“Alwyn is hands-on, young and energetic, and brings new ideas to our approach to production and safety,” CEO Graham Briggs said in a statement.
Pretorius had 20-years of underground, deep-level, gold mining experience in various supervisory and management positions.
He had been an executive of Harmony since 2007 and held degrees in mining and industrial engineering.
Tom Smith, who held the role of chief operating officer, had resigned to pursue other business interests.
“Tom made an invaluable contribution to the mining industry as well as the company. We wish him well in his future endeavours,” said Briggs.