Where is the site located?
GPS: 50° 01′ 41.82″ N, 15° 26′ 3.22″ E
The site is located in the northwestern extension of the Iron Mountains National Geopark, at the termination of the Iron Mountains ridge. The East Bohemian Table spreads on the other bank of the Elbe River.
What is the geological position of the site?
The site is located in the Bohemian Massif, in the marginal area of the Central Bohemian Region, where metamorphosed Proterozoic rocks are exposed. Rocks at this site witnessed the presence of two marine floodings of different ages, volcanic activity, orogenic processes and a significant ore accumulation.
What happened at this site in the past?
– 750 million years
In the Proterozoic, this area was lying on the Southern Hemisphere. It was a part of a seafloor not far from the continent of Gondwana. Here, thick deposits of fine sediments were formed in deeper areas of the sea, periodically redeposited by huge subaquatic slumps. At the same time, subaquatic volcanic activity was taking place, associated with lava effusions and ascent of hot geothermal fluids. These fluids enriched the rock environment with various chemical elements, such as sulphur, iron and manganese.
- 545 million years
The end of the Proterozoic is marked by a rearrangement of lithospheric plates, resulting in the Cadomian Orogeny. The deposited rocks were compressed and, as a result, deformed and weakly metamorphosed. A deep-reaching, thick tectonic fracture was initiated. Newly formed joints were used for the ascent of magma, which thermally affected the ambient rock environment.
- 95 million years
In the latest Mesozoic, this area drifted to the Northern Hemisphere, becoming a part of the Eurasian Plate. It became progressively flooded by Late Cretaceous sea, which was – unlike the previous sea flooding – shallow and warm. This site was located on a seashore, where shoreline cliffs protruded from sandy beaches.
What does the site display today?
Weakly metamorphosed rocks having the character of dark phyllitic shales and greywackes with volcanic dykes and sills are preserved along the northeastern slopes of the Iron Mountains between Týnec n. L. and Zdechovice. They belong to the Chvaletice Proterozoic.
The stratal succession includes a prominent layer of black sulphidic shales with lens-like deposits of iron and manganese ores. The deposit is of sedimentary origin, enriched by mineralized fluids derived from volcanic activity. During subsequent orogenic processes, it became affected by pressure, temperature and material changes.
A lens-shaped body called the Chvaletice massif lies in the area south of Chvaletice and Zdechovice. It is composed of the Chvaletice granite of a characteristic pink colour. The granite contains brittle deformation zones, along which the original rock became altered to a variable degree. The rock is extracted in a quarry at the southern limit of the town of Chvaletice and utilized as aggregate.
Relicts of Upper Cretaceous (Cenomanian and Turonian) sediments have been preserved in the northern vicinity of Chvaletice. They pose original marine deposits – clays, sands and gravels. Over time, they became hardened, mostly by the effect of loading; therefore, they now have the character of sandstones, siltstones and claystones.
What was affected by man?
Iron ore mining has been recorded from the near vicinity since Medieval times (the Chronicle by Václav Hájek of Libočany).
A gradual development of further mineral exploitation dates to the 19th century. At first, ores lying close to the earth surface were utilized. They formed the so-called gossan (“iron hatˮ) formed by the oxidation of sulphidic shales.
In 1945–1954, mineral exploration was conducted in the area between Chvaletice and Zdechovice. It revealed an extensive ore mineralization.
Later, mining of sulphidic shales was started. They were used as a source of sulphur for the production of sulphuric acid and other products needed by the chemical industry.
Mineral mining and processing was run by the company of Chvaletické pyritové manganorudné doly (Chvaletice Pyrite Manganese Ore Mines) in a large open-pit mine 2500 m in length, 500 m in width and ca. 150 m in depth (ten levels).
Manganese ores were also extracted as a by-product but their processing was not real and economic at that time. Waste material was kept in huge heaps between the railway and the Elbe River. These are still being registered as potential manganese deposits.
After the discovery of big sulphur deposits in Poland, mining operations were discontinued in 1975, and the devastated area was used for the construction of the Chvaletice coal-burning power plant. The open-pit mine was turned into a settling pond and became finally filled by fly ash.
The settlement structure of the area became also affected by the mining activities. The original piedmont villages of Chvaletice and Telčice became non-existent. The Chvaletice village was largely demolished, and its church was left on the edge of the open-pit mine. The community of Hornická čtvrť was constructed for the miners. Telčice became the site of a large housing estate whose infrastructure was built within a lengthy process through volunteering of the local population.
The rock environment and groundwater in a broad vicinity became also adversely affected by the mining operations. Groundwater chemistry changed due to weathering of waste heaps from the Chvaletice deposit and of the settling-pond deposits north of the Chvaletice power plant. Groundwater mineralization of 10–150 g/l is primarily affected by the massive occurrence of manganese and sulphur ions. In addition, relatively high concentrations of chlorides, calcium, iron and manganese have been proved, and very high values of oxidizing potential are also typical.
What was discovered?
Mineral exploitation at the Chvaletice deposit led to the disclosure of one of the richest mineral-collection sites in Bohemia.
About 80 mineral species have been documented, and the mineral of chvaleticeite (manganese and magnesium sulphate), found in 1986, was given a name in honour of this site. The most frequent minerals included pyrite (iron sulphide) which appeared in the form of massive mineralization of gold lustre (so-called “kyzákˮ) or in crystal form. Other frequently occurring minerals included pink rhodochrosite (manganese carbonate) and rhodonite (manganese-containing silicate) whose red crystals composed collection specimens of a special aesthetic value. Siderite (iron carbonate), ankerite (iron and calcium carbonate) and quartz (silicon oxide) were also frequently found.
Rare and highly demanded minerals from Chvaletice included helvite, kutnahorite and tephroite. Of special interest were minerals formed by subaerial weathering of sulphides: most notably iron- and manganese-bearing sulphates and phosphates (delvauxite, destinezite, melanterite, vivianite, pyroxmangite).
At present, the site is accessible only at the last level in the western part of the open-pit mine. At this site, outcrops of graphitic shales feature coatings of secondary sulphates, most notably green melanterite, white epsomite and chvaleticeite forming fine pinkish aggregates. All these sulphates are very brittle, friable and not suitable for collecting.
GVO Železné hory 2014
V rámci projektu Železné hory – GVO byly zhotoveny dvě informační tabule. Nacházejí se na západním okraji starých Chvaletic (Hornická čtvrť), při silnici z Chvaletic do Horušic, v místech se širokým výhledem na popisovanou lokalitu.