The historic Sevcin shaft, Pribram district, sunk in 1813 on the site of a medieval mining pit dating from the 16th century | Courtesy of the Mining Museum, Pribram
There are two principal historic silver mining districts in the Czech Republic, both of which date to the beginning of the Middle Ages or earlier. Pribram, the largest, is located 55 kilometres southwest of Prague whereas the other district, Kutna Hora, is located about 55 kilometres to the east-southeast.
The Pribram camp extends for seven kilometres southwest from the town of the same name. It is situated on a plateau at an elevation of 546 metres above sea level and consists of two separate mining areas - the historic Brezové Hory adjacent to the town and the newer Bohutin at the southwest end.
Mineralization occurs in steeply dipping veins up to 10 metres wide that are associated with a swarm of diabase dykes that cut a Cambrian sandstone and arkose sequence. In places, the veins follow the contacts of the dykes. The ore zones occur near and below the Clay Fault, a regional reverse fault that separates the Cambrian sequence from the overlying Proterozoic slate unit.
According to local history, silver mining began at Brezové Hory (Birkenberg) near Pribram about 843 (Phillips, 1884) although the first written documentation, referring to a metallurgical plant, dates from 1311. Work during the Middle Ages, which peaked early in the 16th century, was directed towards secondary Ag-rich minerals within the oxidized zone near surface, famous among collectors for its beautiful suite of secondary minerals (Posepny, 1893). The mining was concentrated in two historic pits called Vojtech and Anna.
Deeper mining began through several shafts in the late 1700s, after a new metallurgical plant was constructed. This probably marked the transition period from the treatment of oxidized ore to mixed sulphide ore. The ore was found to persist to unprecedented depths and these shafts eventually became the deepest in Europe. One of them, Adalbert, became the world’s deepest in 1875 when it reached 1,000 metres during the main period of production.
The silver-lead-zinc ore was eventually mined to a depth of over 1,500 metres in five shafts, until production ceased in 1978. The deepest shaft, Prokop, reached 1,579 metres, with mining conducted on 41 levels. The bottom of the mine is 1,033 metres below sea level. Because Pribram was one of the first deep mines in Central Europe and was found to be dry below 800 metres, it influenced contemporary ideas on whether ore fluids were derived from above or below. F. Sandberger considered diabase dykes as the sources for ore metals; however, his concept was based on incorrect analytical treatment of samples (Miroslav Stemprock, pers. comm., 2005). Pos?epny´ was an advocate of the influence of heat on the circulation of fluids.
There are some differences of opinion about the ore body in the literature. Von Cotta (1870) stated that the ore was strongly oxidized to a depth of 135 metres whereas Posepny, who was considered the district expert, reported that sulphides predominated even near surface. Whereas more modern reports indicated that silver became only a by-product at depth, Phillips (1884) stated that the silver content gradually increased at depth, and Posepny mentioned that ore from a depth of 1,100 metres was the same as that from higher up.
While references to the historic production often use adjectives such as ‘very rich,’ information on silver grades and production is scanty, at least in English. Mention is made of “well-known Pribram minerals” such as freibergite, pyrargyrite, stephanite, Ag-rich galena, and native silver. Beaudoin and Sangster (1992) reported that the historic production from Pr?íbram was over 520,000 tonnes of lead and 3,500 tonnes of silver. Most of the silver was apparently contained within argentiferous galena. According to Posepny (1893, p.61), a sulphide concentrate collected in 1894 averaged 6.06 kilograms per tonne silver (195 ounces per ton), 69% Pb, 7% Zn, 1.3% Sb, and 0.8% As, which is certainly a rich silver ore. The ore supplied to the smelter had in average 0.185% Ag and 23.10% Pb (Posepny, 1893, p. 264).
Between 1948 and 1991, another period of major activity occurred when the lower parts of the mines were exploited for uranium. The economics of uranium production in Czechoslovakia and the German Democratic Republic (East Germany) were completely artificial at that time because it was a strategic initiative related to the Cold War (Cathro, 2005). Production from Pribram totalled 41,700 tonnes of uranium, of which about 6,000 tonnes was from bitumen-uraninite ore. The ore was mined to a depth of 1,450 metres and explored as deeply as 1,800 metres (Kribek et al., 1999). It is quite possible that some of the deep lead-zinc ore mined during the uranium period was also uneconomic.
Pribram also played an important role in Central European mining as the home of an important mining academy that opened in 1849. It also hosts an important mining museum with a rich collection of primary and secondary minerals from the Pribram veins.
The other silver district, Kutna Hora, was an important early source of currency for the Czech Kingdom. In 1276, the town acquired the status of Royal Mining Town, and a mint was founded in 1300. It was actively mined through the 14th century before declining between the late 16th and early 18th centuries. Another period of prosperity occurred from the 18th to early 20th centuries. Like the Pribram district, early mining was directed toward numerous small veins containing Ag-rich galena and silver minerals such as argentite, proustite, pyrargyrite, tetrahedrite, and native silver in a gangue of quartz and lesser carbonate minerals. The bulk of the deposit was composed of Fe-rich sphalerite.
Importance of the Central European silver mines
In the global history of silver mining, Clausthal-Zellerfeld, St. Andreasberg, Freiberg, Pribram, and Kutna Hora were only modest producers. However, the financial contribution that their silver currency made to the German and Czech economies was tremendously important at that time. The silver was an essential factor toward the regional cultural development of Central Europe during the Renaissance. Together with Rammelsberg, which is not a primary silver mine although it is certainly one of the most historic mines in the world, they provided a vital stimulus to the birth of economic geology. In addition, they made significant contributions to mining technology.
The period of Central European silver dominance ended with the Spanish conquest of Latin America. The Romans taught the Spanish how to mine and plunder silver using slave labour, skills that they were to apply so effectively in Latin America over a thousand years later. After the initial flurry of activity in which Spanish explorers and miners acquired and evaluated the pre-hispanic mines, Spain embarked on the most aggressive and successful program of mining exploration and development that the world had ever seen. Within the short period between 1546 and 1591, Spanish miners, aided by German experts, discovered almost all of the great Mexican silver districts. The great silver lode at Potosi, Bolivia, was discovered in 1545. Agricola’s De Re Metallica, which was translated into Spanish in about 1565, contributed to the rapid development of the new mining camps (Cathro, 2000). The amount of silver arriving in Europe from Mexico and other parts of Latin America soon dwarfed the output from Central Europe.
Beaudoin and Sangster (1992) classified Pribram, Freiberg, and the Harz silver camps, together with three camps in North America – Keno Hill, Yukon; Slocan (Kokanee Range), British Columbia; and Coeur d’Alène, Idaho – as part of a distinct family of vein deposits, named “silver-lead-zinc veins in clastic metasedimentary terranes.” They also defined this class of veins as having “characteristic metal ratios and … (being) comprised of galena, sphalerite and a diverse suite of Ag and sulfosalt minerals in a gangue of siderite, quartz, or calcite. The veins are typically enclosed by spatially restricted phyllic alteration, … hosted by monotonous sequences of clastic rocks intruded by gabbroic to granitic plutons, and metamorphosed to at least the greenschist facies. The veins are late features in the tectonic evolution of an orogen, commonly occur near a crustalscale fault, and are not genetically related to felsic intrusions. Mineralization occurs at temperatures near 250° to 300°C from dilute to saline fluids at an average depth of 6 kilometres. Precipitation results from district-scale mixing of up to three distinct fluids and localized boiling. These fluids include a deep-seated hydrothermal fluid, an upper crustal fluid of ultimate meteoric origin, and a late-stage meteoric-dominated fluid. Sulfur is derived from the local country rocks, whereas carbon is derived from organic and/or deep-seated sources. Pb is mainly derived from the local upper crustal country rocks.”
Information about the silver grades of the ore mined in the historic camps is scarce, at least in the English literature. This makes it difficult to compare the average silver grades of the camps, and particularly the silver content of tetrahedrite and its Ag-rich variety freibergite. Because much of the silver occurred as finely disseminated tetrahedrite within galena, Beaudoin and Sangster looked for a way to compare the mining camps and decided to measure the ratios between their silver and lead production, using the formula Ag x 100/(Ag x 100) + Pb. This provides an approximate indicator of the amount of silver contained in galena if one assumes that the amount of silver that is present in other silver minerals and the amount of lead contained in silver-poor galena of a different generation are relatively small components.
They calculated this ratio to be 0.29 for Freiberg, 0.22 for the Harz mines, 0.40 for Pribram, 0.33 for Slocan, 0.29 for Coeur d'Alène, and 0.63 for Keno Hill. Because the available production numbers for the oldest mines are only estimates, their ratios are admittedly only approximate. However, they provide useful indicators, for each camp, of the average amount of silver present in its galena and/or the relative silver grade of its tetrahedrite. Using the production numbers reported in this paper, separate calculations were made for the two camps in the Harz Mountains. Clausthal-Zellerfeld, which contains abundant galena, has a ratio of 0.32. St. Andreasberg, on the other hand, contains little galena, and has a much higher ratio of 0.72. This is probably not a meaningful result because the amount of galena present was so small. The weighted average for the two is 0.33.
BEAUDOIN, G. and SANGSTER, D.F., 1992. A descriptive model for silver-lead-zinc veins in clastic metasedimentary terranes. Economic Geology, 87, p. 1005-1021.
CATHRO, R.J., 2000. The History of Mining and Metallurgy in Latin America, 1500 BC-1600 AD. In VMS Deposits of Latin America. Edited by R. Sherlock and A.V. Logan. Mineral Deposits Division, Geological Association of Canada, p. 14-15.
CATHRO, R.J., 2005. Uranium production from East Germany, Czechoslovkia, and Eldorado, Northwest Territories after 1945. CIM Bulletin, 1087, p. 67-69.
KRIBEK, B., ZAK, K., SPANGENBERG, J., JEHLICKA, J., PROKES, S., and KOMINEK, J., 1999. Bitumens in the late variscan hydrothermal vein-type uranium deposits of Pribram, Czech Republic: Sources, radiation-induced alteration, and relation to mineralization. Economic Geology, 94, p. 1093-1114.
PHILLIPS, J.A., 1884. A Treatise on Ore Deposits. Macmillan and Co., London, 651 p.
POSEPNY, F., 1893. The Genesis of Ore-Deposits. In The Genesis of Ore-Deposits, Second Edition. Edited by R.W. Raymond. The American Institute of Mining Engineers, New York, 806 p.
POUBA, Z. and ILAVSKY´, J., 1986. Czechoslovakia: Mineral deposits of the Bohemian Massif. In Mineral Deposits of Europe. Edited by F.W. Dunning and A.M. Evans. The Institution of Mining and Metallurgy and The Mineralogical Society, London, p. 135-136.
VON COTTA, B., 1870. A Treatise on Ore Deposits (translated from the 2nd German Edition by Frederick Prime Jr. Van Nostrand, New York, 575 p.