The hydrothermal sphalerite- galena-pyrite deposits on the flanks of the Triassic Fedj el Adoun diapir in the Teboursouk mountains of northern Tunisia, post-Pliocene in age, are controlled structurally by two principal fault directions, one parallel to the diapir contact and the other perpendicular to it. Microscopic evidence indicates very low-temperature conditions of mineralization, with abnormal paragenesis of the three sulfides--first galena, then sphalerite, then marcasite-pyrite. The origin is secondary, resulting from solution and redeposition of material derived from hydrothermal ores in basement rocks, with transportation of the lead and zinc by complex chlorides. The diapirism and mineralization are closely related, having a common cause in an active fault zone. Furthermore, the presence of the diapir has affected the ore deposition in two ways--mechanically, by opening and maintaining channelways, and chemically by maintaining the salinity of the solutions.