Iron Oxide Cu-Au Monograph - Volume 4, Abstract

The Ossa Morena Zone (OMZ), in southwestern Iberia, is considered one of the most significant metallogenic belts in Europe. It has a complex, polyphase geologic history, and hosts a variety of classic and unusual ore styles, including magmatic nickel-copper and a number of IOCG-style deposits. These ores are only slightly metamorphosed and deformed, in contrast to older deposits elsewhere, allowing detailed studies to establish their origin and evolution. The OMZ hosts two main styles of IOCG mineralisation: (1) mesozonal albitite-related, replacive magnetite deposits of both Cambrian and Variscan age, and (2) shallower, complex, hydrothermal magnetite-(copper-gold) replacements related to trans-crustal shear zones. Both of these IOCG-styles coexist with Early Cambrian stratabound iron oxide-rich mineralisation found in the same area. The albitite-related deposits reflect complex magmatic-hydrothermal processes, in the form of genetically associated magmatic albite±magnetite rocks which are the product of anatectic rejuvenation of earlier iron-rich (chemical) sediments. The depth extension of the structurally-related shear hosted ores is unknown, although they are also interpreted to be the result of remobilisation of earlier mineralisation by metamorphic fluids channelled along major structures. Coexistence of IOCG deposits with pre-existing stratabound iron-rich sediments is a feature common in many IOCG belts world-wide, suggesting that in many cases, IOCG mineralisation can be derived from hydrothermal/magmatic remobilisation of pre-existing mineral accumulations.