Surface water geochemistry, Oppdal and Rennebu county, South Trøndelag, Norway

Abstract

A geochemical surface water survey, focused on 2nd and 3rd order streams, was carried out in the Oppdal\/Berkåk area. Stream water was collected at about 160 sample sites, covering a 1500 km2 survey area. The main aim was to test wether today's ICP-MS analyses are sensitive enough to use surface water for gold exploration. A number of methodological tests (acidification with two different acids, filtration and acidification in the evening in the hotel) was carried out in addition. The known gold occurrences in the area are marked by gold anomalies in stream water, though at quite low concentrations. An additional Au anomaly (several samples locations) indicates the general Orkelsjøen area as prospective. Anthropogenic activities in the lowlands are marked by slightly enhanced NO3 values in the streams, especially in the Berkåk area. An unusual and intriguing As, Mo, Sb, V anomaly marks the main skiing area near Oppdal and it cannot be decided wether this is an anthropogenic or geogenic signal. Surface water geochemisty in general is quite well reflecting the geology in the area. The methodological tests indicate that it should be sufficient to take unfiltered samples in the field and to acidify these in the evening in the hotel. Such a procedure would greatly increase the productivity for a surface water survey and allow for example to very effectively sample all 1st order streams.