The ^{40}Ar/^{39}Ar dating technique requires the transformation of ^{39}K into ^{39}Ar by neutron activation. Neutron activation has undesirable secondary effects such as interfering isotope production, and
recoil of ^{39}Ar and ^{37}Ar atoms from their (dominant) targets of K and Ca. In most cases, the grains analysed are large enough (>50 μm) such that
the amount of target atoms ejected from the grains is small and has a negligible effect on the ages obtained. However, increasing
needs to date fine-grained rocks requires constraining, and in some cases correcting for, the effect of nuclear recoil. Previous
quantitative studies of recoil loss focus mostly on ^{39}Ar. However, ^{37}Ar loss can affect the ages of Ca-rich minerals via interference corrections on ^{36}Ar (and, to a lesser extent, ^{39}Ar), yielding lower ^{40}Ar*/^{39}Ar_{K} and, thus, an age spuriously too young. New results focused on ^{37}Ar recoil by measuring the apparent age of multi-grain populations of Ca-rich minerals including Fish Canyon plagioclase (FCp)
and Hb3gr hornblende, with discrete sizes ranging from 210 to <5 µm. We use previous result on sanidine grains to correct
for the ^{39}Ar recoil loss. For the finest fractions, FCp and Hb3gr apparent ages are younger than the ^{39}Ar recoil-corrected ages expected for these minerals, with a maximum deviation of −40% (FCp) and −21% (Hb3gr) reached for
grains below 5 μm. We calculate ^{37}Ar-depletion values ranging from approximately 30 to 91% and from approximately 28 to 98% for plagioclase and hornblende,
respectively. This results in *x*_{0} values (mean thickness of the partial depletion layer) of 3.3±0.4 μm (2σ; FCp) and 3.6±1.4 μm (Hb3gr), significantly higher
than suggested by current models. The reason for the substantial ^{37}Ar loss is not well understood, but might be related to the radiation damage caused to the mineral during irradiation. *x*_{0} (^{39}Ar) and *x*_{0} (^{37}Ar) values obtained in this study, along with crystal dimensions, can be used for correcting ^{40}Ar/^{39}Ar ages from ^{39}Ar and ^{37}Ar recoil loss. We also discuss the relevance of our results to vacuum-encapsulation studies and isotopic redistribution in
fine-grained minerals.