The Andover Mine was opened sometime before 1763, prior to the Revolutionary War. The mine is known for having contained the most extensive deposit of hematite in the state of New Jersey. While predominantly hematite, the ore was also intermingled with magnetite. The orebody was between 30 to 60 feet wide and its depth was quite variable.
The southern portion of the mine was worked as a large open pit up to 70 feet deep with some underground stoping. The northern end followed the vein underground where the magnetite largely replaced the hematite. It is estimated that the total length of the ore mined was about 1200 feet.
The mine was worked extensively and the ore was smelted at the Andover Furnace built in 1763. Shortly after the start of the Revolutionary War, the mine was taken into possession by the Continental Congress and worked to provide the army with iron and steel for the war. After the war ended around 1783, the mine was abandoned.