Detailed geochemical studies of a He-U lake anomaly in permafrost, Baker Lake Area, N.W.T. |
| |
| Authors: | Willy Dyck Dwaine Car |
| |
| Abstract: | A strong He-U anomaly, discovered in the Thelon basin of the N.W.T. during a regional U exploration program in 1981, was studied in detail in 1982. The anomaly is confined to a 3-km2 lake situated 160 km northwest of Baker Lake. Lake bottom water and sediment samples taken in June through the ice on a 50 m × 50 m grid, were analyzed for a number of trace and minor elements.In the lake sediments He and U were highly anomalous and parallel the strong anomaly patterns of He observed in the water. Median and maximum values in the sediments were 57 ppm and 396 ppm U, and 296 nL/L and 13870 nL/L He. Regional medians were 4.3 ppm U and 50 nL/L He. Se and V in sediments gave weak but similar anomaly patterns to those observed for U and He.The anomaly is somewhat of an enigma. The unusually high U content indicates an oxidizing, hence, near surface, water regime, and the highly anomalous He flux into the lake and a thick cover of permafrost in the region indicate a very deep source where conditions are normally reducing, rendering U immobile.Coincident anomaly patterns and increasing concentrations with depth of minor and trace elements and gases in the lake water prove that groundwater is the source of the anomalies. Contoured element maps indicate that this groundwater enters the lake in at least four places.The fact that up to 35 ppb U, 6 ppm dissolved O2 and virtually no Fe and Mn, were detected in lake waters above groundwater entry points indicates that the groundwaters were oxidizing with respect to these elements. This is indeed surprising because permafrost is believed to be about 300 m thick in the region; at such depths groundwaters are usually rich in Fe and void of U.The highly anomalous He in this lake indicates deep fractures which serve as conduits for mineralized water entering the lake from depth and creating a frost-free window in the permafrost. The fractures probably penetrate well into the basement for only major deep fractures are known to produce such strong He anomalies. The additional presence of anomalous U suggests U mineralization at depth. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
