Seven more people are reported to have been injured.
The search for survivors has ended. At the same time, rescue workers are reportedly having difficulty reaching the site because of the difficult terrain and the presence of criminal groups.
"These communities have no other economic options than these extremely risky activities. Traditional small-scale mining has practically disappeared," a source from the area told AFP.
Illegal mining is widespread in Nariño, which borders Ecuador to the south. Armed groups control the illegal gold trade and are also involved in drug trafficking and extortion.
Mining accidents are common in Colombia, especially at unregulated sites like this one.