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

quartzite of banked development is most common. This is constituted by alternating bands of cryptocrystalline, opaline substance, and bands of microscopic isometric grains of sugarv texture. The grains are more or less oriented, with c axes perpendicular to the vein wall. Gangue quartzite is sometimes translucent, mostly a lustreless white. It is frequently colored pale yellow or brown by iron hydroxide, greenish by finely distributed chlorite or grey by ore particles of colloid size. It generally occurs on the margin of the thicker parts of the veins, carrying but small amounts of ore, in the form of minute scattered grains. The microscopic study of thin banded vertical vein sections has yielded the following observation : the structure of the gangue quartz exhibits rhythmical, periodic alternation in a sense perpendicular to the fissure wall. The period commences with a comb quartz layer consisting of grains of nearly parallel orientation, the pyramids of which are incrusted by aggregates of minute, shapeless quartz grains of some hundredths of a millimetre in size. This is followed by a quartzine layer of fine fibrous texture. The long axis of the quartzine fibres is parallel to the c axis of comb quartz. Adhering to the quartzine stratum is another irregular layer of aggregates of unoriented minute quartz grains. Quartz grains of gradually increasing size follow, showing transition into another generation of comb quartz. The degree of orientation of the quartz grains is roughly proportional to their grain size. In the case of the aggregates of small grains no orientation at all could be demonstrated, while the orientation of comb quartz is nearly perfect. Ore occurs throughout in the aggregates of minute quartz grains adhering to comb quartz. It is invariably absent in quartzine and comb quartz. The reason of this rhythmicity of quartz formation it as yet unsolved. A third common variety of quartz is the one of closely intergrown crystals of some millimetres size, the long axes of which are perpendicular to the vein wall. On the end of the crystals pointing towards the interior of the veins the pyramid is also developed. Amethyst is also frequent in the veins. Its pale violet phenocrysts generally sit on the walls of smaller gaps or cavities of the vein. The crystals are striated. Of the cryptocrystalline varieties of quartz, chalcedon and opal occur in the form of thin veinlets, or cementing brecciated parts of the vein. Carbonates of the gangue are represented by calcite and dolomite. Coarsecrystalline calcite of 3—4 centimetres' grain size forms bands and veinlets. Its colour ranges from almost liquid transparency through white and brown to black. S. Koch has shown the cause of the colouring to be finely distributed manganese. The calcite phenocrysts of the cavities in the veins exhibit an abundance of forms. Most common are (2131), and the combinations (2131) (4041), (0112) (1010), (0112) (16.0.Ï6.1), (1010) (0001) and (1011) (2131) (3145). Dolomite is found adhering to quartz or calcite, in the form of small spherical grain groups. Ore minerals occur in bands, veinlets, scattered grains, nests and incrustations, or within the quartz crystals in colloid distribution. Their enrichment is variable along strike as well as dip. The quantity interrelations of the individual ore minerals also vary from level to level. Within one and the same level, ore-rich vein sections alternate with poor ones. In the course of mineralization not all of the fissure receiving the vein was gaping : some parts were closed, and this is why some generations of minerals are absent from certain parts of the vein. According to the findings on the deep levels, the surge of mineral-