by DPG Advisory Solutions. Operations Rio Tinto's main business is the production of raw materials including copper, iron ore, bauxite, diamonds, uranium and industrial minerals including titanium dioxide, salt, gypsum and borates. Rio Tinto also performs processing on some of these materials, with plants dedicated to processing bauxite into alumina and aluminium, and smelting iron ore into iron. The company also produces other metals and minerals as by-products from the processing of its main resources, including gold, silver, molybdenum, sulphuric acid, nickel, potash, lead and zinc. Rio Tinto controls gross assets of $81 billion in value across the globe, with main concentrations in Australia (35%), Canada (34%), Europe (13%) and the United States (11%), and smaller holdings in South America (3%), Africa (3%) and Indonesia (1%). Iron ore: Rio Tinto Iron Ore Rio Tinto Iron Ore (RTIO) comprises an integrated iron ore operations in the Pilbara, Western Australia. The Pilbara iron ore operations include 16 iron ore mines, four independent port terminals, a 1,700-kilometre rail network and related infrastructure. Copper and by-products: Rio Tinto Copper Copper was one of Rio Tinto's main products from its earliest days operating at the Rio Tinto complex of mines in Spain. Since that time, the company has divested itself from its original Spanish mines, and grown its copper-mining capacity through acquisitions of major copper resources around the world. The copper group's main active mining interests are Oyu Tolgoi mine in Mongolia, Kennecott Utah Copper in the United States, and Minera Escondida in Chile. Most of these mines are joint ventures with other major mining companies, with Rio Tinto's ownership ranging from 30% to 80%; only Kennecott is wholly owned. Operations typically include mining of ore through to production of 99.99% purified copper, including extraction of economically valuable by-products. Together, Rio Tinto's share of copper production at its mines totalled nearly 700,000 tonnes, making the company the fourth-largest copper producer in the world. Rio Tinto Copper continues to seek new opportunities for expansion, with major exploration activities at the Resolution Copper project in the United States, Winu in Australia, and Oyu Tolgoi underground mine in Mongolia. In addition, the company is seeking to become a major producer of nickel, with exploration projects currently underway in the United States and Indonesia. Although not the primary focus of Rio Tinto Copper's operations, several economically valuable by-products are produced during the refining of copper ore into purified copper.