Geology, mineralization, geochemistry and petrology of intrusions of the Roud Gaz prospect area, southeast of Gonabad

The Roud Gaz area is located 25 km southeast of Gonabad city، Khorasan Razavi province. During Middle Jurassic، shale and sandstone was regionally metamorphosed to slate، schist and quartzite. The Tertiary subvolcanic rocks are mainly monzodiorite to monzonite. These rocks are mostly altered to: argillic، carbonisation، sericitic and silicification- tourmalinisation. Mineralization in the area is mostly as vein type and controlled by fault zones which are trending NW-SE and 85º to 90º dip. The primary minerals are quartz، tourmaline، chalcopyrite، pyrite and the secondary minerals are malachite، azurite and goethite. Lithogeochemical exploration (chip composite method) revealed Cu، Sn، Pb، As (up to 10000 ppm)، Zn (up to 5527 ppm) and Au (up to 325 ppb) anomalies. The least altered rocks are chemically meta-aluminous and medium-potassium. They were formed in a subduction magmatic arc and are strongly enriched in LREE and depleted in HREE and also LILE (K، Rb، Ba، Sr and Th) enriched rather than HFSE (Ti، Nb and Ta)، all features indicate that the magma formed in subduction zone. The positive Eu anomaly، high Sr (411 to 684 ppm) and high (La/Yb) N ratio (more than 21. 55) in all the samples can be attributed to the presence of residual garnet in mantle source. Based on high Sr/Y ratio (more than 67)، Y<8 ppm، Yb<0. 61 ppm and high (La/Yb) N ratio، the parent magma is adakitic type. The magma formed as the result of medium degree of partial melting (25%) from a garnet-amphibolite source. Apparently، these rocks have been only the veins host and have no effect on mineralization. The mineralization of the area is polymetal vein type and related to reduced intrusions in deeper zone.