Statistical software boosts gold mine output

Paul Boughton
Adjusting ramp grade at an Australian gold mine improved haul speeds by 2.6 per cent. Eston Martz reports
Newcrest Mining Limited ( ) is one of the world's top 10 gold mining companies and currently Australia's largest gold producer. Newcrest's Cadia Hill mine, the second-largest open pit gold-copper mine in Australia, produces approximately 300,000 ounces of gold annually.
Newcrest applies the Six Sigma quality improvement methodology and Minitab Statistical Software ( ) to keep the Cadia Hill facility running as efficiently as possible, and to safeguard their prominent role in the gold industry.[Page Break]
Processing ore
Many times per day, a fleet of large haul trucks descends a narrow ramp to the bottom of the Cadia Hill open pit, where each truck picks up an average of 225tons of ore to carry back up the ramp to a crushing machine for processing.
The speed of the loaded trucks ascending the single-lane ramp varies from 8 to 14 kilometres per hour.
Slower trucks, of course, take longer to deliver their payloads to the crusher. Even worse, each slow truck delays all the trucks behind it, hampering the performance of the entire fleet and resulting in a serious loss of productivity.
Minitab’s project team began by identifying the variables that might affect truck speed. They collected data to determine which factors had the most impact, using Minitab to plan their data collection process, determine the sample sizes they needed, and test their statistical hypotheses. They then selected five trucks for on-board data collection.[Page Break]
Collecting data
Team members rode along in the trucks over a two-week period, collecting intensive data using laptops, GPS units, and other equipment.
The team now began testing solutions - and confirming their results. They altered the grade of small sections of the haul ramp, then measured truck speeds over the altered sections.
Comparing the before-and-after speeds with Minitab's 2-sample t-test showed that the grade adjustments increased truck speed significantly.
The team also devised a clear way to identify faulty fuel injectors. They ran each truck at 700rpm and measured injector timing between all 16 cylinders.
Minitab's statistical power and easy-to-understand graphics helped make significant strides in boosting productivity at Newcrest's Cadia Hill mine.
Using Minitab to plan its experiments and analyse its data at each step, the company proved that reducing the grade of the haul ramp from 10.22 to 9.9 per cent in the test section resulted in a 2.6 per cent increase in truck speeds, and reduced variation in truck speed by 7 per cent.
Now the entire haul ramp is being checked and improved, and any sections with a grade of more than 10 per cent will be reduced to 10 per cent or lower. This adjustment is predicted to save at least 8.3 seconds per full uphill trip.
Eston Martz is Senior Creative Specialist with Minitab Inc, State College, PA, USA.
Fig. 1.  Cadia Hill mine produces about 300,000 ounces of gold annually.
Fig. 2. Minitab's easy-to-understand graphics can help make significant strides in boosting productivity.

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