Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with pyrite and anomalous selenium content. Mineralisation here may have reflected very high heat flow in foreland basins north of the emerging Variscan orogenic front, responsible for gold occurrence in the South Wales Coalfield. At Castlecomer, gold (–platinum) is attributed to precipitation with replacive pyrite and selenium from groundwaters at redox interfaces, such as siderite nodules. Pyrite in the cores of the nodules indicates fluid ingress. The underlying Caledonian basement bedrock is mineralised by gold, and thus likely provided a source for gold. The combination of the gold occurrences in coal in Castlecomer and in South Wales, proximal to the Variscan orogenic front, suggests that these coals along the front could comprise an exploration target for low-temperature concentrations of precious metals.

About the speaker

Dr. Liam Bullock is a postdoctoral researcher at the University of Oxford, specialising in geochemistry, petrology and mineralogy. He completed his PhD at Keele University in 2015, where he worked on the evolution of rhyolitic lavas in the Aeolian Islands, Italy. After spending a year working for a UK gold exploration company with an Ethiopian concession site, Liam started his first post-doc position at the University of Aberdeen, investigating critical trace elements in the sedimentary environment. Liam joined the NERC Greenhouse Gas Removal programme in 2018 at the University of Southampton, determining the feasibility of mine waste materials for CO2 sequestration. He recently joined the University of Oxford as part of the same project.