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The Aitik Cu-Au-Ag deposit in the Gallivare area in northern Sweden is Sweden's largest sulphide mine with an annual production of 35 Mt of ore, and the biggest open pit operation in northern Europe. It is proposed in the present study that the Aitik deposit represents a Palaeoproterozoic, strongly metamorphosed porphyry copper deposit that was affected ca. 100 Ma later by a regional IOCG-type hydrothermal event. Consequently, the Aitik deposit might represent a mixed ore system where an early copper mineralisation of porphyry type has been overprinted by later regional IOCG mineralisation. Several attempts have previously been made to genetically classify the Aitik Cu-Au-Ag deposit as a distinct ore type. New geochemical, petrographic, structural, and fluid inclusion results combined with published data have provided the opportunity to present new ideas on the genesis and evolution of the Aitik Cu-Au-Ag deposit. The emplacement of a ca. 1.9 Ga quartz monzodiorite that host the ore at Aitik was related to subduction processes and volcanic arc formation, and synchronous with quartz vein stockwork formation and porphyry copper mineralisation. Highly saline aqueous (38 wt.% NaCl) fluid inclusions in the stockwork veins suggest entrapment at 300 degrees C and a pressure of nearly 3 kbar, a high pressure for a typical porphyry copper ore, but consistent with conditions at associated deep root zones of intrusion-related magmatic-hydrothermal systems. The highly saline fluid formed disseminated and vein-type ore of mainly chalcopyrite and pyrite within comagmatic volcaniclastic rocks, and caused potassic alteration (biotite, microcline) of the host rocks. The early porphyry copper mineralising event was followed, and largely overprinted, by CO2 and aqueous medium- to high-salinity (16-57 wt.% salts) fluids related to a ca. 1.8 Ga tectonic and metamorphic event (peak conditions 500-600 degrees C and 4-5 kbar). Extensive deformation of rocks and redistribution of metals occu, AuthorCount:4

Deposits that may have an affinity with iron oxide-copper-gold (IOCG) deposits in the Archaean and Palaeoproterozoic shield, which includes a large part of Finland, NW Russia, Norway and Sweden, include apatite-iron ore, skarn-related Fe/banded-iron formation (BIF), and epigenetic (or syngenetic) Au/Cu-Au. Apatite-iron ore deposits include the huge Kiirunavaara and Malmberget magmatic deposits, both subjected to deformation and hydrothermal overprinting, while at Tjarrojakka separate examples of both iron oxide-apatite and IOCG may be genetically related, formed epigenetically at around 1.77 Ga. Svecofennian skarn-related Fe- rich deposits, dating from 1.9-1.8 Ga and hosted by c.2.1 Ga greenstones along the border between Sweden and Finland, are accompanied by Au and Cu concentration in Finland but are basically only Fe in the Swedish occurrences. Typically epigenetic Cu and Cu-Au may be grouped into orogenic gold, orogenic gold with atypical metal association, and more obvious IOCG types. Early genetic processes are assumed to have involved concentration of Fe and Cu, with some Au, in 2.3-2.0 Ga supracrustal rocks and deposition of evaporites, before Svecofennian deformation and metamorphism mobilised saline and metal-rich fluids that precipitated varying combinations of ore minerals. A tentative E-W zoning is suggested from the Kuusamo region's possibly syngenetic Au-Co-Cu+/-U through the Central Lapland greenstone belt's orogenic Au and Pajala-Kolari region's skarn-related occurrences to the IOCG and apatite-iron oxide deposits of the Kiruna-Gallivare region of Sweden., Deposits that may have an affinity with iron oxide-copper-gold (IOCG) deposits in the Archaean and Palaeoproterozoic shield, which includes a large part of Finland, NW Russia, Norway and Sweden, include apatite-iron ore, skarn-related Fe/banded-iron formation (BIF), and epigenetic (or syngenetic) Au/Cu-Au. Apatite-iron ore deposits include the huge Kiirunavaara and Malmberget magmatic deposits, both subjected to deformation and hydrothermal overprinting, while at Tjarrojakka separate examples of both iron oxide-apatite and IOCG may be genetically related, formed epigenetically at around 1.77 Ga. Svecofennian skarn-related Fe- rich deposits, dating from 1.9-1.8 Ga and hosted by c.2.1 Ga greenstones along the border between Sweden and Finland, are accompanied by Au and Cu concentration in Finland but are basically only Fe in the Swedish occurrences. Typically epigenetic Cu and Cu-Au may be grouped into orogenic gold, orogenic gold with atypical metal association, and more obvious IOCG types. Early genetic processes are assumed to have involved concentration of Fe and Cu, with some Au, in 2.3-2.0 Ga supracrustal rocks and deposition of evaporites, before Svecofennian deformation and metamorphism mobilised saline and metal-rich fluids that precipitated varying combinations of ore minerals. A tentative E-W zoning is suggested from the Kuusamo region's possibly syngenetic Au-Co-Cu+/-U through the Central Lapland greenstone belt's orogenic Au and Pajala-Kolari region's skarn-related occurrences to the IOCG and apatite-iron oxide deposits of the Kiruna-Gallivare region of Sweden.