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

Providing a window into post-orogenic magmatism in Northern New England: New in-situ Rb-Sr mica, U-Pb cassiterite, and Lu-Hf fluorapatite geochronology from Maine pegmatites.

Paper number: 37-10
Program: Technical Sessions
Time: 11:00 AM – 11:20 AM

Authors

Abstract

We present new in-situ Rb-Sr dates of micas (thirty muscovite, four biotite, and twelve lepidolite) along with six U-Pb cassiterite and two Lu-Hf fluorapatite dates from granitic pegmatites in western Maine. These results reveal at least two Late Paleozoic rare metal pegmatite (Be, Cs, Li) forming events within the Central Maine Belt. Significantly, both events occurred during tectonically quiescent periods. First, the northern Phillips and Rumford pegmatite districts, spanning a ~30 km transect, are late- to post-Neoacadian (Mississippian), where melting is attributed to anatexis during collapse of the Acadian altiplano. The second group, comprising the remaining districts of the Oxford County pegmatite field— a transect that is ~35 km, beginning only ~20 km south of the Newry district— are post-Alleghanian (Permian-Triassic), where the tectonic mechanism for melt generation is still uncertain and speculative, though anatectic derivation appears to be a likely cause. 

In a separate terrane in coastal Maine, mica dates reveal that pegmatites of the Georgetown and Waldoboro districts are syn- to post-Neoacadian (Late Devonian-Early Mississippian), similar to the Phillips and Rumford pegmatite districts.

Broadly, cassiterite and fluorapatite ages are similar and consistently older than coexisting mica ages from the same pegmatite dike. Rb-Sr biotite ages are the youngest relative to cassiterite (ΔT of 27.85 ± 0.85 Ma; 1σ = 1.20 Ma, n = 2); muscovite shows intermediate offsets relative to cassiterite (ΔT = 14.99 ± 2.99 Ma; 1σ = 9.44 Ma, n = 10); and lepidolite ages are most similar to cassiterite (ΔT = 10.06 ± 2.59 Ma; 1σ = 6.85 Ma, n = 7).

Importantly, all of the samples in this study were provided through a museum collection. This demonstrates the value of museum collections with their ability to supply well-documented samples from localities with restricted access or limited material availability in the field. Furthermore, this enhanced regional dataset supports the ongoing development of additional novel geochronometers in Maine’s pegmatites and provides a stronger framework for understanding Late Paleozoic rare metal pegmatite enrichment in Northern New England.

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

doi: 10.1130/abs/2026NE-411483

© Copyright 2026 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.