Abstract: The application disclosed a granular material classifying device comprising a horizontally disposed, transversely unrestricted wind tunnel, having an upstream end, a downstream end, a top end and a bottom end, for directing a horizontal airflow from the upstream end to the downstream end thereof; an air forcing assembly operatively mounted on the wind tunnel for inducing the horizontal airflow therethrough; a particle injection assembly operatively associated with the wind tunnel for free fallingly injecting a flow of granular particles to be classified into the horizontal airflow at an upstream, top end portion of the wind tunnel; and a bottom skirt assembly mounted at a bottom portion of the wind tunnel; the bottom skirt assembly defining at least one transversely unrestricted skirt cavity in fluid communication with the wind tunnel and having a downwardly and inwardly tapering cross sectional configuration adapted to provide a low velocity airflow interface between the wind tunnel horizontal airflow and th

Abstract: A dry material sorting device for selectively sorting mixtures of granular material comprising component materials such as sand and gold having different specific gravities. The use of a horizontal wind tunnel to sort the materials is described. Use of a prescreening device to segregate particles into separate batches based on particle size prior to blowing of the material in the wind tunnel is disclosed. An alternate mode comprising screening of particles after blowing in the wind tunnel using a dynamic screen having variable aperture sizes therein is also disclosed.