The High Court of South Africa certified a class action lawsuit for gold miners who contracted silicosis and tuberculosis while working underground.

The decision could pave the way for the largest class action suits in the county and could cost the gold industry hundreds of millions of dollars according to some analysts.

Judge Phineas Mojapelo said workers who had died of the diseases could be included in the suits, with any damages paid to family members, and that each mining company should be held liable separately for any damages. The suit could include a half million miners.

“We hold the view that in the context of this case, class action is the only realistic option through which most mine workers can assert their claims effectively against the mining companies,” Mojapelo said in a unanimous ruling by three judges.

“Mining companies will be held liable or responsible for their own actions for unlawful emissions,” he said.

Reuters reported that some miners walked out of the courthouse triumphantly with fists raised, while activists sang and danced outside.

In their heyday in the 1980s, South Africa's gold mines employed 500,000 men, and some medical research suggests as many as one in two former gold miners has silicosis.

Silicosis is an incurable disease caused by inhaling silica dust from gold-bearing rocks. It causes shortness of breath, a persistent cough and chest pains, and also makes people highly susceptible to tuberculosis.

The defendants include global miner Anglo American, Africa's top bullion producer AngloGold Ashanti, Gold Fields, Harmony Gold, Sibanye Gold and African Rainbow Minerals (ARM) which have together formed the Occupational Lung Disease (OLD) working group to deal with such issues.

Alan Fine, a spokesman for OLD said in a statement the gold companies were studying the judgment and each firm would decide whether to appeal the court ruling.

There is little precedent in South African law for the class action suits which have their roots in a landmark 2011 ruling by the Constitutional Court that for the first time allowed lung-diseased miners to sue employers for damages.

The claims stretch back decades and involve not just South Africans but thousands of former miners from neighboring countries such as Lesotho, Malawi and Swaziland.

That is why Anglo American, which no longer has any interests in gold mining, and ARM, which no longer operates gold mines, have been named in the claims.

The ruling is separate from a $30 million silicosis settlement with 4,400 miners reached in March by Anglo American and AngloGold.