Background values of gold, potentially toxic elements and emerging high-tech critical elements in surface water collected in a remote northern European environment

Abstract

A geochemical surfacewater survey, focused on 2nd and 3rd order streams, was carried out in the Oppdal/Berkåk area in Norway. Stream water was collected at 168 sample sites, covering a 1500-km 2 survey area. Electrical conductivity, pH, alkalinity and temperature were recorded in the field. Electrical conductivity and pH were also determined once more in the laboratory. The cations Br, Cl, F, NO 2 , NO 3 , PO 4 and SO 4 were determined by ion-chromatography (IC) on unacidified, laboratory filtered samples. Inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) was used to analyse field filtered and acidified samples for 63 elements. In addition, inductively coupled plasma atomic emission spectrometry (ICP-AES) was used to determine 27 elements. One aim of the survey was to test whether today's ICP-QMS analyses are sensitive enough to directly use surface water efficiently for gold prospecting. The two known gold occurrences in the area are marked by low level Au anomalies in stream water (0.006 µg/l). These values are just above the detection limit of 0.001 µg/l and it must be concluded that today's detection limits are still not low enough to use stream water for routine Au (and In) prospecting. The anions as determined by IC were most problematic in terms of number of samples below detection limit. Increased anthropogenic activities in the lowlands are marked by slightly enhanced NO 3 values in the streams. An As, Mo, Sb, V anomaly marks the main skiing area near Oppdal but is probably geogenic. In general surface water geochemistry of, for example, Ca, Ce, Cu, K, La, Rb, SO 4 and Sr reflects the geology of the area well. Methodological tests indicate that it should be sufficient to take unfiltered samples in the field and to filter and acidify these in the evening at home base. The dataset provides a good overview of background concentrations and variation of almost 70 chemical elements in stream water from a remote northern European survey area. Supplementary material: Table S1 showing the analytical program, isotopes measured and detection limits, Table S2 with analytical results of the international reference materials used for quality control and Fig. S1 with geochemical maps for all elements are available at: https://doi.org/10.6084/m9.figshare.c.4012885