No abstract

No abstract

Substrates associated with two historic gold mining sites in north Westland, New Zealand, have locally very high arsenic concentrations (commonly 10-40 wt% As). The substrates consist of iron oxyhydroxide precipitates, and processing mill residues. Waters associated with some of these substrates have high dissolved arsenic (commonly 10-50 mg/L As). Natural revegetation of these very high arsenic sites has occurred over the past 50 years, although some areas of substrate remain bare. Revegetating species include native and adventive shrubs, adventive grasses, rushes, and mosses, and native ferns. Revegetation by higher plants follows initial colonization by mosses, and some shrubs are growing directly in high-arsenic substrate. Shrubs, especially manuka (Leptospermum scoparium), gorse (Ulex europaeus), tree fuchsia (Fuchsia excorticata) and broadleaf (Griselinia littoralis) largely exclude arsenic from their shoots (<10 mg/kg dry weight) irrespective of the As content of the substrate. Likewise, most grasses, and reeds (Juncus spp.), have only modest As contents (typically <100 mg/kg dry weight). However, mosses growing on high-arsenic substrates have strongly elevated arsenic contents (>0.2% dry weight). In particular, the moss Pohlia wahlenbergii acts as a hyperaccumulator, with up to 3% (dry weight) As. Antimony (Sb) contents of all plants are about one thousandth of that of arsenic, reflecting the As/Sb ratio of the substrates. Plant establishment in the high-As substrates may be locally limited by low nutrient status, rather than arsenic toxicity. The shrubs, grasses, and reeds identified in this study are arsenic tolerant and largely exclude arsenic from their shoots so that revegetation with these species, can help to isolate the high-arsenic substrates from the surface environment. These species could be used as phytostabilisation agents on high-arsenic sites that are remote from human habitation. In contrast, the mosses, despite their high arsenic tolerance, are a less desirable component of revegetation of high-arsenic substrates because they actively transfer arsenic from the substrate to the biosphere.

The rare Li-mica taeniolite is described from the Dicker Willem carbonatite complex, Namibia, and from the Alpine carbonatitic lamprophyre dyke swarm at Haast River, New Zealand. At Haast River, taeniolite occurs in sodic and ultrasodic fenites derived from quartzo-feldspathic schists and rarely in metabasites, adjacent to dykes of tinguaite, trachyte and a spectrum of carbonatites ranging from Ca-to Fe-rich types. In Namibia, taeniolite is present in potassic fenites derived from quartz-feldspathic gneisses and granitoids at the margin of an early s6vite phase of the complex and in a radial s6vite dyke emanating from this centre.The occurrence of taeniolite in these totally disparate carbonatite complexes, together with examples of lithian mica from other carbonatite complexes worldwide, raises the question of the status of Li as a 'carbonatitic element'. We argue that lithium is not a consequence of crustal assimilation or interaction, but reflects the geochemical character of the magmatic source. Li, an overlooked and little-analysed element, may be an integral part of metasomatic enrichment in the mantle, and of magmas derived by partial melting of such a source.

No abstract