The Precambrian rocks of Tasmania, Part I-Dolerites of the North-West Coast

Abstract

At least 30 small bodies of dolerite have been found intruding sediments of the Pre-Cambrian Rocky Cape Group along the coast between Sulphur Creek and Crayfish Creek. The igneous bodies are chiefly sills although dykes also occur. The dolerites are characterized by strong deuteric alteration which led to the formation of secondary tremolite-actinolite, chlorite, zoisite, albite, calcite, sericite, sphene, leucoxene, serpentine, and prehnite. These rocks show petrological and chemical affinities with dolerites of a similar age in Western and South Australia. They have certain features in common with the lavas of the Cambrian Dundas Group, but the possibility that these bodies acted as feeders to the flows is discounted on structural and chemical grounds.