Open-cast gold-mining operations in Africa by multinationals have created an ecological and health time-bomb and failed to help local people out of poverty, campaigners said at a book launch Tuesday.

"It's an ecological time-bomb," said Swiss journalist Gilles Labarthe, the author of "Black Gold", which is being published in collaboration with Oxfam France-Agir and the association Survie (Survival).

"The accumulation of ecological degradation and the damage to health caused by open-cast gold-mining is going to ruin the producing regions for generations to come," he added.

Cyanide and mercury contamination of the groundwater had led to cases of paralysis, blindness and numerous miscarriages, he said. The two toxic substances are used to purify the minerals during mining.

In two villages in the southwestern region of Sadiola in Mali, four out of five women miscarried, said Kaou Sissoko, general secretary of the association of Sadiola expatriates in France.

The region hosts one of Mali's main mining operations.

It would cost 16 billion dollars (11.4 billion euros) to clean up the polluted groundwater in Africa, said Labarthe, adding that he feared the countries concerned would have to foot the bill.

Africa holds half the world's known gold reserves and produces 600 tonnes a year -- a quarter of the world's output.

But 80 percent of the major African mines were controlled by multinational companies, which made big profits because of the cheap cost of labour and the tough working conditions, said Labarthe.

He identified the three main companies as AngloGold of South Africa; Barrick Gold of Canada; and US company Newmont Mining. All three were financed by major banks such as UBS of Switzerland and France's Societe Generale.

Gold also served to finance armed movements as in the Democratic Republic of Congo, said Labarthe. And because it can be melted down repeatedly, it is harder to trace back to its origin, he added.

Oxfam France-Agir is the French wing of Oxfam, while Survie is a campaigning group dedicated to exposing French policy in Africa.

A report last month by the International Federation for Human Rights on mining and human rights in Mali commented: "Mali is the third largest gold producer in Africa but harvests only dust."

Under a World Bank-supported scheme, mining companies enjoyed large tax breaks, "depriving the State of the resources that could have been obtained from this economic activity," said the report.

Mali ranks 175th among 177 countries in terms of human development, it noted.