STREAM WATER GEOCHEMISTRY NEAR THE PLUMBAGO NORTH LITHIUM-BEARING PEGMATITE, WEST-CENTRAL MAINE

The Plumbago North pegmatite, located in west-central Maine, hosts spodumene crystals exceeding 11 m in length. Preliminary drilling and bulk samples suggest that it contains >400,000 tons of Li₂O (10 Mt at 4.68 wt% Li₂O) worth approximately 1.5 billion USD and equivalent to the lithium needed to manufacture 16-20 million EV batteries. This study aims to develop a geochemical baseline of surface waters draining from the pegmatite deposit prior to development. We have collected samples seasonally six times between September 2022 and November 2023 from seven locations (Ellis River USGS Site 01054300, Howe Brook, four sites along Spodumene Brook, and a standing water pool in the Plumbago North quarry pit) to document spatial (e.g., proximity to quarry) and temporal (e.g., related to temperature and precipitation) variability. All samples have been analyzed at the University of Alaska Anchorage Applied Science, Engineering, and Technology (ASET) Lab for a broad suite of major and trace cations (ICP-MS) and major anions (IC). Most samples plot in the mixed cation-bicarbonate-rich field on a Piper diagram. Lithium concentrations in Spodumene Brook range from <0.1 ppb (2023.06.23) to 6.6 ppb (2022.09.27) with a mean of 4.5 ppb,,which is >2 times higher than outside of the watershed (Howe Brook and Ellis River; mean 2 ppb). The highest Li concentrations occur in the pit waters (55-167 ppb), well below the EPA-recommended threshold of 700 ppb. Trace levels of some ions enriched in pegmatites are present at very low concentrations (e.g., Rb 1-3 ppb). Ions of potential importance were also detected (e.g., As <0.2 ppb); significantly, U concentrations in Spodumene Brook are less than in the Ellis River (e.g., respectively 0.06 and 0.25 ppb). Our data set, which reveals slightly higher Li concentrations proximal to the quarry and ~2-fold seasonal variability attributed to dilution effects, should serve to guide future development and environmental monitoring.