A review of principle mineralogical and petrological characteristics in Pahnavar Fe-skarn
The Pahnavar Fe-skarn in Siahrood is a typical magnetite-bearing skarn developed along the contact of Qolan quartz-dioritic intrusive body (Oligocene) with upper Cretaceous carbonates (mainly limestone). Qolan intrusive is genetically I-tye and meta-aluminous in composition. It belongs to high-K calc-alkaline series in character, and tectonically developed in post-collision arcs. Two stages of skarnification is recognizable in Pahnavar, 1) pre-mineralization silicate-skarn (stage-I), 2) magnetite-skarn (stage-II). Hornfelsic skarnoid mineral assemblages (principally garnets with lesser amounts of Fe-bearing diopsides) were developed during the stage-I. Garnets are fine-grained, light brown to green mostly displaying moderate anisotropy. They subsequently were replaced by hydrous calc-silicates (epidote, tremolite-actinolite), chlorite, calcite, and quartz. During stage-II, skarn mineral assemblages including garnet (andradite), diopside, magnetite, and quartz were formed by replacing of some of the stage-I calc-silicates, and by filling the veins, veinlets, and cavities. The stage-II andradites are coarse-grained, reddish brown with strong anisotropy, radial and concentric zoning, and penetration and polysynthetic twins. Magnetite is the principal skarn ore in Pahnavar, and chiefly replaces garnets, though occasionally fills the fractures (veins) and pore spaces in garnets showing bladed texture.