Petrology of the intrusive rocks within the Sungun Porphyry Copper Deposit, Azerbaijan, Iran

Abstract

The Sungun intrusive complex hosting the Sungun porphyry copper stock is located about 75 km north west of Ahar, in Azarbaijan province, and intruded along the Sungun anticline into Cretaceous limestone and Eocene tuff and agglomerate of andesitic to trachytic composition. Based on the petrography and geochemistry, it is suggested that the Sungun deposit as a composite stock comprising an early monzonite/quartzmonzonite and a later diorite/granodiorite phase. The parental magma was a medium- to high-K andesite or diorite, initially contained 3 wt% H 2O, and was generated in a continental arc setting. The high-level emplacement of this magma, led to its saturation with H 2O and the exsolution of fluids at an early stage of crystallization, and subsequently Mo and then Cu mineralization. Based on the major- and trace-element geochemistry, especially the behaviour of the immobile trace elements (Y, Zr and Nb) fractional crystallization is suggested as the process that produced the present intrusive rocks. The degree of fractionation was estimated using the Rayleigh fractionation equation, relating the concentration of Zr, Nb and Y in the least evolved sample to the concentrations of these elements in progressively more evolved samples. The results of these calculations indicate that the compositions of the various rock types can be explained by up to 24% fractionation of ferromagnesian minerals [e.g. pyroxene and amphibole] of the diorite magma to produce the more evolved monzonite/quartz-monzonite suite.