Mineral investigations in the Jabal Radwa quadrangle, northwest Hijaz, Saudi Arabia

Wadi sediments in the Jabal Radwa quadrangle in the Northwest Hijaz were sampled for trace element analysis as part of a mineral reconnaissance of Western Saudi Arabia that is being made by the Ministry of Petroleum and Mineral Resources and the U.S. Geological Survey. The Jabal Radwa quadrangle lies between 24?30? and 25?N. latitude and between 38? and 39? longitude. A photomosaic base at a scale of 1:100,000 was used for map compilation.

Except for basalt flows of Tertiary or Quaternary age all the rocks of the area are believed to be of Precambrian age. An older group of slightly metamorphosed mafic and felsic volcanic rocks with interbedded metasedimentary rocks is unconformably overlain by argillite and slightly metamorphosed sandstone and conglomerate. The bedded rocks are cut by many intrusions that range in composition from olivine gabbro to syenite but are predominantly granite, granodiorite, and diorite.

Little is known of the structure of the rocks. The layered rocks are strongly folded and commonly dip at high angles. Faults are common and many appear to be large; some contacts have been offset several hundred meters. Most of the larger faults trend northeasterly or northwesterly but some trend east and others nearly north.