Norwegian anorthosites and their industrial uses, with emphasis on the massifs of the Inner Sogn-Voss area in western Norway

Abstract

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 materil for various industrial applications. Anorthosite with a high anorthite content (An>70) is easily soluble in mineral acid, and the bytownite plagioclase if 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.