Geological and geochemical assessments of volcanogenic Cu-Pb-Zn-Sb deposits of Shurab-Qalechay, east Iran
By: Mohammad Lotfi
The investigated area of Shurab- Qalechay with an areal extent of about 185 Km² is situated in the northern part of the Central Lut between 58°-58° 09' 03" E and 33° -33°37' 19" N.
The Shurab- Qalechay area consists of a clac-alkaline dacitic intrusion which is exposed as several subvolcanic stocks. According to geological and Sr-isotope data the emplacement of this intrusion took place between Upper Eocene and Lower Oligocene (41-43.7 Ma). This age coincides with the Pyrenean episode of middle Alpine Orogeny.
The initial values of 87Sr/86Sr and the behaviors of trace elements in the analyzed samples indicate an origin by partial melting of upper mantle nature for the magmas of this subvolcanic intrusion. Some interaction of sialic crust is likely.
Contemporary to the Pyrenean episode the intrusion was affected by pervasive hydrothermal solutions which caused a strong wall-rock alteration and the deposition of Cu, Pb-Zn, Sb sulfide deposits. Due to reactions between these fluids and the dacitic wall-rocks two different subzones of phylic and argillic alterations were developed.
The fluids responsible, for the phyllic alteration compared with those of argillic alteration show remarkable enrichment of K20, SO3, FeO and Rb. Their homogenization temperature (Th=146-340°C) and salinity (0.35-23.12 NaC1%) are rather higher than in the fluids of argillic subzone (Th=145-275°C, salinity=0.6-16.56 NaCl%). These potassic fluids gave rise to the disseminated type mineralization.
Vein type mineralizations in the argillic subzone were caused by fluids which invaded the fractures. Due to gradients within the Ore-forming fluids (temperature, Pressure) the Ore-Parageneses exhibit a zonality and some overlap.