Genetically related Mo–Bi–Ag and U–F mineralization in A-type granite, Gabal Gattar, Eastern Desert, Egypt

Abstract

Molybdenum–bismuth–silver and uranium–fluorine mineralization in the Gabal Gattar area are genetically related. Both are hosted in fractionated and hydrothermally altered A-type granite. While Mo–Bi–Ag ore is hosted in NS striking quartz veins, the U–F mineralization forms batches and micro-veinlets, controlled by NNE to NW trending structures. U was incorporated in late-magmatic hypogene minerals (e.g. zircon and xenotime) and in U–Th-minerals closely associated with fluorite. Molybdenite, native bismuth, galena, chalcopyrite, sphalerite, aikinite “PbCuBiS3”, berryite “S16(Cu,Ag)6 Bi7Pb3” and native silver were identified in the quartz veins. Fluid inclusions occur in fluorite (Type-1) associated with U minerals and in quartz (Type-2) from Mo-bearing veins. Type-1 and 2 inclusions homogenize at temperatures between 220°C and 106°C, their salinity ranges from 1.3 to 10wt.% NaCleq, respectively. F-rich fluids accumulated at the last stage of granite crystallization, extracted ore metals and deposited them in a shallow hydrothermal system. Mo, Bi and Ag precipitated earlier from saline fluids due to cooling, fluid mixing and wallrock sulfidation. U–F minerals precipitated from low-salinity fluids after high input of meteoric water.