Abstract:

The production of Cu-Zn from volcanogenic massive sulfide (VMS) deposits in the eastern Pontides began in the early 1900s, with the exploitation of high-grade ores scattered across the district. The district still possesses economically important blind VMS and associated sulfide deposits. Careful descriptive documentation of the typical features of these VMS ores illustrated the geological characteristics that are important in identifying ore localities and can be used to define exploration targets. The eastern Pontide VMS deposits are examples of volcanic-hosted massive sulfide deposits that exhibit many of the characteristics typical of bimodal-felsic-type VMS mineralization. Nearly all known VMS deposits in the region are hosted by the Kızılkaya Formation, which is characterized by Late Cretaceous dacitic/rhyolitic volcanic rocks that are typically located at the top contact of the dacitic/rhyolitic pile or within the lower part of the overlying polymodal sequence containing various proportions of volcanic and sedimentary facies. Most VMS deposits are composed of a mound of high-grade massive sulfides formed above a zone of lower-grade stringer veins and disseminated mineralization. The dominant sulfide minerals in most deposits are pyrite, chalcopyrite, and sphalerite. Au also occurs in some deposits. The hydrothermal ore facies are diagnostic of subaqueous emplacement of the Pontide massive sulfide deposits that were deposited on the Cretaceous ocean floor. The immediate host lithologies associated with VMS mineralization have typically experienced intense and widespread alteration. The trace element geochemical signatures of the host rocks indicated that the Pontide VMS deposits likely formed in an extensional tectonic regime during subduction. Major lineaments and circular structures exerted fundamental controls on the locations of the VMS deposits in the eastern Pontide district. Age determinations indicated that almost all of the deposits in this region formed in a restricted time interval between ca. 91.1 and 82 Ma. The sulfur isotope compositions of the ore-forming fluids were consistent with those of fluids derived from modified seawater.

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