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Roros district - Killingdal, Kongens Gruve, Klingenberg, Nye Storwartz, Guldals Grube, Godthap |
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Norway |
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Cu Zn Pb
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Røros district is located in the southeastern Trondheim region of Norway, close to the Swedish border, and embraces pyrite-rich polymetallic sulphide ores in the Central Norwegian Caledonides, including the small Killingdal Cu-Zn, Kongens Gruve Cu-Zn, Klingenberg Cu-Zn, Nye Storwartz Cu-Zn, Guldals Grube Cu-(Zn-Pb) and Godthåp Cu-(Zn-Pb) deposits (#Location: 62° 35'N, 11° 23'E).
Roros is 110 km SE of the city of Trondheim. It is also ~110 km SE of the Lokken orefield, which is 10 km south of Trondheim (see the Lokken record), and 100 km NE of the Folldal orefield (see the Folldal District record).
The deposits of this district have been intensively exploited, mainly for Cu and Zn from the 17th (earliest 1644) and 18th centuries, although the more recent activity has concentrated on sulphur from the associated pyrite (Rui and Bakke 1975; Bjerkgård et al., 1999).
The deposits at Røros are hosted within a Cambrian to Silurian succession of the Scandinavian Caledonides, a belt of late Proterozoic to early Palaeozoic rocks emplaced as a series of thrust nappes (Roberts and Gee 1985; Hacker and Gans 2005), that overlie the Palaeoproterozoic rocks of the Fennoscandian Shield and constitute the northernmost section of the composite Caledonian-Appalachian belt in Scandinavia and eastern North America (Grenne et al., 1999). These rocks were variably metamorphosed during the Siluro-Devonian Scandian orogenesis (Grenne et al., 1999) to lower greenschist, up to upper amphibolite facies, during several phases of deformation (Bryhni and Andreasson 1985) which are reflected in the ore deposits (Craig and Vokes 1992). A trend of the metamorphic grade of the ore deposits increasing in a northeasterly direction is suggested within the Røros district (Rui 1972).
The nappes forming the Caledonides have been grouped into four main allochthons, the Lower, Middle, Upper, and Uppermost Allochthons (Roberts and Gee 1985). The Røros district is located in part of the Upper Allochthon, which comprises the Seve and overlying Köli Nappe systems, consisting of continental rocks thought to represent the outermost margin of Baltica, and ophiolitic rocks interpreted to represent remnant oceanic lithosphere of the former Iapetus ocean (Hacker and Gans 2005).
The district hosts a number of sulphide ore deposits associated with Late Ordovician calcareous phyllites, metagreywackes and local interlayers of possible volcaniclastic origin, that form part of a large, complexly folded synformal structure (Wolff 1967; Rui 1972; Rui and Bakke 1975; Grenne et al., 1999) which has been extensively intruded by a variety of gabbro and trondhjemite sills (Bjerkgård et al., 1999; Grenne et al., 1999).
The Trondheim Nappe Complex of the Southern Trondheim region, has been subdivided, from west to east, into the Støren, Gula and Meråker Nappes and contains Köli sequence rocks (Roberts and Wolff 1981; Gee and Sturt 1985). Köli sequence rocks are recognized over a distance of more than 500 km north of Røros. The Røros district, which is in the east of the Southern Trondheim region, falls within the Meråker Nappe, containing rocks of the Fundsjø Group, composed essentially of a basal mafic magmatic complex, which were subjected to an Early Ordovician (pre-Scandian) tectonothermal event, and a thick overlying turbidite sequence of Ordovician to Early Silurian age. The Fundsjø Group hosts the Killingdal deposit and ores of the Folldal orefield to the SW (Vokes et al., 2003). Grenne et al. (1999) regarded the turbidites in the Meråker Nappe to represent oceanic sequences developed at a distance from the margin of Baltoscandia. In contrast, the Gula Nappe in the western part of the Southern Trondheim region is of probable continental margin or shelf origin.
The entire Trondheim Nappe Complex underwent deformation and metamorphism during the Scandian Orogeny and was thrust over the Seve nappes in the Middle Silurian in response to closure of the Iapatus Ocean (Ihlen et al., 1997).
Most of the Røros massive sulphide deposits (including Kongens Gruve, Nye Storwartz and Klingenberg) occur in turbidite-dominant sequences of the Røros Schists. Sulphide mineralisation is stratabound and mainly massive, composed of either pyrrhotite- or pyrite-dominant, or of both Fe sulphides (Rui and Bakke 1975; Bugge 1978). The total ore production from the main mines in the Røros district was ~6.5 Mt @ ~2.7% Cu and 4.2 to 5.0% Zn (Bjerkgård et al., 1999). Many smaller deposits are distributed throughout the district, although the bulk of production came from the central part of the district north of Røros, and from Killingdal.
The masive sulphide deposits are mostly tabular- or ribbon-shaped, with long axes generally paralleling regional fold axes and stretching lineations (Grenne 1987; Bjerkgård et al., 1999). Deposits are generally thought to be VMS in origin (Bjerkgård et al., 1999; Grenne et al., 1999), despite the deposits being largely hosted by sedimentary rocks, and the apparent discordant relationship between the sulphides and wall rocks in some. The latter relationships are considered to be potentially the result of syndeformational remobilisation and thrusting along the plane of the sulphide horizons superimposed on what may be a primary volcano-exhalative stratabound character of the ores (Rui and Bakke 1975) based on the character of the host succession and comparison with volcano-exhalative ores elsewhere in the Caledonides.
The massive sulphide mineralisation has been interpreted to be coeval with, or marginally younger than Ni-Cu-Cr-(PGE) ores found at deeper crustal levels in the same district (Nilsson et al., 1997).
The Kongens Gruve, Klingenberg and Nye Storwartz deposits are larger massive sulphide deposits hosted within the Røros Formation in the central part of the district, whereas Godthåp and Guldals Grube are hosted within the Røsjo formation north of the main orefield (Bjerkgård et al., 1999). Both the Røros and Røsjo formations are Lower Ordovician in age. The Røsjo Formation underlies the Røros Formation with which it has a transitional boundary (Rui and Bakke 1975). If the interpretation of stratigraphic inversion is correct, this would make them slightly younger but still products of the main ore-forming event in the district.
The Killingdal deposits, which are 25 km north of Røros, comprises two conformable bodies, the North and South ores, discovered in 1674 and 1791 respectively. They are composed of 1.0% Cu, 10.6% Zn, 35% Fe, 42% S, and 1.9% Cu, 5.9% Zn, 41% Fe and 48% S respectively, comprising pyrite with subordinate chalcopyrite, sphalerite and minor pyrrhotite, galena, arsenopyrite, tetrahedrite, bournonite, mackinawite and molybdenite. They were emplaced close to the boundary of the calcareous phyllites of the Kjurudal Formation and the dominantly hornblende matabasalt schists of the Hersjø Formation. Hydrothermal metasomatism produced successive quartz-muscovite and chlorite alteration envelopes to the mineralisation. Working was sporadic to 1850, but by 1984, 3 Mt of ore had been exploited (Banks, 1994).
The Kongens Gruve deposit, which is 10 km NNW of Røros, and hosted by the Røros Formation, was mined from 1657 to 1945, with ~3 Mt of ore extracted. It comprised massive, semi-massive and banded chalcopyrite-sphalerite ore in a gangue of pyrite, pyrrhotite, chlorite and quartz. The ore is characterised by relatively fine-grained pyrite-rich mineralisation with a compositional foliation defined by sphalerite and chalcopyrite variations as well as an associated weak pyrite grain size layering. Sphalerite predominantly encloses ~100 µm grains of pyrite, while chalcopyrite encloses smaller ~40 µm pyrite grains.
The Klingenberg deposit, which is 22 km NE of Røros in the central part of the district, was mined until 1907. It is a coarse-grained pyrite-rich ore body, composed of massive chalcopyrite, sphalerite and lesswer galena, in a gangue of pyrite, chlorite and quartz, with lesser biotite and amphibole. The ore has a pyrite grain-size layering,with a weak chalcopyrite-sphalerite compositional layering and pyrrhotite lenses. There is extensive fracture development and occasional pulverisation of pyrite.
The Nye Storwartz deposit, which is ~9 km NE of Røros, is and was mined until 1947, with 0.15 Mt of ore having been extracted, with 0.075 Mt remaining. The ore is massive, comprising chalcopyrite and sphalerite, in a gangue of pyrite, pyrrhotite, biotite, chlorite and ampbibole. The sphalerite-chalcopyrite has a lensoid compositional foliation, with only minimal, to no fracture development. Pyrite is relatively coarse at ~160 µm.
The Guldals Grube deposit, is hosted by the Røsjo Formation, 30 km just to the east of north from Røros, The deposit was mined out prior to the 20th century, and is characterised by coarse-grained pyrite-rich semi-massive ore, with some evidence of brecciation, and is copper-rich, with chalcopyrite, sphalerite and galena in a gangue of pyrite, pyrrhotite, biotite, hornblende and quartz. There is a preferred orientation of pyrite grains, with extensive fracture development and occasional pyrite pulverization.
The Godthåp deposit is located within a few kilometres to the NE of Guldals Grube, also hosted by the Røsjo Formation and is characterised by fine-grained pyrite-rich ore. This deposit, was also mined out prior to the 20th century. It comprises copper-rich ore, composed of chalcopyrite, sphalerite and galena, in a gangue of pyrite, pyrrhotite and quartz.
The most recent source geological information used to prepare this decription was dated: 2009.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Barrie C D, Cook N J and Boyle A P, 2010 - Textural variation in the pyrite-rich ore deposits of the Roros district, Trondheim Region, Norway: implications for pyrite deformation mechanisms: in Mineralium Deposita v.45 pp. 51-68
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