Which type of dust is NOT a cause of mine explosion hazard?

In the context of mine safety, the risk of explosion is closely associated with the presence of dust that is combustible or can react in explosive mixtures with other substances, especially in enclosed environments. Coal dust is well-known for its combustibility, and lead dust, while primarily a health hazard, can contribute to explosions under certain conditions. Sulfide dust, typically part of mineral deposits, can also be involved in explosive situations in mines.

Mercury dust, on the other hand, does not possess similar explosive properties. Mercury is a heavy metal and while it poses significant health risks when inhaled or ingested, it is not known to create explosive conditions in the mine environment. Thus, it does not contribute to mine explosion hazards in the same way that the other types of dust listed do. This distinguishes mercury dust as the least likely candidate for causing explosions in mining operations, making it the correct answer.