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

MAGNETITE-APATITE MINERALIZATION DURING LATE-STAGE OTTAWAN TRANSTENSIONAL SHEARING: EASTERN ADIRONDACK HIGHLANDS, NEW YORK

Paper number: 37-5
Program: Technical Sessions
Time: 9:25 AM – 9:45 AM

Authors

Abstract

            The eastern Adirondack Highlands contain numerous iron oxide-apatite (IOA) ore deposits that were mined for nearly 200 years. Some of these deposits contain apatite that is highly-enriched in rare earth elements. Recent mapping in the Port Henry quadrangle has revealed that many of these deposits are located within, or just above late-stage transtensional shear zones, related to orogenic collapse following peak Ottawan metamorphic conditions.

   

            The Cheney Mountain shear zone (CMsz) is 1-2 km-wide, left-lateral, ductile shear zone that strikes SE across Elizabethtown, Witherbee, and the recently mapped Port Henry quadrangles. The shear zone can be traced for at least 14 km and was first recognized in new aeromagnetic and LiDAR data funded by the USGS EarthMRI program. On the ground the CMsz is manifested by numerous anastomosing high-strain zones that vary in dip from 20°- 85° to the SW. Mineral lineations plunge around 30° to the SW. Transposed rocks in the hanging wall comprise marble, paragneiss, and the Lyon Mountain Granite Gneiss. The anorthosite-mangerite-charnockite-granite (AMCG) suite with rare calc-silicate marble forms the footwall. Within the shear zone, numerous slivers of mostly AMCG rocks are present. Historically mined IOA deposits are common in the hanging wall from Port Henry to Mineville. A smaller, but similar set of relationships can be seen at the Cheever mine north of the village of Port Henry.  

 

            Samples from deformed and undeformed outcrops of coronitic gabbro were collected from within the CMsz and dated by colleagues at Colgate University. Preliminary findings constrain the timing of shear zone development to be no older than 1020 Ma. This age is similar to hydrothermal zircon growth in the magnetite ore bodies which have ages that range from ~1020 to 1000 Ma. These data suggest that IOA ore formation and REE enrichment is related to transtensional shearing and the development of the CMsz and other minor shear zones in the Port Henry and adjoining quadrangles

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

doi: 10.1130/abs/2026NE-411358

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