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

there remains of the feldspars nothing but a caolinitic mass. Biotite is faded out by the initial stage of alteration, while later, on the emigration of magnesium, it is transformed into muscovite. In the vicinity of the dikes biotite is completely decomposed and there are only some limonitic specks to indicate its previous existence. In the southern part of the main tunnel there is no fresh granite at all. In the end, the tunnel dicloses a mylonitic zone of some width, rich in clay gouges, instead of typical slate. This mylonitic zone is the consequence of the north-east striking marginal fault bordering the Velence Mountains. On the deeper levels (—35 to —70 metres) granite is found to occur in a facies identical with that of the upper ones. The variability of the rock on the individual levels is not so great as to be mappable. Similarly to the higher levels, we also find an alteration increasing towards the dikes. As the tunnels of the lower levels have been kept more close to the dikes, the porphyric character of the granite is somewhat more striking. There is also some difference in the intensity of quartzitization exhibited by the rock, apparently more intense at the deeper levels. Substance and texture of the "dikes". Variation of mineralization along the dip and strike of the "dikes". The quartzite dikes of the Kőrakáshegy consist of light-colored rock containing few cavities of small size, appearing to be entirely massive to the naked eye. A surface outcrop of one of the dikes is found in a quarry on the north-western slope of the hill. The dike is there about 5 metres wide and strikes 30 degrees. Along its strike some fluorite also occurs. A prospecting shaft driven to investigate the fluorite content has found no downward increase of the same but an increased amount of ore mineralization instead. The level tunnel driven out of this shaft towards the North, in a depth of 20 metres below the surface, has hit upon a galena vein of 60 centimetres width, containing sphalerite, chalcopyrite and some few antimonite as well, After the perfection of the inclined shaft, the dikes have been reached also below surface by a number of prospecting shafts and moreover, another formation thought to be a dike was also traversed in the course of the prospecting work. The development of the quartz material of the dikes and their texture is rather inhomogeneous, even within short intervals. The characteristic banded structure of hydrothermal fissure fillings, indicative of rhythmic precipitation, fails to be exhibited by any of these structures. The quartz material of the dikes is massive, lacking any orientation or banded structure. The dike material was in most places transformed into a friction breccia bv tectonic movements. In the more ore-rich parts the ore minerals mostly occur in the crevices of the breccia, appearing to be cementing the same. The dike material sometimes contains horses of fist to head size, exceeding in some instances the volume of the quartzitic ground mass. Another characteristic feature of the Pátka dikes is the lack of the „salband", so characteristic of hydrothermal dikes. The quartz material filling the fissure has in most cases no well-defined limit towards the country rock : the dike material seems, as it were, to digest the latter. There is a frequent occurrence of apophyses of variable size invading the granite, accompanied by a silification of the latter in a circumference of several sq. metres. As the hard, rigid dike rock reacts to mechanical stresses otherwise than granite alreadv fractured by previous tectonics, there is in some cases a certain