site 21

Where is the site located?

GPS: 49° 49′ 51.37″ N, 15° 56′ 51.47″ E

The site lies in the eastern part of the Iron Mountains National Geopark, in the eastern extension of the granite core of the Iron Mountains, forming a rolling landscape with round elevations. The area of the near quarry is used not only for the production of stone but also reveals interesting geological phenomena.

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 which is represented by the Železné hory plutonic complex at this site. This text is therefore focused on rocks which constitute a complex magmatic body solidified at great depths. By the effect of geological processes and geological time, this body got to the proximity of the earth surface.

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, becoming 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.

What does the site display today?

Rocks around Prosetín belong to the Železné hory plutonic complex – an approximately triangular body lying among the towns of Seč in the east, Skuteč in the north and Trhová Kamenice in the south.

This site is located in the northern part of this complex, pertaining to the younger Nasavrky pluton. The rock exposed here is generally called the Skuteč granite – a term used mainly by the stonemasons.

In geological viewpoint, this term denotes a rock group of the granodiorite – tonalite – quartz diorite series, intruded by bodies or dykes of light granite.

The most typical rock is dark grey to greyish-blue, fine- to medium-grained. Its principal light minerals include feldspar (a mineral of the silicate group) and quartz (a mineral of the oxide group). Mafic (i.e., dark-coloured) minerals are represented by biotite (lustrous flakes, a mineral of the silicate group) and amphibole (black-green mineral of the silicate group). Tectonic deformation of rocks at this site is of low intensity, and big blocks of massive rock can be detached.

What was affected by man?

What was affected by man?
The early stonemasons started to work superficial boulders first. They learned to benefit from the natural cleavage of granite and worked stone into simple products of everyday use, like house thresholds, feeding troughs for cattle, fence poles and milestones. Quite often they recruited from farmers. The local mineral wealth started to be utilized more extensively approximately in the latest 19th century. The boom of mining was initiated by the railway construction between Pardubice and Německý (Havlíčkův) Brod, which demanded large volumes of stone. The next acceleration of mining was related with the arrival of Viennese entrepreneurs to Skuteč: they started to supply towns with granite paving stones in large quantities.

At this site, one of the first granite quarries in the Iron Mountains was opened. It is called the Holec Quarry after the name of farmer František Holec.

After the two world wars, the stonemason industry began to decline. Now, numerous abandoned and flooded quarries are distributed around Prosetín. They became a natural element of the landscape. Another pit quarry – the Zach Quarry – was given back to the descendants of the original owners in 1990s. Stone extraction starts with the detachment of relatively large blocks of rock. These are further dimensioned into wall linings, kerbs and paving stones.

What was discovered?

The pit quarry provided an insight in the core of the magmatic body of the Nasavrky pluton, which has a complex zoned structure in this area.

Hitherto conducted research confirmed the presence of two rock bodies (intrusions) of different ages, which pass more or less continuously into each other.

The older intrusion is composed of light medium- to coarse-grained granodiorite often containing sharply bounded inclusions of dark granodiorite. The dark colour is due to the high abundance of mafic minerals.

The younger granodiorite body shows a fine-grained texture. It is homogeneous, with occasional large aggregates (crystal accumulations) of light feldspar.

In addition, numerous dykes and dykelets of light aplite and biotite granite are also present here. Mineral pyrite (iron sulphide) has been documented to form radial aggregates on tensional joints, similar to sun drawings.

“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 Prosetín village, by the road between Prosetín and Skuteč, next to a chapel.

Even granite can smile… (fragmented xenoliths in an aplite dyke) (Daniel Smutek)