Occurrences of excess Ar-40 in hydrothermal tourmaline: Interpretations from Ar-40-Ar-39 dating results by stepwise heating

The occurrences of excess Ar-40 within a hydrothermal tourmaline is discussed in term of the analysis data of syngenetic muscovite and tourmaline from the Lushui hydrothermal tin-tungsten deposit in western Yunnan, China, using the Ar-40-Ar-39 stepwise heating technique. About 80% excess Ar-40 was released in the last step when the tourmaline was fused, corresponding to a release of only similar to 3 % Ar-39 (K), which indicates that most excess Ar-40 was held in the mineral lattice rather than in the channels parallel to the Z-axis. This suggests that the excess Ar-40 was incorporated during crystallization and not diffused into the tourmaline during the post-crystallization history.