Mineralogical and geochemical characteristics of the Benavi ironstone deposit, northern Iraq

Abstract EN

The Benavi ironstone deposit is a stratiform iron mineralization within the Jurassic – Cretaceous sequence of the Imbricate Zone (N Iraq).

It is composed of several mineral assemblages including iron oxides/ hydroxides (hematite, goethite, limonite and magnetite), sulfides (pyrite and arsenopyrite), carbonates (calcite, siderite and ankerite), silicates (kaolinite, chamosite, and glauconite), quartz and apatite.

The main iron minerals are hematite and goethite.

Goethite formed as a result of oxidation processes of pyrite, siderite and chamosite under surface weathering.

Calcite is the main non-iron mineral in the Benavi ironstones, mostly containing Mg+2 and Fe+2, while siderite and ankerite are minor.

Kaolinite and chamosite are the main clay minerals in the ironstone whereas glauconite is trace.

Arsenopyrite is found restricted at the base of the Benavi ironstone outcrop, having dark grey color in the field, associated with chamosite, pyrite, apatite and glauconite.

Chemical analyses showed that Fe2O3 ranges between 3.28 – 33.9 wt.% with an average of 20.44 wt.%, which is considered as a low-grade ironstone deposit.

Replacement of calcareous components by iron minerals is indicated by the very strong negative correlation between CaO and Fe2O3, suggesting epigenetic ore formation by the diagenetic replacements of carbonate rocks.

The significant role of diagenetic processes is supported by the negative correlation of CaO with SiO2, Al2O3, P2O5, Co, Ni and Zn