NEWFOUNDLAND SPODUMENE PEGMATITE PROSPECTIVITY AND EXPLORATION: LESSONS FROM SOUTH LEINSTER, IRELAND

Exploration for spodumene pegmatites in Newfoundland has been hampered by poorly developed exploration models and a lack of successful methods to locate pegmatites through cover or at depth. Lessons learned from our ongoing work on spodumene pegmatites in south Leinster, Ireland, provide useful insights for lithium pegmatite exploration in Newfoundland and elsewhere.

The south Leinster pegmatites lie within the ~2 km wide East Carlow Deformation Zone (ECDZ), which encloses the contact between Ordovician to Devonian plutons of the Leinster Granite batholith and their Ordovician mica schist and amphibolite country rocks. Both simple and spodumene pegmatites intruded around the end of granite plutonism into granites and mica schists. The lack of pegmatite compositional district zoning, coupled with chemical modelling, suggests that the spodumene pegmatites crystallized from fractionated anatectic melts of metasedimentary rocks, in contrast to the parental granite magma fractionation model often applied in mineral exploration. Exploration drilling suggests that the south Leinster spodumene pegmatites are typically 2-20 m thick distinct sheets (semi)continuous for lengths of >1 km, unlike some economic spodumene pegmatites that anastomose into wider bodies. Genetic and geometric characteristics of the Leinster (anatectic) type of spodumene pegmatites provide meaningful distinctions for building exploration models. Most of south Leinster, including the spodumene pegmatite zone, has been correlated with the Gander terrane of Newfoundland, where pegmatite exploration is ongoing.

Leinster spodumene pegmatite geochemical halos extend to at least 6 m for Li, Cs and Sn, with narrower halos for Be, Ta and Nb, reflecting enrichments in these elements in spodumene pegmatites. Exploration work shows that LIBS analysis of mineral chemistry has the potential to increase the detectable widths of halos. Halos significantly expand the potential for soil and stream sediment geochemistry surveys to detect spodumene pegmatites. Furthermore, ongoing Newfoundland exploration indicates that biogeochemical surveys using selective MMI (mobile metal ion) extraction on black spruce bark has potential to effectively detect spodumene pegmatite pathfinder elements through glacial and regolith cover.