37 CRITICAL MINERAL DEPOSITS AND ORE SYSTEMS OF THE NORTHEAST

This session will showcase new findings pertaining to critical mineral resources and hydrothermal-magmatic ore systems across the northeast. We welcome submissions involving fieldwork, geochemical, petrologic, geochronologic, and other approaches from micro- to macroscopic scales.

Tuesday, 24 March 2026
8:00 AM - 12:00 PM
CCC, Room 25

Phosphate mineral species of the Plumbago North pegmatite, Newry, Oxford Co., Maine

Paper number: 37-4
Program: Technical Sessions
Time: 9:05 AM – 9:25 AM

Authors

Abstract

A new spodumene-rich pegmatite was recently discovered on the north side of Plumbago Mountain, Oxford County, Western Maine. The site is about 1.5 km northwest of the famous Dunton gem tourmaline pegmatite. It is an albite-quartz-spodumene pegmatite containing gigantic crystals of spodumene and montebrasite. Some spodumene crystals are more than 11 m in length. The upper portions of the pegmatite contain up to 50 wt. % spodumene, which makes it a potentially significant new lithium resource. Preliminary results indicate that Plumbago North Pegmatite contains about 10 Mt of ore with an average Li2O content of 4.68 wt. %, which is a higher average lithium content than any of the ten top spodumene-producing deposits in the world. Montebrasite occurs in crystals up to approximately 1 m in maximum dimension and has a fluorine content from 0 to 0.213 apfu (atoms per formula unit). Triphylite occurs as masses up to 35 cm and skeletal formations of similar size. Triphylite is Fe-dominant with an Fe content from 0.637-0.650 apfu, a Mn content of 0.293-0.205 apfu, and a Mg content from 0 to 0.001 apfu. Secondary Fe Mn phosphates include vivianite, rockbridgeite, frondelite, ludlamite, heterosite-purpurite, and jahnsite group species, which have similar Fe/Mn ratios as the primary triphylite. In addition, vivianite sometimes pseudomorphically replaces triphylite to a greater or lesser extent. Fluorapatite occurs as small crystals as well as grains in massive pegmatite and is always F-dominant.  Chlorine is sometimes detectable in small amounts. The mineral perhamite has also occurs in some small miaroles as radiating aggregates up to 5 mm across. Overall, the pegmatite is very Li-rich but not as highly evolved as other pegmatites in the region. Boron is very sparse; there is only a thin rim of exometasomatic tourmaline around parts of the pegmatite. The phosphates are Fe-dominant; this Fe-dominance extends to other minerals such as columbite-tantalite, which are Fe- and Nb-dominant.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2

doi: 10.1130/abs/2026NE-411263

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