Geologija (Dec 2010)
Mineral chemistry of polymetallic mineralization associated with altered granite, Hangaliya area, South Eastern Desert, Egypt
Abstract
The Hangaliya gold deposit, located in the South Eastern Desert of Egypt, comprises a series of milky quartzveins along NW-trending Hangaliya shear zone, cutting through granitic rocks of Gabal Nugrus monzogranite. Thisshear zone, along with a system of discrete shear and fault zones, formed in the late deformation history of the area.The quartz vein emplacement took place under a brittle-ductile shear regime. Auriferous quartz veins are slightlysheared and boudinaged within the shear zone, especially in the hematized granite. Hydrothermal alteration ispervasive in the granitic wall rocks including sericitization, chloritization, fluoritization, sulphidization and minorcarbonatization. The altered zones and associating quartz veins contain sulphides, gold, silver, cobalt, bismuth, anduraninite minerals.The Hangaliya gold veins include gold, silver, cobaltite, native bismuth, chalcopyrite, pyrite, galena, ferrocolumbite,fergusonite and uraninite. The Au-ore occurs in the quartz veins and adjacent wall rocks as disseminationin chalcopyrite and pyrite. Presence of refractory native silver, bismuth and cobalt in chalcopyrite is inferredfrom microprobe analyses. Wall rock sulphidization also likely contributed to destabilising the gold-silver, cobalt,bismuth assemblages and precipitation of the minerals in the hydrothermal alteration zone adjacent to the quartzveins. Gold occurs in two main modes: “invisible gold” in sulphides and native gold. Most of the “invisible gold”occurs in chalcopyrite and bismuth. The altered granites in the Hangaliya shear zone are enriched in Au, Ag, Bi, Co,and Ni with chalcopyrite, which suggests derivation of these metals from serpentinites due to interaction with thefelsic Nugrus granite.
