Mineral potential of the Tapuaenuku and Blue Mountain igneous complexes, Kaikoura : desktop studies and geochemical survey

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Jongens, R.; Timm, C.; Christie, A.B.; Smith Lyttle, B.; Leybourne, M.I.; Rattenbury, M.S. 2012 Mineral potential of the Tapuaenuku and Blue Mountain igneous complexes, Kaikoura : desktop studies and geochemical survey. Lower Hutt, N.Z.: GNS Science. GNS Science report 2012/11 [74] p. + 1 CD

Abstract: The Tapuaenuku and Blue Mountain igneous complexes, in the Inland Kaikoura Range, are layered mafic/ultramafic igneous complexes of alkaline geochemistry that have the potential for Ni-Cu-Platinum Group Element (PGE) and Rare Earth Element (REE) mineralisation. GNS Science was commissioned by the Ministry of Economic Development (now Ministry of Business, Innovation and Employment) to undertake a desktop study of both complexes and a new geochemical sampling programme of the Tapuaenuku Igneous Complex so as to potentially raise their mineral prospectivity. Mineral exploration companies in the early 1970s identified and focused on Ni-Cu sulphide mineralisation found in both igneous complexes. In the late 1970s and 1980s, the exploration focus changed towards the potential for PGE, Au and REE mineralisation. Most exploration companies focused on the Blue Mountain Igneous Complex, leaving the larger and more rugged Tapuaenuku Igneous Complex relatively underexplored. Nevertheless, mapping and geochemistry of both complexes has been studied in detail by three Victoria University of Wellington theses. The geological and geochemical data collected by the mineral exploration companies (MR reports) and from University theses have been entered into a Geographic Information System (GIS) which accompanies this report. Derivative maps from the GIS are presented showing the distribution of PGE and REE analyses. Field work and sampling was undertaken in the Tapuaenuku Igneous Complex between March and April 2011. From this, new geochemical analyses for 63 elements were determined for 25 panned concentrate stream sediment samples spanning the entire complex drainage and 30 rock chip samples. The results show elevated REE in rock samples from syenites of the Hodder Intrusives and carbonatite dikes. Panned concentrate samples exhibited elevated REE at many locations. In contrast, PGE concentrations in the analysed rocks are low, with the highest values in the sulphide-rich samples, particularly those around the Crows Nest Cu-Ni sulphide mineralisation zone (13 ppb Pt and 8 ppb Pd). PGE were poorly represented in the panned concentrate samples although anomalous PGE were present in samples from Gut Stream and Staircase Stream. No anomalies were identified downstream from PGE-bearing Ni-Cu mineralisation at Crows Nest. Geochemical analysis indicates PGE concentrations correlate with Cr concentrations suggesting that Cr concentration could be used as a proxy for PGE concentration in whole rock XRF analyses where PGE analyses are unavailable. To date, detailed sampling has been completed only along one stream (Gut Stream). Nevertheless, even the Gut Stream sampling was of insufficient density to identify geochemical trends resulting from sulphur saturation in the magma, which may or may not have been achieved. Future sampling programmes should be high density, and in particular, around mineralised zones in contact with Cr-rich pyroxenites. The REE potentia l of the most alkaline syenite, phonolites and lamprophyric dikes has been demonstrated during this survey of the Tapuaenuku Igneous Complex, although more sampling of the lamprophyric-phonolitic dikes is required to identify targets with REE and related element potential. (auth)