Presentation Information
[G-O-31]Gold distribution in the Eastern Desert of Egypt and its relation to ophiolitic serpentinites from a Neoproterozoic accretionary complex
*Yasser Medhat Hassan Abdelrahman1,2, Atsushi Okamoto1, Abdel-Moneim Eldougdoug2, Mohamed Gobashy3 (1. Graduate School of Environmental Studies, Tohoku University, Japan, 2. Geology Department, Faculty of Science, Cairo University, Egypt , 3. Geophysics Department, Faclty of Science, Cairo University, Egypt)
Keywords:
Serpentinite,Gold,Ophiolite,Egypt,Neoproterozoic
The Eastern Desert of Egypt, especially its central segment, hosts a high number of ancient gold production sites. Gold deposits in this area are mostly vein-type and many of them follow ophiolitic assemblages, which show forearc geochemical signatures. The ophiolitic serpentinites are variably carbonatized and are commonly altered to talc-carbonate assemblages along shear zones. The present work considers both the magnetic susceptibility and the geochemistry of the serpentinites and their associated rocks in relation to their gold contents. The serpentinites from the Eastern Desert shows variable magnetic susceptibility, which is highly controlled by their magnetite content and the size of the magnetite crystals. The susceptibility of talc-carbonate assemblages overlaps with the serpentinites. However, there is no clear relationship between the magnetic susceptibility and the gold content in the serpentinites and their associated rocks. Reconnaissance gold and whole-rock trace element analyses were conducted on 30 representative samples of serpentinites and their derivatives from four areas in the central segments of the Eastern Desert of Egypt. Gold was detected in 18 samples and it ranges from 0.001 to 0.022 ppm. One sample shows a relatively high gold content (0.202 ppm). This sample is composed essentially of coarse-grained antigorite and it is derived from the Fawakhir area, which is known historically for its gold mining. In addition to gold, the sample shows also the highest As (425 ppm), Sb (20 ppm), W (2.35 ppm) and U (1.96 ppm) contents compared to other serpentinites. The REE contents of the sample is higher than the other serpentinites in the area and its chondrite-normalized pattern is relatively flat with distinct negative Eu anomalies. Another quartz-carbonate sample from the Fawakhir area shows the highest Ag (0.582 ppm), Bi (0.252 ppm), Cd (0.428 ppm), Co (129 ppm), Cu (266 ppm), Mo (4.01 ppm), Pb (14.95 ppm), Se (2.68 ppm), Te (0.458 ppm), Tl (0.376 ppm) and Zn (775 ppm) contents among the analyzed samples, but its Au content is relatively low (0.005 ppm). Further work is still needed to understand the relationship between the distribution of gold and other precious and base metals and alteration processes in mantle rocks, which could be possible by the conducting further studies on the serpentinites and their derivative rocks in the Eastern Desert, especially from the Fawakhir area.