Rio Tinto Group is a British-Australian multinational metals and mining corporation with headquarters in London, UK and a management office in Melbourne, Australia. The company was founded in 1873, when a multinational consortium of investors purchased a mine complex on the Rio Tinto, in Huelva, Spain from the Spanish government. Since then, the company has grown through a long series of mergers and acquisitions to place itself among the world leaders in the production of many commodities, including aluminium, iron ore, copper, uranium, coal, and diamonds. Although primarily focused on extraction of minerals, Rio Tinto also has significant operations in refining, particularly for refining bauxite and iron ore. The company has operations on six continents but is mainly concentrated in Australia and Canada, and owns gross assets valued at $81 billion through a complex web of wholly and partly owned subsidiaries. Its head office in the United Kingdom is in the City of Westminster, London, while its Australian head office is in the City of Melbourne.