Cameron Mark Mercer Leah E. Morgan 2025 <p>The ⁴⁰Ar/³⁹Ar geochronology method is used to date potassium-bearing rocks and minerals, based on the decay of ⁴⁰K to ⁴⁰Ar, which provides important temporal constraints for geological events. The USGS Denver Argon Geochronology Laboratory dates samples from a variety of projects, mainly in the USGS Mineral Resource Program and the National Cooperative Geologic Mapping Program, facilitating in-depth research into the timing of geological events and processes. Recent applications of this method include geochronological studies in the Yellow Pine district, revealing mineralization ages that range from 51 to 70 Ma, and investigations into the Bear Lodge alkaline complex, providing insights into the timing of REE carbonatite formation. Additionally, studies at Alunite Ridge highlight the method's potential for understanding concealed mineral deposits. Ongoing projects continue to leverage ⁴⁰Ar/³⁹Ar data to enhance understanding of geologic frameworks and mineral resources, underpinning its importance in modern geochronology and mineral resource assessment.&nbsp;</p> application/pdf en Society for Geology Applied to Mineral Deposits 40Ar/39Ar geochronology supporting mineral resources research at USGS Denver text