MN Sand & Gravel

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Aggregate Mining

Sand and Gravel

The largest mining industry in Minnesota is Aggregate Mining. Getting the quantities and quality of sand and gravel (or crushed stone) necessary for construction have resulted in a statewide effort to locate all of the deposits that are readily available in Minnesota. The Metro counties have been mapped for likely resources and the process is spreading to outstate Minnesota. In the photos below sand and gravel in Maple Grove is mined for construction projects in the Twin Cities area.

In the photo below right part of the mine has been reclaimed with the downtown buildings of Maple Grove, parking lots and ponds. The elevation of the city steets is about 20 to 60 feet less than before the mining started. All gravel is not created equal. In the photos you should be able to see different layers identified both by color and by size. Much of the color difference is due to the composition of the gravel. Glaciers deposited different layers of gravel with the composition depending on the source of the glaciers. Glaciers that traveled over Lake Superior and eastern MN will deposit gravel consisting mostly of basalt, rhyolite and granite (and of course the treasured agate). Glaciers that traveled over western MN will deposit gravel containing limestone and shale. Shale is an unacceptable rock for concrete, asphalt mixtures or as a base for buildings because it will absorb water and then swell. As it increases in size it will cause "popouts" in roads or buildings.

The quarry in the photos just above and below is for crushed limestone. The quarry is located in Burnsville, just off Cliff Road and I35W. Sand used in construction often does not have large enough pieces to provide the correct mixture for road bases or asphalt mixes. In these situations adding crushed limestone can provide the necessary mixture of sizes. In addition the "fines", the powder from the crushed stone, packs very hard when mixed with the larger rock, providing an excellent base for roads. This base drains water very well and is very stable. The limestone in this quarry is not used for dimension stone - stone used directly in building structures - because there are too many joints. The limestone here is mined in a fashion very similar to the taconite mining of northern Minnesota. The rock is blasted and then loaded into large haul trucks and taken to a crusher and sorter. Of course the further work of processing ore. The machines are smaller than those currently used in the iron mines.

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