(57) A gas-swept tube mill has an inlet (2), a grinding chamber (6), a discharge chamber (7) and an outlet (3). The discharge chamber contains a separating rotor (10) which causes coarse fractions of the material to be flung outwards and returned via a scoop (9) to the grinding chamber for further grinding. The vanes of the rotor are surrounded by a frustoconical casing (12) which collects the coarse fraction and directs it backwardly over a corresponding frustoconically shaped wall (15) of the discharge chamber to the scoop (9). The material is swept from the grinding chamber into the discharge chamber through a spreader (13) having a frustoconically flared outlet (14) which spreads the material over the face of the rotor.