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

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.

奥塔哥中部的砂金矿山已堆积了大面积（平方千米量级）的矿山尾矿(mine tailings)，而奥塔哥东部的麦克拉斯造山型金矿(Macraes orogenic gold mine)目前仍在持续堆积此类尾矿。在这类尾矿上构建植被群落，至少需要从岩石中获取部分植物养分。磷是主要的限制性养分：尽管云母片岩(micaceous schist)中分布最广泛的副矿物磷灰石(apatite)的磷含量约为1000 mg/kg，但在数周至数月的时间尺度下，其生物可利用性(bioavailable)极低。氮同样属于重要的限制性养分，但片岩(schist)（尤其是云母片岩）通常含有500–1000 mg/kg的氮，且该类氮在数周至数月的时间尺度内可经水体轻松浸出。牧草类植物从尾矿中吸收的砷含量较为可观（干重可达90 mg/kg以下），但尾矿基质中约1500 mg/kg的高砷浓度并未对植物健康造成不利影响。采用不同氧化程度的片岩覆盖尾矿，是促进植被恢复(revegetation)的最有效手段；适量添加磷肥(phosphatic fertiliser)是可取的，但片岩覆盖层及下方尾矿中的其他养分（包括氮）已具备充足的生物可利用性。