CORRECTED-Mercury poisoning-dark side of Colombia's gold boom

* Colombia the world's top mercury polluter per capita

* Gold-mining mercury use causes sickness in Antioquia (Corrects conversion in paragraph 11 to tonnes from kilograms)

By Diana Delgado

BOGOTA, July 13 (Reuters) - Colombia's gold bonanza has a dark side, U.N. experts said on Tuesday: mercury poisoning spreading from miners to the population of a northwest state where they use mercury to extract the precious metal.

Colombia is one of the world's top mercury polluters, as 50 to 100 tonnes of mercury are lost annually in the process of capturing gold while soaring prices push miners and artisans to extract ever more of the yellow metal, analysts say.

"As prices of gold have been increasing, more artisanal miners are mining and processing gold using mercury which is accessible, easier and cheaper to use," said Marcello Veiga, an adviser to the U.N. industrial development arm.

The Andean nation is the world's No. 1 mercury polluter per capita from artisanal (small-scale) mining, Veiga said. "The number of artisanal miners in Colombia is also increasing."

Miners have used mercury to separate gold for decades, but part of it is lost in the process, contaminating rivers and soils. The environment ministry currently allows mercury but may soon forbid it, with a few exceptions.

In northwest Antioquia state, they use the most damaging process, adding around 120 grams (4.2 ounces) of mercury to 60 kilograms (132 pounds) of ore, without condensing or capturing the mercury, Veiga said.