Běstvina deposit
Where is the site located?
GPS: GPS: 49°49’27.57″ N, 15°37’23.91″ E
The site lies in the northwestern part of the Iron Mountains National Geopark, near its western border, right on the steep slope of the Iron Mountains. Remains after mining activities have been preserved in a forested area.
What is the geological position of the site?
The site is located in the Bohemian Massif, in the Kutná Hora–Svratka Region, where metamorphosed Proterozoic rocks are exposed. These rocks are silent witnesses of the past orogenic processes and the presence of an old fracture in the Earth crust which enriched the rocks by spectacular minerals.
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, fine sediments were deposited in the sea, accompanied by submarine lava effusions.
- 545 million years
The end of the Proterozoic is marked by a rearrangement of lithospheric plates, resulting in major folding – the Cadomian Orogeny. The original rocks were subjected to metamorphism by high pressures and temperatures. A deep-reaching fracture originated in the Earth crust.
– 350–300 million years
At the end of the Paleozoic, the rocks were subjected to another orogenic process – Variscan Orogeny. Again, this process changed their material composition and induced deformation of individual rock bodies. The deep-reaching fracture in the Earth crust became an ascent path for hot fluids derived from metalliferous magma chambers.
What does the site display today?
The main crest of the Iron Mountains at this site is formed by metamorphic rocks of the Kutná Hora Crystalline Complex: chiefly by paragneisses, migmatites and marbles. The rocks were lying close to an old deep-reaching fracture, which is called the Železné hory Fault (Iron Mountains Fault) in this area. As such, they were crushed and fragmented into a dense network of joints and fractures. The pores and fractures were progressively penetrated by hot mineral fluids, which gave rise to a veined hydrothermal mineral deposit.
What was affected by man?
Mine exploration, conducted by the exploration company of Geoindustria Jihlava, was started in 1971 by driving a gallery. The explored deposit was passed on for its exploitation, which lasted between 1973 and 1994 (the last ore cart was loaded on June 16, 1994). The deposit was exploited by the companies of Rudné doly Příbram and Fluorit Sobědruhy. Mining was performed at four levels, with the shaft reaching a depth of 170 m. In total, 8658 m of horizontal galleries and 1508 m of vertical chimneys have been driven. The close ambience was affected by mining activities. The original forest vegetation was removed, and a huge concrete portal of mine entrance was built in the rock face. Spoil heaps were rising next to the mine gallery. These have been covered by vegetation or turned into foundations for supportive operation buildings of the former mine. Now, the site of the former mine features a closed entrance portal to the gallery with rail remains. It lies on a private land – this means that the mine is not accessible. After the closure of the mine, pumping of minewaters stopped and the mine became flooded. Acid minewaters dissolve sulphides and sulphates containing heavy metals. Then, enriched with environmentally hostile substances, they come out onto the surface. A new minewater purification plant, removing these substances, was put into operation in 2003.
What was discovered?
Mineral exploitation concentrated mainly on the production of fluorite (calcium fluoride) and barite (barium sulphide). The deposit yielded 163,247 tonnes of ore material, which was processed especially for the needs of iron-making industry and chemical industry. Cavities in hydrothermal veins produced some good examples of crystal-forming minerals, which became the showpieces of many mineral collections. The Běstvina deposit was very typical by its coloured cubic crystals of fluorite, nice crystal druses of barite, calcite and quartz together with crystals of galena (lead sulphide) and sphalerite (zinc sulphide).
Outcrop of Upper Cretaceous marlstones near a forest road
Where is the site located?
The site lies in the northwestern part of the Iron Mountains National Geopark, near its western border, right on the steep slope of the Iron Mountains. A remarkable outcrop of tectonically deformed marlstones lies near the road to the abandoned Běstvina – Javorka Mine.
What is the geological position of the site?
The site is located in the Bohemian Massif, in the Kutná Hora–Svratka Region, where metamorphosed Proterozoic rocks are exposed. These rocks are overlain by Upper Cretaceous sediments. They provide information on the presence of sea and the subsequent orogenic processes controlled by an old fracture in the Earth crust.
What happened at this site in the past?
– 95 million years
The area composed of older metamorphic rocks, once forming a mountain range, got progressively eroded over millions of years. Finally, it turned into a flat elevation and became flooded by a shallow sea in the Late Cretaceous. This site was located close to seashore, where sediments were deposited. The underlying sediments were unstable, located in the proximity of a deep-seated tectonic fracture (a lineament).
– 25 million years
In the course of the Tertiary, this area was composed of hard metamorphic rocks covered by deposits of the Late Cretaceous sea. It was segmented into separate crustal blocks by fractures. It became incorporated in the Eurasian plate and drifted to the Northern Hemisphere. The Alpine Orogeny in the SE part of Central Europe built the Carpathians and the Alps, and initiated the movement of crustal blocks by as much as several hundred metres relative to one another. The sedimentary cover became soon eroded.
What does the site display today?
The area now displays relics of Upper Cretaceous sediments along the whole southwestern slope of the Iron Mountains – the so-called Long Furrow Cretaceous. The sediments have the character of sandstones, siltstones and claystones; they represent original marine deposits, hardened through ages. Sedimentary rocks formed by fine sand with high calcium content are also called “opokasˮ (spiculitic marlstones). The Czech name itself suggests that the rock is characterized by jointing confined to individual strata. The present dip angle of the originally almost horizontal strata of Upper Cretaceous sediments is due to the proximity of the Železné hory Fault (Iron Mountains Fault). Sediments have been preserved only along the subsided southwestern slope of the Iron Mountains in a narrow strip, segmented into separate blocks. In contrast, they have been completely eroded from the uplifted block of the Iron Mountains.
What was affected by man?
Construction of roads accessing the mining area of Běstvina–Javorka resulted in the opening of man-made exposures of local rocks. Owing to this fact, otherwise hidden geological phenomena have been unveiled.
What was discovered?
Upper Cretaceous spiculitic marlstones are exposed at a roadside. The style of their tectonic deformation evidences the proximity of the Železné hory Fault: the rocks display the so-called rodlike disintegration. The rock disintegrates into elongate rods with diamond-shaped cross sections. This feature originated by a combination of partings along the original bedding planes and a secondary joint system resulting from tectonic forces in the fault proximity.
“The Iron Mountains – a geologically significant region” project of 2014
Two information panels were manufactured within the project of “The Iron Mountains – a geologically significant region”. They were erected near Road 340 from Seč to Běstvina, at the site of its intersection with a forest road, some 300 m north of the community of Zbohov. The described sites are accessible using local forest roads, lying some 1.5 km to the north. The outcrop of Upper Cretaceous spiculitic marlstones above the minewater purification plant has been cleaned of vegetation and small native woody plants.