ABSTRACT

Mine tailings resulting from orogenic gold processing commonly form arsenic (As)-enriched environments. A result of this is that they draw environmental attention in modern gold mining settings and significant effort in long-term rehabilitation. The Alexander River mine processing site in the Reefton area of Westland provides an opportunity to examine the natural rehabilitation of As-enriched tailings that have been left undisturbed for >70 years in a humid environment. These tailings comprise a ∼1 m thick package of finely laminated (mm-scale) sediments that were manually accumulated on a terrace downstream of the gold extraction plant. The tailings sediments are As-rich (up to 5000 mg/kg) due to relict arsenopyrite and As-bearing pyrite. Diagenetic Ca–Fe–arsenate (tentatively identified as yukonite) and As-bearing iron oxyhydroxide have formed during localised oxidation. There was sufficient calcite in the tailings to maintain circumneutral pH in the tailings despite sulphide oxidation. The historical tailing impoundment is now covered by grass, ferns and shrubs, with beech and rimu forest covering several metres at the margins. Leaf analyses indicate that the vegetation is absorbing only minor As. Therefore, the tailings substrate has not halted natural vegetation re-colonisation of this As-rich historical site.

摘要

造山带金加工产生的尾矿通常形成富含砷 (As) 的环境。其结果是，它们在现代金矿开采环境中引起了环境的关注，并在长期恢复方面做出了重大努力。Westland 的 Reefton 地区的 Alexander River 矿山加工场地提供了一个机会，可以检查在潮湿环境中 70 年以上未受干扰的富砷尾矿的自然恢复情况。这些尾矿包括约 1 m 厚的细层（毫米级）沉积物，这些沉积物是人工堆积在金提取厂下游的平台上。由于残留的毒砂和含砷的黄铁矿，尾矿沉积物富含砷（高达 5000 mg/kg）。在局部氧化过程中形成了成岩 Ca-Fe-砷酸盐（暂时确定为育空石）和含 As 的羟基氧化铁。尽管硫化物被氧化，但尾矿中有足够的方解石以维持尾矿中的中性 pH 值。历史悠久的尾矿库现在被草、蕨类植物和灌木覆盖，边缘有几米长的山毛榉和rimu森林。叶分析表明植被仅吸收少量 As。因此，尾矿基质并没有阻止这个富含砷的历史遗址的自然植被重新定居。山毛榉和rimu森林在边缘覆盖了几米。叶分析表明植被仅吸收少量 As。因此，尾矿基质并没有阻止这个富含砷的历史遗址的自然植被重新定居。山毛榉和rimu森林在边缘覆盖了几米。叶分析表明植被仅吸收少量 As。因此，尾矿基质并没有阻止这个富含砷的历史遗址的自然植被重新定居。