An Overview for Gold Mineralization in the Egyptian Segment of the Northern Continuation of the East African Orogen
摘要
Gold occurrences in the Eastern Desert of Egypt have different styles of mineralization that reflect various tectonic settings and/or specific events during the crustal evolution of the Nubian Shield (NS). The crystalline basement rocks of the Egyptian segment host the majority of the primary gold deposits including (IRG/Porphyry, Orogenic type, VMS-related gold), as well as Placer-gold type. The IRG type is linked with late-to post-collision magmatic intrusion (younger granite, gabbro) or Dokhan volcanics that has been observed in some localities (ex: Um Monqul, Um Balad, Abu Dabbab, Atud). The orogenic-gold type is confined to Late arc-continent terrains (~635–540 Ma), formed during the second orogenic event that was responsible for the NNW-SSE Najd Fault System (NFS) and N-S Hamisana Shear Zone. It is well-presented at many localities in Egypt (ex: Atalla, Gidami, Fawakheir, Sukari, Haimur). Some gold deposits (ex: Fatira gold) show combined characteristics reflecting a transition between IRG and orogenic types (hybrid magmatic-metamorphic origin). VMS-related gold in Egypt is categorized into; (1) Auriferous VMS-related island arc volcanics and associated volcanoclastic rocks (Semna, Um Samuki, Darhib), (2) Gold-hosted in Banded Iron Formation (ex: Abu Marawat), and (3) Gossan-related gold type overlying a burred sulfides ore (ex: Hamama). The placer-gold type represents secondary gold deposits, where the gold is found in the modern alluvial sediments that are commonly nearby major primary occurrences (ex: El Sid, Sukari, Umm Ud), or it could also be detected within paleoplacer conglomerates at the base of Nubian Sandstone Formation (ex: hammamat deposits).