The Bingham Canyon Copper Mine, Utah, USA For this exercise, you will use Google Earth and Microsoft Excel to calculate the quantity of rock removed from the Bingham Copper Pit, one of the world’s largest open-pit mines. In addition, you will be able to estimate the percentage of copper ore disseminated in these rocks and the quantity of rock that must be removed for each ton of copper produced.
To locate the Bingham Copper Pit, enter the following coordinates into the query bar of Google Earth:
40.520978, -112.150242 (don’t forget the negative sign in front of the longitude coordinate!)
Fig. 1. Google Earth image of the Bingham Canyon copper mine (“Bingham Pit”), Utah, USA.
Congratulations! You have landed at the bottom of the Bingham Copper Pit southwest of Salt Lake City, Utah, USA! Move your cursor around in the bottom of the main pit to locate the minimum elevation and write it down in your notes.
1. Zoom out so you can examine the full extent of the mine. As you zoom out, notice that the image of the eastern half of the mine pit and the area east of it are much higher resolution than the western mine pit and areas west of it. The area east of the mine is a heavily populated portion of the Salt Lake Valley and has been photographed at high resolution by the National Aerial Photography Program whereas the mountains west of the mine are largely uninhabited, so have not been a priority of the NAPP program.
2. The north-south boundary separating high and low resolution imagery is a convenient marker we can use to help construct a topographic profile across the mine.
3. To construct a topographic profile, begin by enabling the metric measures in Google Earth. This is accomplished by clicking on ‘Tools’ on the menu bar at the top of the page, the clicking on ‘Options’. When the ‘Options’ dialogue opens, you will see in the lower left of the dialogue an ‘Elevation’ option. Choose Meters, Kilometers, then ‘Apply Settings’.
4. Next, you should start up the Microsoft Excel program as you will be entering data generated from Google Earth into this spreadsheet. When the spreadsheet opens, label one column ‘Distance (m)’ and one column ‘Elevation (m)’.
5. Next, return to the Google Earth window and enable the ‘Measure’ tool by clicking on the ‘Tools’ menu, the clicking the word ‘Measure’ (or simultaneously using ‘ctrl + 6’ keys on your keyboard). When the ‘Measure’ dialogue box appears, use the drop down window to choose meters as the units of distance. Also select the tab labeled ‘Path’.
6. Note that the ‘Measure’ icon on your image appears as a box with tick marks along the mid-points. This box can be used to add points along your profile with approximately equal spacing; simply click the first point, then move the box until one of its tick marks is aligned with this point; now click again. The next point is located approximately the distance from the center of the box to a tick mark. This distance varies depending on the level to which you are zoomed into the image. In addition, from point to point, the distance is not precisely the same, but it is close enough for the exercises we are attempting to conduct. If you add a point and want to delete it, simply right click on your mouse and it will disappear.
7. You can determine the approximate spacing to each point by noting the cumulative distance along your profile and entering this distance at each point into the spreadsheet. You will construct an east-west profile across the center of the Bingham Pit. Begin by clicking a point along the east or west edge of the mine pit. When you click this point, note the distance along your profile (the first point will be 0) and the elevation of the point (read along the bottom of the image next to the latitude and longitude). Enter the distance and the elevation into their respective columns in your spreadsheet. Repeat this process until you have traversed the mine pit from north to south.
8. Note that the excavation is approximately cone-shaped. As a consequence, we can estimate the volume of rock removed from the mine by calculating the volume of this cone. Use the Internet to locate the formula for the volume of a cone. Using this formula, calculate the volume of rock removed from the pit by determining the maximum depth of the pit from rim to center. Answer the following questions to help you determine the volume and mass of rock removed from this pit:
a. What is the maximum elevation (meters) of the pit rim? ca. 2,401 m (NOTE: this value may vary somewhat depending on where along the pit rim students take their measurement)
b. What is the minimum elevation (meters) in the bottom of the pit? Ca. 1,681 m (NOTE: this value may vary somewhat depending on where within the pit students take their measurement)
c. What is the depth of the main pit (meters)? ca. 720 m
d. What is the radius of the main pit (meters)? ca. 1,490 m
e. Using the formula for the volume of a cone, what is the volume of rock removed from this pit? ca. 1,672,388,443 m3 (NOTE: quantity may vary somewhat depending on input values, but order of magnitude should be about 1.6 x 109 m3)
f. You have already learned in lab and lecture that density = mass ÷ volume. If the density of rock in Bingham Canyon is 2.8 g/cm3, calculate the mass of rock removed from this pit. Note that you will need to do some conversions to get proper units in your answer.
(NOTE: 1 m3 of rock with 2.8g/cm3 density has a mass of 2.8 metric tons; therefore the mass from volume above is 4,682,687,641 tonnes.)
g. Since mining began in 1904, 15.4 million metric tons of copper have been smelted from this mine. What percentage of the total rock mass mined from the pit was copper? ca. 0.33%
h. How many metric tons of rock must be mined to yield one metric ton of copper? ca. 300T of rock must be mined for each tonne of copper.
i. Did this calculation surprise you? Explain your answer. Students should elaborate a response here.
j. Note that reported ore grade of the Bingham Pit is 0.6%. How does this compare to your estimate above? Discuss potential reasons for this disparity. My estimate is about half that reported. Most likley due to errors in estimates above; could also be due in part to fact that early ores mined from the pit were very high grade, the average 0.6% grade takes into account these very rich ores. The ore grade continues to become lower over time as the richest portions of the deposit are mined.