Petrology, geochemistry and mineralization of Tertiary volcanic rocks associated with subvolcanic intrusive bodies, with special reference to age dating and origin of granites from Arghash ? Ghasem-Abad area, NE Iran

Arghash ? Ghasem-Abad area in NE Iran is located in the rim of the Sabzevar structural zone. Tertiary outcrops include granite and quartz monzodiorite porphyry associated with dacite and andesite volcanic rocks. In the study area, quartz gabbro and quartz monzodiorite dykes intruded the older rocks. Granite and volcanic rocks host Au-Sb-bearing quartz-calcite veins. Mineralized veins are mainly located around the dykes in the southern part of the area. According to geochemical studies, granites have high-K calc-alkaline affinity with transitional I/A-type features. The volcanic rocks with adakitic composition contain high abundances of Sr and Ba. The dykes in the area show characteristics of lamprophyric rocks. U-Pb zircon dating of granite yielded an age of 55.4±2.2 Ma (Lower Eocene). Initial 87Sr/86Sr and εNd values for the granites are 0.704142 and +5.84, respectively. Initial 87Sr/86Sr ratios strongly suggest a depleted mantle source for the magma. This dating demonstrates that the Au-Sb mineralization occurred later than Lower Eocene. Based on field observation, the mineralization is more related to the lamprophyric dykes than to the adakitic rocks.