary history of the Arabian Nubian Shield (ANS). The initial ore-forming fluid was primarily derived from a metamorphic source related to ophiolitic-serpentinite rocks under deep regional conditions of greenschist-amphibolite facies, where the Atalla granitic eruption provided the required temperature conditions for the metamorphic process to take place. Under such conditions, the transportation of ore metals as bisulfide complexes is favoured. The deposition of ore minerals was triggered by fluid-wallrock interaction through fracture pathways in conjunction with a temperature-pressure drop that is likely to have been related to uplift into the crustal levels.

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Mohamed ABD EL MONSEF.2020. Ore Controls and Metallogenesis of Au-Ag Deposits at Atalla Mine, Central Eastern Desert of Egypt[J]. Acta Geologica Sinica(),94(5):1451-1470

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History
  • Received:January 19,2019
  • Revised:December 29,2019
  • Adopted:
  • Online: October 26,2020
  • Published: