Formation of hydrogen peroxide (H 2 O 2 ), an oxidizing agent stronger than oxygen, by sphalerite ((Zn, Fe) S) was examined during its grinding process. It was observed that sphalerite generated H 2 O 2 in pulp liquid during wet grinding and also when the freshly ground solids placed in water immediately after dry grinding. The generation of H 2 O 2 in either wet or dry grinding was thought to be due to a reaction between sphalerite and water where the mineral surface is catalytically active to produce OH free radicals by breaking down the water molecule. Effect of pH on the formation of H 2 O 2 by sphalerite showed that acidic pH values generated more H 2 O 2 . Mixtures of pyrite, chalcopyrite and galena with sphalerite on the formation of H 2 O 2 were also probed. It was shown that the concentration of H 2 O 2 increases with increasing pyrite or chalcopyrite fraction in pyrite–sphalerite or chalcopyrite–sphalerite or galena–sphalerite mixtures but with an increase in galena proportion, the concentration of H 2 O 2 decreased. The oxidation or dissolution of one mineral than the other in a mixture can also be accounted with the extent of H 2 O 2 formation in the pulp liquid in addition to galvanic interactions. H 2 O 2 plays a greater role in the oxidation of sulfides or aiding the extensively reported galvanic interactions since the amount of H 2 O 2 generated with a specific mineral followed the rest potential series of sulfide minerals. This study highlights the necessity of relooking into the role of H 2 O 2 in electrochemical and/or galvanic interaction mechanisms between pyrite, chalcopyrite and galena with sphalerite.