Titanium ore-forming processes and titanium provinces at the southwestern margin of the Fennoscandian Shield
|Location||International Geological Congress,oslo 2008|
|Author||Korneliussen, Are; Ihlen, Peter|
|Holding Date||08 September 2008|
Norway is a major producer of titanium minerals: available resources are very large. Of the approximately 300 known titanium and iron-titanium deposits, more than 90% occur within Proterozoic and Phanerozoic geologic provinces along the western and southwestern coast of Norway, close to the south-western margin of the Fennoscandian Shield. This concentration of titanium deposits is believed to be a consequence of a relatively unstable, continental margin, which was magmatically active for more than a billion years and which favoured the formation of a variety of titanium deposits.
Of the Proterozoic magmatic Ti/Fe-Ti provinces, the Rogaland Anorthosite Province (922-932 Ma) near the southwestern tip of the country is by far the most important in terms of its volume of titanium-enriched igneous rocks and titanium deposits. Other distinct Proterozoic iron-titanium provinces are the Lofoten-Vesterålen province (c. 1900 Ma) in North Norway, the Møre (c. 1700 Ma), Sunnfjord (c. 1500 Ma) and Bergen (c. 1000 Ma) provinces in West Norway and the Bamble province (1000-1250 Ma) in South Norway.
The Bamble province is particularly complex, containing two different types of deposit: magmatic ilmenite - titanomagnetite deposits, formed at an early stage, and later rutile deposits formed by metasomatic alteration (scapolitisation and albitisation) of titanium-rich gabbros and amphibolites under amphibolite facies conditions. In the metasomatic process chlorine-rich fluids leached iron from the mafic source rocks, presumably as FeCl. In this process ilmenite broke down to titanite as a transitional stage, and then to rutile. Thus, metasomatism can be a rutile ore-forming process.
The Caledonian 400 Ma continent-continent collision between Baltica and Laurentia had a major impact on the titanium metallogeny of W. Norway. In this collision, rocks belonging to the western margin of the Fennoscandian Shield experienced high-pressure metamorphism and eclogitisation. The eclogitisation process, in which iron from ilmenite enters garnet whereas the titanium forms rutile, is a highly effective mechanism in transforming large volumes of mafic rock with ilmenite as the dominant titanium-bearing mineral, into rutile-bearing rocks. The most important rutile/eclogite deposits are found in the Sunnfjord province, which includes both ilmenite-rich gabbroic rocks and rutile-rich eclogites. Since TiO2 in rutile is 4-5 times more valuable than in ilmenite, eclogites may represent a major mineral resource whereas the corresponding ilmenite-bearing gabbros are too low grade to be of economic interest, although the titanium content may be the same.