Eskom didn't tell them to shut down. They just indicated that they could not guarantee power. The mines chose to shut down because of safety concerns.
That's what they say but I think its probably just spin, look at Gold Fields' SENS announcement:
MINING AND PROCESSING SUSPENDED AT ALL SOUTH AFRICAN OPERATIONS
Johannesburg, Friday, January 25, 2008: Gold Fields Limited ("Gold Fields")
(NYSE, JSE, DIFX: GFI) reports all mining activities have been suspended at its
South African Operations.
This is due to Eskom requesting their Key Industrial Consumers (KIC) of which
Gold Fields is one, to reduce its consumption to the minimum load possible. This
communication was received yesterday evening.
A decision was taken to put no shifts down last night and no shifts were put
down this morning. Eskom has indicated that "KIC loads will be reduced to
`survival levels` or switched out totally for the next two to four weeks".
"This will have a serious effect on the South African operations and will
negatively affect our gold production. The South African Operations produce
approximately 7000 ounces per day. We are looking at ways to continue operations
and will work closely with Eskom to try and resolve this problem" said Ian
Cockerill, Chief Executive Officer of Gold Fields.