Geochemistry of massive sulphide mineralisation and associated siliceous sediments in the Tangihua Complex, Northland

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Brathwaite, R.L.; Christie, A.B. 2008 Geochemistry of massive sulphide mineralisation and associated siliceous sediments in the Tangihua Complex, Northland. Lower Hutt, N.Z.: GNS Science. GNS Science report 2008/39 14 p.

Abstract: Volcanogenic massive sulphide (VMS) deposits within the Tangihua Complex are associated with lenses of siliceous sediments. The sedimentary lenses are of Late Cretaceous to Late Paleocene age on limited fossil evidence. Boström ratios (Al/Al + Fe + Mn + Cu) of sediments associated with VMS deposits at Pupuke are highly enriched in Fe, indicating a major hydrothermal input. The pyrite + chalcopyrite ± sphalerite massive sulphide mineralisation at Pupuke has a geochemical signature indicative of oceanic crust seafloor VMS deposits and is similar to sulphide mineralisation deposited at high temperatures (350 to >400oC) on some spreading ridges in the Pacific and Atlantic oceans. Pyrite + chalcopyrite + marcasite + sphalerite, with rare galena and elevated gold (6.4-18.0 ppm), mineralisation at Pakotai and Parakao is comparable with lower temperature (200-300oC) mineralisation, enriched in Au, Zn and Pb, which is found on some spreading ridges in the Pacific Ocean. The slight enrichment in Pb suggests a minor continental crust influence in the formation of the Pakotai and Parakao deposits. The small size of the known VMS deposits and extensive deformation of the host sediments and volcanics, suggests that potential additional deposits in the Tangihua Complex will be small. (auth)