Geochemistry and tectonic setting of the volcanic host rocks of VMS mineralisation in the Qezil Dash area, NW Iran: implications for prospecting of Cyprus-type VMS deposits in the Khoy ophiolite

摘要

The uppermost part of the Khoy ophiolite includes submarine volcanic lavas. These rocks are found as two different types including basaltic pillow lavas and andesitic to andesitic basalt massive-sheet lavas known as the Qezil Dash unit. These last rocks host volcanogenic massive sulphide mineralisation (VMS). Concordant small lenticular massive sulphides associated with widespread stockworks, extensive wall rock alteration and simple mineralogical parageneses are characteristic of this mineralisation. The Qezil Dash lavas are characterized by HFSE depletion (such as in Nb, Zr, and Hf) and LILE enrichment, low Yb, Y and Ni contents and low Zr/Hf and Nb/Ta ratios. These rocks have low Ti contents and are of LKT type. These geochemical characteristics can be interpreted as indicating SSZ magmatism and suggesting that the Qezil Dash rocks belong to an early stage of island arc formation. Geochemically, this host rock is comparable with the Lasail unit, part of a volcanic sequence within the Oman ophiolite. In the Troodos and Oman ophiolites VMS mineralisation has occurred at the contacts of MOR-basalt and island arc tholeiite (IAT) lavas, so prospecting for VMS deposits in the Khoy area should be established based on geochemical in vestigations of the volcanic rocks and recognition of their field boundaries.