Geochemical survey of stream sediments, Pukeamaru Range, East Cape

Abstract

Abstract A detailed study of 69 stream sediments and 18 rock samples was made in February 1979 over 25 km2 of the northeast Pukeamaru Range, East Cape, New Zealand, following the discovery in Mangatutu Stream of a boulder assaying 8.5% copper and containing marcasite, chalcopyrite, and pyrite. The geology of this area includes basaltic pillow lavas and volcanogenic breccias of the Matakaoa Volcanic Group, intruded by altered mineralised diorite and minor gabbro bodies. Although more copper sulphide bearing float was found, neither stream sediments nor rock samples showed anomalous copper values at the 95% confidence level. One stream sediment nickel anomaly (421 µg/g) is attributed to a small gabbro body. A zinc anomaly (205 µg/g in stream sediment) is caused by contamination from sheets of galvanised iron. Stream sediments have ranges of: cobalt 25–117 µg/g (mean 58 µg/g); copper 10–63 µg/g (mean 36 µg/g) nickel 24-421 µg/g (mean 66 µg/g); and zinc 49-205 µg/g (mean 97 µg/g). Molybdenum and lead were also determined but were not evaluated because of very low values <5 µg/g). The source of the copper mineralisation is very localised, but the potential of the remaining 250 km2 of the Pukeamaru massif should be rated favourably for the occurrance of massive pyrite-chalcopyrite deposits.