Explain the purification of sulphide ores by froth floatation method?

The purification of Sulphide ores by froth floatation method:
This method is used for the concentration of sulphide ore such as galena $(PbS)$, zinc blende $(ZnS)$ and copper pyrites $(CuFe{S}_2)$
To water tank, finely divide ore is added. Pine oil, eucalyptus oil, xanthates or fatty acids etc are added. Compressed air is passed through water tank.
Metallic sulphide particles of ore are preferentially wetted by oil. They rise to the surface along-with froth.
The gangue particles are wetted by water. They settle at bottom.