Abstract: This study synthesised a zincic salt (ZS) as a depressant for marmatite–galena separation. The effect of ZS on the flotation of marmatite and galena was investigated through micro-flotation tests. 88.89% of the galena was recovered and 83.39% of the marmatite was depressed with ZS dosage of 750 mg·L⁻¹ at pH = 4. The depression mechanism of ZS on marmatite was investigated by a variety of techniques, including adsorption measurements, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopic (XPS) analysis, and time of flight secondary ion mass spectrometry (ToF-SIMS). Results of adsorption tests and FTIR reveal that ZS adsorbed on marmatite surface and impeded the subsequent adsorption of butyl xanthate (BX). The results of XPS and ToF-SIMS indicate that the \mathrmZ\mathrmn\mathrmO_2^2- released by ZS could be chemisorbed on the marmatite surface and depress marmatite flotation.