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St Ives mine, Australia - Mining Weekly

Friday, 21 October 2016

Name: St Ives mine.

Location: The St Ives mining operations extend from 5 km to 25 km south-south-west of Kambalda, in Western Australia.

Controlling Company: Gold Fields.

Brief Description: St Ives is a well-established operation, comprising a mix of ‘owner-mined’, openpit and underground operations supplying the Lefroy carbon-in-leach mill, which has a capacity of 4.7-million tonnes a year. It is estimated that the current known mineral reserves will be depleted in 2020.

Brief History: Gold was discovered at the Kambalda Red Hill camp in 1897. During the following ten years, other gold-bearing locations, such as Victory, were discovered.

The Victory-Defiance complex (Leviathan area) was discovered in 1981. Gold production started at St Ives using a 500 000 t/y treatment plant located at the Kambalda nickel concentrator site, which was later expanded to 1.2-million tonnes a year.

In 1988, a new 3.1-million-tonne-a year carbon-in-leach facility was built 25 km south of Kambalda at St Ives.

A two-million-tonne-a-year heap-leach facility was commissioned in 2001, when Gold Fields acquired St Ives. The 4.8-million-tonne-a-year Lefroy mill was built in 2004 and commissioned in early 2005.

An aggressive exploration programme was started in 2006, with full field air core drilling, the Cave Rocks and Belleisle underground mines were established in 2007. The introduction of the consolidated Leviathan openpit area started in 2008. A year later, the Athena-Hamlet deposit was discovered. This was followed by continued discovery and growth at the Hamlet deposit and the start of the Athena mine, with the first ore intersected in May 2010. The Athena mine reached commercial levels of production in September 2011. The Hamlet development intersected first ore in October 2011, as part of a new mine development programme.

In 2012, stoping started at Hamlet, and Cave Rocks’ life-of-mine (LoM) was extended, and an early-stage discovery was made of a new camp – the Invincible deposit. In addition, conversion to openpit owner mining was completed and heap-leach processing stopped.

The ongoing exploration strategy delivered the Invincible deposit in 2013. First production was achieved at the deposit in the first quarter of 2015. Depth and lateral extensions at Invincible have been identified and, along with the newly discovered Invincible South underground deposit, will be actively explored as part of the 2016 exploration programme.

Products: Gold.

Geology/Mineralisation: Archaean orogenic greenstone gold hosted in several different styles of mineralisation, with lode, supergene and palaeoplacer-style deposits characterising the range of orebody types.

Reserves: Proven and probable reserves as at December 31, 2015, were estimated at 17.60-million tonnes, grading 2.72 g/t gold.

Resources: Mineral resources as at December 31, 2015, were estimated at 29.12-million tonnes, grading 3.35 g/t gold.

Mining Method: Conventional drill-and-blast with truck-and-shovel mining techniques are used at all openpits.

Underground mining at St Ives is predominantly mechanised and conducted by long-hole open stoping, with subordinate cut-and-fill and room-and-pillar stoping for the shallower dipping orebodies.

Major Infrastructure and Equipment: St Ives consists of three openpits, one main underground mine and one gold processing plant with a capacity of 4.7-million tonnes a year, consisting of a semiautogenous mill, gravity circuit and a five-stage carbon-in-pulp circuit. Gold is recovered by electrowinning.

Tailings are currently stored in two paddock-type facilities until a newly approved in-pit tailings storage facility starts operations at Leviathan, which will meet current LoM requirements.

Prospects: Ongoing extensional and brownfield exploration continues and could increase the LoM.

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