Which of the following reactions is an example of autoreduction?

In auto-reduction, no external agent is used as a reducing agent. Here, sulphide ores of less electropositive metals like Hg, Pb, Cu etc. are heated in air so as to convert part of the ore into oxide or sulphate which then reacts with the remaining of sulphide ore in absence of air to give the metal and sulphur dioxide.

Here, Cu itself acts as the reducing agent and also it is being reduced so, this process is termed as auto-reduction.