Geological constraints on magmatic evolution in subduction zones and cumulative factors effective on the fertility of Cenozoic host porphyritic rocks associated with major porphyry copper deposits in the Lut Block and Kerman porphyry copper belt, Iran

Abstract

Iranian porphyry copper deposits (PCDs), resulted from the evolution of Neo–Tethys Ocean during the Mesozoic and Cenozoic, dominantly distributed in the five main tectono-magmatic belts that meanwhile the Kerman Porphyry Copper Belt (KPCB) is the most famous and important belt in the south of Iran while the Lut Block is the oldest and modern known porphyry belt in eastern Iran. PCDs of the KPCB (+Najmabad; group 1) hosting moderate to giant world-class deposits belong to the Oligocene–Miocene. On the other hand, PCDs of the Lut Block (except Najmabad; group 2) formed during the Eocene–Oligocene, are mostly subeconomic to barren. Despite the similarities in tectonic setting, host rock composition, hydrothermal alteration zones, and mineralization type, there are significant differences in geochemical characteristics (depression in MREE/HREE pattern (group 1) vs. horizontal trend (group 2), Sm/Yb greater than 2.4 (group 1) vs. < 3 (group 2)), melting conditions (Eu/Eu* = 0.8–1.2 (group 1) vs. 0.49–0.96 (group 2), La/Yb greater than 20.1 (group 1) vs. < 21 (group 2) and Sr/Y greater than 40.8 (group 1) vs. < 58.1 (group 2)), source composition (Sr/Y, Dy/Yb greater than 1.5 (group 1) vs. < 1.8 (group 2) and La/Yb ratios)), and magma generation depth (Dy/Yb and La/Yb ratios). The review of different geochemical processes shows that alongside the agents such as dehydration, magma generation depth, source composition, Eu anomaly, and oxygen fugacity, the metal source is the most prominent factor in the formation of porphyry type mineralization.