Department of Geosciences, University of Massachusetts, 611 North Pleasant Street, Amherst, MA, 01003, USA.
Environ Geochem Health. 2020 Oct;42(10):3263-3279. doi: 10.1007/s10653-020-00566-7. Epub 2020 Apr 25.
Fragmented ultramafic bodies in New England were important mineral resources until the early twentieth century, yet few studies have addressed their potential to release trace metals to terrestrial and aquatic environments. Here, we evaluate the release of four trace metals (Cr, Co, Mn, and Ni) from a historic serpentine-talc "soapstone" quarry in Blandford, MA, USA. Soil pits, sediment and rock samples, and stream water samples were collected from upslope undisturbed areas, within the mine spoils and mine face, and downslope of the mine. In order to provide a bottom-up approach for understanding metal release, careful petrographic analysis, electron-dispersive spectroscopy, and wavelength-dispersive spectroscopy were employed to provide first-order insight into the mineralogy of the deposit and a determination of potential metal-bearing phases. Trace metals were primarily observed in ultramafic sheet silicates, primary Fe-oxides, and interstitial weathering-related sulfates. Bulk rock concentrations were Cr (1550 mg kg), Co (230 mg kg), Mn (1100 mg kg), and Ni (1960 mg kg); Cr, Co, and Ni were elevated relative to the surrounding country rock. However, soils and sediments total concentrations were comparable to background soil concentrations: Cr (119 mg kg), Co (73 mg kg), Mn (894 mg kg), and Ni (65 mg kg). Moreover, < 0.5% of the total concentrations were bioavailable (0.1 M ammonium acetate extraction), implying that metals are present as insoluble forms. However, ~ 20% of the total Cr, Mn, Ni, and Co concentrations were strong acid extractable, suggesting mobilization over the coming decades. Stream water concentrations of Mn and Cr were < 50 µg L, below concentrations outlined by USEPA drinking water standards, and WHO water guidelines for Ni. These results suggest that transport of Cr, Mn, Ni, and Co from the serpentine-talc as dissolved compounds or sediments is limited by retention within silicate and oxides.
新英格兰的破碎超镁铁质体是重要的矿产资源，直到 20 世纪初，但很少有研究探讨它们向陆地和水生环境释放痕量金属的潜力。在这里，我们评估了美国马萨诸塞州布兰福德一个历史悠久的蛇纹石-滑石“皂石”采石场中四种痕量金属（Cr、Co、Mn 和 Ni）的释放情况。从未受干扰的上坡区、矿区废料和矿面内以及矿区下游采集了土壤坑、沉积物和岩石样本以及溪流水样。为了提供一种自下而上的方法来理解金属释放，我们进行了仔细的岩相分析、电子分散光谱和波长分散光谱分析，以初步了解矿床的矿物学，并确定潜在的含金属相。痕量金属主要存在于超镁铁质片状硅酸盐、原生 Fe 氧化物和间隙风化相关的硫酸盐中。块状岩石浓度为 Cr（1550mgkg）、Co（230mgkg）、Mn（1100mgkg）和 Ni（1960mgkg）；Cr、Co 和 Ni 的浓度相对周围的围岩升高。然而，土壤和沉积物的总浓度与背景土壤浓度相当：Cr（119mgkg）、Co（73mgkg）、Mn（894mgkg）和 Ni（65mgkg）。此外，<0.5%的总浓度是生物可利用的（0.1M 乙酸铵提取），这意味着金属以不溶形式存在。然而，~20%的总 Cr、Mn、Ni 和 Co 浓度是强酸可提取的，这表明在未来几十年内可能会发生迁移。Mn 和 Cr 的溪流水浓度<50µgL，低于美国环保署饮用水标准和世卫组织水准则规定的 Ni 浓度。这些结果表明，从蛇纹石-滑石中以溶解化合物或沉积物形式迁移的 Cr、Mn、Ni 和 Co 的运输受到硅酸盐和氧化物的保留限制。
