Geological, mineralogical, and geochemical characteristics of the sedimentary sequence hosting the Khourmo stratabound copper deposit in Central Iran: Implications for its nature and tectonic setting

Abstract

The Khourmo Cu deposit is located in the northeastern part of the Ravar Copper Belt (RCB), near the southwestern edge of the Tabas Block, situated within East-Central Iran. Copper exploration activities in this region have focused on three mining blocks: A, B, and C. The Khourmo deposit is primarily hosted by the Garedu Red Bed Formation (Fm.), which spans from the Late Jurassic to the Early Cretaceous and is composed of alternating layers of sandstone, micro-conglomerate, and siltstone. The sandstone units are subdivided into oxidized, mineralized, reduced, and bleached zones. The copper mineralization is mainly confined to the reduced gray sandstone layers, especially within ancient fluvial paleochannels, and is represented by a range of sulfide and secondary minerals, including chalcopyrite, bornite, digenite, chalcocite, covellite, pyrite, as well as supergene minerals such as malachite, chrysocolla, and various iron oxides. Geochemical analysis indicates that the sandstone Formations hosting the Khourmo Cu deposit derived from igneous parent rocks of intermediate to felsic composition on an active continental margin. Evidence such as the presence of permeable host rocks, the formation of bleached, oxidized, and reduced mineralized zones, the Cu mineralization within paleochannels, the association of copper with plant fossils, and the occurrence of salt domes beneath the Garedu Red Bed Fm. suggest that the Khourmo deposit represents a stratabound, sediment-hosted Cu mineralization. This type of mineralization likely developed immediately after primary diagenesis of the host rock and before deep burial.