How do we separate two sulphide ores by the Froth Flotation Method? Explain with an example.

(N/A) In the Froth Flotation Method,two sulphide ores can be separated by using substances called depressants.
Depressants selectively prevent one sulphide ore from forming froth while allowing the other to come to the froth.
For example,in an ore containing both $ZnS$ (zinc blende) and $PbS$ (galena),$NaCN$ is used as a depressant.
$NaCN$ reacts with $ZnS$ to form a soluble complex,$Na_2[Zn(CN)_4]$,which prevents $ZnS$ from forming froth,whereas $PbS$ is allowed to come with the froth.