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The Geology and Mining History of Røros, Norway

Last Updated: 31st Dec 2018

By Nathalie Brandes

Declared a World Heritage Site in 1980, Røros is a well-preserved mining town. For 333 years, local mines extracted copper and zinc from sulphide deposits. This long history of mining can be seen in the colourful town, the smelter, and the many mine sites in the surrounding area.

Røros is located in the county of Sør-Trøndelag at the edge of a hilly plateau in the Norwegian Caledonides at an elevation of about 600 m (1970 ft) above sea level (Norway, 1978; Prøsch-Danielsen and Sørensen, 2010). It is situated near the confluence of the Glåma, Håelva, and Hitterelva Rivers. The site was chosen in part because the Hitterelva River is large enough to operate the smelter’s bellows. The mining district occupies a transition zone between the suboceanic and subcontinental climate regimes (Prøsch-Danielsen and Sørensen, 2010). The area is also the transition between the middle and northern boreal vegetation zones, which includes trees such as birch, conifer, and Scots pine (Moen, 1999).

Rocks in the Røros region formed on the floor of the Iapetus Ocean in Cambrian to Silurian time (Ramberg et al., 2008). These sedimentary and volcanic rocks were intruded by gabbro sills and during the Caledonian Orogeny were complexly deformed and metamorphosed to greenschist and amphibolite facies (Nilsen, 1988; Nilsen and Wolff, 1989; Segalstad et al., 2006; Grenne, 2008; Barrie et al., 2010). The ores of Røros are considered volcanigenic massive sulphide (VMS) deposits associated with black smoker hydrothermal vents on the seafloor (Oftedahl, 1958; Segalstad et al., 2006; Ramberg et al., 2008). The host rocks of these stratabound ores are metagreywacke and phyllite (Nilsen, 1988; Nilsen and Wolff, 1989; Grenne, 2008). Although black smoker deposits are generally viewed as seafloor precipitates, Grenne (2008) suggests most of the Røros ores were precipitated by ascending hydrothermal fluids preferentially filling sedimentary beds with favourable porosity and true seafloor precipitates are rare in the district.

The ores at Røros can be divided into two basic types, pyrite and pyrrhotite deposits. Both include varying amounts of chalcopyrite, sphalerite, magnetite, limonite, rutile, galena, arsenopyrite, mackinawite, cubanite, argentite, and molybdenite (Bugge et al., 1975; Segalstad, 2000; Segalstad et al., 2006). Ore grades of the pyrite deposits are typically 1-2% copper and 1-6% zinc. Gangue minerals include quartz, chlorite, and muscovite. The pyrrhotite deposits have a copper grade of at least 1%, but also include minerals such as magnetite and pyrite and fragments of hornblende and chlorite (Segalstad et al., 2006).

The first humans in the Røros area were Stone Age hunters around 5000 B.C. (Daugstad et al., 1999; Norway, 2009). Permanent settlements appeared in the Völkerwanderung and existed through the Viking Age and early Medieval Period, but disappeared after the Black Death of 1349-1350 (Sandnes, 1971). Very few farms returned to the region prior to mining (Prøsch-Danielsen and Sørensen, 2010). According to legend, the original discovery of ore was by a reindeer hunter. Mining in Røros began in 1644 and lasted until 1977 (Nissen, 1976; Norway 1978; Jones, 1999). The original mining venture lasted only three months, but a project shortly thereafter was more successful (Segalstad, 2006). In 1646, Danish-Norwegian King Christian IV granted the Røros Copper Works mining privileges for a radius of 4 Norwegian miles (~40 km) from the first successful mine, the Old Storwartz (Bye, 2008; Norway 2009).

Røros experienced good times and bad over the years. Burned to the ground completely in 1768 and 1769 by the Swedish army, the town was completely rebuilt (Norway 1978). Production from the mines in Røros grew to an output of 600 tonnes/year in 1775. After a period of declining production, in 1888 the Bessemer process was adopted and production rose again, reaching a peak of about 1000 tonnes/ year in the late 1940s (Prøsch-Danielsen and Sørensen, 2010). In 1977, the Lergruvebakken Mine closed, ending an era of 333 years of continuous mining in the Røros area (Segalstad et al., 2006). Total production from the district is estimated to be 6,000,000 tonnes of raw ore producing 120,000 tonnes of copper (Norway 2009).

Recognition of the importance of Røros to Norwegian history and mining heritage began while it was still an active industrial centre. The first efforts of preservation date to 1923 (Bye, 2008). As a result, the city and the mines present an excellent window into history.


References:

Barrie, C.D., Cook, N.J., and Boyle, A.P., 2010, Textural variation in the pyrite rich ore deposits of the Røros district, Trondheim Region, Norway: implications for pyrite deformation mechanisms: Mineralium Deposita, v. 45, p. 51-68.

Bugge, J.A.W., Rui, I.J., and Segalstad, T.V., 1975, Field guide, ore geology graduate course excursion (G24/G48), east Trondheim District: Department of Geology, University of Oslo, 31p.

Bye, M., 2008, A Changing townscape: Røros throughout a century of heritage management: 16th ICOMUS General Assembly and International Symposium, Finding a Spirit of Place—Between the Tangible and Intangible, v. 29, p. 1-10.

Daugstad, K., Binns, K.S., Grytli, E.R., Liavik, K., Prøsch-Danielsen, L., and Vistad, O.I., 1999, Bergverksbyens omland om ressursbruk, vern, kultur og natur i Rørosområdet: NIKU Temahefte, v. 29, p. 1-511.

Grenne, T., 2008, Sulphide ores in Ramberg, I.B., Bryhni, I., Nøttvedt, A., and Rangnes, K., eds., 2008, The Making of a Land—Geology of Norway: Trondheim, Norsk Geologisk Forening, p. 227.

Jones, M., 1999, Røros as a world heritage site in Setten, G., Semb, T., and Torvik, R., eds., Shaping the Land, Volume I The relevance of research for landscape management—tool or critique: Papers from the Department of Geography, University of Trondheim, New Series A, v. 27, p.33-50.

Moen, A., 1999, National atlas of Norway: vegetation: Norwegian Mapping Authority.

Nilsen, O., 1988, The tectonostratigraphic setting of stratabound sulphide deposits in the southern Trondheim Region, Central Norwegian Caledonides: Norges Geologiske Undersøkelse Bulletin, v. 412, p. 55-66.

Nilsen, O. and Wolff, F.C., 1989, Geologisk kart over Norge, berggrunnskart Røros & Sveg: Norges Geologiske Undersøkelse, scale 1:250 000.

Nissen, G.B., 1976, Røros kobberverk 1644-1974: Trondheim, Aktietrykkeriet, 146p.

Norway, 1978, Røros: UNESCO World Heritage Site Nomination Documentation, 18p.

Norway, 2009, Røros mining town and the circumference, Norwegian nomination 2009 for extension of World Heritage Site Røros mining town: UNESCO World Heritage Site Nomination Dossier, 96p.

Oftedahl, C., 1958, A theory of exhalative sedimentary ores: Geologiska Föreningen i Stockhom Förhandlingar, v. 80, p. 1-19.

Prøsch-Danielsen, L., and Sørensen, R., 2010, 333 years of copper mining in the Røros region of the Mid-Scandic highlands, written sources versus natural archives: Journal of Nordic Archaeological Science, v. 17, p. 37-51.

Ramberg, I.B., Bryhni, I., Nøttvedt, A., and Rangnes, K., eds., 2008, The Making of a Land—Geology of Norway: Trondheim, Norsk Geologisk Forening, 624p.

Sandnes, J., 1971, Ødetid og gjenreisning: Oslo Universitets forlaget, 385p.

Segalstad, T.V., 2000, Mining in the Røros District, field guide for environmental geochemistry of ore deposits and mining activities, short course: Röros, Norway, June 2000: SARD Consulting Norge AS & Mineralogisk-Geologisk Museum, University of Oslo, 10p.

Segalstad, T.V., Walder, I.F., and Nilssen, S., 2006, Mining mitigation in Norway and future improvement possibilitites in Barnhisel, R.I., ed., 7th International Conference on Acid Rock Drainage:Lexington, Kentucky, American Society of Mining and Reclamation, p. 1952-1960.




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