State the role of silica in the metallurgy of copper.

Silica, acts as an acidic flux during the metallurgy of Cu. It reacts with impurities of iron and form slag. FeS is present in the form of impurity with Cu₂S ore
$2\mathrm{FeS}+3{\mathrm{O}}_2\to \underset{\mathrm{Gangue}}{2\mathrm{FeO}}+2{\mathrm{SO}}_2$
$\underset{\mathrm{Gangue}}{\mathrm{FeO}}+\underset{\mathrm{flux}}{{\mathrm{SiO}}_2}\to \underset{\mathrm{slag}}{{\mathrm{FeSiO}}_3}$