Geochemistry and geochronology of thevolcano-plutonic rocks associated with the Glojehepithermal gold mineralization, NW Iran

Abstract

Eocene to Oligocene volcano-plutonic rocks arewidespread throughout NW Iran. The Tarom-Hashtjinmetallogenic province is one of the most promisingepithermal-porphyry ore mineralized districts in NW Iran.The Glojeh gold deposit, located in the center of thisprovince, is a typical high to intermediate sulfidation epithermalsystem, spatially and temporally associated witha granite intrusion and associated high-K calc-alkalineto shoshonitic volcano-plutonic rocks. The intrusive complexesof the Glojeh district are characterized by: SiO2contents of 60.9 to 70.7 wt.%, K2O+Na2O of 7.60 to 8.92wt.%, and K2O/Na2O ratios of 0.9 to 1.8. They are enrichedin light rare earth elements (LREEs), and large ionlithophile elements (LILEs), depleted in high field strengthelements (HFSEs), and have weak negative Eu anomalies(Eu/Eu*= 0.5 to 0.9). 40Ar/39Ar geochronology appliedto biotite and feldspar, separated from two intrusives(Goljin and Varmarziar), and two feldspar aliquotsseparated from hydrothermal veins at North Glojeh andSouth Glojeh, was carried out to constrain magmatic andhydrothermal events. Plagioclase (± sericite), from NorthGlojeh and South Glojeh produced ages (42.20±0.34 Ma,and 42.56±1.47 Ma respectively) that overlap with the ageof the Goljin intrusion (41.87±1.58 Ma).Geochemical data for the volcano-plutonic rocks in theGlojeh district, that have87Sr/86Sr isotopic compositionsthat range from 0.706344 to 0.708331, suggest an origin involvingpartial melting of a depleted mantle source duringNeo-Tethyan subduction.

Keywords

• glojeh gold district
• volcano-plutonic rocks
• tarom-hashtjin metallogenic province
• sr isotope
• partialmelting
• geochronology