Laboratory investigations and theoretical considerations on the electrical properties of seafloor massive sulfides

为了满足未来全球对金属的需求，人们对深海采矿的兴趣日益浓厚。海底块状硫化物是一种重要的海洋金属资源。它们产生于海底火山活动区域，特别是洋中脊。由于水下采矿既困难又昂贵，因此对海底沉积物进行仔细的勘探和特征描述是必不可少的。电方法，特别是诱导极化，被认为起着关键作用，因为它们决定了岩石的导电性，而导电性取决于矿物含量。与大陆矿石不同的是，在大陆矿石中存在着丰富的数据，而SMS的电学特性却鲜为人知。海底样品稀少且难以获得，只有少数研究存在。陆相硫化物的结果不容易转移到海底，因为海洋流体的含盐量要高得多，岩石的化学成分和结构也可能不同。在这个项目中，我们测量了来自世界各地的大量短信样本的频率相关电学特性，包括大西洋、太平洋和地中海的沉积物。结果将在矿物学数据的背景下进行分析，以便确定电参数和矿物含量之间的潜在关系，这将构成未来勘探方案的基础。测量之前将进行方法学研究，以确定测量不规则形状样品电性能的最佳程序。SMS样品是有价值的，通常不希望破坏它们，因此使用圆柱塞的标准方法不能适用于所有样品。数据解释将得到广泛的理论考虑的支持，以便对控制矿化岩石电阻抗的物理过程有一个基本的了解。现有的理论完全假设矿物是浸染的，而实验证据表明，连通的矿脉对电导率有巨大的影响，不能忽视。我们的理论进步将把现有的电化学模型与最近为非矿化沉积物开发的新方法结合起来。

In order to satisfy future global demands for metals, there is an increasing interest in deep-sea mining. Seafloor massive sulfides (SMS) are considered an important marine metal resource. They are generated in regions of submarine volcanic activity, in particular mid-ocean ridges. Since underwater mining is difficult and expensive, a careful exploration and characterisation of seafloor deposits is essential. Electrical methods, and in particular induced polarization, are considered to play a key role, because they determine the electrical conductivity of the rocks, which depends on mineral content. Unlike for continental ores, where a wealth of data exists, the electrical properties of SMS are poorly known. Seafloor samples are rare and difficult to obtain, and only a small number of studies exists. Results obtained for continental sulfides cannot easily be transferred to seafloor conditions, because the marine fluids are considerably more saline, and the rock chemistry and texture may differ. In this project, we measure the frequency-dependent electrical properties of a large number of SMS samples from several worldwide locations, including deposits in the Atlantic, Pacific and Mediterranean. The results will be analysed in the context of mineralogical data, in order to identify potential relationships between electrical parameters and mineral content, that will constitute a basis for future exploration programs. The measurements will be preceded by methodological studies to define the optimum procedure to measure electrical properties of samples of irregular shapes. The SMS samples are valuable and it is generally not desired to destroy them, such that standard methods using cylindrical plugs cannot be applied to all samples. The data interpretation will be supported by extensive theoretical considerations, in order to obtain a fundamental understanding of the physical processes that control the electrical impedance of mineralized rock. Existing theories exclusively assume that the minerals are disseminated, whereas experimental evidence suggests that connected veins have a huge influence on electrical conductivity and cannot be neglected. Our theoretical advancements will combine existing models of the electrochemistry with new methods recently developed for unmineralized sediments.