Cathy Rufaut

Phytostabilization of gold mine tailings from New Zealand. Part 2: Experimental evaluation of arsenic mobilization during revegetation.

Revegetation of mine tailings usually requires amendments of phosphorus. However, phosphate addition can mobilize arsenic (As) from the tailings. A 5-mo lysimeter field trial was conducted to quantify As mobilization in gold mine tailings, in association with different P amendment products and different plant species (barley Hordeum vulgare, blue lupin Lupinus angustifolius, rye corn Secale cereale) necessary for short-term revegetation of mine tailings. A simultaneous laboratory experiment was run to examine As mobilization in 1-cm-deep tailings in relation to different P amendment rates. The experimental results showed that the amount of As leached was proportional to the amount of P added. In the larger scale lysimeters, P amendment of <3 g m−2 caused As leaching of 0.5 mg L−1 from unplanted lysimeters and up to 0.9 mg L−1 on average in planted lysimeters. Variable species-amendment combinations produced differences in the amount of As leached and uptaken. Leachates and uptakes were higher with an organic fertilizer amendment than Superphosphate, particularly in combination with barley. Arsenic accumulated in plant biomass to 126 mg kg−1 in shoots and 469 mg kg−1 in roots.

Phytostabilization of Gold Mine Tailings, New Zealand. Part 1: Plant Establishment in Alkaline Saline Substrate

Tailings from the Macraes mine, southern New Zealand, are prone to wind erosion. Use of a vegetation cover for physical stabilization is one potential solution to this environmental problem. This study used field trials contained in lysimeters to 1), test the ability of different plant species to grow in un/amended tailings and 2), provide background information on the nutrient and chemical content of waters in tailings. Barley (Hordeum vulgare), blue lupin (Lupinus angustifolius), and rye corn (Secale cereale) were trialed, using Superphosphate fertilizer and sewage sludge as amendments. Rye corn grew well in fertilizer-amended tailings, but poorly in unamended tailings; barley growth was similar in amended and unamended tailings; blue lupins grew poorly overall. The tailings had alkaline pH (7–8.5) and water rapidly (<1 mo) interacted with the tailings to become strongly saline. Minor acid generation was neutralized by calcite, with associated release of calcium and carbonate ions. Leachate waters were supersaturated with respect to calcite and dolomite. Dissolved sodium concentrations were up to 1000 mg L−1, but elevated Ca2+ calcium and Mg2+ ensured that sodicity was lower than plant-toxic levels. Rye corn is a potentially useful plant for rapid phytostabilization of tailings, with only minor phosphate amendment required.

Rapid plant-cover establishment on gold mine tailings in southern New Zealand: glasshouse screening trials.

The use of a short-term vegetation cover to temporarily control the negative environmental effects of inactive tailings ponds is not frequently practiced during operational mining, but could have some merit. This article reports on a glasshouse trial designed to examine some of the issues associated with short-term vegetation: fast germination of a high proportion of seed, the ability of seedlings to survive in unamended substrates, and potentially toxic substrate. Five nonindigenous plant species were tested—barley (Hordeum vulgare), rye corn (Secale cereale), Italian ryegrass (Lolium multiflorum), red clover (Trifolium pratense), and lucerne (Medicago sativa)—in five different types of substrate: unamended tailings, tailings and fertilizer, tailings and greenwaste, biosolid-blend compost, and local topsoil. The nutrient and heavy metal status (As, Cu, Cd, Ni, Pb) of each substrate type was determined. Plant species performance was monitored over 14 wk. Substrate metal concentrations were low except for As, which was elevated in all substrate types. Plants in unamended tailings grew less vigorously than plants in tailings and compost, or in topsoil. Plant performance in tailings and fertiliser was greatly suppressed following a high fertilization rate. Metal uptake in plants was highest for As (0.4–77 mg kg−1 DW) and Cu (5.3–50.3 mg kg−1 DW). Future field trials are necessary to authenticate findings, but barley and rye corn are promising species for a short-term tailings cover.

Temporal and spatial variability of acid rock drainage in a rehabilitated coal mine, Wangaloa, South Otago, New Zealand.

Abstract The Wangaloa open cast coal mine ceased operations in 1989, with no restoration of the 252 ha site, and moderate acid rock drainage developed. A major rehabilitation programme was initiated in 2002 with removal of exotic vegetation, and extensive planting (>60 000) of native seedlings was begun in 2003. By 2006, most seedlings were thriving, and, combined with adventive exotic weeds, a 70% vegetation cover had been achieved. The site substrates were highly variable on the 10–100 m2 scale, and have been characterised by paste pH (>700 measurements). In 2003, substrates had moderate acidity (pH = 4.5 ± 0.9) with distinctly acid patches (pH down to <2). By 2006, the average substrate pH was essentially unchanged. Some distinctly acid patches had higher pH, and one patch had apparently become more acid. Water compositions (>100 samples from 15 sites) were also highly variable spatially and temporally. Incoming stream and rainwater (pH 5–6) chemically interacted with acid substrates, especially waste rock piles that contain pyrite‐bearing material, and evolved to lower pH (pH down to 3.4), sulfate‐rich waters. A pit lake on the site receives most surface and groundwater runoff, and this lake, with a water residence time of 1–2 yr, controls the site discharge water quality. The lake pH varies on a monthly time‐scale from 4.5 to 6.5, synchronised with pH variations in groundwater boreholes in waste rock. In addition, there has been a general increase in pH of the lake during rehabilitation from consistent pH 4.6–4.8 before rehabilitation to near pH 6 during rehabilitation. The sulfate/chloride ratio of lake water has decreased from 20 to <10 during rehabilitation as well. These changes in lake water composition from year to year may be a result of increased input of rainwater that has had less interaction with substrate than runoff water had before rehabilitation began.

Geology, evaporative salt accumulation and geoecology at Springvale historic gold mine, Central Otago, New Zealand

ABSTRACT The Springvale placer gold mine was developed in distal Pleistocene fan deposits that are dominated by auriferous gravel. The gravel was originally deposited in channels in Miocene mudstone. Mining has removed the gravel, exhuming the mudstone. The mudstone has since become an impermeable substrate for accumulation of evaporitic encrustations, with substrate slurry conductivities up to 20,000 µS. The predominant evaporitic minerals (halite, gypsum and calcite) are derived from marine aerosols in rain with some dissolution of soluble minerals in the sediments. Post-mining erosion of mudstone during rain events has formed muddy and silty outwash pans, which are repeatedly replenished from runoff and accumulate evaporitic salts. The pans have been the principal site of halophyte plant establishment where conductivities exceed 1000 µS. Substrates with conductivity <1000 µS have generally been colonised by adventive plant species. Mudstone outcrops have remained unvegetated and continue to contribute sediment and salts to saline pans.

Geochemical and mineralogical controls on mine tailings rehabilitation and vegetation, Otago Schist, New Zealand

ABSTRACT Large areas (square kilometre scale) of mine tailings have been deposited from placer gold mines in Central Otago, and are being deposited at Macraes orogenic gold mine in east Otago. Establishment of vegetation on these tailings involves at least some provision of plant nutrients from the rock. Phosphorus is the principal limiting nutrient, as the c. 1000 mg/kg P in accessory apatite, most abundant in micaceous schist, is only sparingly bioavailable on timescales of weeks to months. Nitrogen is an important limiting nutrient but schist, especially micaceous schist, typically contains 500–1000 mg/kg N, and this nitrogen is readily leachable with water on timescales of weeks to months. Arsenic uptake from tailings by pasture species is significant (< 90 mg/kg dry weight), but elevated As in tailings substrates (c. 1500 mg/kg) does not adversely affect plant health. Capping of tailings with variably oxidised schist is the most effective way of facilitating revegetation, and some addition of phosphatic fertiliser is desirable but other nutrients, including nitrogen, are adequately bioavailable in a schist cap and underlying tailings.

Coleoptera species in bush remnants at a closed coal mine in southeast Otago

Rehabilitation earthworks and site reconstruction radically changed the abandoned nature of a closed coal mine in southeast Otago. Around 90% of natural vegetation was cleared for replacement mass planting of indigenous shrubs. A small network of mānuka and kānuka bush patches (40+ years old) was retained as remnant ‘islands’ in a matrix of cleared, bare ground. Coleoptera were sampled in three size classes of bush remnants and a mature forest remnant in 2003 to identify which indigenous species had persisted in the modified setting. From 72 samples, 1155 individuals were recorded from 81 species and 24 families. Indigenous species dominated the sampled fauna and, except for the absence of large predatory species, were found to represent a typical southern Otago forest-associated assemblage. Significant multivariate differences in species composition based on relative abundance existed between different remnant size groups. Only 6% of species were distributed throughout all of the bush remnants. A later sample taken in 2010 from 7-year-old plantings on waste rock indicated few shared species with the nearby mānuka–kānuka remnants. Over rehabilitation time, a finely structured Coleoptera community is developing in revegetated habitats at the coal mine.