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

Two Episodes of Mineralization in the Mesoproterozoic Adirondack Highlands Graphite District, New York

Paper number: 37-1
Program: Technical Sessions
Time: 8:05 AM – 8:25 AM

Authors

Abstract

The historic flake graphite mining district in the Adirondack Highlands (near Ticonderoga, NY) operated from the 1850s to the 1920s. There is evidence for two generations of graphite mineralization with distinct carbon sources in the district: syngenetic graphite with an organic origin in Shawinigan quartz schists, and epigenetic graphite with an igneous origin in Ottawan skarns and pegmatites. Most of the production and reserves from the district are from feldspathic quartz schists. Protolith sediments of the schists were deposited in the Trans-Adirondack back-arc basin at ca. 1.25 Ga and were metamorphosed to high grade at 1.18–1.15 Ga during the accretionary Shawinigan orogeny and again at 1.09–1.02 Ga during the Ottawan phase of the Grenvillian orogeny. Major elements and carbon isotopes of graphite from schists (δ13C= –5.4 to –28.1‰ VPDB) are consistent with derivation from organic carbon in protolith sandstones that devolatilized during metamorphism. Some small mines and prospects in the district mined graphitic calcite marbles and clinopyroxene ± scapolite skarns associated with a 1.04–1.01 Ga (Ottawan) pegmatite suite. Hydrothermal flake graphite from pegmatites, skarns, and rare veins have δ13C values that cluster around –5 to –7‰; consistent with deposition from igneous CO2, and are not compatible with precipitation from fluids derived from country rock metapelites or marbles.

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

doi: 10.1130/abs/2026NE-411132

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