Environmental mineralogy and geochemistry of processing residues at Prohibition historic gold mine site, Waiuta, Westland, New Zealand

The Prohibition mine processing site was abandoned in 1951. Part of the site was remediated in 2016, but some remaining processing residues exposed at the surface have elevated As, Cu, Hg, Pb and Zn. Most of these residues consist of haematitic sandy tailings with oxidised As material (As = 4000–9000 mg/kg), and that As is largely immobile in the environment. Minor As-rich flue residues have As contents of 600–4000 mg/kg, from which As may be mobilised into the environment, but dissolved As <0.3 mg/L prevails in associated waters. Lead-rich residues (locally >5 wt% Pb) from an assay office including arsenic-rich glassy slags (locally >3 wt% As) were also deposited. Naturally colonising plants have absorbed low As contents, with <2 mg/kg (dry weight) in shrubs and up to 20 mg/kg (dry weight) in grasses. This natural revegetation appears to be adequate for site rehabilitation.

普罗希比特（Prohibition）矿区选矿场地于1951年被废弃。2016年对该场地部分区域实施了修复治理，但仍有部分残留选矿残渣裸露于地表，其中砷（As）、铜（Cu）、汞（Hg）、铅（Pb）与锌（Zn）含量均显著升高。该类残渣多为搭载氧化态砷物质的赤铁矿质砂状尾矿，砷含量介于4000~9000 mg/kg之间，且该形态的砷在环境中基本不迁移。另有少量富砷烟道残渣，其砷含量为600~4000 mg/kg，其中砷具备向环境迁移的潜力，但场地相关水体中的溶解态砷普遍低于0.3 mg/L。此外，某化验室产生的富铅残渣（局部铅含量＞5 wt%）连同富砷玻璃质炉渣（局部砷含量＞3 wt%）也在此处堆积。自然定植的植物仅吸收了低浓度的砷：灌木干重中的砷含量＜2 mg/kg，草本植物干重中的砷含量最高可达20 mg/kg。该自然植被恢复效果似乎足以满足场地修复的要求。