A CONTEMPORARY REVIEW OF MAINE’S SPODUMENE-BEARING PEGMATITES

The prospect of quarrying spodumene at the Plumbago North pegmatite in Newry, Maine has renewed mining interests in the state as demand for lithium in rechargeable lithium-ion batteries continues to grow.

Spodumene-bearing pegmatites include at least 25 bodies extending across 5 counties in Maine. We review the geology, geochronology, and mineralogy of these pegmatites, and hypotheses about their formation. Five spatially separated pegmatite districts, containing spodumene pegmatites, are strung out over a 60-mile trend in western Maine. From north to south these include: The Phillips- (PH), Rumford- (RU), Greenwood- (GW), Paris-(PA), and Auburn- districts (AU). Spodumene-bearing pegmatites in coastal Maine are also found in the Waldoboro-(WA), and Georgetown (GE)- districts.

Pegmatites in western and coastal Maine were well documented in support of the feldspar industry and during investigations of beryllium resources (RU, GW, PA, and AU). However, many of the pegmatites in the northernmost PH are poorly understood mineralogically or have only recently been discovered. Several new spodumene pegmatites have been noted in the WA but need to be confirmed.

Cassiterite (U-Pb) geochronology has shown that the five pegmatite districts in western Maine follow a NW (~360 Ma) to the SE (~250 Ma) younging trend across the strike of the regional, high-grade metamorphic rocks of the Central Maine Belt. The implication is that a nearly 100 million year history of episodic lithium enriched melt generation existed beginning with the final stages of the Acadian orogeny and continuing until the initial break-up of Pangea. The anatectic model for spodumene pegmatites in western Maine (PH, RU, GW, PA, AU) remains a viable option as geochronology studies of nearby intrusives have yet to reveal a potential parental granite. The WA in coastal Maine shows some promise of a parental-pegmatite connection with spatial and temporal relations (Appleton pegmatite, ~356 muscovite Ar/Ar, a closure temperature) to the nearby Waldoboro pluton (368± 2, zircon) and smaller tourmaline-bearing granites.

The mineral reporting here and historically on Maine pegmatites, coupled with evolving understandings of favorable genetic models provide a better framework for assessing resource potential.