MINERALOGlt AND GEOCHEMISTRY OF SOME PLACER MINERALS IN THE STREAM SEDIMENTS OF DAHAB AREA, SINAI, EGYPT.

Abstract

The stream sediments of Dahab area, southeastern Sinai, Egypt were • studied for their content of economic minerals. These sediments are immature as indicated by poor sorting and other mechanical parameters. They are de1ived from the Precambrian basement rocks, which are mostly represented by granitic rocks in addition to lesser amounts of volcanics and gabbros. The mineralogical investigation revealed tl1at these sediments contain considerable amounts of placer gold, Fe-Ti oxides and zrrcon. The concentrated Fe-Ti oxides comprise homogeneous magnetite and ilmenite in addition to ilmeno-magnetite, hemo-ihnenite and rutile- • hematite intergrowths. Isodynamic separation of some raw samples (size :Shmn) revealed that up to 15.12% magnetic minerals can be recovered.

Zircon shows remarkable variations in morphology, colour, chemistry and provenance. U-poor and U-rich varieties of zircon were discriminated containing uo2 in the ranges of 0.04-1.19 wt% and 3.05-3.68 wt%,

respectively. REE-bearing minerals comprise monazite, allanite and La­

cerianite.

On mineralogical basis, the present work suggests that Dahab stream sediments represent a promising target for further geochemical • exploration for precious metals, especially gold. Fire assay data indicate that placer gold in some of the studied sediments •sometimes reaches 15.34 g/t. It is supposed that the narrow gullies and valleys cutting the basement manifested the development and preservation of gold in this arid environment. Background concentration of gold and variation in lithology suggest multiple source of the metal in the investigated sediments.