Determination of W and Mo in natural spring waters by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) and ICP-MS (Inductively Coupled Plasma Mass Spectrometry): Application to South Nahanni river area, N.W.T., Canada

Abstract The relative merits of analyzing fresh and saline waters for W and Mo by ICP-atomic emission spectrometry (ICP-AES) and ICP-mass spectrometry (ICP-MS) have been examined. A preconcentration step via adsorption of the analytes onto activated charcoal is mandatory in analysis by ICP-AES in order to achieve practical detection limits of 1.2 μg L −1 for W and 0.4 μg L −1 for Mo. This step is also necessary in analysis by ICP-MS for waters high in total dissolved salts (> 1000 mg L −1 ). Application of this procedure results in detection limits of 0.06 μg L −1 for both elements, based on a 100-mL sample volume. The elements were found to be stable in solution in a variety of aqueous environments for a 32-day period. Analysis of the seawater reference material, NASS-1, and of spiked seawater samples, was performed to demonstrate the applicability of the proposed procedure to problematic aqueous matrices. The above methods were applied to 41 samples of waters taken from thermal, cold and iron-rich springs in the South Nahanni River area. Four distinctly anomalous sites (> 15 μg L −1 W) are hot springs spatially associated with Cretaceous granites, and three of these are in the vicinity of known scheelite-bearing skarns or wolframite occurrences. The remainder of the sites, located in folded and faulted sedimentary rocks as well as granites, produced waters with W and Mo abundances at or below detection limits. Determination of W and Mo in spring waters might be a useful adjunct to other exploration geochemical techniques as a means of identifying prospective areas.