Z badań hydrogeochemicznych wschodniej osłony granitu Karkonoszy

Marek Michniewicz

Abstract


Prace hydrogeochemiczne przeprowadzone we wschodniej osłonie Karkonoszy zapoczątkowały regionalne badania chemizmu wód podziemnych regionu sudeckiego. Pozwoliły one na regionalną charakterystykę hydrogeochemiczną omawianej jednostki, wypracowanie wzorca dla dalszych tego typu badań w Sudetach oraz wskazanie stref perspektywicznych w aspekcie złożowym. Całokształt przeprowadzonych prac ukazał zalety metody hydrogeochemicznej, którą obok wykorzystania w regionalnych badaniach hydrogeochemicznych - w szczególności, w Sudetach - należy uznać za godną polecenia w pracach poszukiwawczo-złożowych.

SOME RESULTS OF HYDROCHEMICAL STUDIES ON EASTERN COVER OF THE KARKONOSZE GRANITE

Eastern cover of the Karkonosze granite has been selected as test field for establishing methodological standard for further complex regional hydrogeochemical surveys in the Sudety Mts, taking into account marked differentiation in lithology, traces of polymetallic sulfide mineralization and small area of that geological units (about 11 0 km2).

In order to provide uniform material for the studies and to eliminate the influence of anthropogenic factors, the sampling was limited to springs as the places of concentrated natural drainage of groundwater. Random selection of measurement points provided objective nature of the obtained sample, and the number of measurement points equal 67 (i.e. about 9% of the recorded springs) - its representativeness. The studies covered the following elements of water chemistry: pH, Ca2+,

Mg2+, Na+, K+, Fe total, Mn2+ , SO42- , HCO3- , CI-, F-, SiO2 general hardness, dry residuum, Rn content as ·well as Cu2-, Zn2- and Pb2-. The results of liboratory studies gave the basis for statistic analysis carried out with the use of the Razumowski's method and. therefore, for determining lower vales of anomalous concentrations of individual components. Further studies, carried out taking into account the problems of chemistry of rocks. deposits. geological structure of the studied area and its morphology, made it possible to characterize spatial and genetic aspects of chemistry of groundwater in eastern cover of the Karkonosze granite. It should be noted that the studies on the genesis of ground water were markedly facilitated by fairly good knowledge of geochemistry of rocks of that unit. In establishing regional characteristics, there were differentiated three basic genetic types of anomalous zones: Iithological, tectonic and deposit. The results of hydrogeochemical studies were found to be an important index of geological structure. which is shown by several examples.

The presence of several anomalous concentrations in eastern, marginal part of the Karkonosze granite, along with the lack of any correlations with lithogeochemical factors, suggest tectonic genesis of that phenomenon.

The detailed analysis of chemistry of ground water in eastern cover of the Karkonosze granite showed relatively low original regional background of the total water mineralization (of the order of some tens of mg/dm3). The influences of secondary hydrothermal mineralization. overprinted on the former, result in markedly higher, apparent regional background of the order of over 100 mg/dm3.

The studies made it . also possible to establish methodological standard for further hydrogeochemical surveys of the Sudety crystalline area. The selection of methods appeared appropriate and it is suggested to introduce additional step in the surveys. aimed at accurate tracing of extent of the recorded anomalous zones. It would be also justify to widen the extent of the surveys to comprise measurements of some other elements of groundwater chemistry, depending on the nature of a given geological unit.

The studies ended with selection of areas perspective for further prospecting. A detailed surveying of the Wieściszowice anomaly zone, characterized by . the maximum concentration of the majority of analysed elements, is shown to be fully justified. Other areas which should be covered by prospecting include that of the Okraj pass (characterized by maximum concentration of Pb2-) and the Mniszków zone (maximum concentrations of Zn2+, Rn and Cu2-), situated at the contact of granite and its cover.


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