TUNGSTEN · Formation of a giant tungsten deposit: Metal sources and fluid evolution at Panasqueira, Portugal

Formation of a giant tungsten deposit: Metal sources and fluid evolution at Panasqueira, Portugal

Tungsten is essential in many industrial applications due to its unique properties and the desirable properties that it confers to its alloys (toughness, corrosion resistance, and high strength at extreme temperatures owing to strong covalent bonding). Tungsten is used in a wide variety of industrial and technological applications including surgical instruments, aerospace, and electronics. Annual demand for tungsten exceeds 33,000 metric tons worldwide, and tungsten is listed as a “critical raw material” by the European Commission of Enterprise and Industry. While several factors that affect tungsten precipitation have been identified, the determining factors that lead to tungsten precipitation and how they influence tungsten distribution worldwide remain unclear. The objectives of this project are (1) to characterize the fluids responsible for mineralization at Panasqueira, in the context of fluid evolution, in order to understand the factors controlling tungsten vein deposit formation; (2) to determine the provenance of metals; (3) to develop the analytical methods needed to analyze the mineralizing fluid(s) using state-of-the-art techniques, and implement new quantification methods to interpret the properties of fluids with complex compositions; and (4) to develop a comprehensive model for the formation of economically and technologically important tungsten ore. The main approaches used during the development of this project have been: Firstly, determination of fluid chemistry at Panasqueira through LA-ICPMS analyses of fluid inclusions and determination of rock chemistry changes through combination of XRF and LA-ICPMS. Secondly, evaluation of potential geochemical processes leading to tungsten deposition based on the fluid and rock chemistries observed and on the geological characteristics of tungsten deposits worldwide. The compositions of the mineralizing fluids at Panasqueira have been determined through combination of detailed petrography, microthermometric measurements and LA-ICPMS analyses, and geochemical modeling has been used to determine the processes that lead to tungsten mineralization. We characterized the fluids related to the various mineralizing stages in the system: the oxide stage (tin and tungsten mineralization), the sulfide stage (chalcopyrite and sphalerite mineralization) and the carbonate stage. Thus, our results provide information on the properties of fluids related with specific paragenetic stages. Furthermore we used those fluid compositions in combination with host rock mineralogy and chemistry to evaluate which are the controlling factors in the mineralizing process. The results obtained provide the first comprehensive dataset on quantitative composition of fluids in tungsten-vein deposits and indications on which are the major geologic controls on the occurrence of tungsten mineralization. Therefore, these results provide an approximation to what determines the very localized distribution of tungsten mineralization worldwide.

Data: CORDIS, © European Union