Print8.2.5: Stone for Construction, Chemical, and Other Uses
Before leaving this lesson on open pit mining, I want to mention an important application of this method – stone for construction, chemical, and other uses. You’ll recall from our initial discussion on mining methods that I told you that the common term for this mining is quarrying, not open pit mining. As mining engineers, that does not thrill us because quarrying is the correct term for the mining of dimension stone. However, it doesn’t much matter what we think, because millions of people use the word quarry and quarrying to refer to these open pit operations where stone is mined. Frankly, I suggest that you surrender, and refer to them as quarries as well! That’s what I am going to do here!
If you recall the graphic at the beginning of Lesson 8.1 in this module on surface mining, these stone quarries account for more than a third of all mines in the U.S., numbering over 6000! The majority of the stone that is mined is crushed and used for construction – roadbed, concrete, bituminous concrete, erosion control, and so on. Limestone and sandstone are typically mined, but in some areas, an igneous rock known as trap rock is mined. These construction uses are relatively low value, with the product selling for around $10 per ton. A small but important market exists for chemical grade limestone, manufactured sand, and specialty products such as kitty litter or the small grains incorporated into the surface of roof shingles. These markets will pay upwards of hundreds of dollars per ton for the mined product. Given the importance and size of the quarry industry, I wanted to make a few additional comments on this application of open pit mining.
Everything that we have discussed under the topic of open pit mining applies to quarries, i.e., open pits in which crushed stone is mined. The planning, engineering, equipment, and so on, are the same. Most quarries are smaller than the large open pit mines for recovering metals, and as such, the equipment selection may be different. Wheeled loaders are more likely to be used than shovels, and the haul truck capacity will be smaller. Hydraulic excavators may be used, but it would be rare to find a shovel. The safety, health, and environmental challenges are similar, and the engineering design and production engineering is similar. Looking at this quarry, for example, it would be difficult to distinguish it from any other open pit mine.
If you take MNG 441, you will learn more about the design of these open pits. Also, we offer an elective course focusing on aggregates, with an emphasis on stone quarries.