Introduction
A geophysical investigation was conducted over the northern part of a large gossan near Bi'r Idimah in the Asir quadrangle. The study was made primarily to determine the electromagnetic response of a deposit of massive sulphides found in exploratory drilling. Presumably the geophysical data could be used to trace the deposit and to locate the richest parts of the mineralized zone for additional test drilling. Field measurements were made by the authors during December 1965.
The area is near latitude 18°20'N., longitude 44°20'E, about 20 Km south of Bi'r Idirah (Fig. 1). Most of the area lies in a wadi bounded by low hills that reach elevations near 1250 meters and rise as ranch as 50 meters above the wadi floor. The gossan is exposed in the wadi and near the crests of a few hills in the southern part of the surveyed area. It is underlain by andesite porphyry and greenstone intruded by granitic rocks, and appears to have been displaced laterally by faulting in the central part of the area. An inclined test hole north of the offset cut massive pyrite between depths 98 and 141 feet, 250 and 260 feet, and between depths 299 and 351 feet. This test and the character of the gossan suggest that the mineralized zone continues southward for a considerable distance.
