JOHANNESBURG, South Africa (AP) _ The union representing black miners said mediation efforts Thursday failed to resolve a five-month-old wage dispute with management, and it would hold a strike vote next week.

It also called for the closure of an underground shaft at the Kinross Gold Mine after two separate fires broke out Wednesday near the site of a fire last month that killed 177 miners.

The National Union of Mineworkers, which claims 250,000 members, said workers at gold and coal mines would start voting Monday on whether or not to strike.

The union is seeking a 26-percent wage hike and other benefit improvements. The Chamber of Mines, the industry association, has offered salary increases ranging from 19 percent to 23 percent for both union and non-union miners. The union says the average monthly pay for the nation's 600,000 black miners is 340 rand - $160.

Gold and coal exports account for well over half of South Africa's foreign income. A strike at several gold mines fizzled a year ago when the companies threatened mass dismissals.

The two fires at Kinross Gold Mine, about 80 miles east of Johannesburg, forced the evacuation of 2,000 miners but caused no injuries, said the owner, the General Mining Union Corp.

The company said the fires started when rubber casing on overhead power cables ignited in the mile-deep level of the No. 2 shaft, where last month's disaster occurred.

Cyril Ramaphosa, general secretary of the union, said the company should ''close the No. 2 shaft until the inquiry into last month's disaster is concluded and its results are known.''

Earlier, the Bureau for Information said a gasoline bomb was thrown into a home in the Bonteheuwel mixed-race area near Cape Town. Six people, three adults and three children, were injured.

The bureau said someone threw two hand grenades at the house of a council member in the black township of Soweto. The grenades exploded outside and no one was injured and there was no damage. Black policemen and members of government-backed town councils have been regular targets during the last two years of violence that has taken 2,100 lives.

Meanwhile, Leon Mellet, the bureau's director of internal media told a South African Security Association conference in Durban Wednesday night that there were 60 percent fewer violent incidents since the national emergency was declared June 12.

He said barring foreign television crews from scenes of violence had contributed to the decline. ''We have found that in most incidents the violence was played out for the benefit of the cameras,'' Mellet said.

Emergency rules also bar reporting on security force action and publication of statements considered subversive.

At least 324 people have been killed nationwide since the emergency was declared. The government says most involved blacks killing other blacks.

''More than 90 percent of the population believes that the state of emergency was a great happening,'' Mellet said.