Lithium (Li) is a key element in the development of renewable energy, chiefly because of its role in Lithium ion batteries. The EU classes it as a Critical Element, which means it is of high importance to the economy and there is a high risk to its supply. Lithium occurs naturally in low concentrations in the earth’s crust and in sea water. It is produced today mainly in Australia and South America from two main sources, granitic pegmatites and dry salt lakes formed from brine,. In the EU, small quantities of lithium are mined from pegmatites in Portugal while new resources have been discovered in the Czech Republic and Finland.
In the early 1970s in southeast Ireland, a geological research student discovered what initially appeared to be granitic pegmatites with particularly large feldspar crystals. The “feldspar”, a common mineral in many rock types, was identified as spodumene, a mineral containing almost 4 % lithium and historically one of the world’s main sources of lithium. Mapping defined numerous spodumene pegmatite occurrences in and adjacent to the margin of the Leinster Granite. Mineral exploration in the 1970s suggested the pegmatites did not have commercial potential. However, modern interest in lithium has led to renewed exploration of these deposits, with attention focused on Moylisha in County Carlow. The student who discovered the pegmatites was Peadar McArdle, who would go on to become Director of Geological Survey Ireland.
While the discovery of lithium pegmatites marked southeast Ireland as a potential source of lithium ore, the presence of lithium-bearing minerals was not news in 1970. The occurrence of spodumene crystals in the Leinster Granite in south Dublin was reported in 1836. This “spodumene” is, in fact, an altered version of the lithium mineral and was given its own name, “killinite”, after Killiney Hill where it was discovered. The presence of lithium minerals at Killiney is a reflection of the lithium-rich nature of the Leinster Granite, which contains 5 – 10 times more lithium than most granites.
Geological Survey Ireland has been investigating the geochemistry of rocks and stream sediments in southeast Ireland since the 1970s. It completed its stream sediment survey of the region in 1990 and the resulting geochemical maps reflect the chemistry of the underlying bedrock. Tellus reanalysed these sediment samples a few years ago, availing of more advanced analytical techniques to produce improved maps for many elements. However, Tellus did not analyse the sediments for lithium. Given the current interest in this element and its “critical” status, GSI has recompiled the historic lithium data and released it on its website here. Rock samples collected from the 1970s to the 1990s were also analysed for lithium and other elements – these data have also been released here and they complement the stream data, confirming that the Leinster Granite is a significant repository of lithium in Ireland.