Cabała 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.Z powrotem do publikacje Jerzy Cabała
STRUCTURAL CHARACTERISTICS OF TECTONIC HORSTS AND GRABENS IN THE AREA OF ZINC AND LEAD ORE OCCURRENCE NEAR OLKUSZ
Abstract:
Field survey in underground excavations of Zn-Pb mines in the Olkusz area gave basis for differentiation of structural features in tectonic horsts and grabens. The distribution and linear density of cracks located on both uplifted and downthrown sides of faults were discussed. Various geometry of fault and crack systems depicted in the area allowed to draw conclusion of different type of tectonic stress which have occurred within horsts (tension) and grabens (compression). A proposed thesis assumed distinctive impact of horizontal tectonic movement in the deep basement of Kraków-Myszków large-scale rupture zone on forma- tion of disjunctive tectonic structures on monoclinal, carbonatic deposits of Triassic age. Attention was paid to essential role of certain structural features in secondary processes developing in the Olkusz-Zawiercie area.
SUMMARY
Results of above investigation have clearly pointed out varying character of tectonic stresses which have occurred in the areas of horsts and in grabens. The same rule refers to second-rank structures which are uplifted and downthrown sides of tectonic faults. Energy relaxation in these structures followed in different way. In horsts, tectonic energy was not accumulated but discharged gradually on the systems of tiny cracks and fissures formed under tensional stress condition. Vast fissuring of a carbonatic rock-mass within the horsts enabled spontaneus penetration of descending, oxygen-rich waters into a zinc and lead ore and consequently caused its rapid oxidation.
On contrary, lowered subareas (grabens) were influenced by compressive stress conditions developed during last (Tertiary) tectonic cycle. Dense and well-oriented fault network was formed, with accompanying cracks constricted or scarred over. Structural features of grabens containing additionally impermeable Keuper deposits unabled direct penetration of oxygen-rich waters, hence Zn-Pb ores are weakly oxidized and have rather sulphidic character. Measurements of orientation, linear density and gap width of cracks help describing an orey area as prone or not to become a zone of developed processes of secondary oxidation of sulphides and textural changes of ore.
Some of lowered orey subareas (grabens) are characterized by high oxidation degree of zinc, lead and iron sulphides, however thoroughful structural analysis indicates that, during epigenesis period, the same subareas were uplifted and influenced by tensional stress condition.