Journal of the Royal Society of New Zealand abstracts

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Transport and distribution of magnetite and ilmenite on Westland beaches of New Zealand; with comment on the accumulation of other high-density minerals

J. P. Bradley¹, P. M. Chew¹, and C. J. Wilkins^1*

¹ Chemistry Department, University of Canterbury, Private Bag, 4800, Christchurch, New Zealand.
^* Author for correspondence.

Abstract  Broad features of bedrock geology of Westland, South Island, New Zealand, are favourable towards tracking the transport of detrital magnetite and ilmenite onto beaches. In both North and South Westland there are ultramafic sources supplying magnetite rich in chromium. With this in-built marker the distribution of this magnetite has been followed through chemical analysis. In the intervening Central Westland region where schists supply ilmenite, the ratio of ilmenite to magnetite enables down-river tracking onto adjacent beaches. This is possible because there are variations in the ratio over the region, with a low minimum in the vicinity of the Cook and Waiho rivers. Along the coastal segment north of Greymouth the minor element content of the magnetite remains almost unchanged and matches that carried northwards in the magnetite from the North Westland rivers, which shows its derivation from that source. The proportions of the full range of high-density minerals from all the major Westland rivers have been estimated. The consequent beach sand accumulations depend upon the persistence properties of the minerals.

Keywords   Westland beach sands; New Zealand; river-sands; mineralogy; magnetite compositions; ilmenite to magnetite ratio; persistence; accumulation

R00051 Received 7 September 2000; accepted 5 June 2001
© Journal of The Royal Society of New Zealand, Volume 32, Number 1, March 2002, pp 169–181

PDF file of entire paper: Print-quality (320K)

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