The process of extraction of Au and Ag from their respective ores is based on their solubility in 

The process of extraction of silver and gold using KCN solution is known as cyanide process or Mac Arthur Forrest Process. The main principle of this process that both Ag and Au ores are soluble in KCN to forms a cyanide complex. When this cyanide complex is treated with Zn, then Ag is successfully extracted.

$\begin{array}{ccc}{\mathrm{Ag}}_2\mathrm{S}+4\mathrm{KCN}& \to & 2\mathrm{K}\left[\mathrm{Ag}{\left(\mathrm{CN}\right)}_2\right]+{\mathrm{K}}_2\mathrm{S}\\ 2\mathrm{K}\left[\mathrm{Ag}{\left(\mathrm{CN}\right)}_2\right]+\mathrm{Zn}& \to & {\mathrm{K}}_2\left[\mathrm{Zn}{\left(\mathrm{CN}\right)}_4\right]+2\mathrm{Ag}\end{array}$