Jihadist fighters regularly launch attacks in the region.
A vehicle carrying supplies on a weekly delivery run hit the mine late in the morning six kilometres (four miles) from Samira village, said the GNN in a statement.
The village, which lies not far from Niger's border with Burkina Faso in the southwest, has since 2004 hosted the country's only industrial-scale gold mine.
This assault was just the latest in a series of attacks against Niger's soldiers.
The impoverished Sahel country is grappling with an insurgency by jihadists linked to al-Qaeda* and the Islamic State group*. In the southwest, they also have to contend with jihadist fighters from Boko Haram*.
It is supported by a number of western countries, including France and the United States, who both have military bases there.
* terrorist groups banned in Russia and many other countries