Tellurium in natural and synthetic pyrite: Ore-formation and economic implication

碲（Te）被欧盟列为高度重要的能源关键元素，因为它在快速增长的绿色能源技术领域得到了应用。目前，大多数Te是作为有色金属开采的副产品回收的，主要是通过精炼Cu来回收，基于现有的提取方法，几乎没有机会增加Te的供应。因此，由于需求的增加，在不久的将来可能会出现稀土短缺。热液黄铁矿中的碲含量可达8,000 ppm，通常与其他微量元素（如as和Au）一起富集（高达4.8 wt. %和11,000 ppm）。黄铁矿在各种流体条件下都是稳定的，包括低温和高温，可变的fO2和pH条件。因此，黄铁矿的微量元素化学可以用来定义Te的关键成矿过程，这是迄今为止约束较差的。由于黄铁矿的普遍存在和富集微量元素的能力，它可以被认为是经济上重要的Te寄主。因此，未来Te的供应可能通过处理包括黄铁矿在内的矿物来解决。然而，碲在选矿过程中的行为尚不清楚，如果不加以回收并排放到尾矿中，可能会产生生态毒理学影响。该项目旨在通过提供对浅成热液和卡林型系统中矿石形成的详细了解来弥补这些知识空白；两种不同的矿化类型表明达到经济的Te浓度。最先进的分析技术将用于黄铁矿中Te的完整结构和化学特征，直至微观和纳米尺度。这允许开发一个固体工具来定义Te在黄铁矿中的结合机制，无论是作为结构结合元素还是作为微到纳米尺寸的包裹体。相定量分析将结合矿物和块状矿石的Te化学，定量证明黄铁矿是这些矿床中主要的Te宿主之一。将进行微量元素测绘，以调查黄铁矿中可能的晶内Te变化（即分带），这将用于定义关键的成矿过程，最终为Te提供一种新的微观分析勘探工具。在受控的实验室条件下进行水热实验将有助于确定控制硫铁矿中Te分布的流体参数（如温度、pH、fO2）。由已知Te组成的流体合成的实验黄铁矿的组成允许定义黄铁矿-流体体系中的第一个Te能分配系数（KD）。因此，结合使用自然和合成系统将允许，第一次提供一个定量的了解沉淀和黄铁矿中Te的掺入机制；一种无处不在的矿物，承载着日益增长的经济利益。

Tellurium (Te) is classified by the European Union as an energy critical element of high importance due to its application in the rapidly growing sector of green energy technologies. Currently, most Te is recovered as a by-product from non-ferrous metal mining, principally by refining of Cu providing little opportunity to increase the Te supply based on current extraction methods. Hence, a shortage in Te is likely to be reached in the near future due to its increasing demand. Tellurium in hydrothermal pyrite reaches 8,000 ppm and is typically enriched together with other trace elements, such as As and Au (up to 4.8 wt. % and 11,000 ppm). Pyrite is stable under a wide range of fluid conditions including low and high temperatures, variable fO2 and pH conditions. Thus, the trace element chemistry of pyrite can be used to define the key ore-forming processes of Te, which are poorly constrained to date. Due to its ubiquity and ability to concentrate trace elements, pyrite may be considered as an economically important host for Te. Hence, the future supply of Te may be resolved by the processing of minerals including pyrite. However, the behaviour of Te during the ore-processing is not well understood and if not recovered and sent to tailings it may have an eco-toxicological impact. This project aims to close these knowledge gaps by providing a detailed understanding about Te ore formation in epithermal and Carlin-type systems; two distinct mineralisation-styles suggested to reach economic Te concentrations. State-of-the-art analytical techniques will be used for a full structural and chemical characterisation of Te in pyrite down to the micro- and nano-scale. This allows to develop a solid tool to define the incorporation mechanisms of Te in pyrite either as a structurally bound element or as micro- to nano-sized inclusions. Phase quantification will be combined with mineral and bulk ore Te chemistry to quantitively demonstrate that pyrite is one of the major Te hosts in these deposits. Trace element mapping will be performed to investigate possible intra-crystalline Te variations (i.e. zoning) in pyrite, which will be used to define key ore-forming processes to finally present a new micro-analytical exploration tool for Te. Hydrothermal experiments under controlled laboratory conditions will help to define fluid parameters (e.g., temperature, pH, fO2) controlling the distribution of Te in pyrite. The composition of experimental pyrite synthesized from a fluid of known Te composition allows to define the first Te Nernst partition coefficients (KD) in the pyrite-fluid system. Consequently, the combined use of natural and synthetic systems will allow, for the first time, to provide a quantitative understanding about the precipitation and incorporation mechanisms of Te in pyrite; a ubiquitous mineral hosting an element of growing economic interest.