Situated between the South China Block and the Simao Block, the Ailaoshan Belt is a significant component of the Jinshajiang–Ailaoshan tectonic-magmatic-metallogenic belt of southwestern China. The formation of the Ailaoshan Belt is closely related to the evolution of the Palaeo-Tethys Ocean. In this study, we constrain ages of sedimentation in the Jinchang Au–Ni deposit in the Ailaoshan Belt, using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb ages of the youngest populations of detrital zircons separated from a chert layer and two uncomfortably overlying meta-sandstones. The combined data of the meta-sandstone samples from the Yiwanshui Formation yielded a concordant age of 250.8 ± 0.6 Ma (mean square weighted deviation (MSWD), 2.8; n = 26). The chert sample from the Jinchangyan Formation yielded a concordant age of 347.0 ± 1.5 Ma (MSWD, 2.8; n = 16). Detrital zircons from the meta-sandstone are characterized by low rare earth element contents (∑REE) and low Y, and high U and U/Yb ratio, suggesting a continental crustal origin. Zircons in the meta-sandstones were derived mainly from pre-collision subduction zone magmatic rocks related to the closure of the Palaeo-Tethys Ocean. In contrast, detrital zircons from the chert contain relatively high ∑REE and Y, and low U and U/Yb ratio, suggesting an oceanic crust origin. Zircons in the chert bed were derived mainly from ophiolites related to seafloor spreading in a branch of the Palaeo-Tethys Ocean.