Numerous volcanic rocks crop out along eastern and western marginal areas of the Lanping basin in the middle segment of the Sanjiang multiple orogenic and metallogenic belt in western Yunnan Province. However, copper deposits are developed exclusively on the western margin of the basin, which form a vein-type copper metallogenic belt about 150 km in length. Most vein-like copper orebodies are hosted in volcanic and strongly deformed sedimentary rocks. However, the age of the ore-hosting rocks remains unclear. Detailed field study and zircon U/Pb analysis of andesitic pyroclastic rocks were conducted in the Dazong copper ore deposit located in north-central segment of the western Lanping copper metallogenic belt. The lithology of two zircon U-Pb dating samples is crystal and vitric tuff, volcanic breccia-bearing tuff respectively, which represented the first and second rhythm of the volcano-eruptive sedimentary cycle. Some conclusions have been reached: ① the ore-hosting volcanic rocks have a thickness of 1 904 meters consisting of three volcanic sequences;② the ²⁰⁶Pb/²³⁸U weighted average age of magmatic zircons of the first rhythm tuff layer is 247.2±4.4 Ma (n=21,MSWD=2.7), and the ²⁰⁶Pb/²³⁸U weighted average age of magmatic zircons of the second rhythm tuff layer is 243.8±6.4 Ma (n=9, MSWD= 1.5),suggesting that the volcanism took place in 244~247 Ma,which belongs to Early to Middle Triassic; and ③ the strongly deformed sedimentary rocks were overlain by the Early Triassic volcanic rocks, and thus should belong to the Upper Permian. Therefore, the ore-hosting volcanic-sedimentary assemblage in the Dazong copper orefield formed during the Late Paleozoic to Early Mesozoic, and might have resulted from the Paleo-Tethyan orogenic movement. According to the difference of the ore-hosting rocks, the Dazong Early to Middle Triassic volcanic rocks-hosted copper sulfide mineralization is only one type of many vein-type copper deposits in the western margin vein-type copper metallogenic belt of the Lanping basin. These vein-type copper deposits or ore occurrences all have no obvious strata or lithologic specificity, and should be classified as a strong tectonic deformation controlled and post-filling hydrothermal deposit.