The geology, geochemistry and structure of two scheelite deposits in the Vioolsdrif-Goodhouse area NW Cape

Two scheelite deposits in the Vioolsdrif-Goodhouse area were investigated by means of diamond drilling in order to furnish information on the nature, origin and extent of the mineralisation. The sheelite mineralisation prospect is contained within two types of veins, viz lenticular quartz veins in a steeply dipping shear zone, and a parallel series of low angle quartz feldspar tension veins. Regional compressive or shear stresses acting on rocks of different mechanical properties are believed to have led to the development of this mineralised fracture pattern. Scheelite mineralisation occurs in a series of parallel fracture zones characterised by heavily tourmalinised veins and breccias. Although inconclusive it is believed that the tourmaline veins and breccias result from the infilling of structures produced by combined tectonic and hydrothermal explosive effects. The tectonic fracture control to mineralisation appears to be related to major fault movement. A wall-rock alteration study carried out on both scheelite deposits revealed that propylitic alteration, spatially and probably temporally related to mineralisation appears to have played an important role in chemically controlling scheelite mineralisation. The alteration of favourable host rocks released calcium and made it available to tungsten-bearing complexes in the hydrothermal solutions which thus induced the precipitation of scheelite