Abstract: Virgin ore in granular form is enriched by air flotation classification separating at least a large part of the gangue. Suspension of the ore is effected immediately as supplied to the inlet section of the classification trough by copious upward flow of air from the air-diffusing floor plates after which separation is accomplished as the suspension flows through the trough. An adjustable gate in the partition which separates the inlet section of the plenum from the classifier section is adjusted to maintain a relatively very high pressure and consequent copious air flow as compared with the pressure of the plenum from which air is supplied in more moderate quantities to the diffuser floor of the classification trough downstream of the partition. The trough is free of any obstruction that would impede the flow of gangue to its discharge end. Flotation air is supplied to the plenum only at the inlet section and a bleeder valve regulates the total flow to the air-diffusing floor plates of the apparatus.