The Jabal as Sukkah quadrangle (21/43 B) lies in the southern Najd region within the Arabian Shield between lat 21°30' and 22°00' N. and long 43°30' and 44°00' E. The oldest rocks exposed are a very thick sequence of volcanic flow rocks of mostly felsic to intermediate composition interbedded with volcaniclastic and sedimentary rocks. The layered rocks reflect a less primitive state of crustal evolution than has generally been ascribed to this sequence. These rocks were deposited upon an emerging basement of mafic to intermediate composition, and the sedimentary materials reflect a source terrane of mostly intermediate to felsic character.
The layered rocks were subjected to three separate episodes of compressional deformation, each followed by appreciable talc-alkalic plutonism. Each of the plutonic suites contains a differentiated series that began with the emplacement of mafic to intermediate rocks, progressed to talc-alkalic granites, and terminated with an end-member granite rich in silica and total alkalis.
The petrography and rock chemistry indicate that the more alkalic members of the talc-alkalic granites were capable of generating ore-bearing fluids and perhaps ore deposits of large size in the region. However, subsequent erosion likely removed all but some of the deeper, smaller vestiges of such deposits from within the study area. No exploitable deposits were found during the course of this investigation.
