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

The Origin and Influence of Hydrothermal Fluids on Kyanite Quartzite Petrogenesis in the Virginia Piedmont

Paper number: 37-3
Program: Technical Sessions
Time: 8:45 AM – 9:05 AM

Authors

Abstract

The world’s largest kyanite (Al2SiO5) mine is located at Willis Mountain, Virginia and is unique for its high purity kyanite quartzites (up to 30 wt.% kyanite). The protolith of Willis Mountain and neighboring localities is debated as either sedimentary (Espenshade and Potter, 1960; Cochrane, 1986) or hydrothermally altered igneous rock (Dickerson, 2000; Owens and Pasek, 2007; Ingle, 2025). Fluid sources impart a measurable chemical fingerprint on the oxygen isotope signature of altered minerals. This project examines oxygen isotopes of kyanite and quartz separates from key localities within the Virginia Piedmont to (1) identify isotopic variation with geography and kyanite chemistry and (2) investigate the temperature of kyanite-quartz equilibration and the isotopic signature of possible fluid sources associated with kyanite and quartz crystallization. O-isotope analyses were performed at the University of Madison-Wisconsin by laser fluorination and mass spectrometry. 

Kyanite and quartz separates from four distinct kyanite-quartzite localities were analyzed, listed from north to south (O-isotope thermometer of Zheng et al., 1993). White kyanite at Willis Mountain yielded δ18O(Ky)=7.2–7.9‰ and δ18O(Qz)=10.3–10.5‰ (n=2), corresponding to Teq=~590–650ºC and δ18OH2O,calc=8.0–8.7‰. Light blue to white-gray kyanite at Leigh Mountain yielded δ18O(Ky)=-0.2–0.7‰ and δ18O(Qz)=2.6–2.9‰ (n=5), corresponding to Teq=610–750ºC and δ18OH2O,calc=0.5–1.7‰. Blue-green kyanite at Madisonville yielded δ18O(Ky)=~3.4‰ and δ18O(Qz)=~6.0‰ (n=2), corresponding to Teq=630–690ºC and δ18OH2O,calc=~4.2‰. Light blue to blue-green kyanite at Blue Rock Road yielded δ18O(Ky)=7.6‰ and δ18O(Qz)=10.7‰ (n=1), corresponding to Teq=580ºC and δ18OH2O,calc=8.3‰. The δ18OH2O,calc shows distinct fluid sources and possible mixing: δ18OH2O,calc of +0.5 to +4.2‰ provide possible evidence for mixing between seawater/meteoric and magmatic-derived fluids. Significantly higher δ18OH2O,calc (>8‰) indicate a possible distinct source of igneous-derived hydrothermal fluids. There is no observed relationship between δ18O values and kyanite color or geography. These results suggest that the O-isotope signatures reflect interaction with fluids involved in the transformation of the protolith at elevated temperatures (T=~580–750ºC) rather than original protolith values. Further in situ O-isotope analyses will help assess isotopic equilibrium and multiple possible kyanite growth episodes in CL- and trace-element-zoned kyanite.

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

doi: 10.1130/abs/2026NE-411151

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