1 Cabaˇa J., 2002: Geological Structure and Physical Features Of

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

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 - 6T - 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). The Devonian epigenetic dolomites occurring in Zbrza region also show the high values of specific density, kept within the limit of 2,82 g/cm3. The Devonian and Triassic formations connected with process of epigenetic dolomitization show the increased values of specific density whereas values of primary Roethian and dolomites as well as Gogolin limestones are

not bigger than 2,78 g/cm3 (Fig. 3).

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Fig. 3 Histograms of specific density of rocks(M) in Triassic and Devonian formations

Porosity n [%]

Porosity of the examined rocks decreases with depth. For the Triassic formations at a depth of 140 œ 150 m it changes from 5% to 20%. Consequently, for the Devonian formations, which are far down, the porosity is less than 8% .

5 P = 14,536 - ,0521 * m, Coef. of correlacion = -,5517 30

25 Regression 95% level of trust 20

n -porosity [%] 10

0 20 60 100 140 180 220 260 300 m - depth from ground surface [m] Fig. 4 Relationship between porosity (n) and depth of occurrence (m) of rocks in borehole; PZ-1, PZ-2, PZ-3, PZ-4 (Zawiercie ”I‘ Zn-Pb ore deposit) .

Generally, the changeability of porosity is distinctly noticeable according to lithology that is observed in profiles. Ore-bearing dolomites and Diplopora dolomites occurring in the Triassic formations and also in the top of the Devonian ones indicate remarkably the higher value of porosity in comparison with the Gogolin limestone as well as with deep-lying Devonian calcareous dolomites and limestones. There seems to be a conspicuous connection between subsidiary dolomitization appearing in the [ m ] Devonian and Triassic formations and well-marked Q increase of porosity of these rocks. T3 n [%]

2 Absorption capacity nw [%] T2

Weight absorption capacity was mainly analysed T2 dk

and by comparing its values with porosity, the 1I-II T2 correlation between the two parameters was found. f - coefficient of succinctness For Diplopora dolomites and Roethian dolomites, 3 T1 the absorption capacity ranges from 4 to 6% whereas for the Devonian and Triassic ore-bearing

nw [%] dolomites is less (2 œ 4%). Gogolin limestones and D deeper lying Devonian rocks are characterized by absorption capacity less than 2% (Fig 5). Fig. 5 Changeability of porosity (n) [%], absorption capacity (nw) [%] and coefficient of density of rocks (f) in profile borehole PZ-3

6 Strength properties of rock

Complex research including shear strength, tensile strength, comprehensive strength as well as crack tests for rocks in pre-critical and post-critical states should be made, to gain a broad view of rock strength properties. However, although succinctness tests were only made for the rocks in the investigated area, their results let the author get a suitable rock strength classification.

Density of rocks (f)

The values of coefficient of density of rocks (f) were determined according to the Protodiakonov method. For the Triassic formations the variability of these values are of 1œ10 and for the Devonian ones from 2 to 20. The lowest variability of the coefficient is observed for the Gogolin limestones and Roethian dolomites whereas the highest one is connected with the Triassic ore-bearing dolomites and Devonian rocks. Based on the Protodiakonov rock classification taking into account the coefficient of density of rocks (f), the oreœbearing dolomites were classified under classes from II (for

strong rocks) to VI (for relatively weak ones) (Fig. 6).

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Fig. 6 Histograms of coefficient of density of rocks (f) in Zawiercie ”I‘ Zn-Pb ore deposits

7 Gogolin limestones show relatively high values of the coefficient of density of rocks, however, the highest ones belong to the Devonian formations. According to the Protodiakonov classification, the rocks whose coefficient of density of rocks (f) equals 15 are classified as rocks with very high density while those with f = 20 as rocks with extremely high density. The degree of variability, is affected not only the physical properties of rocks, but also by the density of cracks, the tectonic activity, the breccia process and the intensity of subsidiary changes connected with hypergenesis. Lower density of rocks occurring in the top of the Devonian formations, Gogolin limestone and Diplopora dolomites can be connected with redeposition of argillaceous materials, chemical and physical desintegration of dolomites and limestones, leaching of cracks and caverns as well as interlayer joints.

Conclusions

Physical and strength properties of Devonian and Triassic rocks were changed due to epigenetic development of mineralization. The highest values of porosity can be found in the primary dolomites which belong to the Upper Bunter sandstone (Roetian) and to the Middle Muschelkalk limestone. The Devonian dolomites which occur deeper have lower values of porosity than the similar ones appearing in the Triassic formations. The development of mineralization has a big influence on increase of density of rock, simultaneously decreasing porosity of rocks and their absorption capacity. The zones of mineralization are characterized by cracks and interstices, which are macled by calcite, barite and Zn-Pb-Fe sulphides. Simultaneously there is a clear correlation between quantity of argillaceous materials occurring in a rock and a decrease of its succinctness. Intervals enriched with argillaceous materials also correlate with the mineralised karst zones. Their coefficients of density of rocks are lower in comparison with ore-bearing dolomites occurring in the surroundings. The dispersed mineralization of Zn-Pb sulphates can be found in these dolomites. Devonian and Triassic dolomites show distinctly the higher values of specific density in contrast to limestones and dolomites belonging to the Lower and Middle Muschelkalk limestone. On the average, the increase of density (2,7 œ 2,82 g/cm3) does not seem to be high and for this reason it is difficult to estimate how far the geophysical methods can be used in such a case.

8 However, the difference in porosity and density of secondarily mineralised and dolomitized rocks may be more clearly visible for geophysical methods in case of watered rock mass. That is why early recognition of hydrogeological conditions is absolutely necessary for the examined rock mass.

References

Buˇa, Z., M. Jachowicz & J. Aaba 1997. Principal characteristics of the Upper Silesian Block and Maˇopolska Block border zone (southern Poland). Geol. Mag. 134 (5): 669-677. Cambridge University Press. Cabala, J. & L. Teper 1990. Testing of strike-slip style of the NE border of the basis of structural studies in Zawiercie region (in Polish). Pap. Centr. Mining Inst. Series Additional: 96-108. Katowice. Cabaˇa J., 1995: Structural characteristics of tectonic horsts and grabens in the area of zinc and lead ore occurence near Olkusz. In Mechanics of Jointed and Faulted Rock. Balkema edited by H.P. Rossmanith . Institute of Mechanics, TU Vienna April p. 335- 340. Gaˇkiewicz T. & S 9liwiEski 1985: Charakterystyka geologiczna TlUsko-krakowskich zˇóV cynkowo-oˇowiowych. Rocz. PTG, nr 53, s.63-90. HaraEczyk C., 1994:KaledoEskie krakowidy jako górotwór transpresyjny. Prz. Geol., nr 11, s.893-901. PiniEska J. (red): 1999: WˇasnoTci wytrzymaˇoTciowe i odksztaˇceniowe skaˇ. Cz. III Jura Krakowsko-CzCstochowska. Katalog t. 5 Wyd. Uniwersytet Warszawski. Vrabetz E. & M. 9lusarek 1993: Proekologiczna technologia wzbogacania rudy Zn-Pb ze zˇoVa Zawiercie. Rudy Metale. R. 38, nr 6 s. 151-155. Aaba J.: 1996: PóWnokarboEska aktywnoTş przesuwcza strefy granicznej bloków górnoTlUskiego i maˇopolskiego. Prz. Geol., nr 2, s.173-180.

9 Jerzy Cabaˇa

Wydziaˇ Nauk o Ziemi, Uniwersytet 2l3ski

Budowa geologiczna i niektóre cechy fizyczne górotworu w obszarze zˇo=a Zn-Pb Zawiercie

Streszczenie W obszarze zˇoVa Zawiercie I w latach osiemdziesiUtych wykonano badania mineralogiczne, chemiczne, technologiczne rud Zn-Pb oraz analizC bazy zasobowej. Przeprowadzono takVe badania cech fizycznych (gCstoTci wˇaTciwej, porowatoTci, wspóˇczynnika zwiCzˇoTci, nasiUkliwoTci) skaˇ w otworach zlokalizowanych w rejonie projektowanych szybów. Dane z tych badaE pozwalajU okreTliş i porównaş niektóre cechy fizyczne górotworu triasowego i dewoEskiego. Cechy fizyczne i wytrzymaˇoTciowe skaˇ triasowych i dewoEskich zostaˇy zmienione w wyniku rozwoju epigenetycznych procesów mineralizacji. NajwyVszymi porowatoTciami charakteryzujU siC pierwotne dolomity naleVUce do górnego pstrego piaskowca (retu) i Trodkowego wapienia muszlowego. Dolomity wystCpujUce gˇCbiej w dewonie majU niVsze porowatoTci od podobnych dolomitów w triasie. Rozwój procesów mineralizacji wpˇywa na wzrost zwiCzˇoTci skaˇ oraz zmniejsza ich porowatoTş i nasiUkliwoTş. Strefy okruszcowane charakteryzujU siC zabliWnionymi przez kalcyt, baryt, siarczki Zn-Pb-Fe spCkaniami i pustkami. Obserwuje siC jednoczeTnie wyraWnU zaleVnoTş miCdzy iloTciU materiaˇu ilastego w skale a zmniejszeniem jej zwiCzˇoTci. Interwaˇy bogate w materiaˇ ilasty korelujU siC ze strefami skrasowiaˇymi. W okruszcowanych strefach krasowych wspóˇczynniki zwiCzˇoTci sU niVsze w porównaniu do otaczajUcych je dolomitów kruszconoTnych cechujUcych siC wystCpowaniem rozproszonej mineralizacji siarczkami Zn-Pb. WyraWnie zaznaczajU siC wyVsze gCstoTci wˇaTciwe dolomitów triasu i dewonu w porównaniu do wapieni i dolomitów dolnego i Trodkowego wapienia muszlowego. 9redni wzrost gCstoTci od 2,7 do 2,82 g/cm3 nie jest wysoki i trudno wskazaş czy bCdzie moVliwe wyznaczenie tej granicy metodami geofizycznymi. JednakVe róVnice w porowatoTci i gCstoTci skaˇ wtórnie zdolomityzowanych i okruszcowanych mogU byş lepiej czytelne dla rozpoznania metodami geofizycznymi, szczególnie w sytuacji górotwór bCdzie zawodniony. Dlatego konieczne jest wczeTniejsze rozpoznanie warunków hydrogeologicznych badanego górotworu.