REE potential of the Nordkinn Peninsula, North Norway: A comparison of soil and bedrock composition

Abstract

Regional-scale, low-density sampling, geochemical surveys using a variety of different sample materials have repeatedly indicated the Nordkinn Peninsula (northern Norway) as a substantial rare earth element (REE) anomaly. Recently, a more detailed soil geochemical survey, covering about 2000km2 at a sample density of 1 site per 2km2, was carried out in the area. The new geochemical survey outlined a large area (several hundred km2) where the soil samples contained several hundred and up to over 2000mg/kg aqua regia extractable REE. In the surroundings of the highest soil anomalies, bedrock samples were collected for a mineralogical and compositional characterisation of the metasedimentary bedrock with focus on the possible economic potential.The REE concentrations obtained for aliquots of bedrock following aqua regia extraction, 4-Acid digestion and Li-borate fusion/decomposition closely match the results from soil pulps after an aqua regia extraction. Total contents for the REE determined in bedrock using the above methods range between 19 and 429mg/kg, indicating an overall limited economic REE potential and the predominance of the light REE over the heavy REE. In terms of petrography, essentially all the bedrock samples are characterised by the presence of detrital, altered and locally even decomposed allanite (a LREE-incorporating, epidote-group mineral) and minor xenotime (a HREE-incorporating phosphate) while texturally stable REE phases are scarce. It is the poor condition of the REE minerals that makes them prone towards acidic leaching and, given similar results for all of the above preparation methods, even the relatively weak AR extraction dissolved the REE almost completely from the samples. The REE anomaly observed for the soil samples thus rather reflects the state of alteration of the REE phases than ore-grade concentrations in the underlying bedrock.