Manganese deposits of the Drum Mountains, Utah

More than 15,000 tons of manganese ore has been produced from small deposits in the Drum Mountains in west-central Utah. Lenses of rhodochrosite, now largely weathered near the surface to manganese oxides, lie parallel to the bedding of Cambrian dolomites and shales near faults that are nearly normal to bedding. Two varieties of rhodochrosite, one fine-grained, dark-gray or black, and massive, the other coarser-grained, pink, and generally occurring in veinlets in the gray variety, are present. The gray contains less MnCO ₃ and FeCO ₃ , but more CaCO ₃ and MgCO ₃ than the pink variety. The deposits are interpreted as bodies that replaced favorable dolomite or limestone beds. The gray rhodochrosite first replaced the dolomite or limestone; the pink variety later formed veinlets in the gray rhodochrosite and replaced it to a small extent.