Genesis of the rare metals mineralisation in Um Safi acidic volcanics, Central Eastern Desert, Egypt

Abstract

The rare metals mineralisation in Um Safi area occurs in the acidic volcanics (mainly rhyolite and volcanogenic tuffs). The microscopic investigation revealed that they are highly altered and subjected to several alteration processes where the hydrothermal solution played the master role in redistribution of the rare metals. The mineralogical study configured three groups of rare metals mineralisation including: (a) rare metals of the radio-elements (thorite), (b) rare metals of the trace elements and REEs (zircon, xenotime, chernovite, ferro-columite, allanite, bastnäsite and cerianite) and (c) rare metals of the base metals (tungsten minerals and cassiterite). The assemblage of Wolframite–Heubnerite–cassiterite–copper and fluorite associated with sulfides indicating magmatic to hydrothermal transition mineralisation. The hydrothermal fluids rich in F and As cause the alteration of some primary minerals such as xenotime, allanite and wolframite into the secondary chernovite, bastnäsite and schellite, respectively. The study also clarified that the emplacement of granitic offshoots into rhyolite played an important role in the re-distribution of some rare elements.