Summary
The Geological Survey of Norway (NGU) was contacted by Nordland Mineral (T. Vrålstad) in May 2010 to evaluate the potential of economic rare-earth-element (REE: Ce-Lu, Y) and Zr-mineralisations and related Be-, U-, Th-, (W-) mineralisations in Proterozoic basement windows and overlying Caledonian nappe complexes in central and northern Nordland between Mo i Rana in the south and Ofotfjorden in the north. The economic background for the study is the increasing demand for several of these elements. The general aim is to identify Zr-REE mineralisations with =2 wt.% REE(+Y) which are possibly enriched in Be, U and Th as well.
Accessible literature and mineralogical, geochemical and geophysical data on REE-mineralisations and Zr-, Be-, U-, Th-, (W-) mineralisations, which might be associated with REE-mineralisations, were studied in order to indicate potential target areas for future exploration activity. The primary focus was to evaluate the potential of (1) the Høgtuva Be-REE-U-Sn mineralisation, (2) strongly fractionated granite intrusions, (3) REE-fluorite mineralisations, (4) regional REE anomalies in stream sediments and tills, (5) REE-silicates (allanite) in granites, (6) NYF pegmatites, (7) hydrothermal Fe-deposits with associated REE enrichments, (8) Th- and allanite-bearing rocks by checking regional radiometric measurements and (9) basement granites which possibly contain 2-3% REE-oxides by checking NGU databases. The results of the study indicate that mineralisations and mineralisation types named under points (1), (3), (6) and (7) are currently not of economic interest.
The major outcome of the study is, that some of the more evolved Proterozoic TIB- type granites (TIB – Trans-Scandinavian Igneous Belt) of the Tysfjord basement window have a potential for sub-economic to economic Zr-REE-mineralisations. The possible carriers of the mineralisation are zircon and allanite. The identified Zr-REE-enriched TIB-2 granites are SiO2-rich, subalkaline, metaluminous A-type (anorogenic) granites with low (Na2O+K2O)/CaO ratios (<6; Figs. 37-40). They represent a specific final fractionation trend of the TIB-2 granites. These mineralisation types are relatively unknown but have been described from Saudi Arabia. Possibly exploration target areas for Zr-REE-mineralised TIB-granites are suggested.
