Check option A: Roasting of Malachite produces Cuprite

• Malachite is basic copper carbonate: $\mathrm{CuCO_3\cdot Cu(OH)_2}$
• On heating in limited or no air (calcination/decomposition), it gives copper(II) oxide: $\mathrm{CuCO_3\cdot Cu(OH)_2 \xrightarrow{\Delta} 2CuO + CO_2 + H_2O}$
• Cuprite is: $\mathrm{Cu_2O}$
• Malachite does not directly produce cuprite on roasting in the standard extraction description.

Hence, A is incorrect.

Check option B: Calcination of Calamine produces Zincite

• Calamine is zinc carbonate: $\mathrm{ZnCO_3}$
• On calcination: $\mathrm{ZnCO_3 \xrightarrow{\Delta} ZnO + CO_2}$
• Zincite is: $\mathrm{ZnO}$

Hence, B is correct.

Check option C: Copper pyrites is heated with silica in a reverberatory furnace to remove iron

• Copper pyrites is: $\mathrm{CuFeS_2}$
• During extraction, after partial roasting/smelting, iron oxide forms and is removed by silica as slag: $\mathrm{FeO + SiO_2 \rightarrow FeSiO_3}$
• This is done in a reverberatory furnace.

Hence, C is correct.

Check option D: Impure silver is treated with aqueous $\mathrm{KCN}$ in the presence of oxygen followed by reduction with zinc metal

• This is the cyanide process used for extraction of silver from argentite-type ores.
• Silver dissolves in cyanide solution in presence of oxygen: $\mathrm{4Ag + 8KCN + O_2 + 2H_2O \rightarrow 4K[Ag(CN)_2] + 4KOH}$
• Then silver is recovered by displacement with zinc: $\mathrm{2K[Ag(CN)_2] + Zn \rightarrow K_2[Zn(CN)_4] + 2Ag}$

Hence, D is correct.

Final selection

Correct statements are: $\boxed{B,\ C,\ D}$

Comparison with stored answer

• Stored correct answer: B, C, D
• Derived answer: B, C, D

So, the derived answer agrees with the stored answer.