Five examples of disseminated rare element mineralization with sufficient resource potential to warrant exploration and detailed study occur in association with late Precambrian, posttectonic alkali granites in the northwestern Arabian shield. All are characterized by enrichment in a suite of granitophile elements, which typically includes Nb, Ta, Sn, rare earth elements, Y, Th, U, and Zr, but they differ in size, geometry, mode of occurrence, and lithology.Two types of mineralization can be distinguished. The Jabal Sa'id type, represented by the Jabal Sa'id aplite-pegmatite, the Jabal Hamra' silexite, and minor pegmatites occurring near at least two other alkali granites, is characterized by high total iron to total alkali ratios and high K•O/Na•O ratios. The Ghurayyah type, represented by the essentially microgranitic Ghurayyah, Jabal Tawlah, and Umm al Birak intrusions and minor dikes at a fourth locality, is characterized by major oxide abundances approximating those of typical alkali granites. Both types evolved from alkali granite magmas formed by high-temperature, dry melting of late Proterozoic island-arc crust. They probably represent crystallization under deuteric (Ghurayyah type) and hydrothermal (Jabal Sa'id type) conditions of residual fractions enriched in granitophile elements and volatiles. Rare earth element distribution patterns probably reflect the composition of the volatile phases.Systematic surface sampling has been undertaken over all five occurrences, and pilot drilling programs have been completed at Ghurayyah, Jabal Tawlah, and Jabal Sa'id. Indicated resources range from 6 million metric tons (Jabal Tawlah and Umm al Birak) through ñ20 million metric tons (Jabal Sa'id and Jabal Hamra') to 440 million metric tons (Ghurayyah). The highest average grades for Nb (3,400 ppm), Sn (380 ppm), Y (5,200 ppm), and Zr (37,000 ppm) occur at Jabal Tawlah; the highest Ta grades (200 ppm) at Ghurayyah; and the highest U (130 ppm) and Th (830 ppm) grades at Jabal Sa'id. Enhancement in light rare earth elements occurs at Jabal Hamra' (La, 2,600 ppm and Ce, 3,400 ppm) and sporadically at Jabal Sa'id (La, 600 ppm and Ce, 1,300 ppm). Extreme enrichment in heavy rare earth elements and Y occurs at Jabal Tawlah, Ghurayyah, and Jabal Sa'id.Mineralogical studies indicate that Nb may be present in columbite-tantalite or pyrochlore; rare earth elements are concentrated in monazite, bastnaesite, and synchesite-Y; Th is present in thorRe; and zircon is invariably abundant.