Uwagi o występowaniu cyrkonów w aluwiach bloku karkonosko-izerskiego

Andrzej Grodzicki

Abstrakt


REMARKS ON ZIRCON OCCURRENCE IN ALLUVIAL DEPOSITS OF THE KARKONOSZE - IZERA BLOCK

Summary
During the schlich investigations made within the Karkonosze-lzera block area, the author paid attention to the occurrence of zircon that is one of the main components in the heavy fraction found to occur in alluvial deposits of the area in study. More detailed research of zircon according to statistical method, concerning among .others morphology, elongation of grains, quantitative relation of idiomorphic grains to subrounded grains, size of crystals, or characteristic optical properties, is broadly used at present and permits to draw interesting petrogenetical conclusions, being also important in solution of sedimentological problems, in determination of alimentation sources, etc. Particular attention is paid to the fraction 0,12 - 0,06 mm, where very interesting and well preserved forms of heavy minerals, particularly of zircon, have been encountered. Zircon is found in samples in changing quantities. The highest percentage of this mineral (up to 63,97%) has been ascertained in the alluvial deposits of the streams which cut the Karkonosze granites and pegmatites. On the other hand, within the Izera granite-gneisses the schlich samples reveal a slight amount of zircon only. The morphological analysis of zircon has demonstrated that metamorphic rocks are characterized by the predominance of subrounded zircon grains. The percentage of idiomorphic grains in greater. Zircons from the metamorphic rocks are characterized by lower maxima of elongation values, those from the granites – by higher ones.

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