The news was confirmed by police and unionists, this is the latest violent incident in the strike-hit sector.
The NUM said the attackers were members of the Association of Mineworkers and Construction Union (AMCU), but officials of the rival union were not immediately available for comment on Friday.
The miner was on his way to work on Thursday when he was attacked by four armed men who poured petrol on him and set him on fire, police spokesman Thulani Ngubane said.
The man identified two of his attackers as AMCU members before dying of his injuries on Friday, NUM spokesman Erick Gcilitshana told Reuters.
“Intimidation has been the lifestyle of the miners since the arrival of AMCU in the industry,” he added.
AMCU emerged as the dominant union in South Africa’s platinum belt in 2012, after winning over tens of thousands of members from the NUM in a vicious turf war that killed dozens of people and triggered a wave of wildcat strikes.
The hardline union is in its fourth week of a strike at Amplats, Impala Platinum and Lonmin, demanding that monthly wages be more than doubled to 12,500 rand.