Mineralogy geochemistry and evolution of the Miv

Authors: Saeed Alirezaei Morteza Einali Peter Jones Shohreh Hassanpour Reza Arjmandzadeh

Publish Date: 2015/06/09

Volume: 105, Issue: 3, Pages: 849-868

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Abstract

An Upper Miocene 912 ± 019 Ma biotite 40Ar/39Ar shallow pluton and numerous dykes and sills of felsic–intermediate compositions intruded the Upper Cretaceous flyschtype sediments in the Mivehrood area northwest Iran The intrusions caused extensive thermal metamorphism and metasomatism leading to the formation of hornfels and skarn A massive skarn 1–10 m thick immediate to the intrusive contact is bordered by a banded skarn 100–400 m thick that grades outward into hornfels and original sediments The Mivehrood pluton is characterized by steep REE pattern high Al2O3 1464–164 wt and Sr 380–786 ppm and low MgO 13–34 wt Y 48–107 ppm and Yb 035–095 ppm characteristics typical of highsilica adakites Skarn formation started with thermal metamorphism followed by anhydrous prograde and hydrous retrograde stages Prograde and retrograde mineral assemblages are developed in both skarns represented by garnet–clinopyroxene–wollastonite and epidote–actinolite–scapolite–chlorite respectively Granditic Fbearing garnet dominates clinopyroxene in both skarns The banded skarn contains minor scapolite of marialite composition The calcsilicate mineral assemblages and the mineral chemistry allow the Mivehrood skarn to be classified as a calcic oxidized skarn Mass balance assessments suggest that Fe Si and S were significantly enriched and Na LILEs and LREEs were strongly depleted in the massive skarn In the banded skarn Na K Si and S were enriched Significant dehydration and carbon degassing occurred in both skarns Stockworks veins and replacement bodies of pyrite ± chalcopyrite locally occur in the pluton and the dykes and in the skarns The δ34SCDT values for the sulfides fall in a narrow range around 00 ‰ suggesting a magmatic source for sulfur and possibly the hydrothermal water and solutes involved in the skarn formationThe research was financially supported by East Azarbaijan Bureau of Mines EABM We would like to express our sincere thanks to H Farahmand the director and S Gholami the chief geologist at EABM We greatly appreciate M Zarghami a former geologist at EABM for proposing the subject and for his support throughout the studies

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