Heavy mineral rich beach sands of the Waitakere coast, Auckland, New Zealand

Abstract

Heavy mineral rich beach sands of the Tasman Sea coast of the Waitakere Ranges, west of Auckland City, include major minerals plagioclase, augite, titanomagnetite, and quartz, with minor ilmenite, hypersthene, hornblende, biotite, and potassium feldspar, and accessory zircon and apatite. Major sources for the sands are Taupo Volcanic Zone rhyolitic volcanics, delivered via the Waikato River, and Taranaki andesitic volcanics, via the longshore drift. Longshore trends from south to north include a slight fining, a reduction in rock fragments, an increase in heavy mineral content, and a tendency for the feldspar/quartz ratio to decline. Ilmenite is a significant component; it is derived from the Taupo Volcanic Zone (not from the Waitakere Ranges as previous authors have suggested), and it increases in quantity from south <to north. However, it does not replace titanomagnetite.The Taupo Volcanic Zone could have supplied all of the ironsand on the west coast north of the Waikato River mouth. Longshore trends and distribution of ironsand and other minerals on the continental shelf all strongly suggest a net northwards littoral drift of sand, which would be expected from the prevailing south-southwesterly wave approach. Possible contributions of sand from relict continental shelf accumulations, and from a large igneous body which underlies the continental shelf, cannot be evaluated.

Spectral reflectances of three tiger beetle subspecies (Neocicindela perhispida): Correlations with their habitat substrate

“…The coastal sands on which the three subspecies of Neocicindela perhispida occur are described in Schofield (1970) and Hamill & Ballance (1985). The dark sands at Bethell's Beach are rich in volcanic-derived heavy minerals, especially titanomagnetite ("ironsand'').…”

Formation of magnetite‐enriched zones in and offshore of a mesotidal estuarine lagoon: An environmental magnetic study of Tauranga Harbour and Bay of Plenty, New Zealand

“…Such 'ironsand' or 'black sand' placer deposits are particularly prevalent on the open west coast of the North Island of New Zealand [Carter, 1980;Bryan et al, 2007], and form an economically important resource for New Zealand's titanium and iron ore industry. Previous studies have shown that andesitic rocks from Mt Taranaki are the primary source of this black sand and that the northerly directed littoral drift system plays a key role in accumulation and distribution of these deposits along the west coast [Kear, 1979;Hamill and Ballance, 1985]. Bryan et al [2007] investigated the spatial and temporal variability of titanomagnetite placers on west coast beaches using hydrodynamic modeling and mineralogical analyses.…”

Storm Dispersal of Volcanogenic Sands from Buenos Aires, Where Heavy-Metal Concentrations Are Heavy-Mineral Segregations

“…Concentrations at the coast or inner contine ntal shelf may ( result from selective sorting Komar & Wang, 1984;Isla, 1991;Frihy & Komar, ) ( 1993;Boon & Berquist, 1991, relict accumulations Nelson, 1971; Paulson & ) Owen, 1996 , or either to spatial or temporal variations of provenance or erosive ( processes Pilkey, 1963;Swift et al, 1971;Scheidegger et al, 1971;Woolse y et al, ) 1975;Jones & Davies, 1979;Hamill & Ballance, 1985;Paulsen & Owen, 1996 . ( ) In a much broader approach, Potte r 1994 stressed that the mineral composition of South American be ach sands is controlled by the tectonic history and climate.…”