Copper endowment of the magmatic rocks from Eastern Sakarya Zone (Türkiye): insights from zircon and apatite geochemical evolution

Abstract

Recent investigations into the factors controlling the formation of Cu (± Mo) porphyry deposits—through the integration of bulk-rock geochemical and isotopic data with the composition of accessory minerals such as zircon and apatite—are yielding valuable new insights into the magmatic processes that govern ore fertility. This research focuses on an Eocene post-collisional porphyry system and its Late Cretaceous host rocks within the Central Tethyan belt in the Eastern Sakarya Zone (Türkiye) to understand magmatic evolution and to identify geochemical markers in bulk rocks, zircon, and apatite that can effectively distinguish ore-forming magmatism from barren (Late Cretaceous) magmatism in the same zone. Combined bulk-rock major/trace elements and Sr–Nd-Pb-Hf isotopic data, along with in-situ Hf- and Nd-isotope analyses of zircon and apatite, suggest that the Eocene dacite porphyries were derived from an enriched sub-continental lithospheric mantle (SCLM). The compositions of zircon and apatite support the reliability of established fertility indicators for distinguishing between fertile and barren porphyry systems. Our results demonstrate that mineralization-related porphyries contain zircons with higher Eu/Eu* and Ce/√(U × Ti) ratios and show trends of decreasing Dy_(n)/Yb_(n) and Eu/Eu* (with Yb), which point to deep crustal amphibole fractionation. Apatite from the mineralized dacite porphyries is characterized by higher Eu/Eu*, Sr/Y, and V/Y ratios, along with elevated εNd(t) values, compared to apatite from the Late Cretaceous magmatic rocks. These geochemical and isotopic signatures suggest that the mineralized dacite porphyries were derived from an oxidized and hydrous magma source generated within an enriched lithospheric mantle domain, reflecting a more fertile arc-related magmatic environment than the evolved and less fertile sources of the Late Cretaceous magmatism.