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

• Applicant: Dr. Manuel Keith
• Subject Area: Mineralogy, Petrology and Geochemistry ; Palaeontology
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 428999008

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.

• DFG Programme: Research Grants
• International Connection: Greece, United Kingdom, USA
• Co-Investigators: Dr.-Ing. Dirk Berger; Professorin Dr. Sarah Anne Gleeson; Dr. Christof Kusebauch; Dr. Ferry Schiperski
• Cooperation Partners: Dr. Sarah Hayes; Professor Dr. Stephanos P. Kilias; Dr. Daniel J. Smith