It is not lawful for any company or individual to leave open any pit or other hole outside of an enclosure of a greater depth and breadth than 2 feet; provided, however, such pit or hole may be left open by enclosing the same with a fence or other enclosure that would be a safeguard against horses, cattle or other domestic animals falling into the same; provided further, that this section shall not apply to pits or holes made by any company or individual while bona fide engaged in actual mining operations, such pits and holes to be enclosed as herein provided when said mining operations shall cease or be discontinued.