Quantitative cathodoluminescence mapping with application to a Kalgoorlie scheelite

Area of Science:

• Geochemistry
• Materials Science
• Analytical Chemistry

Background:

• Cathodoluminescence (CL) spectroscopy is a valuable technique for analyzing mineral luminescence.
• Quantitative analysis of trace elements using CL has been challenging.
• Understanding trace element distribution is crucial for geological and materials science applications.

Purpose of the Study:

• To develop and validate a method for quantitative analysis of trace-element distributions using cathodoluminescence spectra.
• To demonstrate the capability of the method for mapping rare earth elements (REEs) and their charge states in minerals.
• To apply the method to a scheelite sample for detailed geochemical analysis.

Main Methods:

• Quantitative analysis of cathodoluminescence spectra via Gaussian peak fitting for REE intensities.
• Correlation of CL intensities with independently measured trace element concentrations (down to ppm levels).
• Hyperspectral mapping of a scheelite sample, calibrated against laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data.

Main Results:

• Demonstrated positive correlation between CL intensities and trace element concentrations for REEs.
• Successfully mapped micron-scale zoning of Sm3+, Dy3+, Er3+, and Eu3+/Eu2+ in scheelite.
• Identified preserved Eu2+/Eu3+ valence states in scheelite, indicating conditions since its 1.63 billion-year crystallization.

Conclusions:

• The developed method enables quantitative mapping of trace element abundances and charge states using cathodoluminescence.
• This approach provides a powerful tool for geochemical and materials characterization.
• The study highlights the preservation of multiple europium valence states in ancient scheelite.