Geologic map of Lake Valley manganese district, Sierra County, New Mexico

The Lake Valley district was originally developed as a manganese-silver district, but the known silver-bearing ore bodies have long since been worked out.  The critical shortage of manganese during World War II renewed interest in the manganese deposits; from October 1941 through June 1942 the U. S. Geological Survey and the U.S. Bureau of Mines conducted a cooperative exploration program in the district.  This exploration demonstrated that the Lake Valley district contained about 175,000 tons of ore; approximately 37,000 tons has subsequently been mined.  The present reserves are estimated to be approximately 140,000 tones of ore with a manganese content of more than 10 percent and an average content of 16.4 percent; about 75,000 tons of the ore has manganese content of more than 15 percent and an average content of 20.7 percent.