Origin of Fe Ti mineralization in the Late Jurassic to Early Cretaceous Kahnouj ophiolitic complex, Makran accretionary prism, SE Iran

Abstract

The Kahnouj ophiolitic complex is part of the large Makran accretionary prism, SE Iran, and from the base to top consists of ultramafic-mafic rocks (Band-e-Zeyarat complex), diabase sheeted dikes, and volcanic rocks (Dar Anar complex). The Late Jurassic to Early Cretaceous (156 to 121 Ma) Kahnouj crustal section consists of layered gabbros with ultramafic sill-like bodies at the base that grade upward into variable isotropic gabbros. The Fe Ti ore mineralization of the Dar Gaz district is hosted within the central part of the Kahnouj complex, consisting of coarse-grained gabbro (152.7 ± 5.1 Ma), fine-grained pyroxene-hornblende gabbro, hornblende gabbro (126.5 ± 1.6 Ma), diabase dikes (122.1 ± 2.4 Ma), and granitoid rocks associated with minor feldspathic wehrlite. Economic oxide mineralization (up to 25% FeO + TiO 2 ) is mainly composed of: (1) Intergrown titanomagnetite (containing up to 19 wt% TiO 2 and 0.26 to 1.74 wt% V 2 O 3 ) and ilmenite with hercynite and chromian spinel exsolutions at their boundaries; (2) ilmenite lamella (containing up to 52 wt% TiO 2 and 1 to 3 wt% V 2 O 3 ) in titanomagnetite; and (3) discrete oxide minerals and minor sulfides displaying interstitial textures with formed by fractional crystallization and gravitational settling. Microtextures in the coarse-grained gabbro imply that water-rich fluids migrated along grain boundaries in a ductile regime, causing partial melting and growth of secondary hornblende, An-rich plagioclase, oxide mineral refertilization, and spinel group minerals developed at the boundaries between ilmenite and titanomagnetite. • Kahnouj ophiolitic complex (KOC) formed in the Late Jurassic to Early Cretaceous in a back-arc basin. • The Dar Gaz Fe Ti mineralization is hosted within the central part of KOC in isotropic gabbros. • The Oxide mineralization formed by gravitational settling of intercumulus oxide liquids. • Later partial melting of coarse-grained gabbros generated a melt with more Fe Ti mineralization.