The incorrect statement related to the metal extraction processes is 

A mixture of PbS and PbO undergoes self-reduction to produce Pb and SO₂ .

In the extraction process of copper from copper pyrites, silica is added to produce copper silicate. 

Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction produces blister copper

In cyanide process, zinc powder is utilized to precipitate gold from $\mathrm{Na}\left[\mathrm{Au}{\left(\mathrm{CN}\right)}_2\right]$.