In Situ Hydrogen Measurements in Garnet

Metamorphic fluids are important for concentrating valuable elements including W and Fe in skarn systems. In situ measurements of water concentration and H isotopes in garnet can be used to understand the movement of fluids and the development of skarn systems. In situ δD measurements require a matrix-matched garnet reference material, but garnet reference materials of the Ca-rich compositions found in skarns are not publicly available. Four Ca-rich grossular grains were found to meet the requirements for use as a garnet reference material including: free from inclusions, homogeneous in major element composition and both bulk and in situ δD, and high-water concentration. The Kara skarn deposit in Tasmania, Australia was evaluated to investigate fluid flow processes during W and Fe skarn formation using one of the four developed garnet reference materials. The Kara skarn deposit has Ca-rich garnet found in three textures. The water content and H isotopic composition was measured on traverses across garnet from all three texture types. The δD values of grains from each texture fall below the isotopic signature range for magmatic or carbonate source fluids indicating input of meteoric fluids. Water concentrations and/or δD had oscillatory variations in all three textures indicating distinct pulses of fluids within the system as these grains grew. Water concentrations along traverses ranged from approximately 370 ppm to 10,800 ppm with Texture I generally having a higher water content than Texture II. Hydrogen isotopic compositions were highly variable, with variations over 150‰ across all textures. These ranges and oscillatory variations indicate a complicated history of skarn development that was primarily dominated by distinct and repeated pulses of fluids form different sources, but with a major input of meteoric fluids.

Department dc:contributor.department

Geology

Year dc:date.issued

2026

Author dc:creator

• Bickerstaff, Kathryn

Advisors dc:contributor.advisor

• Penniston-Dorland, Sarah
• Newcombe, Megan

Language dc:language.iso

en

Identifier

https://doi.org/10.13016/bhsp-428a

OAI identifier oai:identifier

oai:drum.lib.umd.edu:1903/35996