The accident in Plateau State occurred on Tuesday morning, police spokesman Alfred Alabo said.
"Preliminary investigations show that the miners were exposed to a sudden release of lead oxide and other gases such as sulfur and carbon monoxide, which are toxic to humans, especially in confined or poorly ventilated spaces," he said in a statement.
The miners were reportedly unaware that the gases were toxic and therefore continued their work.
The Nigerian government has now closed the mine and an investigation is underway.
