Slate deposits of Newfoundland

The slates of Newfoundland are situated in the eastern part of the island and belong to the 'Avalon Zone' ('Avalon Terrane') which collided with Laurentia during the Acadian period.

Giller (1974) mentioned also Ordovician slates on the west coast, running from Bonne Bay to Humber Arm and they show a purple, green and blue colour. The economically more interesting slate deposits of the 'Bonavista Formation' occur in the eastern part of Newfoundland and are a subject for ongoing geological investigations in respect to the quality and exploitability.

The slates belong to the Early-Cambrian 'Bonavista Formation' which lies within a narrow and NE-SW striking syncline. In this syncline the subvertical to vertical fracture cleavage plane changes at the southern end - on Random Island - to a fanning fracture cleavage (Tuach, 1993). This syncline is accompanied by steep normal- and reverse faults which run parallel to the cleavage plane.
According to Tuach, the different slates are juxtaposed at this faults. The 'Bonavista Formation'; can be found at Keels, Nut Cove, Trinity Bay up to Grieve on Random Island. Its length parallel to the strike is about 31 mi. and the thickness of the slate beds varies between 886 - 4,921 ft. (Giller, 1974).

The formation comprises reddish, purple and green slates, sometimes including thin calcareous layers and in some regions on the basis quartz conglomerates (King et al., 1988 in Tuach, 1993). According to Giller (1974), these slates can be directly correlated to the Early-Cambrian slates of Wales. On Random Island the relation between purple, green and red slates is 70 : 20 : 10, although this colour relation is not constant along the strike.