The quarry of Horní Dvorce is located in the north-western part of the cadastral area of Horní Dvorce in the South Bohemian Region. A small to medium grained granite of the Mrákotín type is the main rock type here. The rock is located under a cover, which is represented here by sandy-clayey soils, loamy sands and clayey-rocky rubbles. Granite is mined in block structures, exclusively for the needs of coarse and fine-stone production with the use of natural block separation of the rock.
Spatially and genetically, the deposit of Horní Dvorce is part of a large massif of granitoid rocks referred to as the central pluton. The deposit is located on the western edge of this pluton and consists of two-mica granite, which is mostly medium to coarse-grained. The rock texture is omnidirectional, the structure is porphyritic. In the vicinity of the village of Horní Dvorce, the granularity of the rock changes significantly. It is noticeably reduced with disappearing phenocryst. There are two basic facies here – grey-brown to yellowish granite and grey granite with a bluish tinge. The deposit contains both elements of so-called large tectonics and small tectonic elements. In some parts of the quarry, there is a significant increase in the frequency of one direction of crevices – the so-called crushed zones. The rock in these zones is practically unusable for any type of stone production.
The supply openness is sufficient for exploitation. Under the existing conditions, the service life of the deposit is estimated to approximately the year 2029. Preparatory work is carried out immediately prior to the actual mining operations. Basically, it is the creation of open areas in rock massif so that it is possible to implement the exploitation of the raw material for the needs of classic rough stone production. Disconnection is carried out by means of explosives with sliding effect, particularly by black blasting powder. The creation of open areas, i. e. the actual preparatory work for exploitation, is carried out on the deposit via the so-called “penetration of the street” by means of rock explosives. When conducting the exploitation works, the tectonic structure of the rock massif is used to the maximum extent so that the artificial creation of other degrees of freedom is minimal. Mining is carried out in three levels whose height does not exceed 10-metre blocks which are gradually excavated from top to bottom according to natural blockiness and separation. The progress of walls of particular floors as well as the progress of mining work within the floors goes from south to north in the master plan. However, this general direction is not strictly observed in particular cases, as the detailed direction of advance is limited by the local tectonic structure of the rock massif. The actual mining operations are carried out primarily by small-scale blasting operations with the use of explosives with sliding effect.
The current product range includes products of rough stone production. The “Mrákotín-type” granite in grey, yellowish and yellow-grey colour is the raw material here. The production programme is divided into several groups including mainly road construction programme, rough stone production for technical constructions, rough stone production for other constructions and mining of granite blocks intended for further processing.
For World of Stone provided by authors:
Ing. Martin Štrejbar, Ph.D., doc. Ing. Milan Mikoláš, Ph.D., Ing. Petra Gernová
Photo: Ing. Martin Štrejbar, Ph.D.