J KAU: E<I"I, Sci., .ol .6.pp 1-33(1413 A .H . /I993 A .D .) A Comparative Study of Five Volcanic-Hosted Sulfide Mineralizations in the Arabian Shield A.M. AL-SHANTI*, O,R. EL-MAHDY*, M.A. HASSAN""" and A .A . HUSSEIN"""* '" Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia, """Nuclear Materials Corporation, Ma'adi, Cairo, Egypt, *""'The Egyptian Geological Survey and Mining Authority, Cairo, Egypt ABSTRAC "T. Investigation of five volcanogenic base metal sulfide occurr- ences in the Arabian Shield (Ash Shizm, Umm Ad Damar, As-Safra, AI Musayna'ah, and Umm Ash Shalahib) showed that they are located within Hulayfah calc-alkaline volcanic rocks or its equivalents. The investigations included field, petrographic, mineralogical and chemical studies. Felsic, calc-alkaline rock assemblages host these occurrences, with a pre- dominance of rhyolitic rocks and some andesites. Basalt occurs only in the vicinity of the Ash Shizm mineralization. These rocks were regionally metamorphosed to low greenschist facies grade. Deformation and contact metasomatism affected parts of these occurrences producing foliation and local skarn development. The intensity of metamorphism and deformation varies between localities. Later episodes of hydrothermal activity over- printed zones of mineralizations producing sericitization, chloritization and silicification. Geotectonieally, these mineral occurrences were formed in different set- tings. Ash Shizm bimodal volcanics were probably deposited in an exten- sional regime in a back arc basin. Umm Ad-Damar, As Safra and AI Musayna'ah calc-alkaline volcanics are interpreted as formed within an is- land arc environment, while Umm Ash Shalahib volcanics could be consi- dered similar to Andean type deposits related to an active continental mar- gin environment. Ore microscopic investigations of the mineral as- semblages in the five occurrences indicated primary orcs that have been coarsened and deformed to variable degrees giving the ores their charac- teristic brecciated nature reflected in the associated pyrite and other metamorphic texture present. Despite the extensive exploration programs carried out in the five areas by DGMR, no economically worthwhile deposit has been recommended for exploitation. The quantity and/or grade of these deposits, besides their