Sulphide ores of metals are usually concentrated by froth floatation process. Which one of the following sulphide ores offers an exception and is concentrated by chemical leaching?

Solution :
Galena $$(PbS),$$  copper pyrites $$\left( {CuFe{S_2}} \right)$$   and argentite $$\left( {A{g_2}S} \right)$$  are are concentrated by froth floatation process but sphalerite $$\left( {ZnS} \right)$$  is concentrated by chemical leaching.