Remobilization and mineralization of selenium-tellurium in metamorphosed red beds: Evidence from the Munster Basin, Ireland

Selenium and tellurium are vital elements for the ongoing development of carbon-free energy generation, but are only recovered in small volumes as by-products of base and precious metal processing. Security of supply of these commodities is of high importance as their demand is forecast to increase in the near future, thus more research is required on the varying mineralization systems where their occurrence and behavior are poorly understood, such as sedimentary basins and metasedimentary terranes.The Munster Basin of southern Ireland is a good study area for sedimentary Se-Te in such environments as it has a regionally-high soil selenium anomaly, and is characterized by Devonian terrestrial red beds, which were metamorphosed during the Hercynian (Variscan) Orogeny. The area also contains ore-grade biogenic sediment-hosted copper and remobilized vein-hosted copper sulfides, which are prospective for chalcophile selenium and tellurium.Quartz vein-hosted Se-Te mineralization was identified across the Munster Basin, accompanied by trace gold-silver-mercury accessory phases. New sulfur isotope data reinforces the model of sulfur and selenium remobilized from a biogenic red bed source, which reflects a wider association of selenium deposits with oxidizing environments. The co-occurrence of tellurium mineralization suggests that it too may be concentrated in oxidizing environments. Associated traces of gold add to a growing body of evidence that gold is also transported and precipitated in oxidizing conditions in continental basins.