Hydrothermal wall rock alteration at Kurdeman gold mine area, Eastern Desert, Egypt

The shear zone-related gold mineralization of Kurdeman in the Eastern Desert of Egypt is hosted by greenschist facies metavolcanic and talc-carbonate rocks of Pan-African age. The gold deposit comprises boudinaged quartz veins enveloped by alteration zones. Chlorite-sericite, carbonate-chlorite-sulfide, carbonate-sericite, and sericite constitute four distinct alteration zones which extend inwards to the mineralized quartz veins. Chlorite and carbonate-chlorite alteration zones are derived from the pre-existing talc-carbonate rocks. The geochemistry of the alteration system was statistically investigated using discriminant and factor analyses. Six factors were estimated; factors 1 and 2 are assigned to the pre-existing rock forming minerals and dominated by the rare earth elements. Throughout hydrothermal alterations, the HREE seems to be more mobile relative to the LREE. Factor 3 signifies sericitization, whereas factor 4 largely represents carbonatization and silicification, and somewhat chloritization and gold-sulfide mineralization. Factor 5 characterizes the Au-sulfide mineralization, whereas factor 6 includes Ag which separated from the Au-association due to its high mobility. The background and threshold values as well as the mobility of the elements have been calculated. The relative sequence of element mobilities is: Ag > Cd > As > > Sb > Au > Cu. Arsenic, Hg and Sb form supra-ore haloes and could be employed as valuable indicators throughout the exploration. The preliminary reserve evaluation suggests that the amount of gold considering the limited anomalous areas of the explored adits is about 0.32 tons, signifying a probable promising mineralization. Gold precipitation is related to the formation of dolomite-ankerite solid solution and sulfides. The high CO2/H2O ratio and the availability of elements such as Mg, Ca, and Fe resulted in reducing the solubility of gold and precipitated carbonate and pyrite. Gold was transported as hydrosulfide complexes and precipitated under alkaline conditions below 352 degrees C. Silicification led to the enrichment of Au in the carbonate-chlorite-sulfide alteration zone.