The Ozarks contain ore deposits of lead, zinc, iron and barite. Many of these deposits have been depleted by historic mining activities, but much remains and is currently being mined in the Lead Belt of southeast Missouri. Historically, the lead belt around the Saint Francois Mountains and the Tri-State district lead-zinc mining area around Joplin, Missouri, have been important sources of metals. Mining practices common in the early 20th century left significant abandoned underground mine problems and heavy metal contamination in topsoil and groundwater in the Tri-State district.