Kongsberg (silver ore deposit)
The Kongsberg silver ore deposit is located in southern Norway and was the largest and most productive silver deposit in Norway, where mining was carried out in the Kongsberg silver mine (now part of the Norwegian Mining Museum ) from 1623 to 1958 . It is an igneous - hydrothermal dike deposit with metal-containing impregnations of the adjacent rock. The most important ore was metallic ("solid") silver .
Geology and the genesis of deposits
Structural and stratigraphic the surrounding rocks of the silver deposit are Kongsberg the Proterozoic applied Baltic shield assigned. Petrographically, it is mainly a concordant alternation of para and orthogneiss (quartz-plagioclase-biotite-gneiss, hornblende gneiss and cataclastic actinolite-hornblende gneiss). Amphibolite storage tunnels ( metamorphosed from former diabases ) are included in this series . The series of rocks are severely deformed and folded by tectonic forces. The fold flanks are steeply erect. Geologically more recent series consist of post-tectonic granitoid intrusions and Cambro-Silurian sediments of the Oslofelt. The general structural directions run roughly north-south.
In the Permian , about 225 million years ago, intense tectonic movements took place in the earth's crust in the region around Oslo, resulting in deep fractures, crevices and faults. Because these fracture structures reached into the upper, magmatic, i.e. glowing liquid areas of the earth's mantle , vertical magma movements were activated. During the rise of the hot magmas and in contact with water, aqueous, metal and mineral-containing hydrothermal solutions were created , which were still in liquid form at up to 400 ° C due to the extremely high overlying pressure of the rock layers, which were up to several kilometers thick. Depending on the chemical composition of the magma and the surrounding rock along the ascent paths, defined metal and mineral associations, so-called parageneses, could form in the upper areas of the earth's crust during cooling . Depending on the geometry and opening width of the tectonic elements, mineral dykes with a thickness of a few centimeters to several meters formed. In addition to the formation of (mostly ore-free) mineral veins, amphibolites impregnated with metal sulfides are typical of the Kongsberg silver ore deposit. Because of their rust-brown color and their lack of gloss, they are called “Fahlbånds” in the local miners' language and were the most important ore carriers of the deposit.
Mineralogy and ore distribution
In general, it is an igneous deposit of the hydrothermal phase of the so-called Bi-Co-Ni-Ag formation of the Schneeberg - Kongsberg type (in the more recent literature on deposit research, the term "bismuth-cobalt-nickel-silver association" is used for this type of mineralization “Used). The most economically important ore is metallic silver ("solid" silver). These silver enrichment zones are linked to the aforementioned “pale bands”. Argentite (silver sheen), on the other hand, rarely occurs. Further ore minerals occur in traces as displacement residues of several hydrothermal phases. These can be genetically divided into three groups. The oldest formation consists of feldspars , epidotes , chlorite , quartz , fluorite , axinite and pyrite and metal sulfides. Another group, which can only be detected in traces, is formed from fluorite, sulfides and Co-Ni arsenides. The third generation consists mainly of metallic (low-mercury) silver and calcite . Calcite occurs in steeply dipping, narrow dikes that are discordant to the structural direction of the surrounding rock. In the intersection and penetration areas with the sulphide-bearing amphibolites, the aforementioned “pale bands”, however, there are suddenly increasing ore enrichments in the form of solid silver (“vein refinement”). These locally occurring silver concentrations and the type of accompanying mineralization in the enrichment zones are due to reactions of the hydrothermal solutions with the sulfide-impregnated amphibolites. In addition, the precipitating effect of cobalt-nickel-arsenides on silver leads to an increase in the concentration. In the older literature, the term “calcareous, solid silver veins (Kongsberg type)” is used for this type of mineralization (Schneiderhöhn 1955). The mineralization differs not only genetically, but also clearly depth-oriented (so-called " zoning "). Silver is found in the upper depth range. Cobalt and nickel ores, on the other hand, are located at medium depths. In the lower-lying, underexposed part of the deposit, uranium and iron accumulations also occur.
Silver ore grades
Silver ore levels (solid silver) from the Kongsberg deposit in the mineralogical and deposit history collections of the TU Bergakademie Freiberg
literature
- Odd Arne Helleberg: Kongsberg sølvverk 1623-1958: kongenes øyensten - rikenes pryd ; 2nd edition, Forlaget Langs Lågen 2010; ISBN 978-82-92053-41-6 .
- Kristian Moen: Kongsberg Sølvverks historie. 1623-1957. Sølvverksmuseets venner, 1967. p. 512.
Individual evidence
- ↑ Starmer, IC: The Geology And Evolution Of The Southwest Part Of The Kongsberg Series. University of London 1975.
- ^ O'Nions, RK; Heier, KS: A Reconnaissance Rb-Sr Geochronological Study Of The Kongsberg Area, South Norway, Oslo 1972.
- ↑ Helleberg, OA: Kongsberg sølvverk 1623-1958: congenes øyensten - rikenes pryd ; 2nd edition, Forlaget Langs Lågen 2010; ISBN 978-82-92053-41-6 .
- ↑ L. Baumann, E. Kuschka, T. Seifert: The storage facilities of the Erzgebirge, 2001.
- ↑ Baumann, L., Nikolskij, IL, Wolf, M .: Introduction to geology and exploration of deposits, VEB Deutscher Verlag für Grundstoffindindustrie 1979.
- ↑ Schneiderhöhn, H .: ore deposits, VEB Gustav Fischer Verlag Jena 1955.
Coordinates: 59 ° 37 ′ 58 " N , 9 ° 35 ′ 58" E