The Ernest Henry open pit: 1998 – 2011
Ore was mined from the pit using traditional drill and blast and truck and shovel methods. Blasting occurred on an as needs basis and the broken rock was then hauled from the pit by 140 tonne dump trucks with a carrying capacity of around 220 tonnes each for processing at our on-site concentrator.
The project was based on an optimised pit design to recover as much as was economically possible of the Ernest Henry copper gold orebody. We completed mining the open pit in December 2011.
The completed open pit mine is 1.5 kilometres by 1.3 kilometres across at its widest points and 530 metres deep. Close to 700 million tonnes of material was mined throughout the mine's life.
Areas of the pit are still maintained so that the underground portal or doorway, which is located in the pit, can continue to be utilised as the main point of entry for our underground mine.
Transitioning to underground: 2009 – 2014
With the economic life of the open pit due for completion in 2011, we announced in 2009 we would invest $589 million to transition to underground shaft mining as well as magnetite processing.
We constructed a magnetite processing plant adjoining our existing concentrator and exported our first magnetite concentrate in June 2011. We later suspended magnetite production in August 2013 when the business case was no longer supported by market conditions. Parts of the magnetite circuit have since been reconfigured into the concentrator circuit to improve existing copper concentrate production.
When the Ernest Henry open pit mine was completed in December 2011, we commenced trucking ore from underground via a decline at rates of around three million tonnes of ore per annum, producing around 25,000 tonnes of copper and 35,000 ounces of gold in concentrate annually. We also worked simultaneously to construct our kilometre-deep underground hoisting shaft and associated infrastructure.
In June 2011 we acquired the nearby Mount Margaret Mining Project, which we developed as a satellite open pits project to increase our production profile while our underground shaft development project was undertaken. We commenced production at Mount Margaret in July 2012 and placed the operations into care and maintenance in March 2014 following completion of the E1 North open pit.
Steady state operations: 2014 and beyond
Today Ernest Henry Mining is a low-cost underground copper and gold producer with a current life-of-mine expectation of 2026. While our operations have entered a 'steady state' phase, we continue to explore ways to improve our performance and operations across the site and into the future.