A zone of crustal weakness associated with the Zuni Lineament in the southern half of New Mexico has been delineated by lead isotope measurements, a microearthquake study and magnetic depth soundings. The lead results of Slawson and Austin (1962) revealed the possible existence of a northwest trending zone of isotopically similar lead, bounded on either side by isotopically variable leads. This feature passes through Socorro and Alamogordo, New Mexico, and is coincident in this area with the Zuni Lineament. The microearthquake results (Sanford and Long, 1965) show that a shallow crustal zone of weakness is associated with the isotopically similar zone. The magnetic results (Schmucker, 1964; Livingstone, 1966) confirm that the structure is shallow, and also indicate that it may be a region of high electrical conductivity. It is suggested that this zone of weakness centred on the Zuni Lineament has served as a conduit system for hydro-thermal mineralizing solutions which carried the lead to its final sites of deposition. The lead was originally introduced into the Precambrian rocks about 1550 m.y. ago, mixed with radiogenic rock lead of that age about 30 m.y. ago, and then, finally emplaced. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate