Estanho de Rondônia S/A (ERSA) consists of the Santa Barbara mine, in the city of Itapuã do Oeste, and the foundry located in Ariquemes. Cassiterite is extracted at the mining unit. In Ariquemes, the cassiterite is fused and transformed into grade "A" tin in the form of ingots. The deposit has demonstrated reserves of almost 30,000 tons that, when considered in conjunction with resources, equal over 60,000 tons of tin contained in all of ERSA. The foundry has a nominal capacity to process 3,600 tons of tin metal annually.
The acquisition of ERSA, in 2005, was strategic for CSN as tin is used to make tinplates, a high value-added coating used in packaging products. The company is the only manufacturer of this product in Brazil and one of the five largest in the world.