Chromitite and platinum group elements in the Iraqi Zagros suture zone, ne Kurdistan region, Iraq : an overview

Abstract EN

The podiform chromitite ore-fields of the Iraqi Kurdistan Region have been investigated by various authors in Mawat, Penjween, Qalander and Rayat localities; all of which are situated in the Iraqi Zagros Suture Zone (NE of Kurdistan Region).

They are found in a serpentinized dunite halo hosted within peridotite units that represent the remains of the obducted ophiolite complexes of Iraq.

Their original sites of crystallization imply ocean spreading and plate convergence, followed by subsequent re-emplacement by thrusting.

Tectonically, the chromitite of Mawat and Penjween ophiolite complexes as well as those of N-Shitna area are considered as supra-subduction type, whereas the chromitites at N-Qalander and Rayat can be interpreted as the products of MORB-like melts.

Chromite forms small lensoidal ore bodies in the northeastern part of the ophiolite sequences, surrounded by dunite envelops of variable thickness and dimensions and show transitional boundaries to harzburgite.

The chromite occurrences in the Iraqi Zagros Suture Zone resemble the world Cretaceous and Tertiary ophiolite ores with respect to their peridotite host rocks, geochemical characters and podiform shape.

The composition of ore-forming chromites in depleted mantle rocks of Kurdistan Region are rather uniform, showing high Cr-number [Cr/ (Cr+Al)]; mostly (0.7 – 0.8), while the values of Mg-number [Mg/ (Mg+Fe2+)] are more variable (0.44 – 0.73).

Two textural types of inclusions are distinguished in the chromite: 1) Silicate minerals (mainly serpentine chlorite, amphibole, olivine and clinopyroxene) and 2) Platinum group minerals (mainly laurite RuS2).

The perfect euhedral shape and sharp boundaries of the laurite crystals suggest early precipitation from a primitive magma, free growth at high temperature and later entrapment, as laurite inclusions, in the chromian-spinel.

The presence of Os-rich inclusion in the chromites of Qalander and Mawat ophiolite complexes suggests that sulfide-undersaturated parent magma was involved in the formation of the chromitites