NGU-BULL 436, 2000 - PAGE 103 Norwegian anorthosites and their industrial uses, with emphasis on the massifs of the Inner Sogn-Voss area in western Norway JAN EGIL WANVIK Wanvik, J.E. 2000: Norwegian anorthosites and their industrial uses, with emphasis on the massifs of the Inner Sogn- Voss area in western Norway. Norges geologiske undersøkelse Bulletin 436, 103-112. Anorthositic rocks are common in several geological provinces in Norway. Many occur at scattered localities in different parts of the country, but the two largest anorthosite complexes in western Europe are situated in western Norway. These two Precambrian massifs, the Inner Sogn-Voss province (~ 1700 Ma), and the Rogaland province (~ 930 Ma) have been investigated for use as a raw material for various industrial applications. Anorthosite with a high anorthite content (An >70) is easily soluble in mineral acids, and the bytownite plagioclase of the Sogn anorthosite makes it well suited for industrial processes based on acid leaching. The high aluminium content, ca. 31% Al2O3, has made these occurrences interesting for various industrial applications, especially as an alternative raw material for the Norwegian aluminium industry. With this goal in mind, geological investigations and processing studies have been carried out at various times during the past century. At present, a refined process utilising both the silicon and the calcium contents of the anorthosite has renewed industrial interest in these acid soluble anorthosites. Jan Egil Wanvik, Geological Survey of Norway, N-7491 Trondheim, Norway. Introduction Anorthositic rocks are common in several geological prov- inces in Norway and occur at many localities in different parts of the country (Fig. 1). Most of the bodies are of relatively small size, but a few are of appreciably larger dimensions. Among these are the Bergen Arc anorthosites (Kolderup & Kolderup 1940), and most prominently, the 500 km2 Roga- land province and the 700 km2 Inner Sogn-Voss province. These are the two largest anorthosite occurrences in western Europe and are of considerable interest for industrial applica- tions. Anorthosite is an almost monomineralic, feldspathic rock with a great variety of industrial applications (Table 1). Anorthosite massifs are known to host important ore depos- its such as ilmenite and are, in many cases, excellent sources for high-quality rock aggregate and also for dimension- stone. The exploitation of anorthosite for industrial mineral products is growing, and the potential for future production of aluminium and other important constituents from anorthosites is considered to be quite considerable. It is primarily the high aluminium content of the Sogn anorthosite which makes it attractive for a variety of indus- trial end uses. The aluminium content can be utilised in vari- ous processes. Most importantly, anorthosite can be leached with mineral acids in order to facilitate the liberation of alu- minium. Simultaneously, the calcium component is liber- ated, and is thus available for other potential applications. Laboratory investigations (Graff 1981) have shown that plagi- oclase (albite NaAlSi3O8 - anorthite CaAl2Si2O8) has a solubil- ity which is highly dependent upon the An content of plagi- Fig. 1. Distribution of anorthosites (red) in Norway. Modified after Qvale oclase (Fig. 2). Anorthosite with An<50 is almost non-soluble (1982b). Boxed area – Fig. 3. NGU-BULL 436, 2000 - PAGE 104 JAN EGIL WANVIK Processing Products Uses Specifics Physical. Plagioclase grains with crystal Aggregates Light coloured road surfaces, gardens, structure intact (dry or wet mineral Building materials Concrete elements, dimension stone, industrial floors processing) Abrasives Scouring powder, toothpaste, sand blasting Fillers, extenders, coatings Paint, plastics, rubber Chemical Aluminium chlorides Aluminium metal Aluminium oxide (alumina) Flocculent Water and waste water treatment (acid or alkaline Aluminium sulphate (alum) Flocculent/sizing Paper manufacture leaching) Calcium carbonate Binder Asphalt Calcium nitrate Catalyst Organic reactions Calcium silicate Alumina speciality products Ammonium nitrate Cellulose insulation Silica gels and sols Cement components Sodium silicates Cosmetics and pharmaceuticals Sodium carbonate Food processing Nitrogen fertiliser Speciality metallurgical uses Synthetic wollastonite and zeolite Silica residue Fillers and extenders Polyester and epoxy resins, Poly- urethane varnishes Coating White enamel Absorbent Kitty litter, radioactive pactides Silicon production Cement additive Melting Fully or partial melting of Ceramics Floor and wall tiles, electrical porcelain, plagioclase grains bioceramics, ceramic glazes Glass fibre Mineral Wool Rockwool Welding fluxes Table 1. Various industrial uses of Al-production cells Cryolite bath insulation anorthosite. Norwegian commer- cial and tested uses marked in ital- Direct reduction Al-S -alloys, Al- and Si- metal. ics. in mineral acids, whereas labradorite plagioclase (An50-70) is anorthosites into two categories; acid soluble and not acid partly soluble. Only anorthosites containing plagioclase with soluble. more than 70% An (bytownite) are proven to be fully soluble. Large areas of the Voss-Sogn massifs (Figs. 3 and 6) are of Such basic anorthosites are relatively rare, but the large mas- outstanding quality concerning acid solubility, making them sifs in the Sogn-Voss region contain immense quantities of ideally suited for several industrial applications (see below). easily soluble anorthosites with an Al2O3 content of about Acid-soluble anorthosite might also be present in some 31%. This makes these bytownite-anorthosites a potential of the much smaller occurrences in Norway, but none of the alternative to imported bauxite as a source of aluminium ore other major anorthosite deposits are composed of soluble for the large Norwegian aluminium industry, and they have plagioclase (Qvale 1982b). The ~75 km2 Bergen Arc been evaluated for this purpose at various times since early in anorthosites, for example, are dominated by a plagioclase th the 20 century. with An<50 (Kolderup & Kolderup 1940). The anorthosites of the 500 km2 Rogaland province (Fig. 1) are dominated by andesine - plagioclase (An40-50) (Duch- esne et al. 1987) and are thus also insoluble in acids. This Main Norwegian anorthosite deposits anorthosite complex is best known for its large norite-hosted With regard to industrial uses it is adequate to group ilmenite deposit at Tellnes. However, the anorthosite itself JAN EGIL WANVIK NGU-BULL 436, 2000 - PAGE 105 Fig. 2. Plot of solubility vs. anorthite content of plagioclase. Modified af- ter Graff (1981) and Qvale (1982a). has several industrial applications. The altered, white variety is mined for aggregate and filler purposes, and an attractive, massive brown variety with blue labradorescence in some plagioclase crystals is quarried as dimension stone (Heldal & Fig. 3. Anorthositic rocks of Inner Sogn and Voss. Lund 1995). A summary of the anorthosite occurrences in Norway has been given by Qvale (1982a). In this report Qvale also gives a drilling were carried out in Kinsedal by Norsk Hydro (Carstens comprehensive overview of the geology and mineralogy of 1942). The work culminated in the building of a complete the Sogn-Voss anorthosite provinces. Wanvik (1999) pre- plant for underground mining, transport and shipping of sented an overview of the same area with emphasis on the anorthosite. Up to 300 men were employed there and some criteria and geographical variations regarding potential 15,000 tonnes of rock were produced before sabotage ended industrial use. the work in 1945. In the mid 1960s, underground mining of white Norwegian investigations and anorthosite began in Nærøydal (Figs. 4, 7 and 8) in the altered zone along the thrust at the base of the Gudvangen-Mjølfjell developments massif. Production has continued since that time. Products Historical perspective have included white road aggregate, white concrete ele- The potential for exploitation of the anorthosite for various ments, and abrasives for use in toothpaste and cleaning purposes has been evaluated at different times since the agents. Annual production has varied between 10,000 and beginning of the 20th century. Goldschmidt (1919) was the 100,000 tonnes of anorthosite. Part of the production has first to propose the idea of utilising anorthosite as a raw been exported, and the most recent development is the ship- material for the production of aluminium and aluminium in ping of anorthosite to a Swedish producer of mineral wool. combination with other elements. Two years earlier, he intro- Throughout most of the 20th century, the major potential duced his idea to A/S Elektrokemisk Industri and also carried end-use of the Sogn-type anorthosite has been considered out the first regional investigation of the anorthosites of the to be as an alternative aluminium raw material to bauxite, Inner Sogn area (Goldschmidt 1917). Goldschmidt found that based on the solubility of this anorthosite type in mineral the massif in the Nærøydal area contained the best quality of acids. Leaching with acids, such as HCl and H2SO4 is very well easily soluble anorthosite. He also located a deposit in established in the Norwegian Anortal process (Kvande 1987, Kinsedal, east of Lustrafjord, which was suitable for a leach- Braaten 1991). In the mid 1970s, the formation of the Interna- ing process to liberate the aluminium component. Investiga- tional Bauxite Association (IBA) triggered