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

amount of crumbling of the granite along the dike, while the quartzite material retains its massive homogeneous texture. Microscopic investigation yields a monotonous mineral constitution of the fissure-filling dikes. There is a complete lack of rhytmic precipitation structures The ground mass of the dike is a sprinkle of close-spaced small angular anhedrous quartz fragments within a crystalline matrix of very fine grain size. Some of the quartz grains show the effect of secondary resorption, the resorbed part being substituted by a host of crystals of the matrix of about millimetre size. The consituent quartz of the surrounding granite also occurs in the dike material, in the form of fragments of 2 to 3 millimetres in size. A thin section from the 70 metre level is thought to have shown small silicified rags of slate. There is a sporadic occurrence of zircon and muscovite. At some points of the dike thin veinlets of fluorite are observed. In other instances fluorite occurs in knots or nests of 2 to 3 centimetres diameter. There are, however, no idiomorphic fluorite grains in this case, either ; fluorite occurs, instead, in aggregates interwoven with quartz, whose veinlets are visible, however, onlv on intense magnification. The youngest generation of quartz contains also minute aggregates of comb quartz. Small knots of sphalerite are likewise encountered. The ore mineralization has taken place after the formation of comb quartz. As a third modification of fissure-filling quartzite there is a dark, grey to black massive variety, reminding of lydite on first sight. It contains, according to analyses, one per cent of sphalerite and two of fluorite. It sometimes forms blocks of the size of some cu. metres. Under the microscope this variety shows a texture identical with that of the previously described light-colored ones. The light and dark varieties may occur side by side, in which case the transition may be sharp or gradual. The mineral containing the ore and fluorite could not, however, be demonstrated by microscopic investigation, because of the exceedingly fine grain of this variety. These elements must therefore occur in very fine distribution. The ore was precipitated most probably at a rather low temperature, in colloidic form ; this should account for the dark hue of the quartz. Of the incontiguous quartzite bodies, disclosed by the tunnels, not all contain ore minerals. Ore is throughout found to cement the fractured, brecciated quartz. The cementing ore mostly consists of massive sphalerite. Phenocrysts of ore minerals are totally lacking in the entire area. The quartzite bodies containing workable amounts of ore occur independently of each other on the individual levels, but their properties are wholly identical. As to their spatial distribution, no regularity at all could be demonstrated. The parallelizaticn in the vertical sense of the ore-bearing fissure fillings traversed on the individual levels is rather unreliable. Solely the ore-bearing zone disclosed on the —35 metres level, back of the shaft, may be considered as the continuation of the material worked at the bottom level of the inclined shaft. However, this supposition may only be verified by driving a shaft through the suspected ore body. It may be imagined, on the other hand, that the ore-bearing zones traversed in the —35 and —70 metres levels, back of the shaft, are independent and that their continuation should be looked for vertically upwards. In the case of the Kőrakáshegy occurrence there is no reason to speak of veins in the conventional sense of the word. The quartzitic fissure fillings, separated along the tunnels by zones of massive granite, must not be con-