More victims might still be trapped in the debris, Defence Minister Mahamat Abali Sala told Reuters.
The mine is located in the Tibesti region, where the discovery of gold nearly a decade ago led to a surge in illegal mining.
The illicit industry has attracted Sudanese refugees looking to make enough money to get to Europe.
A landslide caused the collapse, though accidents are common in the illegal mines due to a lack of oversight and unsafe practices.
The accident occurred in Kouri Bougoudi in the Tibesti Province, which is largely lawless with little government presence.
News of the cave-in spread slowly because of the remoteness of the area and a current state of emergency in the province.
Correspondents say that – following the discovery of gold deposits in Kouri Bougoudi – there have been numerous clashes among rival ethnic, local and foreign groups which began in 2012 and 2013.
In addition to refugees, the mines have attracted gangs, traffickers and rebels fighting the army.