The metal obtained by self reduction process is

The sulphides of less electropositive metals such as mercury (Hg), copper (Cu), lead (Pb), tin (Sn) are reduced without the use of any additional reducing agent. Examples are given below.

$2\mathrm{HgS}+3{\mathrm{O}}_2\to 2\mathrm{HgO}+2{\mathrm{SO}}_2; 2\mathrm{HgO}+\mathrm{HgS}\to 3\mathrm{Hg}+{\mathrm{SO}}_2$

$2\mathrm{PbS}+3{\mathrm{O}}_2\to 2{\mathrm{SO}}_2; 2\mathrm{PbO}+\mathrm{Pbs}\to 3\mathrm{Pb}+{\mathrm{SO}}_2$

$2{\mathrm{CU}}_2\mathrm{S}+3{\mathrm{O}}_2\to 2{\mathrm{CU}}_2\mathrm{O}+2{\mathrm{SO}}_2; 2{\mathrm{Cu}}_2\mathrm{O}+{\mathrm{Cu}}_2\mathrm{S}\to 6\mathrm{Cu}+{\mathrm{SO}}_2$