31 CRITICAL MINERAL DEPOSITS AND ORE SYSTEMS OF THE NORTHEAST (Poster)

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.

Monday, 23 March 2026
1:30 PM - 5:30 PM
CCC, Ballroom C

A Small Tin-Granite In The Western Adirondacks, New York State.

Paper number: 31-0
Program: Technical Sessions
Time: 1:30 PM – 1:30 PM

Authors

Abstract

A cassiterite-bearing, felsic gneiss (interpreted as a meta-granite) has been identified in the Brantingham NY, 7.5 minute quadrangle in a 16,000 m2 area of exposed metagranite bedrock on the north side of Fish Creek valley.  The tin-granite was sampled in a small prospect pit located 46 meters WNW of a magnetite-ilmenite-corundum prospect (Malanoski and Darling, 2019, GSA abs) in the same metagranite host rocks.

The cassiterite occurs as 0.5-3.0 mm, fabric-forming, highly irregular, anhedral grains in a quartz + plagioclase + mesoperthite + biotite + pyrite + magnetite + ilmenite felsic gneiss.  The areal extent of cassiterite mineralization is currently unknown, but is not expected to be large, as cassiterite was not observed in metagranite exposures 40 to 90 meters to the south and east, respectively.  No hydrothermal cassiterite + quartz veins were observed, but the pyrite appears to be texturally secondary, suggesting at least some late hydrothermal activity.  Instead, the cassiterite is interpreted as a primary igneous phase.

Cassiterite was identified in thin-section by its brown-color in plane-polarized light and at least five tin L-emission lines from an energy-dispersive spectrographic (EDS) X-ray analysis using a JEOL scanning electron microscope at SUNY Cortland.  Spot analyses are nearly pure SnO2; the only other element detected was about 0.5 wt.% SiO2.  However, this silicon, with its K-alpha peak at 1.74 keV, is more likely produced by an M-alpha peak from either tantalum (1.71 keV) or tungsten (1.775 keV).

Both magnetite and ilmenite occur as accessory phases, but the ilmenite is minor and is observed in the cores of magnetite grains suggesting early reduction and later oxidizing conditions.  This may be significant because Sn2+ is thought to be more soluble in reduced felsic melts, with later oxidation possibly causing cassiterite crystallization (Linnen et al., 1996, GCA).  Tin-granites are interpreted to form from large-scale intracrustal melting during mantle upwelling in a back arc basin setting (Lehmann, 2021, Lithos), and in this occurrence, possibly associated with the Trans-Adirondack basin of Shawinigan-age (Chiarenzelli et al., 2011, Geosphere).

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

doi: 10.1130/abs/2026NE-411158

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