Provenance of titanomagnetite in ironsands on the west coast of the North Island, New Zealand

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Previous studies on the provenance of titanomagnetite-rich ironsands on the west coast of the North Island, New Zealand, have suggested that the main source is from erosion of andesitic volcanic rocks of the Taranaki volcanoes, with a lesser contribution from ignimbrites of the Taupo Volcanic Zone (TVZ) in, and north of, the Waikato North Head ironsand deposit. Here, we compare the results of electron probe microanalysis of titanomagnetite grains in samples of coastal and river sands (sinks), with a dataset (compiled from the published literature) of analyses of titanomagnetite in volcanic rocks erupted from Mt. Taranaki and TVZ volcanoes (potential sources). A principal components analysis was conducted on a five element (MgO, Al2O3, TiO2, MnO, FeO) dataset of Fe-Ti oxide compositions to identify groupings in multivariate space. The composition of titanomagnetites in the sinks from Whanganui to Waikawau Beach (southern sector) are similar to those of Mt. Taranaki andesites as sampled in the published literature; minor contributions from both Ruapehu andesites and TVZ ignimbrites are also present. The composition of titanomagnetites in the sinks at both Waikato North Head deposit and in the ironsands from Taharoa to Muriwai Beach (northern sector) are consistent with a composition of titanomagnetites that is present in the rivers that drain the Taranaki volcanoes and their ring plain debris avalanche and lahar deposits, but not a composition that is represented in the literature for Mt. Taranaki volcanic rocks. A minor proportion of the titanomagnetite grains in the Waikato North Head ironsand deposit and the coastal ironsands from Port Waikato north to Muriwai Beach appear to be sourced from ignimbrites of the TVZ.