|
About 16 small lens-shaped bodies (20 to 140 m in length) of kyanite quartzite are located 20 km SSE of the village Skjomen in northern Norway, 10 km S of the southern end of the Skjomendalen. The rocks are exposed at a high plateau called Juovva¿orrú ca. 1000 m a.s.l.. The kyanite quartzites belong to the Sørdalen supracrustal belt, which is part of the Palaeoproterozoic Rombak basement window (Korneliussen and Sawyer 1989). The kyanite quartzite occurrences are limited to a 3.5 km long, steep dipping, lens-shape body of volcanites at the southeastern edge of the Sørdalen Supracrustal Belt. The sequence of the Sørdalen Supracrustal Belt is mainly composed of porphyritic, mafic, intermediate and felsic volcanites. Lenses of kyanite quartzites are tectonically intercalated within the volcanic rocks. The rocks are assumed to have ages between 1.91 and 1.88 Ga (Korneliussen and Sawyer 1989). The rocks of the Sørdalen Supracrustal Belt were metamorphosed under amphibolite facies conditions at 6 kbar and ca. 575°C (Sawyer 1986). The age of the prograde metamorphism is unknown. Occasionally, the rocks were effected by greenschist-facies metamorphism related to the Caledonian deformation.
The kyanite content of the Juovva¿orrú deposit is below 25 wt.% and quartz varies from 75 to 98 wt.%. Accessory minerals are rutile and zircon. The average crystal size of quartz is 0.247 mm (200 measurements). Quartz has planar grain boundaries and occasionally 120° triple-junctions between grains. It contains commonly tiny rutile needles. Kyanite plates are about 160 µm in length. The crystals contain common quartz inclusions.
Quartz from the Juovva¿orrú kyanite quartzites has low average Al of 10.5 ppm and of Ti with 2.9 ppm (6 analyses). Concentrations of Ge and Be are about 0.8 and 0.1 ppm, repectively. Li, B, Mn, K, Ca and Fe are generally below the limit of detection. The quartz of the Juovva¿orrú kyanite quartzite is the purest among the Norwegian kyanite quartzite deposits. |
