Biogeochemical orientation survey, Luck at Last mine area, Coromandel New Zealand

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Dunn, C.E.; Christie, A.B. 2014 Biogeochemical orientation survey, Luck at Last mine area, Coromandel New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2014/60 112 p.

Abstract: A small biogeochemical orientation survey was conducted in the vicinity of the former Luck at Last gold and silver mine in the Hauraki Goldfield, Coromandel Volcanic Zone, located 6 km west of Whangamata. Common plant species were Monterey Pine (. Lower Hutt, N.Z.: GNS Science. Pinus radiate), Corsican Pine (. Lower Hutt, N.Z.: GNS Science. Pinus nigra), silver tree fern (. Lower Hutt, N.Z.: GNS Science. Cyathea dealbata [‘ponga’]), wood fern (. Lower Hutt, N.Z.: GNS Science. Dryopteris spp), and scattered rough tree fern (. Lower Hutt, N.Z.: GNS Science. Dicksonia squarrosa [‘wheki’]). Sampling of pine bark and needle litter, and foliage of ferns was conducted over a three day period late in November 2013 and generated 116 samples (including field duplicates) which were analysed for 53 elements. The primary objective was to establish multi-element concentrations in tissues of common plant species as a GNS Science reference database for future studies. The relationship of elevated element values to known Au-Ag mineralisation was a secondary objective. Known mineralisation consists of a single epithermal, auriferous quartz reef (1.5 m wide on average) in hydrothermally altered, flow banded rhyolite and rare andesitic tuffs. The predominant fern species was the silver fern, with somewhat fewer wood fern; a combination of these species provided the best vegetation coverage and so the emphasis in this report is on the data from foliage of the two fern species. Differences in element uptake required that the data be levelled using median levelling to generate response ratios before plotting. Kriged plots of the levelled fern data indicated a strong linear relationship of Au, Ag, Sb and Pb to the north-easterly trend of the Luck at Last auriferous quartz vein. Cesium and Rb were enriched in the same area, and both indicated an additional zone of relative enrichment to the south. Arsenic was enriched near an old adit and to a lesser degree in the south, where enrichments of Cs, Rb and Hg were noted. Other elements exhibited trends of enrichments suggesting a spatial zonation of trace elements outward from the area of precious metal enrichment around the quartz vein. This could be element zonation related to the mineralised quartz vein, or another exploration target. (auth)