CRG Marine Geosciences, Department of Earth and Ocean Dynamics, Earth Sciences Faculty, University of Barcelona, Spain.
CRG Marine Geosciences, Department of Earth and Ocean Dynamics, Earth Sciences Faculty, University of Barcelona, Spain.
Sci Total Environ. 2022 Mar 1;810:151183. doi: 10.1016/j.scitotenv.2021.151183. Epub 2021 Oct 29.
Mining activities are essential to our society, but ore extraction and treatment produce waste that must be stored in safe places without harm to the environment. For a long time, seafloor disposal has been viewed as a cheap option with barely visible impacts. In Portmán Bay, SE of Spain, large amounts of tailings from open pit sulphide mining were discharged directly into the coastal sea over 33 years, thus forming a massive deposit that completely infilled the bay and expanded seawards over the inner continental shelf. Here we present the first multiproxy physicochemical characterization of the submarine tailings in Portmán Bay, mostly by using non-destructive techniques, also including pre-dumping and post-dumping sediments. Eight distinct sedimentary facies, grouped in four stratigraphic units, have been thus identified in a set of up to 4.3 m long gravity cores totalling more than 60 m. Geogenic and anthropogenic geochemical proxies consistently allow differentiating pre-dumping sediments from tailings. Potentially toxic metals if made bioavailable can reach high concentrations in units including or formed exclusively by tailings (i.e. up to 3455, 2755 and 1007 mg kg for Pb, As, and Zn, respectively). Some physical properties, such as magnetic susceptibility, are particularly useful as the tailings are rich in Fe-bearing minerals (>30% Fe in some layers). Estimated sedimentation rates show a strong gradient from proximal to distal locations, with rates in excess of 50 cm yr to less than 1 cm yr. We ultimately document the history of the transformation of Portmán Bay from an almost natural state to a new condition after a long period of massive dumping of mine tailings. Our study provides guidance to further assessments in a context where the diversity of marine environments impacted by the disposal of mine waste is expected to grow in the near future.
采矿活动对我们的社会至关重要，但矿石开采和处理会产生废物，这些废物必须储存在安全的地方，而不会对环境造成危害。长期以来，海底处置一直被视为一种廉价的选择，几乎没有可见的影响。在西班牙东南部的波特曼湾，大量露天开采硫化物矿的尾矿在 33 年的时间里直接排入沿海水域，从而形成了一个巨大的沉积物，完全填满了海湾，并向内陆架内部扩展。在这里，我们首次对波特曼湾海底尾矿进行了多参数物理化学特征描述，主要使用了非破坏性技术，还包括了倾倒前和倾倒后的沉积物。在一组多达 4.3 米长的重力岩芯中，总共超过 60 米，共识别出 8 种不同的沉积相，分为 4 个地层单元。利用地球化学和人为地球化学示踪剂，可以一致地区分倾倒前的沉积物和尾矿。如果具有生物利用性，潜在的有毒金属可以在包括或仅由尾矿形成的单元中达到高浓度（分别为 Pb、As 和 Zn 的 3455、2755 和 1007mgkg）。一些物理性质，如磁化率，在尾矿中富含含铁矿物（某些层中超过 30%的 Fe）时特别有用。估计的沉积速率显示出从近到远的强烈梯度，速率超过 50cmyr 到小于 1cmyr。我们最终记录了波特曼湾从几乎自然状态到长期大规模倾倒尾矿后形成的新状态的转变历史。我们的研究为进一步评估提供了指导，因为预计在不久的将来，受处置矿山废物影响的海洋环境多样性将会增加。
