A gearbox assembly for a charging installation of a metallurgical reactor includes a stationary casing housing a gear assembly. The casing includes a bottom section with a central opening. The assembly further includes a rotor mounted within the casing for rotation about a first axis, which defines an axial direction. The rotor includes a support for the gear assembly, wherein a lower section of the support is disposed within the central opening. To provide for a better protection of a gear assembly, the bottom section includes a first annular portion extending radially inwards to a first radius. The lower section has a second annular portion extending radially outwards to a second radius that is greater than the first radius. The second annular portion is disposed adjacent to the first annular portion. The first annular portion includes a ring element disposed for sliding contact with the second annular portion.