Magmatic Hydrothermal Systems: Porphyry and Skarn Deposits of Turkey
Muğla Sıtkı Koçman University, Department of Geological Engineering, TR-48000, Muğla Turkey
The geological endowment of Turkey has largely been gained by interplay between the NeoTethys ocean and Afro-Arabian passive margin and Eurasian active margin since the Permian. Starting from Early Cretaceous, the opening, final closure, and terminal suturing of the Tethys oceanic realms, resulted in subductional and postcollisional events, collision of continental fragments and voluminuous magmatism. These events generated voluminous calc-alkaline and alkaline magmatism, which reflects a transition from arc to postcollisional settings and the effects of collision and onset of crustal thickening and subsequent extension between ca. 110 and 9 Ma. Collectively, the magmatism created a fertile metallogenic environment with abundant porphyry Cu, orthomagmatic, volcanogenic massive sulfide, skarn, epithermal, and iron oxide Cu-Au deposits, clustering in narrow arc segments, and post- to late-orogenic transtensional and transpressional settings. Both alkalic and calc-alkalic porphyries are present. The alkalic porphyry deposits (Kisladag and AS) are more like Au to some extent Au-Cu type, and refer to the youngest phase of the mineralization and economically more significant compared to calc-alkalic counterparts. In many deposits, copper is associated with gold, including those at the southeastern Anatolian orogenic belt (SEAOB). The Cu-only or Au-only deposits/prospects are numerous in the western Anatolian province (WAP) while Mo-only and Mo-Cu prospects are widespread in the Pontides and central Anatolian crystalline complex (CACC). Of these, Cu and Au are being mined in WAP and SEAOB. Subvolcanic environments with preserved extrusive rocks are the preferred setting for porphyry Cu-Au and Au systems in the WAEP while plutonic and volcano-plutonic environments are more common in Pontides and CACC. The porphyry systems are clustered mainly along arc-parallel faults, crustal-scale transverse faults, and normal and detachment faults. Based on geologic, geochemical, and 40Ar/39Ar geochronological data, four metallogenic episodes have been identified within these continental fragments. The magmatic rocks hosting these systems are characterized by a gradual increase in La/Yb ratios, and southward shifts of the magmatic locus with time, particularly in western Anatolia. The skarns and skarn deposits, an important class of mineral deposits in Turkey, were formed between Late Cretaceous and Oligo-Miocene period. These deposits are the prime sources of iron, tungsten, lead and zinc commodities of Turkey. The skarns in Turkey are generally classified as calcic exoskarns and occasionally as magnesian exoskarns. The economic mineralization are largely confined to calcic exoskarns with exception of some Fe-skarns hosted by endoskarns. The vast majority of Fe-, and Fe-W skarns are associated with endoskarn assemblages whereas some Fe-, and Pb-Zn-skarns are associated both with calcic and magnesian exoskarns. The skarns that coexist as proximal calc-silicate assemlages within major high-level porphyry Cu systems are largely controlled by regional, large-scale structures such as strike-slip faults or core-complex systems.