Przejawy uranonośności w osadach górnego kambru na tle promieniotwórczości naturalnej pokrywy osadowej wyniesienia Łeby

Abstract

URANIUM MANIFESTATIONS IN THE UPPER CAMBRIAN DEPOSITS AGAINST THE BACKGROUND OF NATURAL RADIOACTIVITY OF THE SEDIMENTARY COVER WITHIN THE ŁEBA ELEVATION

Summary

Geophysical measurements made in deep boreholes completed within the Łeba elevation (Fig. 1) yielded data to construct a profile of natural gamma PG radiation intensity in the sedimentary cover of this area (Fig. 2). Technical data of the measurements are given in Table 1. An anomaly of gamma radiation has been ascertained to occur at the Cambrian-Ordovician boundary. The quantitative characteristic of this anomaly is given in Table 2. The anomalous horizon corresponds here to black bituminous claystones of Upper Cambrian age, interbedded with limestones and mineralized with pyrite. A stratigraphical gap, found to occur at the Cambrian-Ordovician boundary, comprises the uppermost horizons of the Upper Cambrian and the Tremadocian (K. Lendzion, 1970). Chemical determinations of uraniun (Table 3) demonstrate that its contents amount here to some hundred g/t. In accordance with the results of radiometric measurements, the highest uranium contents are found at the top of the Upper Cambrian deposits. The concentration of the uranium in the Upper Cambrian claystones shows three populations (Fig. 5B). The first population, the dominant of which amounts to 28,9 g/t, makes here the geochemical backgound. The second one, with its dominant equal to 73,7 g/t, comprises the syngenetic sorption concentration of uranium at the top of the Upper Cambrian deposits, whereas the third one, having its dominant amounting to 257,5 g/t, is related to a lamina, which most probably has secondarily increased contents of uranium due to the erosional processes of the higher horizons of Cambrian age. The results of some analyses made at random of several selected rare chemical elements do not suggest any relation to an enrichment in uranium here. On geophysical data compared with the results of chemical analyses we can draw a conclusion that the degree of uranium concentration increases westwards, most probably due to a somewhat different, very likely also due to a later development of the Upper Cambrian deposits in the region of Smołdzino and Łeba, as compared with the region of Żarnowiec (Figs 3 and 4). The uranium concentration in claystones of Upper Cambrian age within the Łeba elevation, related to the whole faunistic correlation of these deposits with the uraniferous alum slates in Scandinavia (K. Lendzion, 1970) points to a fact that they are a fragment of the deposits laid down in a vast basin supplied in the past with a big amount of uranium, most probably transported from the destructed crystalline rocks of Scandinavia.