Dunn, C.E.; Christie, A.B.; Waldron, H.M. 2012 Biogeochemical orientation surveys, Reefton, New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2012/25 60 p. + 1 CD
Abstract: Biogeochemical orientation surveys were conducted in two areas near Reefton – the T38 target (T38) and the Blackwater Creek (Waiuta) prospects, both potential orogenic gold quartz vein systems. Six common plant species were sampled: black beech (Nothofagus solandri), red beech (Nothofagus fusca), silver beech (Nothofagus menziesii), Westland quintinia (Quintinia acutifolia), ferns (Blechnum spp.) and rimu (Dacrydium cupressinum). Sampling was conducted over a 4 day period and generated a collection of 241 samples. Data in this report are from the analysis for 53 elements in 169 of these samples. At the T38 target prospect, foliage from three species of beech was analysed and the element distributions plotted. Differences in element uptake by the three species required the data to be levelled (response ratios) before plotting. Two northwesterly trending zones of enrichment were identified, one with coincident enrichments in Ca, Ba, As, Sb, Cu, Li, Cs and Rb, and the other with coincident enrichments in Au, Co, Mo, Mn, Se, REE and Pb. However, in general, element concentrations were not particularly remarkable, except for one site yielding 4.8 ppb Au, about 50 times background levels of Au (<0.2 ppb Au). This was coincident with slightly elevated levels of several other elements commonly occurring as pathfinder elements for Au (e.g. Bi and Se). At the Blackwater Creek prospect, Waiuta, foliage from the small tree Quintinia was analysed. No indications of Au mineralisation were identified, although it appears that Quintinia is less sensitive to many elements than the beeches. There are two zones of distinctly different chemical composition: 1) in the north there are relative enrichments of B, Ba, Cd, Cu, Hg, Li, Mg, Ni, P, Rb, Sb, Sr and Zn; 2) in the south the coincident suite of elements is Ca, Cr, Cs, Mn, Mo and Pb. Additional information on the relative uptake of elements by ferns (notably high levels of REE) and the conifer rimu provides what is probably a first database for New Zealand on multi-element concentrations in these common species, and these can be used as baseline data for future surveys. Other than some encouraging pioneering work undertaken at Massey University in Palmerston North from about 1970-1990, the application of biogeochemical methods to exploration for mineral deposits has received little attention in New Zealand. Elsewhere in the world, modern analytical technology is providing significantly greater insight to the distribution of a wide range of elements within and among plants, with the result that there is a burgeoning list of exploration success stories. In New Zealand, the addition of fundamental baseline data on the chemical response of plants to a wide range of commodities concealed by overburden warrants developing, testing and adding to the options available to the explorationists.
Notes - appendices available on request
