Hydrogeochemical investigations in boreholes at the Stripa mine. The hydrochemical advisory group and their associates

摘要

Geochemical investigations at Stripa are continuing. The stable nuclides (sup 2)H, (sup 18)O,(sup 34)S, (sup 40)Ar and (sup 87)Sr, as well as the unstable nuclides (sup 3)H, (sup 14)Cl, (sup 226)Ra, (sup 234)U and (sup 238)U. In addition, the concentrations of the stable nuclide (sup 37)Cl and the unstable nuclides (sup 37)Ar, (sup 39)Ar, (sup 85)Kr and (sup 129)I were measured in water samples from Stripa. Isotopic compositions of chlorine and iodine of the water in the granite do not match isotopic compositions found in the rock, suggesting a lack of equilibrium between the rock and the water. In situ production of (sup 36)Cl, (sup 37)Ar, (sup 39)Ar, (sup 85)Kr and (sup 129)I is taking place in the subsurface in the granite at rates which exceed the atmospheric production of these radionuclides. Theoretically, in situ production of (sup 3)H and (sup 14)C must also take place but at much lower rates. The isotopic composition of sulfate in the groundwater in the Stripa pluton reflects the geochemical history of the groundwater, as well as the origin of the sulfur or sulfate. A study of the Rb-Sr chronology, as well as the (sup 87)Sr/(sup 86)Sr ratios of rocks, minerals and fluids, suggests that the Stripa granite was intruded 1.71 Ga ago and that later hydrothermal activity, perhaps 1.63 Ga ago, formed moderately high temperature minerals along fractures. High temperature minerals dominate fracture fillings at depth, while calcite is more common nearer the surface. Characterization of natural organic compounds dissolved in groundwater from Stripa indicated the presence of long- chain fatty acids, including fulvic acids, and cyclic hydrocarbons. Groundwater more than 600 m below the surface has several characteristics which suggest that, even though lateral migration has taken place, most of this water has been isolated from the atmosphere for several thousand years and possibly as long as a few hundred thousand years. (Atomindex citation 24:022263)