The first commercial copper mining district in Nevada was at Yerington in Lyon County. The Ludwig Mine opened in 1865, but the district produced only modest amounts of copper until a railroad was built to the district in 1911, and a smelter built in 1912 at nearby Thompson. The Anaconda Copper Mine produced from an open pit from 1918 to 1978. The copper ore bodies are contact metamorphic replacement deposits in limestone. Production through 1921 was 39 thousand tonnes of copper.