30 computer systems/software
Statistical software helps boost gold mine output
Adjusting ramp grade at an Australian gold mine improved haul speeds by 2.6 per cent which helped save more than $835 000 in one year. Eston Martz reports.
the second-largest open pit gold-copper mine in Australia, produces approximately 300 000 ounces of gold annually.
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But its low-grade ore requires costly bulk mining and treatment techniques. 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.
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
ewcrest 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,
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.
Newcrest Mining tasked Six Sigma Black Belt James Kovac to reduce that variability and increase the average speed of the ascending trucks.
Kovac and his 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.
Collecting data
Team members rode along in the trucks over a two-week period, collecting intensive data using laptops, GPS units, and other equipment.
They determined that two factors had a major impact on truck speed: the slope of the ramp, and the trucks’ fuel injectors.
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. Then they switched off each cylinder in turn, leaving the other 15 to maintain the 700rpm.
If the remaining cylinders were not significantly affected when one was switched off, that cylinder was underperforming and therefore needed a new fuel injector.
The test has now been incorporated into fleet maintenance procedures at the gold mine, using control charts produced by Minitab macros to quickly display results.
Results
Minitab’s statistical power and easy-to-understand graphics helped Kovac and his team make significant strides in boosting productivity at Newcrest’s Cadia Hill mine.
Fig. 1. With Minitab Statistical Software, Newcrest Mining can get an additional load of ore per truck each day from its 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
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