Geochemical, fluid inclusion and isotopic (O, H and S) constraints on the origin of Pb-Zn +/- Au vein-type mineralizations in the Eastern Pontides Orogenic Belt (NE Turkey)

Abstract

The mineralization area (Altinpinar, Torul-Gumushane) is situated in the Southern Zone of the Eastern Pontides Orogenic Belt (EPOB), which is one of the important metallogenic provinces in the Alpine-Himalayan belt and is intruded by the late Carboniferous granitic rocks (Gumushane Granitoid), an early to middle Jurassic volcano sedimentary unit consisting mainly of basaltic-andesitic volcanic and pyroclastic rocks (Senkoy Formation) and Eocene basaltic-andesitic volcanic rocks (Alibaba Formation). The studied Pb-Zn +/- Au mineralizations are related to silica veins ranging from a few millimeters to a maximum of 40 cm in thickness and are localized within fracture zones developed along the contact between the Gumushane Granitoid and Senkoy Formation. Silicic, sulfidic, hematitic, argillic, intense chloritic and carbonate alteration are the most common types from the fault lines toward the outer zones. Cavity filling and banded structures are widely observed. The mineral paragenesis comprises galena, sphalerite, pyrite, chalcopyrite, tennantite and quartz. Mineral chemistry studies indicate that ion exchange occurs between Zn and Fe in sphalerites, and the Zn/Cd ratio of sphalerites varies between 50.65 and 144.64. The homogenization temperatures measured from fluid inclusions vary between 170 degrees C and 380 degrees C, especially between 250 degrees C and 300 degrees C, and the wt% NaCl eqv. salinity of ore-forming fluids is between 2.4 and 7.3 (4.7 on average), supporting an epithermal system in their origin. The values of sulfur isotopes, which are obtained from pyrite and galena minerals, range between -83 parts per thousand and -2.3 parts per thousand., indicating that sulfur, which enables mineral formation, originates from magmatic genesis. The average formation temperature of the ore is 317 degrees C as determined with a sulfur isotope geothermometer. The values of oxygen and hydrogen isotopes vary between 8.5 parts per thousand. and 10.2 parts per thousand and -91 parts per thousand and -73 parts per thousand., respectively. With regard to the compositions of oxygen and hydrogen isotopes, fluids comprising the mineralization are formed by the mixture of magmatic water and meteoric water. This situation is supported by the fact that the increase in the homogenization temperature indicates dilution with surface water but depends on the increase in the salinity of fluid inclusions. Considering all the data, it is clear that the studied mineralization is an epithermal vein-type mineralization that is related to granitic magmas. (C) 2015 Elsevier B.V. All rights reserved.