Heavy minerals in Cretaceous sediments of East Coast, North Island and Marlborough

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Smale, D. 1993 Heavy minerals in Cretaceous sediments of East Coast, North Island and Marlborough. Lower Hutt: Institute of Geological & Nuclear Sciences Institute of Geological & Nuclear Sciences science report 93/05 29 p.

Abstract: Heavy minerals in 89 Cretaceous sediments from Marlborough and 35 from North Island East Coast show that the dominant provenance consisted of indurated and low-grade metamorphic Torlesse-type rocks, producing suites dominated by diagenetic epidote group minerals and semi-opaque debris, and detrital ilmenite, zircon, and garnet. Vigorous leaching of the latest Cretaceous rocks (post-Motuan in Marlborough) by intrastratal solution has removed virtually all the epidote minerals. In the Awatere area this leaching has been less conspicuous, but the epidote remaining shows solution effects. Another effect has been concentration of ilmenite, zircon, and possibly garnet, tilinite and apatite, although the latter three may have been derived from other Torlesse rocks. A biotite-chlorate population has everywhere been an important influence in the early Late Cretaceous, but it died out in the Piripauan. Pyroxene has been derived from penecontempomneous volcanics, especially near Mt Lookout, in Seymour Stream, and in the Mangaotanean in both southern and northern East Coast. In most places it occurs without epidote minerals, but both epidote and pyroxene occur in the Hodder and Coverham areas. Magnetite has an erratic distribution, probably as a result of sorting, though it could be due to local provenance variation. An olistostrome in the Penk River can be distinguished on heavy minerals from the overlying alternating unit, but both olistostrome and underlying alternating unit in the Wharekiri Stream are similar to the Penk oustostrome. (auth)