Potential role of alkaline aqueous fluids in the formation of supergene and low-temperature hydrothermal mineralizations: experiments and natural analogues

热酸性流体对矿床形成的重要性，特别是在热液环境中，已经得到了合理的理解。在大多数热液体系中，碱性流体是金属和其他溶质的重要迁移介质，而pH >>7的碱性流体在成矿作用中的作用除少数例外外，几乎没有受到限制。这是因为，不仅许多地球化学参数和关键金属在这种流体中的行为是未知的，而且对于许多元素，甚至最基本的信息，如天然碱性沃茨的浓度数据，根本无法获得。这一严重的知识差距阻碍了对其在矿床形成过程中的潜在作用进行任何可靠的评估。然而，碱性流体是普遍存在的，并出现在许多地质环境中，从内陆湖泊到地下水到海洋热液流体。这些流体可能有助于形成表生和低温热液矿床。在这里，我们打算通过识别碱性溶液和与高pH值溶液相互作用的岩石中的高场强元素的地球化学和同位素指纹来限制碱性流体对矿床形成的潜在贡献。为了实现这一目标，我们将首先调查HFSE的分布（例如，稀土元素和Y、Sc、Zr、Hf、Nb和Ta）以及欧洲碱性湖泊中Sr和Nd的同位素组成（例如，奥地利、匈牙利）、东非和美国。在表征了主要、次要和痕量溶质的地球化学和其他重要的物理化学参数之后，将这些溶液的未经处理的等分试样用于一系列不同岩石和潜在原生岩的浸出实验。这些实验将通过使用模拟简化的自然解决方案的人工解决方案的实验来补充。在碱性条件下，HFSE及其同位素在水-岩作用过程中的活动性没有得到很好的限制。该项目将首次提供一个综合数据库，介绍几个地点碱性沃茨中高频SE和同位素分布情况，从而填补一个重大的知识空白。它将提供有关碱性流体如何与岩石相互作用以及它们如何影响水-岩石相互作用期间关键元素的流动性的重要信息。沥滤液和固体残留物中的地球化学特征可用作碱性流体参与的指纹，并将帮助地球化学家和经济地质学家评估此类流体是否有助于形成表生和低温热液矿床。这项研究将补充地球化学建模，最后，从实际矿床的地球化学数据的比较，其中碱性流体的形成所描述的矿床的潜在贡献将进行调查。

The significance of hot, acidic fluids for the formation of ore deposits, especially in hydrothermal settings, is reasonably well understood. Such fluids are widely recognized as the most important transport media for metals and other solutes in most hydrothermal systems.In contrast, the role of alkaline fluids wth pH >>7, in ore formation is, with few exceptions, only poorly constrained. This is due to the fact that not only are many geochemical parameters and the behavior of critical metals in such fluids not known, but that for many elements even most basic information such as concentration data for natural alkaline waters, are simply not available. This severe knowledge gap prevents any reliable assessment of their potential role during the formation of ore deposits. Alkaline fluids, however, are ubiquitous and occur in many geological settings ranging from endorheic lakes to groundwater to marine hydrothermal fluids. Such fluids could have contributed to the formation of supergene and low-temperature hydrothermal deposits. Here, we intend to constrain the potential contribution of alkaline fluids to the formation of ore deposits by identifying geochemical and isotopic fingerprints of high field strength elements in alkaline solutions and in rocks that have interacted with high-pH solutions. To reach this goal, we will first investigate the distribution of HFSE (e.g., rare earth elements and Y, Sc, Zr, Hf, Nb and Ta) and the isotopic composition of Sr and Nd in alkaline lakes in Europe (e.g., Austria, Hungary), East-Africa, and the US. After having characterized the major, minor and trace solute geochemistry and further important physico-chemical parameters, untreated aliquots of these solutions are used for leaching experiments with a range of different rocks and with potential protores. These experiments will be complemented by experiments using artificial solutions that mimic simplified natural ones. The mobility of HFSE and their isotopes during water-rock interaction in alkaline conditions is not well constrained. This project will, close a significant knowledge gap by providing, for the first time, a comprehensive database of the HFSE and isotope distribution in alkaline waters from several locations. It will provide important information on how such alkaline fluids interact with rocks and how they affect the mobility of critical elements during water-rock interaction. The geochemical signatures in the leachates and the solid residues may be utilized as fingerprints of the involvement of alkaline fluids and will help geochemists and economic geologists alike to assess whether such fluids contributed to the formation of supergene and low-T hydrothermal ore deposits. This study will be complemented by geochemical modeling and finally, a comparison to geochemical data from actual ore deposits, in which the potential contributions of alkaline fluids to the formation of the described deposits will be investigated.