(U-Th)/He dating of fluorite: application to the La Azul fluorspar deposit in the Taxco mining district, Mexico

摘要

The (U-Th)/He dating method was applied to fluorite of the La Azul fluorspar deposit, Taxco mining district, Mexico. Ages often U-rich (4-94 mug/g) samples range from 30 to 33 Ma (mean 32 + -2 Ma, 1 sigma). This age range is interpreted as the time of primary fluorite precipitation and is close to the K/Ar age of sericite from a small fluorspar deposit (Los Treboles) in the same area, and the K/Ar age of the nearby volcanic succession, which is thought to be the main source of fluorine in both deposits. This age is also in concordance with the very few published ages of epithermal deposits in southern Mexico. The dating of fluorite by other methods, particularly for young samples, is a difficult task. We believe that the (U-Th)/He method, which has been applied before to thermochronological studies of apatite, zircon, titanite and hematite, can be used as a tool for direct dating of fluorite with microgram per gram levels of uranium and thorium.