Concentrations of heavy minerals in the prograded coastal sequence of southeastern South Australia are generally low, partly as a result of the high content of locally derived biogenic carbonate in many of the sediments. Terrigenous input to the nearshore region appears to have been relatively slight, and the operation of concentrating mechanisms minimal. The highest heavy-mineral concentrations recorded in the area (up to 1.2% total heavies) occur in a sand of probable Pliocene age underlying Quaternary beach and dune deposits. In general, the heavy-mineral suite present in the sediments consists of between 25 and 45 percent magnetite-plus-ilmenite, 5 and 20 percent leucoxene, 5 and 25 percent zircon, 5 and 30 percent tourmaline, and between 0 and 10 percent amphibole, epidote, rutile and garnet. Andalusite, sillimanite, kyanite and staurolite occur as minor components in many assemblages. Sialic igneous, reworked sedimentary, metamorphic and to a slight extent mafic igneous components are present. Probable sources include the igneous rocks of the Padthaway Ridge, metamoraphic and sedimentary rocks of the Fleurieu Peninsula and Kangaroo Island, and older Tertiary sediments. Variations in the suite are defined by cluster and Q-mode factor analysis. Higher concentrations of heavy minerals occur within the older (probably Pliocene) ridges of the western Victorian Murray Basin. These ridges which approximately parallel the southeast South Australian ridge sequence, are siliceous, and commonly contain thin bands of concentrated heavy mineral (up to 20% total heavies in the bands) in the lower part of the Parilla Sand. The suite is mineralogically mature (generally 50-70% opaque, 15-30% tourmaline, 3-5% rutile, 5-15% zircon and 1-3% others) and differs considerably from that present in the southeast South Australian sequence. The difference reflects differences in provenance of the two areas and the probable modification by intrastratal solution of the assemblages originally present in the older deposits.
