A South African lawyer said on Tuesday he was preparing a class action lawsuit against leading gold mining firms on behalf of thousands of former miners who say they contracted silicosis, a debilitating lung disease, through negligent health and safety.

Attorney Richard Spoor, whose legal battle against a South African asbestos-mining company led to a $100 million settlement in 2003, said he would file class action papers with the High Court in Johannesburg within the next few months.

We have a very important meeting with our advocates on Monday to thrash out the final form of the application, Spoor told Reuters.

He said he had so far signed up 6,876 plaintiffs from South Africa and Lesotho, the landlocked kingdom that has provided hundreds of thousands of migrant workers to South Africa's gold mines over the last century.

The principal targets of the suit would be AngloGold Ashanti, Gold Fields and Harmony Gold - South Africa's three biggest gold miners - and minor producer DRD Gold, Spoor said.

Frans Barker, chief operating officer of the Chamber of Mines and the main industry spokesman on silicosis, declined specific comment.

We're continuing with our work on these issues, irrespective of the class action. We wouldn't like to respond to the class action itself because that depends very much on the merit of specific cases, he said.

The planned suit, which has little precedent in South African law, has its roots in a landmark ruling by the Constitutional Court a year ago that for the first time allowed lung-diseased miners to sue their employers for damages.

The plaintiff in that case, Thembekile Mankayi, had sought 2.6 million rand ($342,000) in damages, loss of earnings, medical bills and pain and suffering caused by silicosis and tuberculosis allegedly contracted while working for AngloGold from 1979 to 1995.

Mankayi died days before the ruling.

Spoor would not be drawn on the size of any desired settlement, but industry research suggests the mining houses could be facing a bill running into the billions of rand should they lose.

At their height 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.

A 2009 paper by researchers from Johannesburg's Witswatersrand University and University College, London, estimated that there were 288,000 cases of compensable silicosis in South Africa.

It also assessed the industry's unpaid compensation liability at 10 billion rand at 1998 values. Today, that is worth 27 billion rand - more than $3.5 billion. ($1 = 7.5948 South African rand)

(Reporting by Ed Cropley; Editing by Ed Stoddard)

South Africa Gold