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

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). Gamet 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. Postdepositional changes due to intrastratal solution, evident especially in Cretaceous-Paleocene sediments, have removed epidote and titanite, and concentrated ilmenite, zircon, gamet, 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.

Heavy minerals and the provenance history of Waitemata Basin sediments (early Miocene, Northland, New Zealand)

“…Of those that have, most are from Hays Stream near Red Hill, Papakura, and contain prominent clinopyroxene. Various criteria suggest that the Hays Stream samples may be atypical: the greenish outcrop appearance as opposed to the more usual grey of Waipapa Group rocks; work by Mayer (1969); samples from material derived almost exclusively from Waipapa Group; the rare other samples examined (Smale 1988a); and comparable Torlesse rocks elsewhere in New Zealand (Smale 1990). Only a further sampling programme could establish this definitely.…”

“…Having selected the number of factors, the program then generates the heavy mineral assemblages they represent, and their proportion in each sample. These factors and their heavy mineral assemblages, though purely statistical, often resemble those of potential source rocks, and can be a guide to them (e.g., Smale 1987).…”

Heavy minerals in the Torlesse Terrane of the Wellington area, New Zealand

“…Heavy minerals were separated from material in this range using sodium polytungstate solution with a specific gravity of 2.90. The resulting concentrates were examined petrographically, and proportions determined by counting all grains in successive fields of view until a total of 300^00 had been reached (Smale 1990). Cluster analysis of results (Table 1, Fig.…”

“…Rakaia rocks tended to have substantially more biotite, titanite, and apatite (Smale 1990). In the Wellington rocks the high proportion of biotite in Cluster C is similar to that in North Canterbury Rakaia rocks, and suggests a granitic source, as for the Canterbury rocks.…”

Variations in sandstone diagenesis with depth, time, and space, onshore Taranaki wells, New Zealand

“…Consistent with this, the composition of the Kapuni Group indicates that its provenance was mainly granitic, with minor schist and altered acid volcanic rocks. Staurolite in the McKee Formation in McKee and Maui wells (Smale & Morton 1987;Smale 1990) suggests some input from the Takaka Terrane. Intense weathering of the provenance area in the Eocene reduced the feldspar component in the upper part of the group.…”