The chemical composition of plena, sphalerite and pyrite surfaces has been analysed after dry and wet grinding, and after treatment with water and aqueous solutions of potassium alkylxanthate by means of Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. The total metal concentration in the aqueous phase has been determined by means of atomic absorption spectrophotometry. The reaction between aqueous plena slurries and ethylxanthate ions has also been studied calorimetrically. In the reaction between oxidized galena and alkylxanthate ions in aqueous solution solid lead(II) alkylxanthate is formed on the surfaces. The formation takes place via dissolution of soluble oxidation products of plena on the surface followed by the precipitation of solid lead(II) alkylxanthate. It has been shown that lead(II) alkylxanthate is formed as the only detectable alkylxanthate species on the surface. Chemisorbed complexes of ethylxanthate ions are formed on sphalerite surfaces in aqueous and acetone slurries. The ethylxanthate ions are coordinated to zinc(II) ions in the outermost surface layer of sphalerite. Dialkyl dixanthogen is formed as the only surface species in the reaction between oxidized pyrite and aqueous solution of potassium alkylxanthate. Adsorbed oxygen and iron(III) have been excluded as possible oxidation agents. The oxidation products of the disulfide ion in pyrite, e.g. S2O72- and S2O82-, are instead proposed to be responsible for the oxidation of alkylxanthate ions to dialkyl dixanthogen. The formed diethyl dixanthogen is physisorbed on the surfaces of pyrite.