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Platinum mineralisation potential of the Longwood Igneous Complex, New Zealand

Das Platin Mineralisations Potential des Longwood Komplexes, Neuseeland

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Summary

The Longwood Igneous Complex is situated at the southern tip of the South Island of New Zealand. The Complex is 32 km long and up to 12 km wide and is part of a more extensive north-trending belt of late Paleozoic volcanic, volcaniclastic and intrusive rocks.

The complex is comprised of an extensive series of layered gabbros (Pahia Layered Series) together with diorites, trondjhemite and granitoids.

Exploration by Sigma Resources has located significant platinum-in-drainage anomalies which are derived from a 10 km x 1 km area of largely plagioclase-rich, olivinebearing cumulate rocks within the Pahia Layered series. Grains of platinum and palladium sulphide, arsenide and alloy minerals have been identified in placer deposits derived from this area. A total of 1,500 ounces of platinum was reported to have been recovered as a by-product of historic placer gold mining of these deposits. Platinumgroup element mineralisation in float rocks (up to 3.0 ppm Pt and 3.3 ppm Pd) and significant platinum-in-soil anomalies (peak value 0.47 ppm Pt) have been found within this area.

The mineralised troctolite and olivine-gabbro float and adjacent exposures are broadly similar to the anorthosite-troctolite-olivine gabbro zones within the Banded Series of the Stillwater Complex. The mineralised rocks are leucocratic plagioclaseolivine adcumulates with minor clinopyroxene oikocrysts, primary amphibole and sparse (<0.5%) sulphide. Sulphide minerals are pyrrhotite, chalcopyrite, pyrite and secondary copper sulphides. The similarity of this mineralisation style and its host rocks to the JM Reef of the Stillwater Complex and AP and PV mineralisation of the Penikat Intrusion highlights the excellent potential for discovery of a large stratiform platinumgroup element deposit in the Pahia Layered Series.

Zusammenfassung

Der Longwood Igneous Complex liegt au der Südküste der der Südinsel Neuseelands. Er ist 32 km lang und 12 km breit und ist Teil eines Nord-Süd verlaufenden Gesteinsgürtels paläozoischer vulkanischer, vulkano-klastischer und intrusiver Gesteine. Der Komplex beinhaltet geschichtete Gabbros (Pahia Layered Series) gemeinsam mit Dioriten, Trondjhemiten und Granitoiden.

Bedeutende Platinanomalien in Bachsedimenten, die aus einem ca. 10 x 1 km großen Gebiet mit Plagioklas-reichen, Olivin-führenden Kumulat-Gesteinen stammen, wurden von Sigma Resources lokalisiert. Platin- und Palladiumsulfide, -arsenide und -Legierungen wurden in Seifenlager-stätten, in diesem Gebiet nachgewiesen. Insgesamt wurden 1500 Unzen Platin während der historischen Bergbautätigkeit auf Gold in diesen Lagerstätten als Nebenprodukt gewonnen. PGE-Mineralisation (bis 3.0 ppm Pt und 3.3 ppm Pd) in Geschieben und bedeutende Pt-Bodenanomalien (max. 0.47 ppm Pt) wurden in diesem Gebiet entdeckt.

Die mineralisierten Troktolit- und Olivin-Gabbro-Gerölle und benachbarte Aufschlüsse zeigen weitgehende Ähnlichkeit mit der Anorthosit-Troktolit-Olivin-GabbroAbfolge der Banded Series des Stillwater Komplexes.

Die mineralisierten leukokraten Gesteine führen Plagioklas und Olivin als Kumulusphasen sowie untergeordnet Klinopyroxene, primäre Amphibole und geringe Mengen (< 0.5 %) an Sulfiden. Als Sulfide kommen Magnetkies, Kupferkies, Pyrit und sekundäre Kupfersulfide vor. Die Ähnlichkeit dieser Mineralisation und ihrer Nebengesteine mit dem JM Reef des Stillwater Komplexes und der AP und PV Mineralisation in der Penikat Intrusion läßt die Pahia Layered Series als geeignetes Gebiet für die Entdeckung großer stratiformer PGE-Lagerstätten erscheinen.

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Cowden, A., Ruddock, R., Reay, A. et al. Platinum mineralisation potential of the Longwood Igneous Complex, New Zealand. Mineralogy and Petrology 42, 181–195 (1990). https://doi.org/10.1007/BF01162690

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