Evidence of boiling in ore-forming process based on quartz textures and fluid inclusions studies, a case study in Mamouniyeh Cu deposit, Iran

Boiling is one of the common processes that lead to the formation and enrichment of precious metal deposits. The investigation of the spatial relations between fluid boiling and deposition of precious metals is a valuable tool in exploration of epithermal deposits. Fluid boiling, isothermal mixing and surface dilution of fluids processes are important factors for the instability of chloride and sulphide complexes, which lead to the simultaneous deposition of Fe-Cu and then deposition of sulphide phases in the final stages of mineralization which are caused by a sudden decrease in pressure in the fractures. To investigate evidence of boiling and its role in mineralization we have studied fluid inclusions and quartz textures in the Mamouniyeh Cu deposite in the middle part of Urumieh-Dokhtar magmatic arc in Iran. Evidence for fluid boiling, such as different liquid-vapor ratios of fluid inclusions, the coexistence of fluid inclusions with different salinities and co-existing liquid single-phase fluid inclusions with vapor single-phase fluid inclusions and breccia, crustiform and colloform textures of quartz indicate that boiling process occurred during the formation and growth of minerals. The study of 138 fluid inclusions in ore-bearing silica veins shows the similar density values from 0.8 to 1 g/cm³ for quartz with pyrite + chalcopyrite, chalcopyrite and chalcopyrite + specularite ± pyrite ± chalcocite mineralization systems. Adjacency of multiphase fluids with vapor-rich fluid inclusions indicates that fluids are trapped at the boiling point, that is, in the state where the vapor is in equilibrium with the liquid. As a result of this boiling part of the Cu in the fluids was deposited as chalcopyrite. Evidence shows this process probably occurred at a depth of about 700 meters below the water table and lithostatic pressure of about 16 MPa. In the case study area, boiling, mixing of magmatic fluids with meteoric fluids and cooling process by oxide and sulphide complexes, that this mixing process has reduced the temperature and salinity in the system and caused oxide-sulphide mineralization include chalcopyrite, pyrite, bornite, specularite, and secondary ore minerals include chalcocite, covellite, azurite, malachite, chrysocolla, goethite, and limonite which related to granodiorite, monzonite and gabbro-diorite intrusive rocks.