The prehistoric mines at Krzemionki lie in a mining field which is shaped like a parabola with arms of unequal length – a shorter one on the northeast and a longer one on the southeast. The field covers approximately 78.5 ha, its width ranging from about 25 m in the northeastern part to about 200 m in the northern part. The complete length is about 4.5 km. More than 4000 prehistoric mines are estimated to lie within this mining field.
Particular mining units represent different kinds of mines characterized by different depth and different systems of exploitation. This was dependent on the location of the flint-producing banks and the engineering and geological characteristic of the deposits. Four kinds of mines have been distinguished:
Pit mines. Simple mines in the form of pits sunk to a depth of no more than 2 m.
Niche mines. Mines of this kind reached from 2.5 to 4 m in depth. At the bottom, characteristic niches were excavated horizontally into the flint-bearing layer, reaching more than 2 m in length, in order to expand the exploitation area.
Pillar-chamber mines.Depth mines reaching 5-6 m below ground surface. Characteristic rock pillars were left unexcavated in order to protect against possible roof collapse. Exploitation of the flint took place in areas from 5 to 8 m away from the shaft.
Chamber mines. The deepest and biggest of the mines in Krzemionki, at the same time the most advanced technologically. They reached a depth of 9 m with mine faces located as far as 20 m from the shaft. The underground exploitation area could have had a size of even a few hundred square meters.
Mining must have involved specialized clans of miners and flint-tool producers with the essential geological and technical expertise. The subterranean mining area was from 55 to 120 cm high, restricted for all practical purposes to the actual flint-bearing layer which was no more than a meter thick. All the work was done on hands and knees or lying down. Work conditions were exacerbated by the constantly low temperature (from 5 to 9ºC) and very high humidity. Burning chips of resinous wood provided sufficient light and little smoke. It has even been suggested that this form of lighting may have additionally forced proper air circulation in the deepest parts of the mines. High geological and engineering expertise of these early miners is contrasted by the simple tools they used to work underground. These were mainly axes made of stone, flint or antler, supplemented with pounders and mallets, as well as a whole set of wooden tools. There was no set period of exploitation for the different mines; some remained in use even for 300 years. The miners at any given time numbered from a few to several. Their work covered flint extraction, transport of the material to the surface and processing of the mineral.
The flint extracted from the limestone was segregated on the spot and only the best quality pieces brought up to the surface in baskets or bags. Flint processing sites were located in the immediate neighborhood of the shaft opening. There, the flint concretions were broken up into smaller pieces and these formed into flint tools – axes and chisels. In the heyday of banded flint as a raw material for tools, that is, in the first half of the 3rd millennium BC, “products” from Krzemionki were traded as far away as 660 km from the mines!