T he correct statement(s) related to the metal extraction processes is(are)

Extraction principles for Pb, Cu and Au are frequently asked in JEE. Let us examine each statement one by one.

Statement A: A mixture of PbS and PbO undergoes self-reduction to produce Pb and $$SO_2$$.
During the smelting of galena, part of the ore is first roasted to $$PbO$$ while the rest remains as $$PbS$$. In the furnace they react as
$$PbS + 2\,PbO \;\longrightarrow\; 3\,Pb + SO_2$$
Lead metal is produced without adding any external reducing agent; hence the process is called auto- or self-reduction. The statement is TRUE.

Statement B: In the extraction of copper from copper pyrites, silica is added to produce copper silicate.
In the reverberatory furnace, $$CuFeS_2$$ is partially roasted to give $$FeO$$. Silica flux removes this iron impurity as
$$FeO + SiO_2 \;\longrightarrow\; FeSiO_3\;(\text{slag})$$
The slag is iron silicate, not copper silicate. Therefore the statement is FALSE.

Statement C: Partial oxidation of sulphide ore of copper by roasting, followed by self-reduction, produces blister copper.
Roasting converts some $$Cu_2S$$ into $$Cu_2O$$:
$$2\,Cu_2S + 3\,O_2 \;\longrightarrow\; 2\,Cu_2O + 2\,SO_2$$
On heating, the remaining $$Cu_2S$$ and the freshly formed $$Cu_2O$$ react:
$$Cu_2S + 2\,Cu_2O \;\longrightarrow\; 6\,Cu + SO_2$$
The copper obtained contains dissolved $$SO_2$$ which escapes on cooling, giving a blistered surface (blister copper). Hence the statement is TRUE.

Statement D: In the cyanide process, zinc powder is used to precipitate gold from $$Na[Au(CN)_2]$$.
Gold is displaced by the more electropositive metal zinc:
$$2\,Na[Au(CN)_2] + Zn \;\longrightarrow\; Na_2[Zn(CN)_4] + 2\,Au$$
Thus zinc powder indeed precipitates gold. The statement is TRUE.

Therefore the correct statements are:
Option A, Option C and Option D.