That mound--there used to be more of them--is mine spoil, or, in local parlance, slime (spoil + lime, since it's mostly limestone). That area is nearly hollow with the the numerous and massive lead mines, so it is known as the Old Lead Belt, at one time, this was the largest producer of lead in the world. It was once possible to travel from Doe Run all the way up to Desloge underground. You can tour the mine in Bonne Terre, just to the north, to get an idea of what the mines were like, and, as ASE guy hints, you can tour Federal Mill #3 next to Park Hills (better known to old timers as Flat River, Elvins, Rivermines, et. al.) to see how the lead was processed. The area was also well provided with railroads--the Bonne Terre & Mississippi
River RY, the St. Francis County Traction, the Missouri - Illinois, and the Missouri Pacific nee St. Louis and Iron Mountain (which ate all the other up) moved ore, goods, and people there beginning in the late 1800s until the advent of the common infernal combustion engine and the shift to the New Lead Belt (Viburnum-Buick area to the east).
It used to be possible to take your jeeps and other 4x4s up and down those massive piles, but that sport ended years ago for reasons that are probably obvious.
Anyone interested in mining, engineering, railroad, or mechanical history should take some time to study what happened there.