Document Type
Thesis
Date of Degree Completion
Spring 2024
Degree Name
Master of Science (MS)
Department
Geological Sciences
Committee Chair
Chris Mattinson
Second Committee Member
Hannah Shamloo
Third Committee Member
Carey Gazis
Abstract
The oxidation state of a magma (measured by oxygen fugacity, fO2) controls what reactions are favored during crystallization and what elements are concentrated and potentially precipitated into minerals, making it a key factor in ore-forming processes as some commodity elements are best concentrated under specific redox conditions. Tungsten (W) is best concentrated under reducing magmatic conditions, a characteristic that makes constraining magma oxidation state, done through analysis of zircon trace elements, an essential tool in plutonic tungsten deposit exploration.
This research analyzes the zircon trace elements of several Cretaceous-age intrusions in the region surrounding the now-inactive Germania tungsten mine in the Adam’s Mountain and Hunters (AMH) 7.5 minute quadrangles, located in northeastern Washington. These intrusions range from granite to granodiorite, and previously determined zircon U-Pb age calculations give two age populations, 100.3 Ma to 104.7 Ma and 71.8 to 74.7 Ma respectively, with the W-bearing intrusions belonging to the older population. Zircons from thirteen samples of W-mineralized and unmineralized intrusions from both age populations were chemically analyzed to constrain magma oxygen fugacity and zircon crystallization temperatures associated with tungsten mineralization.
The W-bearing AMH intrusions have fO2 values relative to the quartz-fayalite-magnetite (QFM) buffer ranging between -2.0 and +2.1, indicating more reduced conditions; zircons from the unmineralized intrusions have slightly higher fO2 values relative to the QFM buffer, ranging between +0.10 and +3.6, indicating more oxidized conditions. The W-mineralized AMH intrusions also generally have zircon crystallization temperatures 700°C. The distinct differences in magma fO2 relative to the QFM buffer and zircon crystallization temperature correlating with tungsten mineralization suggests that zircon chemistry can be used as a tool to quantify the potential for tungsten mineralization in a crystallizing magma chamber. By applying the zircon geochemical results of AMH plutons known to contain tungsten to those from plutons of unknown mineralization, exploration for plutonic tungsten deposits can be conducted more efficiently.
Recommended Citation
Gaudette, Robin, "Constraining Magma Oxidation State through Zircon Trace Elements: Estimating Tungsten Mineralization Potential in Northeastern Washington" (2024). All Master's Theses. 1947.
https://digitalcommons.cwu.edu/etd/1947