||The quartzite complex of Austdøla comprises a heterogeneous lithology dominated by quartzitic rocks (>92 vol.% SiO2). It extends about 5 km in N-S direction and 800 m in E-W direction and forms, togehter with the Trælhaug quartzite complex (Eidfjord), an exotic unit within autochthonous Lower to Upper Proterozoic magmatic gneisses west of the Mandal-Ustaos Fault. The rocks underwent a medium- to high-grade metamorphism resulting in medium-grained quartzite with bluish colour.
In 2005 the quartzite complex was sampled and analysed by NGU along a E-W traverse exposed at the Osafjell bom vei at an altitude of 800 to 900 m a.s.l.. A ca. 130 m wide and relative pure (>95 vol.% SiO2) quartzite band occurs at the W margin of the complex. Irregular batches and veinlets of medium-grained feldspar (5 mm) are common within the quartzites. Accessory minerals are magnetite, biotite, chlorite and pyroxene. The quartz contains sub-microscopic needles of rutile (<0.005 mm). Occasionally, the quartzite is crosscut by mafic dykes and irregular pegmatite dykes (<0.5 m in thickness). The average grain size of the bluish quartz in the quartzite is 3 mm. The pure quartzite becomes darker and banded after 150 m towards E. The dark quartzite contains also irregular batches of feldspar and is relative rich in muscovite (ca. 5 vol.%). The dark variety is about 50 m in thickness. The central part od the complex consists of feldspar-bearing banded quartzite (about 150 m wide) hosting folded ultramafites, pegmatitic schlieren of feldspar and boudins of amphibolite, fine-grained monzonite and granodiorite (0.5 to 50 m in size). The layering of the quartzite is caused by variations of the biotite, chlorite and feldspar content. The quartzite becomes more homogeneous towards E where it forms a ca. 150 m wide variety. However, the quartzite here contains pegmatitic feldspar schlieren which form about 10 to 20 vol.% of the rock. The following 150 m wide band at the E contact of the quartzite complex represents a melange of banded and folded quartzites, mafites, (grano-)diorites and migmatites.
LA-ICP-MS analyses of quartzites from Austdøla reveal, that they contain quartz of low chemical raw material quality caused by the high Ti content of about 50 ppm. Due to the heterogeneous lithology, mineralogy of the quartzites and the low chemical raw material of quartz the deposit at Austdøla cannot be considered as a potential quartz deposit.