ABSTRACT

In order to obtain the mineralization ages of the Dongchuan Copper Deposits, two quartz samples and a siliceous breccia were analyzed using the ⁴⁰Ar-³⁹Ar technique by crushing in vacuum and then by stepped heating of the powders of two of them. The results indicate that the vein-type copper mineralizations took place 780∼700 Ma ago and further show that the ⁴⁰Ar-³⁹Ar technique by crushing is an effective, widely-applicable and promising dating method for the mineralization ages of the hydrothermal deposits. The mineralization ages are in good agreement with the ages of the widely distributed magmatic rocks in the South China, which means that the pulses of anorogenic magmatic activities during the period of the breakup of Rodinia (Park et al., 1995; Li, Z. X. et al., 1999, 2002; Li, X. H. et al., 2002) were accompanied by the copper mineralizations in Dongchuan. Strong differences between the results of the crushing and heating experiments of two samples imply that the gases released by crushing were mainly from the fluid inclusions and those by heating were from the minerals of the samples, which is supported by microscopic observations of the thin sections and the results of EPMA and XRD analyses.