Mineralization characteristics of Lead-Zinc-Copper deposits in Akdağmadeni Region (Northern Central Anatolia, Türkiye): Integration of field study, geochemical, isotope, and geophysical data

Abstract

The Akdağmadeni region is one of the important Pb-Zn-Cu metallogenic provinces in Türkiye. Most of the Pb-Zn-Cu deposits in the region are located near granitoid intrusions within metamorphic rocks, and they are typically classified as skarn-type ores associated with granitoids. However, no relationship has been determined between the Başçatak prospect and any granitoid outcrop. This raises the question of whether the Pb-Zn-Cu mineralization in the region is related to granitoids or if magmatic processes remobilized pre-existing mineralization. Observations from field studies suggest that mineralization in the Başçatak prospect is a stratiform type, metamorphosed occurrence that might have occurred earlier than the granitic intrusions. The geochemical data indicated that the granitoids have low-grade, subeconomic Cu potential and no Zn productivity potential, supporting these observations. Geophysical data also show that there is no intrusive body beneath this prospect. Granitoid-related deposits (Karapir - Ortaköy and Akçakışla) exhibit two distinct occurrences around the contact between the granite and the surrounding metamorphic rocks. The first type of occurrence (O-1) is formed at the contact and contains magnetite, pyrrhotite, and chalcopyrite. The second type of occurrence (O-2) is located outside the contact and is rich in sphalerite and galena. Both O-1 and O-2 contain skarn minerals along with ore minerals. The δ34S values of sulfide minerals from the deposits range from −0,7 to 7,5 ‰ (V-CDT). These values overlap with those of both magmatic sulfur and reduced sulfur from seawater-dissolved sulfate, making it difficult to suggest a sulfur source without additional data. Lead isotope compositions of the galenas from all deposits plot above the average crustal growth curve, suggesting an upper crustal and orogenic source similar to Western Mediterranean and Türkiye type materials described in the literature for the lead, source in different time intervals. Furthermore, Pb isotope geochemistry suggests a contemporaneous age with the host metamorphic rocks (Carboniferous – Lower Permian) for the Başçatak prospect. These results support observations indicating a syn-genetic formation for the Başçatak prospect. The age range of granite-related deposits forms two sub-groups:105–77 Ma and 61–50 Ma corresponding to the Upper Cretaceous and Paleocene transition. These data indicate that that the galenas were formed in two different stages in these mineralizations. Stratiform mineralization in the Başçatak prospect likely formed either through exhalative sedimentary processes by hydrothermal fluids or through chemical sedimentary processes under reductive conditions in a marine environment during metamorphism. O-1 appears to have been formed by hydrothermal fluids developed during granitic magmatism. A plausible formation process for O-2 involves the leaching of sulfur, lead and other metals from Başçatak type enrichments in metamorphics, with transportation and deposition within the epidotized calc-schist and marbles outside the granitoid contacts. The uplift of granitic intrusions prepared the channels and depositional environment for O-2 and caused heating of the hydrothermal fluids during this mineralization period.