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The Vigsnes province comprises part of Karmøy ophiolite complex in the southwesternmost part of the Norwegian Caledonides. The complex is part of an immature arc–supra-subduction zone (SSZ) ophiolite sequence of Laurentian affinity that includes the Karmøy–Bømlo–Hardanger area (Grenne et al. 1999). The ophiolite is assumed to have formed at a spreading axis in a marginal basin positioned above a subduction zone, as the result of back-arc spreading or arc rifting, and is thus a SSZ ophiolite (Pedersen & Furnes 1991). The sequence upwards from ultramafic and mafic intrusive, sheeted dykes, pillow lava, pyroclastic rock, volcanoclastic rock, pillow lava and sedimentary units is well exposed. Several Cu-Zn deposits, mostly of VMS category, and a few vein deposits, are mainly confined to the lower pillow lavas and the sheeted-dyke complex (Visnes Group).
The most significant VMS deposits are Vigsnes and Rødkleiv, which are located only 650 m apart. The Vigsnes deposit was discovered in 1865 and a Belgian company already commenced production in the following year. In 1880, when French interests took over, it was the largest mining company in Norway, with 3 000 persons directly or indirectly occupied, but mining ceased in 1894 due to the declining Cu content of the ore. Small-scale production took place in 1970–71. Small-scale test mining was carried out on the Rødkleiv deposit before regular production started in 1910. The mine closed in 1971.
The ore bodies at both Vigsnes and Rødkleiv are in a 50–60 m wide zone dominated by chlorite-rich greenschist that represents sheared dykes and lava of the Visnes Group. The shearing is assumed to post-date the formation of the massive sulphide bodies (Scott 1992). The strike of the sequence is NW–SE with a steep dip towards the NE and across the island. The stratigraphy of the hosting sequence from footwall to hanging wall: greenstone, chlorite schist, ore, chlorite schist, greenstone with minor intercalations of felsic metavolcanic rocks and magnetite, and chert (Geis 1957). At the Vigsnes mine, six cigar- or plate-shaped ore bodies were exploited to a depth of 732 m. The two largest of these were 400–450 m long, up to 175 m wide and with thicknesses of the order of 5–30 m. At Rødkleiv, two ore bodies were mined, the West and East ore bodies, separated by a fault. The western ore body was ruler shaped and exploited from the surface to a depth of 400 m, whereas the eastern ore body was more irregular and was discovered at a depth of 210 m. The possible easterly extension of the eastern ore body was exploited from the minor Hinderaker mine.
The massive sulphide ores are banded and pyrite rich. In the Vigsnes deposit, chalcopyrite and sphalerite are enriched in the upper parts of the sulphide bodies, and chalcopyrite is also enriched in the thinner part of these. Minor stringers or veinlets and dissemination of chalcopyrite also occur in the hanging wall. The Rødkleiv ore is dominated by pyrite with thin bands of sphalerite with more irregular enrichments of chalcopyrite, especially on the hanging-wall side.
Several minor massive sulphide deposits exist to the SE, along strike from Vigsnes and Rødkleiv, for example, Hinderaker, Sletthei, Knoff/Huelva and Jordan. The Sørstokke deposit is located at the SE side of Karmøy (total production of 7300 t with 0.5–0.6 % Cu) (Geis 1957). Both massive and disseminated pyrite-chalcopyrite occurrences are in doleritic greenstone in the lower part of the ophiolite complex.
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