The future: Argyle as an underground operation

It is planned that Argyle will conclude mining in the AK1 open pit in 2010. At this time it will no longer be viable to continue accessing the ore body through an open pit operation because the lamproite "pipe" narrows and continues at depth. For this reason, 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 of the underground block-cave mine commenced immediately after approval by the Rio Tinto Board and is expected to be completed in 2010. Once in production, the underground mine will extend Argyle’s mine life to at least 2018.

The process

Working toward an underground future began in 2001, when Argyle embarked on a pre-feasibility study that examined the full range of underground alternatives and transition strategies.

The pre-feasibility study was presented to the Rio Tinto investment committee in February 2003 and resulted in approval and funds to:

• Complete a full feasibility study into developing a 'block cave' underground mine.
• Construct an exploratory decline, which will confirm design criteria, reduce risks of delay and produce data to contribute to the full feasibility study.

Both the exploratory decline and the full feasibility study were completed in 2005 and the decision was made in December to proceed with development of an underground mine.

The full feasibility study addressed a comprehensive range of technical, economic, social and governance aspects and therefore constituted a significant undertaking.

Milestones in the process of determining underground feasibility included:

• 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