Road Work and Construction Aggregate

Gravel mine for road project

After my post on the Berkeley Pit in Butte, Montana berkely-pit-butte-montana it is worth considering another resource society demands - gravel aggregate. When I was taking classes on economic geology, my professor pointed out that while we students were excited about finding gold, copper, diamonds, oil, coal or any number of things that glitter or can be burned, there was money to be made investigating gravel. It was a resource in high demand everywhere.

To put gravel into perspective: Peabody Energy recently submitted the winning bid for mining a coal deposit in the Powder River Basin of northern Wyoming with a bid of $0.95 per mineable ton. A mineable ton of gravel in western Washington will typically be on the order of $1.50 with some variability due to location and a range of quality. Of course getting to the coal seam requires stripping of many tons of rock per every ton of coal.  

In my case as a geologist it turns out that exploration and assessment of aggregate (gravel) and bedrock for construction has dwarfed my explorations for metals. My metals work has been limited to providing interpretations of the geology of deposits someone else already found in order to inform further explorations that was then done by others. I should add in most cases my interpretations were such that they could be termed bad news for the potential for further rich finds.

The gravel mine pictured above is a classic road construction mine. A source for road material was required for the specific project, and if a source could be found near the project, a lot of tax dollars would be saved on construction costs. Hence, a thin gravel unit close to the site became attractive even though it was otherwise not a particularly noteworthy deposit.

What if a nearby deposit could not be found? One solution would be to pay a lot more for hauling material from a distant source or alternatively redesign the project so that a lot less aggregate material is required, or design the project so that otherwise poor quality material could be used. This is typical work for road engineers and work that geologists are sometimes called upon to support. For the road project pictured above, a source of material was available very near the proposed road construction site.