Abstract Ultramafic rocks are considered as the most important geogenic sources of Cr whose hexavalent species is of environmental concern. In tropical to subtropical areas (e.g. New Caledonia, Brazil, Philippines), prolonged and pervasive weathering of ultramafic rocks produces Ni laterite ores which are further enriched in Cr. While elevated levels of Cr have been identified in Ni laterites, Cr availability and export from these deposits and its contribution to natural waters remain poorly understood. Therefore, this study examined the speciation and flux of Cr in a Ni laterite profile through sequential extraction and leaching experiments coupled with physical, mineralogical, and geochemical characterization. These were correlated to the behavior and export of Cr in surrounding surface waters studied through hydrochemical investigation. This work demonstrates, through the example of the Rio Tuba Ni laterite deposit, that pervasive weathering of ultramafic rocks in tropical areas generate very important reservoirs of Cr(VI). Although Cr is primarily fixed in insoluble fractions (>89%) and least in bioavailable and easily mobilizable phases (

中文翻译：

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镍红土剖面中的铬含量及其对周围地表水的影响

摘要 超镁铁质岩被认为是最重要的 Cr 地质来源，其六价物种受到环境问题的关注。在热带到亚热带地区（例如新喀里多尼亚、巴西、菲律宾），超基性岩长期和普遍的风化作用产生镍红土矿石，这些矿石进一步富含铬。虽然在镍红土中已发现铬含量升高，但对这些沉积物的 Cr 可用性和出口及其对天然水的贡献仍知之甚少。因此，本研究通过连续提取和浸出实验以及物理、矿物学和地球化学表征，研究了镍红土剖面中 Cr 的形态和通量。这些与通过水化学调查研究的周围地表水中 Cr 的行为和输出相关。这项工作通过 Rio Tuba Ni 红土矿床的例子表明，热带地区超基性岩的普遍风化产生了非常重要的 Cr(VI) 储层。尽管 Cr 主要固定在不溶性部分 (>89%) 中，而在生物可利用且易于流动的相中最少（