Lamprofiry z okolic Zawiercia

Abstract

Badania mineralogiczno-petrograficzne lamprofirów z otworów wiertniczych ZMZ 41 i ZMZ 94 w Zawierciu oraz P-8 koło Krzywopłotów wykazały, że występują wśród nich minetty, minetty-kersantyty oraz semilamprofiry minetto-i kersantytopodobne. Skały te reprezentują grupę lamprofirów (semi-lamprofirów) wapniowo-alkalicznych, związanych z granitoidami.LAMPROPHYRES FROM THE VICINITIES OF ZA WIERCIE The paper presents results of phase (microscopic, X-ray, and thermal) and chemical studies on more or less strongly altered lamprophyre rocks from three boreholes in the vicinities of Zawiercie (Fig. I). The rocks are characterized by porphyritic structure, in which the role of phenocrysts is mainly played by phlogopite (Table Ill, Fig. 11; Table IV, Fig. 13). This mineral is usually very well preserved and strongly pleochroic: α - pale yellow, β = γ - yellow-brown. K-feldspars, as a rule preserved as relics only, predominate in groundmass. Depending on their development (which is varying from isometric to fibrous), groundmass displays micro-to fine-crystalline, dendritic (Table Ill, Fig. 12) or, locally, spherulitic (ocellar) structure. Chemical composition of the rocks is characterized by high summative content of iron and manganese (from about 6.7 to 15.5 wt. %) and alkali (4-7.8 wt. %), usually with marked predominance of potasium on sodium. The rocks are usually strongly altered, mainly due to calcitization or dolomitization, kaolinitization, montmorillonitization, sericitization or chloritization. Barite, calcite, dolomite, quartz, and some-times ore minerals, mainly pyrite, are found in fissure veinlets. With the use of the W. Wimmenauer (1973) systematics, minettes, minette-kersantites, and minette-and kersantite-like semilamprophyres were identified among the studied rocks. The rocks represent a group of calcium-alkali lamprophyres (semilamprophyres), which should be regarded as related to post-orogenic granitoid complexes with reference to the latest views (W. Wimmenauer, 1973). The rocks from the vicinities of Zawiercie possibly correspond to fioaJ stages of the Variscan orogeny and most probably they are younger than the co-occurring Variscan granitoids and vein equivalents of the latter.