Atypical, High-Fe2O3, Alpine-Type Chromite Mineralization at Guneyocak, Sivas Province, East-Central Turkey

Abstract

The Güneyocak chromite mineralization is hosted by the Upper Cretaceous Divrigi ophiolitic melange, which consists of serpentinite, serpentinized harzburgite and dunite, gabbro, diabase dikes, pyroxenite, blocks of limestone, and radiolarite. Serpentinites were intensely listwaenitized near the mineralization and in other locations in the study area. The Guneyocak chromite mineralization is of interest because of its internal structure and abundant, repeated chromitite bands, as well as for its chemistry. These features are unusual for ophiolite-hosted chromite. Major-element chemistry shows that the chromites have very high Fe2O3 and MgO and very low FeO. The Guneyocak chromites are classified as of Alpine type on the basis of host-rock lithology and Cr2O3, Al2O3, FeO(T), and Cr/Fe values. However, the very high Fe2O3 and MgO and very low FeO compositions of the chromites do not correspond to those of an Alpine-type chromite deposit. Repeated chromite banding and high Fe2O3 content of the chromite strongly suggest repeated oxygen fugacityf(O2) fluctuations and that the Guneyocak mineralization formed at relatively shallow depths. The Güneyocak chromite is characterized by a slightly boninitic character, which represents high partial melting under conditions of high oxygen fugacity. We conclude that the Guneyocak chromite mineralization formed in the uppermost part of the ultramafic rock series of the Divrigi ophiolitic melange.