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Modification of a Palaeoproterozoic porphyry-like system: integration of structural, geochemical, petrographic, and fluid inclusion data from the Aitik Cu-Au-Ag deposit, northern Sweden
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0003-4711-7671
Department of Geological Sciences, Stockholm University.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
Vattenfall.
2012 (English)In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 48, p. 306-331Article in journal (Refereed) Published
Abstract [en]

The Aitik Cu-Au-Ag deposit in the Gällivare 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 °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 °C and 4–5 kbar). Extensive deformation of rocks and redistribution of metals occurred. Magnetite enrichment locally found within late veins, and late amphibole-scapolite and K feldspar alteration within the deposit, are some of the features at Aitik implying that aqueous fluids responsible for IOCG-mineralisation (200–500 °C and ~ 1 kbar) and extensive Na-Ca alteration in the region during the 1.8 Ga tectonic event also affected the Aitik rocks, possibly leading to addition of copper ± gold.

Place, publisher, year, edition, pages
2012. Vol. 48, p. 306-331
National Category
Geology
Research subject
Ore Geology
Identifiers
URN: urn:nbn:se:ltu:diva-5955DOI: 10.1016/j.oregeorev.2012.05.002Local ID: 4252e38a-e980-4ce0-8a3a-d19ab42ed43aOAI: oai:DiVA.org:ltu-5955DiVA: diva2:978831
Note
Validerad; 2012; 20120511 (ysko)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved

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