Boros István (szerk.): A Magyar Természettudományi Múzeum évkönyve 50. (Budapest 1958)

Kaszanitzky, F.: Genetic relations of the Pátka-Kőrakáshegy ore occurrence, Velence area, North Central Hungary

The knotty slate is of a macroscopically massive texture ; it has a silky lustre, a grey or somewhat reddish brown color and it shows excellent stratification. Because of its exceedingly massive habit the stratification is sometimes invisible to the naked eye. Under the microscope the matrix of the rock consists of small, colorless, transparent grains of quartz and of a network of shapeless muscovite flakes of very small size. The texture exhibits some kind of foliation. At some points small spots of limonite occur amongst the muscovite flakes. This matrix exhibits close-spaced brownish spots of green tint. These consist mostly of flakes of muscovite and of a smaller proportion of greenish biotite. In the slate exhibiting stratification thes spots or knots are also visible with the naked eye. In some intances of more intense contact metamorphism, andalusite will also appear in the knots, in the form of a network of minute needlelike crystals. The knots also contain some limonite. The dip of the slate is subjet to intense variation, indicating excessive tectonic contortion of the entire complex. At some points of the slate body quartzite veins of smaller width will be observed, vanishing within 1 to 2 metres. On the western part of the Kőrakáshegy the contact of granite and slates is visible in the form of a dike of granite porphyry. The contact is here also of a tectonic nature. Along the surfaces of foliation of the slate there are tourmaline-bearing quartzite veins of filament-like appearance, the thin colorless or pale-green lathes of tourmaline weawing through the quartzite substance. There also occurs in the area a tourmaline-bearing quartzite dike about 1 metre in width which may be traced to a length of several metres. This dike is of a cellular consistency, containing a number of cavities. The walls of the cavities are studded with quartz phenocrysts. The greenish-brown squat crystals of tourmaline sometimes form contiguous veinlets. The formation of this dike is a result of a post-magmatic activity of the granite mass, preceding ore mineralization. In this capacity, it might represent the pneumatolytic phase. Magmatic (granitic) rocks. The magmatic rocks partaking in the constitution of the Kőrakáshegy are granite, granite porphyry and aplite. Granite, being the country rock of ore formation, occurs in a contiguous mass on the south-eastern part of the Kőrakáshegy. However, it is mostly prevented from cropping out by a cover of young (Pannonian) sediments. In the subsurface workings the granite is found to be intensely altered, especially in the neighborhood of dikes. Fresh granite never contains any amphibole and is, as a matter of fact, a granitite consisting of orthoclase, quartz and biotite. The granite contains a number of siliceous veins, carrying disseminated crystals of violetcoloured fluorite. The aplite dikes of 2 to 3 metres width occurring in the granite mostly strike north-east ; they are of a massive texture and of a light greyish color. They contain porphyric grains of quartz and grains of altered biotite. The granite seen in the workings of the mine is mostly altered by hydrothermal and tectonic processes. The feldspar is caolinitized, biotite is changed into muscovite. Quartz is, however, resistent to alteration and consequently some parts of the rock attain a character resembling quartz porphyry. As has been already stated by J. Kis s, the alteration of the granite is seen to become more intense towards the south along the main tunnel of north-south strike. Around the northern end of the tunnel there is fresh granite interwoven with quartz veins : the granite is gradually becoming more and more altered towards the south, on getting closer to the dikes. The alteration is first indicated by an initial stage of sericitization of orthoclase, whilst in the vicinity of the dikes