Sulphide ores of metals are usually concentrated by froth flotation process. Which one of the following sulphide ores offer an exception and is concentrated by chemical leaching?

Argentitie or Silver glance, $\mathrm{Ag}_2 \mathrm{~S}$ is an ore of silver. Silver is extracted from argentite by the mac-Arthur and Forest process (leaching process). $\begin{aligned} & \mathrm{Ag}_2 \mathrm{~S}+4 \mathrm{NaCN} \rightarrow 2 \mathrm{Na}\left[\mathrm{Ag}(\mathrm{CN})_2\right]+\mathrm{Na}_2 \mathrm{~S} \\ & 4 \mathrm{Au}+8 \mathrm{KCN}+2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2 \rightarrow 4 \mathrm{~K}\left[\mathrm{Au}(\mathrm{CN})_2\right]+4 \mathrm{KOH} \end{aligned}$ Related Theory Leaching is the selective dissolution of the desired mineral leaving behind the impurities in a suitable dissolving agent.