Pb-Zn deposits and salt-bearing diapirs in Southern Europe and North Africa

Abstract

Many diapirs with Triassic evaporite successions in southern Europe and North Africa are accompanied by strata-bound Pb-Zn mineral deposits. These are of two types: (1) epigenetic mineralization filling cavities, exhibiting analogies with Mississippi Valley-type deposits; and (2) syndiagenetic mineralization in sediments rich in organic materials. This second type is very similar to the so-called (volcanic) exhalative type. In most of these ore deposits, diapirism seems to be a determining factor in the development of base metal concentrations. Diapir growth can be divided into four distinct stages: initiation, ascent, piercement, and subsequent deformation. Study of North African and southern European deposits has led to a genetic model of diapir emplacement and associated Pb-Zn mineralization. The source of these metals is unknown. The transport of the metals is provided or facilitated by the brine from adjacent Triassic evaporites. Deposition of sulfides occurs where the deep fluids meet the upper beds. These deposits can be remobilized with each new phase of diapir growth.