Cabaˇa J., 2002: Geological structure and physical features of rock mass in Zawiercie Zn-Pb ore region. Publ. of Inst. Geoph. Pol. Ac. Sci. Monografic Volume M-24 (340) p. 195-203. GEOLOGICAL STRUCTURE AND PHYSICAL FEATURES OF ROCK MASS IN ZAWIERCIE Zn-Pb ORE REGION Introduction A lot of work to discover and document Zn-Pb ore deposits has been done for 30 years in SilesiaœKraków region. Among well-recognised deposits only few ones such as Klucze or Zawiercie ”I‘, have fulfilled some conditions as to the quality and resource criteria. Zn-Pb ore resources being exploited at present (e.g. in Pomorzany mine or Trzebionka mine) have already been depleted in great part and it is predicted that mining activity will have been finished there by the year 2006. However, taking into account the economic aspects, e.g., low price of metals and high price of production, it seems unprofitable to invest in building a new mine. In the late 80‘s, detailed studies were carried out in the Zawiercie ”I‘ deposit. Collected data from the boreholes (PZ), mineralogical and chemical technology analyses (Vrabetz, and 9lusarek, 1993) as well as laboratory tests determining physical parameters of rocks such as density, porosity, density of rocks and absorption capacity let the author determine and compare some physical features of Triassic and Devonian rock mass. Geological structure of rock mass including Zn-Pb ore deposits The Zawiercie deposit as well as other Zn-Pb ores occurring in Olkusz-Zawiercie region is situated west of the KrakówœLubliniec tectonic fold zone (Fig. 1). The deposits of this region, including Zawiercie lie over the vast transpressive Paleozoic shearing zone (NW-SE direction) (Aaba, 1996). In Zawiercie region, the Paleozoic complex consists of the Cambrian, Silurian, Ordovician, Lower and Middle Devonian formations and it is relatively shallow. In Klucze and Olkusz region (south-east of Zawiercie) the Paleozoic complex is additionally represented by Carboniferous and Permian formations. The landscape from ZawiercieœChechˇoœKluczeœOlkusz to DCbnik has a characteristic appearance of the uplifted Devonian formations lying in accordance with NW-SE oriented tectonic fold zone. It indicates the importance of the zone in forming the structural features of the Paleozoic rock mass (Cabaˇa and Teper, 1990; HaraEczyk, 1994, Buˇa 1994, Aaba 1996). The tectonic fold zone occurs on the boundary of crystalline Maˇopolska massif and Upper- Silesia massif (Buˇa, et al., 1997). In Zawiercie region the Triassic formation is deposited 1 directly on eroded surface of the Paleozoic complex consisting of the Silurian, Ordovician, the Middle and Upper Devonian formations (Cabaˇa and Teper, 1990). Gda%sk Lubliniec PWarszawa ola Myszków nd T Zawiercie Katowice PZ-3 Kraków ZawiercieSosnowiec Siewierz Goˇuchowice Zawiercie I Tarnowskie Zn-Pb Ore Góry C2 Bytom Chechˇo TKlucze Bolesˇaw C2Sosnowiec Sˇawków Olkusz UT SC B Jaworzno T C2D!bnik Trzebinia 010 km Krzeszowice Chrzanów - 1- 2 - 3 - 4- 5 C - 6 T - 7 2 Fig. 1 The map showing the limit of zinc and lead mineralization in the Triassic & Devonian deposits. 1 - erosional edge, 2 -fault, 3 - uplifted Devonian sediments, 4 - zones mineralised with Zn-Pb sulphides, 5 - fault zone Kraków-Lubliniec (KLFZ) (after Buˇa 1994), 6 œ Upper Carboniferous sediments (USCB œ Upper Silesian Coal Basin), T œ Triassic sediments (after Gaˇkiewicz and 9liwiEski, 1985). Devonian and Triassic formations in the Zawiercie ore deposit The lithological structure and thickness of the Devonian and Triassic formation were determined on the basis of data obtained from 25 boreholes which had been located in the west and central part of the Zawiercie ”I‘ deposit. The Devonian formation is represented by carbonate rocks such as fine-crystalline dolomites and calcareous dolomites which are grey or pale grey compact and cavernous as well as cracked. Dolomites are locally mineralized with Zn-Pb-Fe sulphides and then their structure is similar to the Triassic ore-bearing dolomites. There can also be found calcareous clay shales and grey or dark-grey, fine-crystalline compact limestones. In some cores taken from boreholes, the breccia of tectonic origin and also karst forms filled up with crystalline calcite, argillo-arenaceous substance and argillo-limoniteous one were observed. Ore-bearing dolomites mostly occur in top of the Devonian formation and they continue as Lower and Middle Triassic superincumbent sediments. However, dolomites and dolomitic limestones occurring in the top of the Devonian formation with a thickness of 30 œ 70 m are quite changed. This is a result of a long-term hypergenic activity. These macroporous and cracked dolomites are saturated with argillaceous 2 substance which fills vertical fissures, cracks and karst pockets; therefore, the rock mass is less coherent. The size of the karst caverns existing in the rock mass is from 2 to 3 metres and calcite mineralization, barite mineralization (ZL 8-9) and also dolomitization (veiny dolomite fills fissures ZL 8-19) can be found in their adjacency. The karst systems occurring in the top of the Devonian formation were backfilled with crush breccias, which poit to the rocks characterised by weak features of strength . A considerable changeability of ore-bearing dolomites occurrence can be found in the Devonian formation. These dolomites were not formed as a strataband-typed horizon but they seem to be connected with irregularly developed zones of dolomitization. The development of the Devonian dolomitization depended on certain primary features of rock mass, such as porosity, macrocavernicity, fissuring and the course of tectonic process. In particular, the variability of these features is noticed in the tectonically uplifted Devonian formations (Cabaˇa, 1995), of which is the Zawiercie region an example. Triassic formation in the uplifted area is represented by discordantly lying epigenetic ore- bearing dolomites, Diplopora dolomites and Keuper argillaceous sediments (Fig. 2) which come into direct contact with Devonian formations. More complete Triassic complex, including Roethian dolomites, Gogolin limestones, ore-bearing dolomites and Keuper sediments can be found in the area where the Devonian formation occurs at a depth of 70 œ 100 m. Breccias and conglomerates are typical of the Lower and Middle Triassic series. During the Triassic period, the uplifted Devonian rocks became a recharge area for carbonate sediments (Cabaˇa and Teper, 1990). SSW NNE [ m ] a.s.l. 350 2 T 2 T2 2 T 2 300 T2 dk 2 1I-II T2 T 2 T dk 2 T dk 2 2 D 250 T dk 1I-II 2 T 2 1I-II 3 T T 1 2 200 1I-II T 2 3 3 T 1 T 1 D S 150 - 1 - 2- 3 Fig. 2 . Geological cross-section in west part of Zawiercie I Zn-Pb ore deposits. 1- Zn-Pb ore-bodies zone, 2œ 3 1I-II tectonic breccia, 3œ faults, Sœ Silurian, D- Devonian T1 - Roet, dolomites T2 - Gogolin limestones 2 T2dk - Ore-Bearing dolomites T2 - Diplopora dolomites T3- Keuper. 3 Physical features of the Devonian and Triassic formations Well-recognised physical features as well as regularities in their forming in the Devonian and Triassic rocks surrounding ore deposits are essential in search for commercial metal concentrates. Determination of rock mass characteristics has a great effect on a proper economic exploitation. The uplifted Triassic formations, for example horsts, differ in structural properties from the lowered ones such as trenched faults (Cabaˇa, 1995). Therefore, it is suggested that uplifted Devonian formations can vary from the subsided ones of the same age. For the aim of studying perspective ore deposits and designing of exploratory holes in the areas of Zawiercie ”I‘, Klucze and Chechˇo, it is crucial to examine carefully the morphology of the top of Devonian formations. Differentiation of physical properties of these shallow- lying rocks (0 œ 100) affords the possibilities for applying geophysical methods using seismic exploration, electrical-resistivity surveying and magnetic surveying. The greater the number of data, including the properties of rock mass, the better the interpretation of the geological structure. To determine some features of rock mass, laboratory tests establishing with specific density, porosity and absorption capacity were carried out according to the Polish Standards PN-66/B- 04100 and PN-85/B-04101. After macroscopic observations the drillœcores were divided into similar segments to obtain visually homogenous samples. A total of 810 running metres of drill cores were used and about 220 analyses were carried out for each laboratory test mentioned above. From 1984 to 1986, the drill cores were taken from boreholes numbered PZ-1, PZ-2, PZ-3, PZ-4 to estimate the physical features of the rocks of this region with the aim of designing pit shafts and headings for Zawiercie Zn-Pb Mine. However, the results of that study have not been used in any significant way that time, because finally the building of the mine seemed to be non-economical. But those results have just been computerized by the author using STATISTICA programme (Stat Soft Firm). According to the setting of data base, it is possible now to present most of the regularities connected with physical features of the rock mass, in particular lithological parts of Zawiercie deposits, what was just shown in this article. Specific density ρρρ [ g/cm3] The results of specific density tests obtained from the samples of drill cores are in a range of 2,68 œ 2,88 g/cm3. For the Triassic rock mass the highest values are characteristic of Diplopora and ore-bearing dolomites as well as dolomites occurring in the top of Devonian 4 formations (2,78 œ 2,86 g/cm3) (Fig. 4). Slightly lower values of specific density (2,68 œ 2,74 g/cm3) were determined for the Triassic dolomites taken from the Siewierz quarry and for the ones appearing in the Chrzanów basin (PiniEska, 1999).