Argyle has been an open pit mine for more than 25 years, but as the lamproite "pipe" narrows and continues at depth, it will soon become unviable to continue accessing the ore body through the open pit.

This is why in 2001, Argyle began investigating the feasibility of developing an underground mine After a great deal of work, a proposal to construct an underground block cave mine was successful, with the Rio Tinto board approving funding of the project in December 2005.

Construction commenced immediately but the project was slowed in 2009 due to the global financial crisis.

With the diamond market continuing to recover, the Rio Tinto Board gave approval in September 2010 for the project to be ramped up and completed.

Construction activity will ramp up in the first half of 2011, with targeted production rates of nine million tonnes a year forecast within two years.

The open pit will close in 2012 and following a transition from the current open pit operation, the underground will be fully operational in 2013. The project will extend the life of the mine until at least 2019.

The extended mine life will generate enduring benefits for the Kimberley region, building on Argyle’s significant contribution to economic development over the past quarter of a century.

Milestones in the process of building the underground:

• July 2001 - Argyle embarks on a pre-feasibility study.
• February 2003 - Argyle presents the pre-feasibility study to the Rio Tinto Investment Committee.
• November 2003- construction of the exploratory decline commences.
• November 2004 - Argyle reaches a new agreement with Traditional Owners, securing their approval to construct a potential underground mine.
• May 2005 - the exploratory decline intersects the AK1 ore body for the first time.
• September 2005 - the exploratory decline is completed.
• December 2005 - the Rio Tinto Investment Committee approves development of the proposed underground block cave mine.
• December 2005 - construction and development of the underground block cave mine commenced
• January 2009 – the project is slowed at a result of the global financial crisis
• September 2010 – Rio Tinto Board approves ramp-up of the project. Underground mine expected to be fully operation in 2013.