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Doña Inés de Collahuasi, a Chilean mining company, operates the world's fourth largest copper mine. The operation comprises two principal porphyry copper deposits, Ujina and Rosario, as well as a smaller deposit called Huinquintipa that contains only sulphide mineralisation and copper oxides. It is a joint venture owned by two mining majors, Swiss-based Xstrata and London-based Anglo American, with 44 percent of the shares apiece.