Mineralogy and geochemistry of metalliferous sedimentary rocks from the Upper Cretaceous VMS deposits of the Eastern Pontides (NE Turkey)

Abstract

Metalliferous sedimentary rocks, despite being limited in scope, are important stratigraphic horizons within the volcanogenic massive sulfide (VMS) deposits in the Upper Cretaceous volcanic belt of the Eastern Pontides. The metalliferous sedimentary rocks compose a distinctive genetic class. The abundance of such rocks in the Eastern Pontide district provides a basis for study and description that may be more widely applied in other VMS districts. The metalliferous sedimentary rocks generally form layers less than 1.5 m thick above stratiform massive sulfide ores. The metalliferous sediments are largely composed of quartz and hematite. While the Si ± Fe content of sediments directly overlying the stratiform massive sulfide ores is high, an increase in the amount of carbonate is observed in sediments that are not directly overlying the ores. The metalliferous sedimentary rocks were formed by the mixing of mainly chemical components and to a smaller degree detrital components in various proportions due to sedimentation processes occurring on the seafloor. Of the major constituents of the metalliferous sediments, Si, Fe, Cu, Zn, Pb, Sb, and Au generally have a hydrothermal origin, whereas Al, Zr, and Ti are from detrital volcanic and volcaniclastic components. The high levels of U and V indicate a seawater origin, pointing to a submarine environment for the formation of the Eastern Pontide metalliferous sedimentary rocks. The composition of the metalliferous sediments of Eastern Pontide VMS deposits implies that these sediments carry a continental-arc provenance signature. Silica (±iron)-rich rocks in the Eastern Pontides can be used as guide horizons in exploring for volcanogenic massive sulfide deposits in the district since they formed close to the sulfide ores and their areal extents are much greater than those of the sulfide ores. In comparison with their analogues on a global scale, these rocks are broadly comparable to silica- and iron-rich sedimentary rocks in the VMS-bearing districts of the Urals.