Distribution and provenance of heavy minerals in the South Island: A review

Abstract

Abstract South Island heavy mineral distribution has been studied to help determine provenance and distinguish lithostratigraphic units in Cretaceous and Cenozoic sedimentary basins. Most Cretaceous and Cenozoic sediments reflect derivation from local basement rocks, chiefly granitoids of the Karamea and Golden Bay terranes and older sedimentary rocks of the Karamea, Torlesse, Caples, Murihiku, and Maitai terranes. The granitoid rocks in Fiordland are characterised by both hornblende and biotite, but in Westland and west Nelson biotite predominates. Biotite is also dominant in most sedimentary rocks of the Karamea terrane (Greenland Group and Preservation Formation). Torlesse and Caples samples are characterised by epidote and “semi-opaque debris”, which are also prominent in derived sediments. Much of the Torlesse is biotite rich, reflecting its granitic (Karamea Suite) source, but in derived sediments biotite is not prominent, probably because it did not withstand recycling. Caples terrane samples contain hornblende and pyroxene, reflecting their more volcanic source. Post-mid-Cretaceous volcanics have contributed new material to the basins in Canterbury and east Otago; volcanics decreasing in age to the south have provided magnetite (Cretaceous-Eocene) and hornblende (Eocene-Oligocene). Garnet varieties indicate a range of sources, largely granitic and volcanic. High-grade metamorphic minerals are present only in the Charleston Metamorphic Group, some schists, contact aureoles, and in the limited sediments derived from them. Post-depositional changes due to intrastratal solution, evident especially in Cretaceous-Paleocene sediments, have removed epidote and titanite, and concentrated ilmenite, zircon, garnet, and tourmaline. A widespread change in provenance near the base of the Miocene, especially prominent in the Murchison Basin and south of Westport, may have been related to the inception of major movement on the Alpine Fault.