Genesis of Chromitite in Qalander Area, Northern Iraq

Abstract

The study area is an isolated ultramafic complex composite of harzburgite-dunite-chromitite association in Qalander area, abut 10 km east of Mergesur, Erbil City, northern Iraq. The chromite-bearing rocks are located within lower part of Walash Volcanic Series of Paleocene-Eocene age. They form concordant, podiform bodies with cataclastic and pull-apart texture that occur in two localities (A and B). Electron microprobe and X-ray diffraction analysis indicate that the studied chromites are of alpine-type, Cr-rich in location A and Al-rich in locality B. The disseminated chromites in harzburgite have Cr# of 0.35-0.87 ; and 0.42-0.56 in localities A&B respectively and Cr# rang between 0.38-0.48 in the dunite associates of localities B. The disseminated chromites of both localities are richer in Fe and TiO2 than the associated massive chromite. Olivine and pyroxene are primary inclusions in chromitite, while serpentine, chlorite and calcite represent the secondary inclusions as alteration products of the primary inclusions. The distinctive Cr# displayed by chromitite of two localities (A&B) are attributed to harzburgite from two different tectonic setting. Chromitites, however are formed by wall rock-melt interaction involving refractory harzburgite from different tectonic environment leading to two chemically distinct Cr-rich chromite domains. High Cr# of chromite of locality A, suggest supra-subduction zone environment, indicates genetic linkage with some bonitite, or high-Mg arc tholeiities which are available in supra-subduction zone; lower Cr# in location B suggest mid-oceanic ridge setting.