GEOLOGICAL AND GEOCHEMICAL STUDY ON SOME DYKES AND HOSTING SYENOGRANITE IN SHEIKH SALEM AREA, SOUTH EASTERN DESERT, EGYPT

Sheikh Salem area (45 km west of coastal Mersa Alam town ,south Eastern Desert of Egypt) is occupied
by Precambrian basement rocks including volcaniclastic metasediments, metagabbro-diorite complexes,
metavolcanics and syenogranite. The studied area is dissected by numerous dyke swarms. The syenogranite
is of I-type and characterized by peraluminous nature.
Two sets of nearly vertical dykes cut the syenogranite. The younger one trends NNW-SSE, while
the older trends ENE-WSW. The younger dykes are lamprophyres and mainly composed of plagioclase,
hornblende, pyroxene and olivine. Calcite, epidote, antigorite and chlorite are secondary minerals, whereas
opaques are accessories. The older dykes are andesites and mainly composed of plagioclase, hornblende.
Saussurite, calcite, and epidote are secondary minerals, whereas opaques are accessories.
The separated minerals from the lamprophyre samples include graphite, pyrite and zircon. A very
important observation is the occurrence of graphite in most lamprophyre samples. The original magma of the
lamprophyres is of high K-calc alkaline to shoshonitic type with basaltic nature, while the original magma
of the andesites is of high K-calc alkaline to calc alkaline type with andesitic nature. The lamprophyres have
high content in Y, Ni, Cu, V and Zr, and low content in Rb, Pb, Zn, Ba and Ga compared with andesites.
Both the lamprophyres and andesites show enrichment in Ba, Rb, Pb, Sr, Zr, Zn and Y and depletion in Cr
and Ni compared with primitive mantle.
The Syenogranite of Sheikh Salem area shows background radioactivity level giving eU contents of 7.4
ppm while eTh average content is 18.7 ppm and the mean value of eU/eTh ratio is 0.42.