Boros István (szerk.): A Magyar Természettudományi Múzeum évkönyve 51. (Budapest 1959)

Kaszanitzky, F.: Genetic relation of ore occurrence in the Western Mátra Mountains, North Eastern Hungary

phenocrysts of centimetre size. The faces of the dominant bisphenoid are slightly curved and frequently corroded. Young chalcopyrite, of a somewhat lighter yellow than the older one, is a formation succeeding main ore minerals. It generally enmeshes with its exceedingly fine veinlets the tectonically shattered particles of the latter. It frequently attacks older ores, partly replacing or digesting them. When appearing in greater grains or smaller contiguous veinlets, it invariably contains minute inclusions of older galena and sphalerite. Digested hexahedra of old pyrite are also frequent. Between crossed niçois young chalcopyrite shows a spectacular structure characterized by polylamellar twinning. On the upper level the individual chalcopyrite grains are lined by chalcocite and covellite. The amount of chalcopyrite is subordinate as related to sphalerite and galena. However, it becomes somewhat more abundant with depth. On the deepest (—200 metre) level of the Károly vein the amount of old chalcopyrite is touching on that of galena. On the top level it is, on the contrary, entirely absent. The distribution of the younger generation is more ore less uniform. As has been mentioned, the most important mineral of the occurrence is sphalerite. It occurs in a variety of forms. In weathered parts of the veins, in kaolinitized gangue, cyrstals of centimetre size sometimes occur. It forms, however, generally bands of 0,5 to 5,0 centimetre thickness of massive ore. The grain boundaries become apparent on structural etching, and lamellar twinning is also frequently seen. The grains often exhibit zoning, due to the rhythmicity of crystal growth. There is an older and a younger shpalerite generation. Old sphalerite is dark brown, due to its high iron content. Under the microscope it shows a characteristic reddish-brown internal reflex. The iron content is, according to an analysis published by S. Koch, 4,02 per cent. Old sphalerite contains great amounts of chalcopyrite in the form of inclusions and unmixing products. As has been mentioned above, the rhythmic alternation of these two minerals is also frequent. Dark sphalerite sometimes contains the digested remains of old galena, too. However, old dark sphalerite surrounded by old galena was also encountered. This shows that old galena only partly preceded dark sphalerite, while the rest of it was formed simultaneously with the same : but, whereas most of galena was digested, most of old sphalerite remained intact. The amount of young light sphalerite exceeds that of the old one. Young sphalerite is the predominating ore mineral of the deposit. Its iron content is much smaller (2, 47 and 2, 67 per cent respectively, according to analyses by Grass ell y). Under the microscope it is easily distinguished from the older set by its brownish yellow internal reflex. It was formed jointly with young galena. It contains frequently inclusions of both galena generations. As contrary to old sphalerite, it contains but very seldom inclusions of chalcopyrite. Chalcopyrite as a product of unmixing is totally absent from this generation. Grain outlines obtained by structural etching indicate a rhombdodecahedral development of young sphalerite. The grains are often made up of polylamellar twins. The fissures of shattered grains are often filled by young chalcopyrite. Chalcopyrite and young pyrite sometimes even replace sphalerite. Old sphalerite is predominating on the lower levels of the Károly vein and in the Bányabérc vein. In the rest of the veins its amount is exceeded by that of young sphalerite.