40Ar-39Ar dating of the quartz samples from two mineral deposits in western Yunnan (SW China) by crushing in vacuum

The primary aim of this study is to investigate the possibility of dating fluid inclusions of quartz samples using the 40Ar-39Ar method by crushing in vacuo. The samples are from the Lushui Tin-tungsten Deposit and the Shangmanggang Gold Deposit in western Yunnan, SW China. Coexisting muscovite S-90MS and quartz S-90Qw in a piece of tungsten ore from the former deposit were selected, and the isochron age of S-90Qw by crushing (38.6 +/- 1.9 Ma) shows excellent coincidence with that of S-90MS by stepped heating (38.6 +/- 0.8 Ma). The isochron age and plateau age by crushing of the quartz SMG-8Qz from the latter deposit indicate that the gold mineralization occurred at similar to 144 Ma. These ages are respectively agreeable with the evaluated ages from the geologic facts. In addition, since the potassium concentration (calculated from 39Ar released by crushing) in the quartz sample SMG-8Qz was as high as 0.24%, electron-probe analysis was applied to investigate the occurrence of potassium, and the results reveal that the majority of potassium scattered in the microcrystal quartz grains.