Metalliferous sediments within lava sequences of the Sumail ophiolite (Oman): Mineralogical and geochemical characterization, origin and evolution

Abstract

Lens-shaped siliceous pelagic sediments and metalliferous deposits sampled in the Wadi Salahi block of the Sumail ophiolite are interbedded within the successive lava flows of the extrusive sequence. Petrological, mineralogical and geochemical characteristics of these sediments allow their oceanic environment of deposition and their early diagenetic and later hydrothermal transformations to be defined. The sediments are primary radiolarian oozes deposited in a highly productive and open equatorial pelagic realm. The biogenic components are mixed with hydrothermal metallic compounds similar to those found in the axial zone of modern active ridges. The deposits are subsequently transformed by various oceanic hydrothermal events which are expressed by specific secondary parageneses. The sedimentary lenses from the lower lava sequence are epidotized, whereas the uppermost lenses from the upper lava unit contain pumpellyite. Some peculiar lenses are not affected by these oceanic metamorphisms; for instance, the deposits closely associated with the Zuhan orebody which are Fe- and silica-rich with scarce sulfates, or the manganiferous sediments located at the top of the lower lava sequences which were earlier lithified by the deposition of the overlying lava flows. Nowhere in the whole sedimentary section described were detrital or volcaniclastic remains found, disproving the possibility that these sediments may have been deposited in a seamount or island-arc environment.