GENETIC AFFILIATION OF GOLD AND URANIUM MINERALIZATION IN EL-MISSIKAT GRANITE, CENTRAL EASTERN DESERT, EGYPT

Abstract

Gabal El-Missikat granitic pluton is affected by two fault systems trending NW-SE (the oldest) andENE-WSW directions. It is one of the uranium occurrences in the Eastern Desert of Egypt. The northwesternmargins of El-Missikat pluton, along its contact with the gneissose quartz diorite, are dissected by numerousreactivated fractured shear zones running generally ENE-WSW to NE-SW and dipping about 600-700 toSE. Many white (oldest), smoky or black and jasperoid (youngest) silica veinlets fill the fractures of theseshear zones.These veins are of irregular shape and variable thickness ranging from few centimeters to aboutthree meters. They are chiefly affected by silicification, sericitization, hematitization , kaolinization andhydrothermal alterations processes. The smoky black veins are hosting secondary uranium and fluorite-,sulphide-gold mineralizations.Polished surface studies, ICP-ES and Atomic Absorption as well as Scanning Electron Microscopemeasurements recorded galena, pyrite chalcopyrite, sphaleriteand molybdenite in the black and jasperoidmineralized veins. Gold associated with ore mineral assemblage as pyrite, chalcopyrite, sphalerite, galena,sheelite and iron oxides. The identified sulphide minerals not bearing gold are recorded. Gold are relativelycoarse-grained, massive and metallic yellow or stretched bronze colored particles.The recorded secondary U minerals associates the sulphide gold-mineralization in the black andjasperoid silica veins.Regarding the mobility of both uranium and gold, U4+mobilized in oxidizing medium and migrate andtransport as U6+, then deposited later as U4+ when the medium changes to be reducing characterized byhigh ƒO2 . On contrary, gold mobilized when the medium is complex AuCl3- ion bearing. Consequently, El-Missikat granitic pluton affected by oxidizing Au and Cl3- bearing high temperature hydrothermal solutionsthat leached U4+, W and Mo from the granitic mass as U6+, later decrease of temperature, both U and golddeposited as well as the sulphide minerals of Pb, Zn, cu, Fe and Mo in the high temperature hydrothermalfluids were deposited with increase of S+2 ion.