~(40) Ar-~(39) Ar Dating of Quartz from Ore in the Baiyangping Cu-Co Polymetallic Ore-Concentrated Area, Lanping Basin, Yunnan

摘要

Ar- Ar fast neutron activation age spectrum of quartz in ore collected from the Baiyangping Cu-Co polymetallic ore-concentrated area, Lanping Basin, is saddle-shaped. The plateau age, minimum appearance age and isochron age shown on the spectra are 56. 53 +-0.43 Ma, 55. 52 +- 1. 78 Ma and 55. 90 +-0. 29 Ma respectively. The age data are consistent with each other within 1σ uncertainties. Because the given initial ~(40)Ar/~(36)Ar value of 294. 7 +- 1. 14 is very close to Nier' s value (295.5 +- 5 ) , both plateau and isochron ages may be considered as the forming time of quartz. So the age of 55. 90 - 56. 53 Ma represents the forming age of ore deposits. It is obvious that the ore deposits were formed during the Early Himalayan period.