The 10th International Conference of Jordanian Geologists Association April 3-5, 2011
ABSTRACT
Despite being generally of vein-type mineralization, most of the historic Egyptian gold deposits are associated with extensive, variably mineralized alteration zones. This observation warrants new comprehensive studies to detect possible low-grade, high tonnage ore zones in the region. In this context, spectral analysis based on processed ASTER imagery data combined with mine-scale geological maps, geochemical and mineralogical data from several gold mining localities within the Allaqi-Heiani and Hodein districts, in the extreme south of the Eastern Desert of Egypt, reveal the reliability of spectral analysis techniques in identification of hydrothermal alteration zones, extending
beyond the already known ancient mine sites. The high coincidence of the spectral analysis results
and measured mineral concentrations demonstrates the power of ASTER imagery data to map spectral
signatures associated with vein-type gold deposits in the study area. Furthermore, tracing along the
major transpression structures aided resolving structural and mineralogical criteria relevant to
exploration in the rigorously arid southern Eastern Desert of Egypt.
Field and remote sensing studies indicate that gold oreshoots (several ppms scale) and related
hydrothermal alteration halos (hunderds of ppbs to a few ppms scale) occur in three main geologic/structural settings, namely: (I) steeply-dipping anastomosing silicified shear zones between allochthonous listvenized ophiolitic blocks and underlying arc-related volcanic and volcaniclastic or metapelitic sediments, with or without foliation-concordant granophyric offshoots (e.g., El-Beida, El-Anbat, Korbiai, Um Egat, Um El-Tuyor El-Foqani, Um Garayat and Haimur deposits), (II)moderately-dipping mylonitic zones, along which syn-orogenic granitoid sheets tapered into the variably sheared island arc volcanic/volcaniclastic host rocks (e.g., Wadi Khashab, Seiga and Shashoba deposits), and (III) reactivated shears along intrusive contacts of arc-related gabbroic intrusions and host carbonaceous metapelitic/psammopelitic metasediments, commonly close to
granitic dyke-like bodies (e.g., Betam and Um El-Tuyor El-Tahtani deposits).
The predominance of ductile deformation features (e.g., buckled and boudined styles,
recrystallization and shear banding) over brittle brecciation in the mineralized quartz veins, and
association with syn- to late-orogenic ganitoid stocks suggest formation of the orebodies synkinematically with transpression. The auriferous structures are consistently of higher order relative to the terrane collision suture structures (i.e., Allaqi-Heiani deformation zone). As a result, gold metallogeny in the region is attributed to major tectonic/thermal activities concomitant with repeated fault rupture and sealing throughout folding and transpressive deformation. The latter are temporally linked with post-accretionary shortening increments in the Arabian-Nubian Shield between ~630 and 550 Ma.
Keywords: Gold metallogeny, Auriferous alteration zones, ASTER, Post-accretionary structures,
Arabian Nubian Shield, South Eastern Desert of Egypt |
