Nowe podczwartorzędowe wychodnie lamprofirów w Górach Świętokrzyskich

Abstract

NEW SUB-QUATERNARY OUTCROPS OF LAMPROPHYRES IN THE ŚWIĘTOKRZYSKIE MTS.

Summary

In the light of the geological structure, the paper presents the position of the lamprophyres found to occur in the marginal zone, between the Klimontów anticlinorium and Łagów synclinorium (Fig. 2), gives a description of new lamprophyre outcrops, and illustrates the physic microscopic and microscopis features of weathered lamprophyres. Sub-Quaternary lamprophyre outcrops have been ascertained during the earth workings in the Wszachów - Iwaniska block, at a depth of 0.7-4.2 m. They occur in the Cambrian formations, at the Cambrian - Emsian boundary zone, and in the Emsian formations. Moreover, they have been encountered by 6 shallow bore holes, as well. Lamprophyres have also been investigated in an uplifted block near Kabza. The lamprophyres here considered occur in several elongated disjunction zones of a WNW-ESE direction, characterized by varying nature and various genesis. Lamprophyre dikes have been found to appear also in the shearing-off discontinuities, within the marginal part of the Cambrian formations in the Klimontów anticlinorium (bore holes: Wszachów 1, Iwaniska 1, Iwaniska 3; ditches: in the southern part of Zielonka, and near Wzory - Fig. 3). Magnetic anomalies that reflect the presence of these lamprophyres disappear beneath the Devonian cover (Fig. 2). The next zone is remote about 100-400 metres northwards, and the lamprophyres use tectonic contact of Cambrian and Emsian, as well as fractures within the rigid rocks of Emsian age in the Łagów synclinorium (bore holes: Wszachów 2, Iwaniska 2, test pits: Zielonka – Fig. 4 – Poręba Górna and Poręba Zaldowska). The northernmost zone is represented by a lamprophyre series pierced by bore hole Stobiec-1a, at a thrown dislocation, in the Middle Devonian dolomites. Near Stobiec, the total width of the three zones of lamprophyres amounts, approximately, to 1.2 km. The lamprophyre dikes of the southern zone reveal an abrupt (75-90°) dip southwards, and those of the northern zone - a northern dip. The dip at the lamprophyre near Stobiec is unknown. The mineralogic-structural nature of the dikes points to a multiple formation process of the lamprophyres. Most probably, the lamprophyre material intruded or was active twofold, at least, during the recurring periods of favourable orogenic-tectonic conditions. Part of the lamprophyres represents a generation of older lamprophyres (probably of pre-Devonian age), part, in turn, younger ones, post-Devonian, in age. The lamprophyres appear as dikes, interbedded veins, and various intermediate forms between dike and sill. For the most part the lamprophyres occur in the form of fine, single or composite, dikes (1-4 m) attached to the longitudinal disjunction zones. The thickness of the lamprophyre forms ranges from 0.01 to 17.0 m. Three stages of lamprophyre weathering process have been distinguished to appear in the hypergene zone: initial, intermedite and final. Depending upon the weathering stage, both physical and geophysical features of lamprophyres change their mineral composition and vary considerably. In the more advanced weathering stages the lamprophyres take rusty colour (due to limonitization process), or became decoloured, the colour changing into creamy-white (due to kaolinitization process). Moreover, in this case they are light, porous, their magnetic properties decrease or disappear completely (Table 1). These changes are due to the varying mineral composition in the hypergene zone. In the weathered lamprophyres are found, beside primary minerals preserved as relics (biotite, feldspars, magnetite, apatite), also their alteration products, as well as supergene minerals such as hydrobiotite, vermiculite, chlorites, calcite, quartz, chalcedony, kaolin, and Fe hydroxides (Tables I-II). In the final weathering stage, the rock is built up mainly of supergene minerals among which kaolin predominates (Figs. 6; tabl. II, Figs. 15-17). The lamprophyres here considered are easily accessible in the areas, where longitudinal disjunctive zones of lamprophyres cross with the axes of transversal elevations, i.e. where considerable groups or "swarms" of dikes have been produced. In such areas, the lamprophyre outcrops are found to occur immediately under a thin Quaternary cover, the magnetic anomalies being characterized by considerable amplitudes. It is therefore suggested to begin prospections for new lamprophyres in the future in such sites of course.