No abstract

No abstract

The Ribe Formation is a regionally extensive Miocene sand aquifer that is present in western Denmark at depths ranging from 100 to 300 m below ground surface. Groundwater chemistry and isotope data collected from more than 40 wells show that the Ribe Formation mainly contains high quality Ca-bicarbonate type groundwater of Holocene age (100-10 000 a BP). Pleistocene age groundwaters, identified on the basis of stable isotopes, noble gases and corrected 14C values, are present below the island of R0m¢, in discharge areas near the coast, and in hydraulically isolated inland areas. The groundwater age distribution in the Ribe Formation was successfully simulated with a numerical groundwater flow model and particle tracking only when the 14C content in groundwater was corrected for both geochemical reactions and diffusion. The results indicate that geochemical and physical processes significantly influence the 14C content of groundwater and that the correction factors required for the two processes are of the same magnitude. Flow modelling results indicate that Pleistocene groundwaters were emplaced at depth within the Ribe Fromation under low base-level conditions that prevailed throughout the late Pleistocene -near the coast these waters are essentially isolated from the present flow system, and Pleistocene freshwater may be present offshore. Seismic surveys show that conditions offshore are favourable for the presence of Pleistocene freshwater within the Ribe Formation and other aquifers.

No abstract

The resources in a large syngenetic deposit of low‐grade uranium (U) ore with thorium at Kvanefjeld, South Greenland, were evaluated by spectrometric gamma‐ray logging of 23 boreholes, 46 mm in diameter and 200 m deep. The borehole probe's detector contained [Formula: see text] of sodium‐iodide, and the photomultiplier gain was stabilized electronically using barium‐133 ([Formula: see text]) reference gamma rays. The downhole measurements were carried out at depth intervals of 25 cm, and for each stationary position of the borehole probe, counts were accumulated for 100 sec in four energy windows. The calibration constants of the spectrometer system were determined by calculating the average number of U and thorium (Th) counts per meter of borehole and comparing these with the U‐Th concentrations in 1‐m sections of analyzed drill core. The sensitivity and the background count rate in the uranium window varied appreciably from one hole to another; this variation is believed to be caused by emanation of radon (Rn) from the borehole walls. Block calculations based on individual calibration constants for the boreholes logged made it possible to obtain a reliable estimate of the tonnage of U. This estimate was only slightly different from the tonnage evaluated from a large number of core assays.