ASARCO LLC is a mining, smelting, and refining company based in Tucson, Arizona, which mines and processes primarily copper. The company is a subsidiary of Grupo México. Its three largest open-pit mines are the Mission, Silver Bell and Ray mines in Arizona. Its mines produce 350,000,000 to 400,000,000 pounds (160,000,000 to 180,000,000 kg) of copper a year. ASARCO conducts solvent extraction and electrowinning at the Ray and Silver Bell mines in Pima County, Arizona and Pinal County, Arizona and a smelter in Hayden, Arizona. Before its smelting plant in El Paso, Texas was suspended in 1999, it was producing 1.5 million pounds of lead and 2.0 million pounds of zinc per day, as well as 60 million pounds of copper per year. The company's name is an acronym for American Smelting and Refining Company.