Szakáll Sándor - Fehér Béla: A polgárdi Szár-hegy ásványai (Topographia Mineralogica Hungariae 8. Miskolc, 2003)

Bevezetés (Szakáll Sándor)

into secondary precipitations. Minerals detected in these veins, encrustations and impregnations include goethite, hematite, birnessite and pyrolusite (pers. commun, of I. Dódony; see Fig. 4). Andésite dykes and propylitization The crystalline limestone was intruded in some places by rhyolite and andésite dykes. The andésite dykes, 1-6 m in thickness, have been exposed both in the quarry and in the lead ore mine. The andésite is intensively weathered; its mafic minerals have been altered into aggregates of secondary minerals. The propylitization of the andésite is characterised by a paragenesis of albite, actinolite/tremolite, epidote, chlorite, nontronite, biotite, glauconite, carbonates and rutile. Contact metamorphic minerals of skarn zones Tremolite and actinolite crystals detected by earlier authors in the crystalline limestone can be considered as products of the contact metamorphism. Skarn parageneses have been developed along the contact of the andésite dykes with the limestone. These 5-50 cm thick zones are composed of calcium silicates and carbonates. Based on mineralogical and petrographical investigations, the skarn zones can be classified into the following types: endoskarn represented by clinopyroxenes, garnet, epidote and feldspars (albite and potassium feldspars), vesuvianite-bearing transition zone and exoskarns characterised by the dominance of diopside and wollastonite, respectively. It should also be mentioned that a number of low temperature calcium silicates were found in the wollastonite skarn. Skarn zone has not been developed along the contact of rhyolite dykes with the limestone. Galena-bearing ore formation Especially in the northern edge of the Szár Hill, galena-bearing aggregates in connection with quartz veins occur in the crystalline limestone. These are considered as a product of the andesitic magmatism. The largest galena masses form stockworks and nest-like aggregates. The largest galena stocks had been exploited between 1938-1954. Parageneses of the ore deposit are connected to the formation of a) quartz veins; b) aggregates of galena accompanied by sphalerite and tetrahedrite; c) iron- and manganese-bearing calcite; d) the oxidation zone with cerussite, pyromorphite, bindheimite and malachite as principal minerals. Scattered concretions of pyrite-bearing quartzite and pyrite were found in the Lower Carboniferous, anchizonal slate (Szabadbattyán Limestone Formation). They were discovered in the excavations of the lead ore deposit. The rock forming minerals of the slate are montmorillonite, illite, kaolinite, chlorite, quartz and feldspars.