Conglomerates
Where is the site located?
GPS: 49°58’10.07″ N, 15°32’15.03″ E
The site lies in the northwestern part of the Iron Mountains National Geopark, in the area of rather gently inclined northeastern slopes of the Iron Mountains.
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 Proterozoic rocks have been preserved. Rocks at this site originated in the oldest sea in the Czech territory. Volcanoes on the seafloor clustered to form an island arc.
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 parts of the sea, periodically redeposited by huge subaquatic slumps. At the same time, submarine volcanic activity was taking place here, associated with lava effusions. The volcanoes occasionally reached above sea level with their tops, rendering emission of volcanic material into the atmosphere and its re-sedimentation in water and on dry land.
– 550 million years
The end of the Proterozoic is marked by a rearrangement of lithospheric plates, resulting in the Cadomian Orogeny. Then, several adjacent microplates merged together to form the foundation of the Bohemian Massif. The original sedimentary and volcanic rocks in this area were subjected to only weak metamorphism but basically retained their original appearance.
What does the site display today?
The area between Litošice and Sovolusky is formed by Proterozoic rocks ranked within the Sovolusky Group of the Železné hory Proterozoic. Local rocks include grey shales (lithified fine sediments), grey greywackes (lithified coarser sediments) and phyllitic shales (weakly metamorphosed fine sediments).
The most spectacular rocks are the Litošice conglomerates, preserved near the Křížový rybník Reservoir near Litošice. As suggested by their name, these rocks are composed of pebbles of various sizes (reaching even tens of centimetres in size) cemented by sand-sized matrix.
Forested areas around Litošice feature scattered cliffs of volcanic rocks. They are composed of minute lithified fragments of volcanic rocks (tuffs) interspersed with solidified lava bodies. These are referred to as dyke rocks of olivine tholeiites, meta-andesites and meta-rhyolites (formerly spilite–keratophyre formation), locally in the development of tuffs or tuffites.
What was affected by man?
Landscape around this site is characterized by very old bedrock. This was subjected to long-lasting erosion. By now, it has been levelled, eroded and covered with younger sedimentary rocks. Occurrences of natural rock outcrops are therefore very important from the viewpoint of geosciences. The outcrops unfortunately concentrate to forests, and soon become overgrown by vegetation and poorly accessible. Vegetation occasionally completely obscures the geological phenomena. Here and there, geologists make good use of small artificial exposures generated, e.g., by road construction.
What was discovered?
Rocky outcrops of the Litošice conglomerates are ranked among the Czech type localities of Proterozoic conglomerates. The Litošice conglomerates were in the focal point of scientists, with the first research dating to 1891 (Jan Krejčí). The study of pebbles (rock composition, roundness, deformation) provided information on events preceding the conglomerate deposition (e.g., granite pebbles suggest the presence of an older magmatic body; gneiss pebbles suggest that metamorphism must have taken place).
The origin of the Litošice conglomerates is still a subject of dispute. One of the theories assumes that they were formed by a glacier which scraped, abraded and accumulated the pebbles. If so, this would be a proof of a Proterozoic glaciation.
Another theory explains their origin in marine environment, as a result of a subaquatic slump of pebble material into greater depths dominated by the deposition of fine sediments.
As revealed by previous research, volcanic rocks at this site were subjected to subsequent weak metamorphism (low-grade metamorphism) characterized by the presence of specific minerals (pumpellyite and chlorite).
A small spoil bank
Where is the site located?
GPS: 49°58’57.75″ N, 15°30’3.68″ E
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 Proterozoic rocks have been preserved. Rocks at this site originated in the oldest sea in the Czech territory. Volcanoes on the seafloor clustered to form an island arc.
What happened at this site in the past?
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. Thick deposits of sediments accumulated on the sea bottom, and were periodically redeposited by subaquatic slumps. At the same time, submarine volcanic activity was taking place here, associated with lava effusions and ascent of hot thermal fluids. These fluids enriched the rock environment by various chemical elements, such as sulphur, iron, manganese and phosphorus.
What does the site display today?
Weakly metamorphosed rocks having the character of dark phyllitic shales and greywackes with volcanic dykes and sills are grouped within the Chvaletice Proterozoic. These rocks have been preserved along the northeastern slope of the Iron Mountains.
The sequence of strata includes a remarkable bed of black sulphidic shales with lens-like deposits of iron and manganese ores. The ore-bearing strata are of sedimentary origin, enriched by mineral solutions derived from volcanic activity. They were subsequently affected by pressure, temperature and material changes associated with orogenic processes. The area is referred to as the Chvaletice Ore Belt.
What was affected by man?
Minerals of the Chvaletice Ore Belt were exploited primarily in an open-pit mine near Chvaletice. In the near vicinity of Litošice, however, exploratory and mining activities were also taking place in the past. Manganese ore mining was commenced by the Prague Railway Society in the year 1920. Mining was performed in an open pit, although remains after underground mining were present in the area. No precise documentation on the old mine workings has been retrieved.
Mineral exploration realized in the broader area in 1945 to 1957 was aimed at the increase of production at the Chvaletice deposit. Then, exploratory drilling was performed here (LT-6). By that time, the old mine shaft had been walled already. Remains after mining (area of mining operations and spoil tips) are now overgrown by forest vegetation, and the old spoil banks form only small elevations in the present relief.
What was discovered?
Material deposited in the spoil tips and spoil banks was discovered by mineralogists soon. Mineralogically highly valuable specimens of phosphate-group minerals were being unearthed at this site from 1950s to the present. The site is unique by the occurrence of phosphates of multiple generations.
These minerals are of no special beauty from the laymanʼs view. They mostly have an appearance of bulbous or kidney-shaped aggregates of brownish colours (destinezite, delvauxite).
At this site, some of the mineral species have been discovered for the first time in the Czech Republic (prime finds). These include alabandite (manganese sulphide) found in 1954 and koninckite (hydrous iron phosphate) found in 2004.
“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 are located on the square in the centre of the village of Litošice, in a close proximity of a stone menhir from the Litošice conglomerate installed at this site by the local community before. A small area has been polished on the stone to display the individual constituents of the unweathered rock. The best preserved outcrops of the Litošice conglomerates lie some 500 m to the north in a forest near the Křížový rybník Reservoir. Outcrops right of the forest road leading from the reservoir to Seník have been cleaned, and a metallic plate has been mounted here, bearing the name CONGLOMERATE (GPS: 49°58’18.17″ N, 15°32’39.15″ E).
Remains after mineral exploitation are located about 1200 m to the west of the information panels, in a forest by the road towards the Vinice gamekeeperʼs lodge.