The fate of arsenic in low to medium temperature hydrothermal systems

砷是一种有毒元素，存在于大多数浅层流体系统中，有时浓度非常高，对健康构成相当大的风险。涉及砷的浅层地质和地球化学过程得到了相对较好的调查，不会成为本提案的主题。然而，它们通常与在较高温度的水热系统中预富集砷有关，在水热系统中，元素砷以各种氧化态沉淀，如自然砷、砷化物、亚硫化物和硫化物(很少以亚砷酸盐或砷酸盐的形式存在)。在低于250°C的温度下，天然砷、雄黄、雌黄和钴镍铁砷化物起着重要作用。该项目将在一个众所周知的地区(德国西南部施瓦茨瓦尔德)研究它们的组合、形成条件、热力学相关系、结晶溶液的组成以及导致它们沉淀的地质/地球化学过程(冷却、流体混合、流体-岩石相互作用)，该项目涉及来自不同地层水平(因此在不同温度下形成)的完美大样本集，以了解砷循环的较高温度部分及其与低温、浅层过程的联系。这项工作将涉及矿物化学、流体包裹体和共生分析以及热力学计算。

Arsenic is a toxic element present in most shallow fluid systems, and sometimes in very high concentrations which pose a considerable health risk. The shallow geological and geochemical processes involving arsenic are relatively well investigated and will not be the topic of the present proposal. However, they are typically related to pre-enrichment of arsenic in higher temperature, hydrothermal systems from which the element arsenic is precipitated in various oxidation states such as native arsenic, arsenides, sulfarsenides and sulfides (and, rarely, as arsenites or arsenates). At temperatures below about 250°C, native arsenic, realgar, orpiment and Co-Ni-Fe arsenides play an important role. Their assemblages, their conditions of formation, their thermodynamic phase relations, the composition of the solutions they crystallize from and the geological/geochemical processes responsible for their precipitation (cooling, fluid mixing, fluid-rock interaction) will be investigated in this project in a well known region (Schwarzwald, SW Germany) involving a perfect, large sample set from different stratigraphic levels (and, hence formed at various temperatures) in order to understand a higher temperature part of the arsenic cycle and its connection to the low-temperature, shallow proccesses. This work will involve mineral chemical, fluid inclusion and paragenetic analyses as well as thermodynamic calculations.