Mixed type sulfide deposits in Northern Tunisia, regenerated in relation to paleogeography and tectonism

Abstract

Analyses were made of sulfur isotopes and major and minor element (Fe, Pb, Zn, Cu, Hg, Cd, Bi, S, As, Tl, Sb, …) contents of a well characterized suite of minerals from ore deposits wether associated with vulcanism, metamorphism, Cretaceous sedimentary facies or Tertiary detrital-rich and molasse deposits. Paleogeography, tectonism and ore genesis are closely related: periods characterized by intense deformation (Middle and Upper Jurassic, Middle and Upper Cretaceous and Oligocene-Miocene) enable deposition of polymetallic syngenetic/epigenetic sulfide deposits; in contrast, during tectonically less active periods, the ore genesis appear to be clearly restricted. Mineralogy, sulfur isotopes, abundant sulfosalts and minor element abundances (Ag, Hg, Cd, Bi) point to important remobilization and repetitive mineralization stages the latest of which postdated the Alpine orogeny. The origin of Upper Cretaceous mineralizations hosted in local black shales, is thought to be found in metals brought up from deep-seated, eventually endogenic hydrothermal fluids. These deposits may later act as a transition base metal source for Tertiary deposits, during and after the Alpine tectogenesis, along with the new-additions of metals from presumably endogenic sources. Even though admixtures of diagenetic connat fluids somehow hampered geochemical information, it is concluded that ore deposits from Northern Tunisia are mixed-type and closely related to paleogeographic environments and tectonical history of the region. The previous prominent role of Triassic salt diapirism as a metallogenic factor is discussed but not confirmed.