RIO TINTO LTD'S wholly-owned Argyle diamond mine in Western Australia's north east Kimberley is well and truly in its transition phase as the operation goes underground. However, it is now likely the expansion will cost much more than the 760 million US dollars previously budgeted. Although a new quarterly production record was set at its 60 percent-held Diavik joint venture (with Aber Resources Corporation) in Canada's Northwest Territories in the June quarter thanks to higher grades, Rio's Argyle output remained constrained due to lower grade feeds associated with current mining locations.
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