site 23

Where is the site located?

GPS: 49° 53′ 20.56″ N, 15° 50′ 20.13″ E

The area lies in the central part of the Iron Mountains National Geopark, in the proximity of its northern boundary. Its relief lowers into the flat East Bohemian Table towards the Chrudim area in the south, and a slope of the Iron Mountains rises towards the Nasavrky area in the north. This site is located in an old mining village, where accumulated minerals were exploited and processed by our ancestors for centuries.

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 with a variety of geological units. Here, the Železné hory plutonic complex of magmatic origin borders with specific metamorphic rocks along its northern margin and with sedimentary rocks deposited by Late Cretaceous sea.

What happened at this site in the past?

– 350–300 million years

Carboniferous and earliest Permian times (the fifth and sixth periods of the Paleozoic era) were marked by unrest due to major orogenic processes (Variscan Orogeny). Progressive collision of two continents – Laurasia in the north and Gondwana in the south (this area lies at its margin) – created the supercontinent of Pangea. This area became a part of a large mountain range of the Variscides (Hercynides), which extended from todayʼs Spain across southern England, France and Germany, as far as to central Europe. This mountain range became a solid basement of the Bohemian Massif. The orogenic processes resulted in bending, fracturing and shifting of the existing rock masses, inducing the rise of huge volumes of hot magma. Some magma batches ascended along deep-reaching fractures and reached the earth surface. Other portions of rising magma remained under the surface and constituted large, loaf-shaped bodies. The ambient rock complexes were subjected to material change and dynamic deformation by the effect of orogenic pressures.

– 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 also shallow but – unlike the previous sea flooding – warm. This site was located on a seashore where shoreline cliffs protruded from sandy beaches, breaking the waves. The sea was inhabited by various bottom-dwelling organisms, such as oysters or brachiopods.

What does the site display today?

This site is located on the northern margin of the Železné hory plutonic complex, represented by the Nasavrky pluton in the area where it is lined by the so-called Lukavice Series. This series forms a belt, which can be traced from Hrbokov across Trpišov to the area of Lukavice, where it wedges out. It comprises rocks of probably subvolcanic origin. This means that their solidification and crystallization occurred not deep under the earth surface, prior to the rise of the pluton – either in Early Paleozoic or in Proterozoic times. The exact origin and appearance of these rocks has not been fully explained yet: they were subsequently subjected to dynamic deformation and material change. This combination of processes produced specific rocks, such as porphyries, porphyroids, metarhyodacites and sericitic schists.

The presence of a major tectonic structure, aiding the ascent of hydrothermal fluids, resulted in an intense ore mineralization. One of the dominant minerals is gold-shining pyrite (iron sulphide), which forms veins, lenses and impregnations, most frequently in sericitic schist.

In the south, rocks of the Lukavice Series pass into granitic rocks of the Nasavrky pluton; they are enclosed by granitic magma in places. The Nasavrky pluton is represented by the Žumberk granite at this site.

Upper Cretaceous sediments of the Bohemian Cretaceous Basin have been preserved in the northern vicinity of the Lukavice village. They are represented by yellow to greyish-green coarse- to medium-grained sandstones of Cenomanian age.

What was affected by man?

Mineral mining and processing has a long history beginning in the 16th century and terminating at the end of the 19th century. The latest extensive geological survey of the region was conducted in the first half of the 20th century. Mineral resources in this area were discovered successively, with the first processed mineral being limonite (hydrated iron oxide) – it forms at the shallowest depths, in the so-called iron hat (or, gossan). It was used for the production of iron. Pyrite (iron sulphide) was discovered later, after the mining pits deepened, and became the principal exploited mineral. It was processed for sulphur and alum. Sulphur was produced especially when the mines were in possession of the Auerspergs: it was used as a component for the preparation of gunpowder. Underground mining progressively developed and four shafts were excavated. The last of them, the Bartholomew Shaft, reached the depth of 163 m. The break of the 18th and 19th centuries is also marked by the growth of a chemical plant, which finally became the largest one in the whole Habsburg monarchy. Besides the isolation of sulphur, production of sulphuric acid was introduced.

Pumping of minewater was an important assignment at the Lukavice shafts. This work was considerably discomforted by the damage induced on water pumps and water pipes by acidic minewaters. In the early 19th century, the mines and the chemical plant yielded an annual profit of 220,000 goldens for their owner. The profession of a miner was held in deep esteem at Lukavice, often passing from fathers to sons. Closure of the Lukavice mines in 1892 was probably called by the competitive prices of pyrite from abroad and by the need of high financial costs for the modernization of the mine and the chemical plant. In addition, geological exploration of 1950s corroborated poor prospects of this area towards further pyrite mining. At the same time, a huge pyrite deposit was confirmed in the Chvaletice area at the northwestern end of the Iron Mountains.

Underground mining and related mineral processing left behind undesirable traces on the environment. Old spoil tips in the village and the former settling ponds became sources of contamination. Material from the spoil tips was still in use for chemical industry in the 1950s.

What was discovered?

Solution of the geological puzzle of the origin and age of rocks of the Lukavice Series was attempted several times by the geologists, mainly in the 20th century. Their opinions were by no means unanimous. Much information was obtained from extensive geological exploration of the deposit conducted in the early 1950s. Then, old mine workings around the preserved Bartholomew Shaft were revised, and a new drilling survey (20 boreholes, max. 110 m deep) was completed in the Lukavice area including the excavation of four new test shafts (about 35 m deep). New information was summarized by Dr. Jindřich Vodička in his study of 1966, where the main rock types were described. Light-coloured quartz porphyry is the most significant one. Its very fine-grained groundmass contains phenocrysts of quartz and altered feldspars. Another important rock is sericitic schist (sericite is a flaky, altered mineral of the silicate group).

Dr. Jindřich Vodička worked for the Geological Survey in Prague. He was also very active in promotion of geosciences among the public. He possessed wide range of knowledge in the field of history and in all geology-related issues in the Iron Mountains region, acting as a local patriot. He was spreading scientific knowledge in lectures and articles in an understandable and enjoyable way among children, adult listeners and readers. He was equally enthusiastic in photographic documentation of geological phenomena as well as the landscape as a whole.

“The Iron Mountains – a geologically significant region” project of 2014

An information panel was manufactured within the project of “The Iron Mountains – a geologically significant region”. It was erected in the centre of the Lukavice village, in front of the portal of the Bartholomew Shaft.

Pyrite (Daniel Smutek)