Containers in the mines may randomly drop loot when destroyed. Containers are equally likely to be crates or barrels; the possible contents are not affected by the type of container. At most one item will be dropped by a container, although multiple copies of that item are possible.
Most containers respawn every time you enter a level. Containers on platforms in the Mines, however, are only spawned the first time you enter a level. After those containers are destroyed, no new containers will appear on the platforms.