Zircon U-Pb geochronology and petrology of intrusive rocks in the C-North and Baghak districts, Sangan iron mine, NE Iran

摘要

Porphyritic granitoids that host the Sangan iron mine deposit belong to the Khaf-Kashmar-Bardaskan volcanoplutonic belt in northeastern Iran. These intrusive rocks, mostly quartz monzonite to syenogra-nite porphyries, have been divided into three groups on the basis of crosscutting relationships and zircon U-Pb dating: (1) group 1, 42.3 ± 0.8 Ma, (2) group 2, 40.0 ± 0.5 Ma, and (3) group 3, 39.2±0.6 Ma. The group 1 and 2 rocks host magnetite mineralization, whereas the group 3 intrusions are interpreted as syn-mineralization. They have features typical of high-K alkali-calcic to calc-alkalic magnesian rocks and are metaluminous to weakly peraluminous formed in a volcanic arc setting. Mantle-normalized, trace-element spider diagrams display enrichment in large ion lithophile elements, such as Rb, Ba, K, and Cs, and depletion in high field strength elements, e.g., Nb, Ti, Ta, Zr, Y, and heavy rare earth elements, with moderate to strong light rare earth elements enrichment ((La/Yb)_N = 24.8-7.6) and a negative Eu anomaly. The parental magmas are probably derived from partial melting of mantle that had been metasomatized by a slab-derived fluid. During the upward migration of these melts, additional input of crustal materials could account for the high K characteristic for most of the intrusive rocks around the Sangan mine area. Textural evidence and mineral assemblages indicate the Sangan Fe-skarn is an oxidized magmatic-hydrothermal system caused by the group 3 intrusions.