Fe–Cu mineralization of Tangal-e-Sefid; a magnetite rich massive sulfide deposit from Kuh-e-Sarhangi district, Central Iran

The Tangal-e-Sefid Fe–Cu mineralization forms syngenetic stratiform deposit in the Late Neoproterozoic volcano sedimentary sequence from the Central Iran. Early Cambrian metamorphic rocks are associated ore-bearing geologic units. The mineralization includes early oxide phase as a magnetite-rich bodies that are overprinted by a pyrite-chalcopyrite-rich sulfide phase. The most current alteration zone includes propylitic-carbonate, chlorite, sericite and silicic with a well-developed distribution of chloritization, especially in the layered part. Magnetite, pyrite and chalcopyrite comprise the primary main mineral assemblage, which is accompanied by malachite, covellite, hematite and goethite as the secondary minerals associated with epidote, chlorite, quartz and calcite minerals. Magnetite chemistry reveals the hydrothermal evolution of mineralization, and all the examined magnetite fall within fields of magnetite from VMS deposits. Fluid inclusion analysis of quartz and calcite coexisting with magnetite represent homogenization temperature range of 198 °C and 357 °C with a cooling trend from the massive toward the layered parts. The measured fluid salinity identifies two distinct medium-salinity fluids with mean values corresponding to 15 and 22 wt% NaCl. There is no significant difference in terms of temperature and salinity measured in calcite and quartz minerals. However, the average measured temperature values of fluids trapped in calcite (189–336 °C) are slightly lower than quartz (227–357 °C). Since the ore deposit distribution is spatially associated with actinolite schist, thermometric data of actinolite show temperature fluctuations of 310–315 °C and mineral formation pressures of 2.5–3 Kbar, which are correlated with the low-grade metamorphism. Primary hydrothermal fluids derived from submarine magmatism in an extensional system of seafloor were enriched in Fe and Cu (± Zn and possibly Pb) and it is the responsible for the first stage of magnetite formation and following the overprinting pyrite and chalcopyrite mineralization. The ore deposit geometries associated with magnetite mineralization and sulfide replacement styles; reveals that in the second stage of mineralization, hydrothermal fluid is mixed with oceanic water and eventually metal sulfides are deposited. The mineralizaton zone associated with the volcano-sedimentary sequence is affected by low-grade regional metamorphism related to Pan-African orogeny and represent the green schist territory as the VMS deposits related to Archean.