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Occurrence, geochemistry and provenance of REE-bearing minerals in marine placers on the West Coast of the South Island, New Zealand

ABSTRACT The occurrence, concentration and geochemistry of REE-bearing minerals in beach sands along the West Coast of the South Island of New Zealand is reported as a proxy for the composition of adjacent uplifted Holocene marine terraces. The strandlines of 13 beaches along this coast contain REE-rich allanite (average: 15% REO), monazite (82% REO) and xenotime (83% REO), with allanite being most common and xenotime having a restricted range. Other REE-rich phases are apatite (average: 2259 ppm), zircon (1756ppm), epidote (761 ppm), titanite (699 ppm) and scheelite. Geographical trends to the distribution of these minerals are not entirely clear, but there is an influx of titanite and allanite north of the Grey River and an increase in apatite, allanite, monazite and epidote north of Little Wanganui River. In-situ trace elements and/or 87Sr/86Sr isotopes indicate allanite, monazite and xenotime to be likely mainly derived from exhumed Paleozoic and Cretaceous granites, with minor amounts from the Alpine Schist metasedimentary rocks. The main source of the analysed apatite is likely also the granitoids, with contributions from the Greenland Group and Alpine Schist. When the REE abundances in the beach sands are compared to the size of the uplifted adjacent Holocene terraces, Waimangaroa terrace may contain the highest concentration of REE, followed by the Little Wanganui and Barrytown terraces.