The bodies of eight miners killed by FARC guerrillas were found on Thursday near a gold mine in a mountainous section of the southwestern Colombian province of Cauca, Caracol Radio reported.
A miner who survived the attack by pretending to be dead notified authorities of the killings.
A group of armed men wearing hoods surprised the miners, told them they should not be in the area and opened fire, the eyewitness, who was wounded in the attack, said.
Army troops, police and Attorney General's Office investigators have arrived in Alto de Ovejas, located outside the city of Suarez, where the killings occurred.
The miners were likely killed by Revolutionary Armed Forces of Colombia, or FARC, guerrillas, officials said.
The miners are not from the area and moved here because of "gold fever," Suarez Mayor Luis Antonio Colorado told Caracol Radio.
The FARC, Colombia's oldest and largest leftist guerrilla group, was founded in 1964, has an estimated 8,000 to 17,000 fighters and operates across a large swath of this Andean nation.
President Alvaro Uribe's administration has made fighting the FARC a top priority and has obtained billions in US aid for counterinsurgency operations.
The FARC, whose leader is Alfonso Cano, has suffered a series of setbacks in recent years.
On July 2, 2008, the Colombian army rescued former presidential candidate Ingrid Betancourt, US military contractors Thomas Howes, Keith Stansell and Marc Gonsalves, and 11 other Colombian police officers and soldiers.
The FARC had been trying to trade the 15 captives, along with 25 other "exchangeables", for hundreds of jailed guerrillas.