The thesis describes a systematic investigation of detrital heavy minerals from the catchment of the Taramakau River, which drains both the Alpine schists and Tuhuan granites. Samples were taken from small feeder streams within source rocks, at various stages down river, from the river mouth and from the beaches to the north and south of the mouth. Information has been gained on persistence characteristics of the minerals and their accumulation in the beachsands. Within the granites of the Hohonu Range batholiths a zone of hydrothermal alteration was discovered. Both stream sediments and X-ray fluorescence analysis of rock samples have shown there is no associated mineralisation, although the original nature and extent of the zone is unknown. Concentrates from the Kanieri Company's dredge operating in the lower Taramakau have shown that a more complex suite of minerals including cassiterite, monazite, uraninite and thorite lie buried beneath the present river gravels. (This is the first discovery of a significant uraninite deposit in New Zealand). A survey of beachsands from Hokitika southwards to Milford Sound has shown that those beaches in proximity to the Alpine schist belt contain almost exclusively a very uniform suite of typically schist-derived minerals. From Jackson Bay southwards where the schists give place to a greater variety of rock-types there is a corresponding change in the heavy mineral suites within the associated beachsands. While no studies have previously been made specifically on the provenance and accumulation of detrital minerals in this area, the results are discussed in relation to the details of Hutton's (1950) mineralogical investigation of West Coast beachsands and dredge concentrates.