South African Treasury chief to leave post in June
The rand weakened following the news of the departure of an experienced hand at the National Treasury, where he worked for 23 years, with the last five years as director-general.
Mogajane planned "to pursue new opportunities outside of the public sector," the ministry said in a statement.
Mogajane said he chose to leave and had declined a request from Finance Minister, Enoch Godongwana to stay on.
"I humbly declined the request and I appreciated it. I am not leaving because I am angry with anybody or I don't like this and that, none of that," Mogajane said.
"I am leaving because I think I have served (the country) enough, I have done what I needed to do. I leave with a very heavy heart but I must move on."
"With Finance Minister, Godongwana already representing policy continuity of sorts, investors will be less concerned about the change in director-general than they might otherwise have been," said Razia Khan, chief economist for Africa and the Middle East at Standard Chartered.
"That said, there will still be great interest in who succeeds Mogajane, to ensure that there is broad institutional continuity."
In its annual budget unveiled in February, the Treasury said it expected public debt to peak sooner and at a lower level than earlier thought, as mining tax receipts support revenues.