Geology, structure, texture, fluid inclusion and formation model of Michigan type copper mineralization in the Sebandoon deposit, Northeast of Iran

The Sebandoon copper deposit is located in the northern part of the Sabzevar subzone. The rock units exposed in the area consist of upper Cretaceous volcano-sedimentary sequences of trachyte, trachyandesite, basalt, split, shale, dacite and sandstone. The Sebandoon native copper deposit comprises stratabound mineralization which is hosted in split basalt. The main ore structures and textures in the deposit include disseminate, veinlets, open space filling and replacement forms. The ore mineral assemblages are simple and consist of native copper, coprite and malachite and main gang minerals are zeolite, calcite, quartz, chlorite and epidote. Fluid inclusion studies on ore-bearing zeolite reveal that majority of primary inclusions are liquid-rich two-phase (LV) ones. The studies indicate homogenization temperatures were between 228 and 340°C and salinity varied between 0.6 to 5.7 wt% NaCl eq. Based on the evidence from geology, mineralogy, alteration, fluid inclusion, and geodynamic environment, the Sebandoon copper deposit is similar to Michigan copper type deposits, in which copper was leached from the basaltic rocks during burial metamorphism and the ore-forming fluids moved upwards and subsequently deposited as native copper due to low pressure and mixing with meteoric fluids.