U-Pb geochronology and petrogenesis of intrusive rocks: Constraints on the mode of genesis and timing of Cu mineralization in SWSK area, Lut Block

The South-West Sorkh-Kuh (SWSK) area, part of the Tertiary volcanic-plutonic rocks in the Lut Block, eastern Iran, comprises volcanic rocks intruded by intrusive rocks of hornblende diorite and biotite quartz monzonite compositions. Biotite quartz monzonite has been intensively affected by quartz-sericite-pyrite, argillic and silicification alterations and hornblende diorite shows weak propylitic and carbonate alterations. Disseminated, stockwork and vein-type styles of mineralization are associated with intrusive rocks. The vein-type mineralization with NW-SE trend is hosted by hornblende diorite. The ore in vein-type mineralization consist of quartz, chalcopyrite, pyrite, and secondary Cu-Fe minerals. Disseminated and stockwork mineralizations consist of quartz, pyrite, chalcopyrite, and secondary minerals replacing biotite quartz monzonite and hornblende diorite intrusive rocks. The highest grades in terms of Cu (3%), As (1.3%), Mo (150 ppm), Pb (362 ppm), Zn (743 ppm), and Au (278 ppb) are associated with vein-type mineralization. Intrusive rocks causing mineralization, are of metaluminous to peraluminous types with calc-alkaline to high-K calc-alkaline affinity formed in a volcanic arc setting. The enrichment of LILE (Ba, K, Cs, Sr), depletion of HFSE (Nb, P, Ti) and enrichment of LREE relative to HREE indicate the formation of source magmas above a subduction zone. The results of zircon U–Pb dating give constraints on the timing of emplacement of biotite quartz monzonite and hornblende diorite bodies at 40.16 ± 0.72 and 20.1 ± 2.1 Ma, respectively. The younger date extends the time span of mineralizations in the Lut Block from Middle Eocene to Early Oligocene (42–33 Ma.) reported by previous researchers to more recent Early Miocene times. The initial 87Sr/86Sr ratios and εNd values of both biotite quartz monzonite and hornblende diorite reside in the restricted ranges of 0.7055–0.7066 and−0.33 to +1.88, respectively, consistent with an origin above a subduction zone followed by crustal contaminations of the initial magma compositions, especially with regard to biotite quartz monzonite. The zircon U-Pb ages as well as geochemical and radiogenic isotope data for the intrusive bodies associated with mineralization in this study are in accordance with previous studies on intrusive bodies related to porphyry copper deposits in the Lut Block. In contrast to previous studies, this study further extends the span of mineralization events to at least Early Miocene times