Estanho de Rondônia S.A. (ERSA), a subsidiary of Brazilian steel company Companhia Siderúrgica Nacional (CSN), is a private mining company based in Ariquemes, Rondônia state. ERSA owns the Santa Barbara tin mine in Itapuã do Oeste and a smelting plant in Ariquemes. The company extracts cassiterite (tin ore) from Santa Barbara, which it transforms into tin lingots in the Ariquemes smelting plant. The mine has an annual mining capacity of 1,200t, while the smelting plant has an annual production capacity of 3,600t of tin. Companhia Siderúrgica Nacional acquired ERSA in 2005.