Six of the miners died on the spot.
The seventh who sustained serious injuries succumbed to his wounds, the same sources said, adding that the truck transporting them had overturned.
A dozen other passengers were injured in the accident.
They were heading home from gold panning with a quantity of rocks containing gold.
The gold mining areas in the north and north-west of Mauritania have, in recent years, witnessed many fatal accidents, most of which were due to artisanal mine collapses.