Progressive crushing (40)Ar/(39)Ar dating of a gold-bearing quartz vein from the Liaotun Carlin-type gold deposit, Guangxi, southern China

Carlin-type gold deposits are among the largest hydrothermal gold deposits in the world. However, direct dating the metallogenic age of these deposits is difficult, because not all deposits provide material suitable for conventional radiometric methods. Syn-mineralization stage quartz veins from these deposits usually contain abundant fluid inclusions, which allow fluid inclusion (40)Ar/(39)Ar dating. In this study, progressive crushing (40)Ar/(39)Ar dating has been performed on a gold-bearing quartz vein from the Liaotun Carlin-type gold deposit in northwestern Guangxi, China. Argon isotopes liberated from the later steps yielded an isochron age of 200.7 ± 2.1 Ma. We infer that Ar-bearing gas was extracted from the primary fluid inclusions, and that the age of ca. 200.7 Ma reflects the timing of gold mineralization. The initial (40)Ar/(36)Ar ratio corresponding to the isochron is 298.0 ± 4.3, which is statistically indistinguishable from the value for air, indicating that the ore-forming fluids probably mainly derived from gravitational pressure flow in the basin of air-saturated water. Our preliminary study shows the feasibility and great potential of (40)Ar/(39)Ar dating of gases from fluid inclusions by progressive crushing of quartz veins to date the mineralization age and decipher the fluid origins of Carlin-type gold deposits.