I'm researching a series of U-REE-Cu-Au deposits in Australia, which host REE in epidote-group minerals. Following the approach of Deer, Howie and Zussman, I calculated the chemical formulas based on EPMA data using 12 ideal O, 8 ideal cations and all Fe as Fe3+.
I tried correcting the total Fe content for Fe2+ and Fe3+ following Droop (1987). However, this approach doesn't seem to work well. I think it's because the minerals are slightly metamict and contain vacancies.
I'm also trying to recreate the REE vs Al plot of Petrik et al (1995) and use it to estimate the Fe3+ to total Fe ratio. However, I can't find formulas to calculate the ratios of Fe3+ to total Fe based on this plot. Does anyone have the formulas or could recommend a publication that explains the workflow?
Thank you,
Christina Loidolt
Hello,
If I remember correctly, it is assumed that all Fe is trivalent in epidotes. This is worth reading:
https://www.researchgate.net/publication/228997733_Recommended_nomenclature_of_epidote-group_minerals
https://www.researchgate.net/publication/329364618_A_Windows_program_for_calculation_and_classification_of_epidote-supergroup_minerals