Basha-Diamer Dam with a rated hydroelectric potential of 4500 MW and storage capacity of about six million acre feet of water has been proposed to be built at the River Indus. A site about 42 km downstream of Chilas town near Basha has been proposed for the dam. Huge quantities of coarse aggregate are available in the area. However, there is no mine-able fine aggregate deposit around the proposed site for the dam. Present studies show that the nearest substantial source of fine aggregate for the Basha Dam is Chilas sand deposit. Chilas sand was deposited on the irregular rock terrace of Chilas norites and contains no interbedded glacial component. These sands are overlain by a thick sequence of well-rounded Indus gravel that in turn, at places, is overlain by glacial till. The beds of this deposit are nearly horizontal or gently dipping towards the Indus river and contain associated oversized material. The coarse aggregate is composed of amphibolite (0.4% to 5.8%), diorite (8.5% to 41.2%), dolerite (0 to 2.1 %), leucocratic fine-grained S-type granite (1.9% to 8.1%), S-type granite mylonite (3.3% to 18.9%), pyroxenite (0-1.17%), greenstone (0 to 3.6%), norite (12.1 % to 19.2%), S-type microgranite (14.7% to 35.6%) and vein quartz (0 to 1.2%). The granite mylonite fraction of coarse aggregate is potentially deleterious with alkali silica reaction potential. The sand component of this deposit is composed of diorite/tonalite/amphibolite (0.5% to 2.5%), dolerite (0.3% to 0.9%), granite/granitoid (5.8% to 36.5%), Jasper* (0.2% to 0.3%), limestone (0 to 0.6%), schist/gneiss (8.6% to 42.7%), quartzite/polygrain quartz (2.7% to 5.2%), biotite/vermiculite (1.0% to 8.0%), epidote (0 to 2.1%), feldspar (3.8% to 8.7%) and garnet (0 to 1.1 %). These sands contain minor reactive rock fragments. However a peculiar problem of Chilas sand is the presence of vermiculite that may expand in the cement concrete. The engineering properties (BS 812, 1965) of Chilas sand are good, and are broadly comparable with Lawrencepur sand. The compressive strength of mortars is within the limits specified by CP-110.