The National Union of Mineworkers (NUM) said on Friday that its branch chairman at Eastern Platinum Mine, a unit of Lonmin, was shot by unknown assailants and subsequently died in hospital.
The shooting is the latest in a spate of such incidents on the platinum belt, which has been the scene of an often violent turf war between NUM and its arch rival the Association of Mineworkers and Construction Union (AMCU), underscoring the social risks of investing in South Africa's mining sector.
Police could not be reached immediately for comment.
NUM spokesman Livhuwani Mammburu said the shooting happened on Thursday night and that the man died later in hospital. He said the miner's wife was also shot in the attack and was recovering.
Lonmin spokeswoman Wendy Tlou said the company's head of security "has confirmed a murder and attempted murder. We are still awaiting official information from the police and don't know the motive at this stage".
Several AMCU members were shot dead on the platinum belt last year, while NUM members have also been attacked. The houses and cars of NUM members at Harmony Gold's Kusasalthu mine were torched in the gold sector late last year.
Dozens of South African miners have been killed in violence stemming from labor unrest in recent years, including 34 who were shot dead by police in August 2012 during a wildcat strike at Lonmin's Marikana mine.