Tracking the history for a new prospection of subsurface assets

Located in the South-Eastern Poland, the Holy Cross Mountains are known for many places of occurrence of hydrothermal metal-bearing vein mineralization. In many ways, ores located here are similar to those known in historical mining districts of the Schwarzwald or the Harz Mountains. The Holy Cross Mountains consist of two tectono-stratigraphic units. The Paleozoic core, composed of Cambrian to Lower Carboniferous strata, was folded during the Variscian orogeny in late Carboniferous. The Paleozoic sequence is locally intruded by minute sub-volcanic dykes and sills of Early Silurian and Early Devonian age and overlain unconformably by Permo-Mesozoic sedimentary sequence with facies characteristic for both German and Polish basins. The Permo-Mesozoic strata was folded and faulted during the Alpine orogeny. Tectonic activity in that period caused an uplift and exhumation of Paleozoic rocks in the central part of the Holly Cross Mountains.

Fig.1. View from the Miedzianka Hill to the Miedzianka village and further SE, February 2019 (photo: P. Kuć).

In the past the region of the Holy Cross Mountains was called the Old-Polish Industrial Region (Zagłębie Staropolskie) and had great importance as an area of mining and processing of iron, lead, zinc and copper ores. The history of metal mining began already in the second century BC and, with different intensity, production lasted until the 1970s. Available records indicate that, along with the production of lead, zinc and copper, also small amounts of silver and gold were obtained. The main deposits associated with Lower/Middle Devonian black shale, Middle and Upper Devonian carbonate rocks and lower Zechstein of Permo-Mesozoic cover were located near villages of Miedzianka, Miedziana Góra, Karczówka and Szczukowskie Górki. Currently no metal production continues in the Holy Cross Mountains and ore prospection done by the Geological Institute in the 50ies to 70ies of the last century did not discover any new deposits, though contributed greatly to understanding of the origin of the ores. Nevertheless, there is still little known about the original ore mineralization, its mineral-petrographic characteristics or tectonic factors controlling its distribution.

New research of archival data showed that historical extraction of metals was conducted only in shallow subsurface – within weathering and cementation zones, down to historical groundwater level at about 80 m below land surface. The nature of the original mineralization, not as amended by weathering and cementation processes, is very poorly recognized. Few available samples of ore veins were taken either from the mining shafts but above a groundwater table or from mining waste heaps, which gives no information of the actual depth of the sample or the place of origin.

Fig. 2. Ore mineralization (malachite, chalcopyrite and pyrite) – the Miedzianka PIG-1 core (photo: P. Kuć).

Therefore, for a full understanding of ore formation processes, it is necessary to obtain new research material originating from the primary veins. So now, more than half a century since the last investigation, the Polish Geological Institute again undertakes both laboratory and field work in order to review and re-evaluate the metal ore potential of the region. The proposed directional drilling is intended to document the occurrence of the zone of mineralized veins and to obtain cores with raw, non-weathered ore samples. Drilling of the first investigative borehole, the Miedzianka PIG-1, located in the historical area of the copper deposits “Miedzianka” has just started. The target depth is 600 m and the inclination of the drilling is 60⁰ towards NWN-N (fig. 3).  It is supposed to allow for the intersection of tectonic zones expected to be associated with poly-metallic ore deposits.

Fig. 3. Geological cross-section through Miedzianka area (after Rubinowski Z., 1971: Ore deposits and their metallogenic position in the Holly Cross-Mountains (in Polish). Biul. IG, 241: 1-164.). 1 – Givietian, Frasnian: limestone, 2 – Famennian: shale with limestone lenses, 3 – Bunter sandstone: sandstones and mudstones, 4 – Bunter sandstone: karstification products – residual clays, rubble, 5 – Quaternary: weathered rocks, 6 – vein ores in karst caverns (residuum), 7 – impregnated ores in clays on contact of Trassic and Devonian, 8 – ore veins, 9 – assumed range of weathering and cementation zones, 10 – contemporary groundwater table, 11 – old underground mine levels, 12 – Miedzianka PIG-1 borehole, 2019.

 

Piotr Lenik, Szymon Ostrowski and Monika Konieczyńska,
PIG-PIB, Poland

 

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