* Coal union rejects wage offer, seeks mediation
* Workers looking for increases of up to 15 percent (Adds details)
By Peroshni Govender
JOHANNESBURG, Aug 12 (Reuters) - Wage negotiations between workers in South Africa's coal sector and the employers' body, the Chamber of Mines, were deadlocked late on Wednesday and will now go to mediation.
"The employer came back with nothing after we rejected their offer. We have declared a dispute and will go through a mediation process," Peter Bailey, the coordinator for National Union of Mineworkers told Reuters.
South Africa's National Union of Mineworkers (NUM) earlier rejected salary increases of 5 percent to 6.5 percent from the Chamber of Mines, calling the offer "insulting".
Workers want pay increases of up to 15 percent, while the chamber - which represents firms such as Glencore, Anglo American Coal and Exxaro - had offered a revised wage rise from its initial offer of 4 percent to 6.5 percent.
"We feel that offer is an insult. We know that commodity prices are low but we have a mandate from our members and we have to fight for better increases," the NUM's acting spokesman Livhuwani Mammburu said.
The Chamber of Mines proposed its revised offer on Tuesday and is meeting with unions again on Wednesday and could possibly offer a further increase.
Coal prices are at near-decade lows and have fallen around 10 percent this year on a supply glut and expectations are that demand from top consumer China will shrink further.
The smaller Solidarity union, which represents mostly professional workers in the sector, is asking for a 9 percent pay increase. (Editing by James Macharia and David Evans)