Evolution of metal-bearing fluids at the Nussir and Ulveryggen sediment-hosted Cu deposits, Repparfjord Tectonic Window, northern Norway

• Published in: Norwegian Journal of Geology
• Main Authors: Mun, Yulia, Strmic Palinkas, Sabina, Kullerud, Kåre, Nilsen, Kjell S., Neufeld, Kai, Bekker, Andrey
• Format: Article in Journal/Newspaper
• Language: English
• Published: Norsk Geologisk Forening 2020
• Subjects: VDP::Mathematics and natural science: 400::Geosciences: 450; VDP::Matematikk og Naturvitenskap: 400::Geofag: 450; Norway; Nussir; Repparfjord; Ulveryggen; Fennoscandia; Northern Norway
• Online Access: https://hdl.handle.net/10037/20062; https://doi.org/10.17850/njg100-2-5

The Palaeoproterozoic greenstone belts of Fennoscandia are metamorphosed and deformed volcanic and sedimentary rocks that formed in basins with a high base-metal ore potential. One of these, the Repparfjord Tectonic Window (RTW), is exposed in the Caledonides of northern Norway and contains several sediment-hosted Cu deposits including Nussir and Ulveryggen. The RTW is composed of mafic metavolcanic rocks (metabasalts, volcanoclastic metabreccia and metatuffite) intercalated with carbonate-siliciclastic sedimentary rocks (dolomitic marble, metasandstone to metapelite). This succession was deformed and metamorphosed up to greenschist to lower amphibolite facies during the Svecofennian Orogeny (c. 1.84 Ga). The Cu-mineralisation at the Nussir deposit is hosted by a dolomitic marble. It occurs mostly in the form of quartz-carbonate veins with chalcopyrite, bornite, chalcocite and covellite as the main ore minerals. In contrast, the Ulveryggen mineralisation is predominantly disseminated within a metasiliciclastic succession and dominated by chalcopyrite, bornite, chalcocite, covellite and neodigenite. Mineralogical, geochemical, stable isotope and fluid-inclusion studies provide insights into the evolution of the Cu-bearing fluids. A wide range in homogenisation temperatures (135–350°C at the Nussir deposit and 102–520°C at the Ulveryggen deposit) and fluid-inclusion salinities (from 0.35 up to 36 wt.% NaCl equivalents) suggest an evolving system with brines developed by subsurface evaporite dissolution. Fluid-inclusion and Cu-sphalerite geothermometry data constrain the temperature-pressure conditions of the Cu mineralisation in the Nussir deposit at 330–340°C and 1.1–2.7 kbars. High salinities at relatively high temperatures within the ore-bearing fluids imply that Cu was transported predominantly by Cu-chloride complexes. The interaction of ore-bearing fluids with carbonate-rich host lithologies is proposed as the main mechanism for deposition of the Cu mineralisation at Nussir. In contrast, at the Ulveryggen ...