In the extraction of copper from its sulphide ore, metal is finally obtained by the oxidation of cuprous sulphide with ${\mathrm{Cu}}_2\mathrm{O}$. ​ It is an example of auto reduction. 

${\mathrm{Cu}}_2\mathrm{S}+2{\mathrm{Cu}}_2\mathrm{O}\mathrm{ }\to 6\mathrm{Cu}+\mathrm{ }{\mathrm{SO}}_2$