In a historic class action decision spearheaded by U.S. plaintiffs firms Hausfeld LLP and Motley Rice and their South African counsel, a court in Johannesburg on Friday greenlighted a four-year-old class action against 32 mining companies on behalf of current and former miners sickened with deadly silicosis and tuberculosis.

As many as a half million current and former gold miners with silicosis may be eligible to join the litigation, which was filed in August 2012; an additional large number of mine workers with tuberculosis will also be covered as a separate class. An estimated quarter to a third of all who worked in the mines are said to have contracted occupational lung diseases, so potential damages are steep. Estimates range between $660 million and a few billion dollars.