Cinnabar (HgS) and galena (PbS) on roasting often gives their respective metals but zinc blende (ZnS) does not. The reason is

On roasting all these sulphide ores are partly converted into their respective oxides since the oxides of Hg and Pb are unstable. While that of zinc is stable, therefore, oxides of Hg and Pb bring about the reduction of their sulphides to metals, but zinc oxides do not reduce ZnS to Zn metal.HgS+2HgO (unstable) ⟶Δ3Hg+SO2PbS+2PbO (unstable) ⟶Δ3Pb+SO2ZnS+2ZnO (stable) ⟶3Zn+SO2