How is Limestone Mined?
Limestone quarrying occurs above and below ground. Since mineral rights are separate from property rights, quarries can use underground mining to remove rock underneath land they cannot purchase. Underground mining is also used if the desired rock unit is deep enough that removing the overburden (waste rock) is too expensive.
Limestone quarries require blasting, because the rock is too hard to remove with heavy equipment. Surface mines begin by blasting out a small depression, and growing this hole wider and deeper until the desired rock unit is reached. Larger blasts are used at surface mines, as 100s of feet of rock are removed in one blast, yet the blasts are still contained and only create minor shaking outside the mine property. Most quarries install a seismograph by nearby houses that is independently measured by geologists to ensure the shaking is not strong enough to cause damage.
This limestone quarry in Carmel, IN has both above ground and underground operations quarry in Carmel, IN. All limestone mined here is used to make cement and concrete around Indianapolis. The mine exposes the sedimentary rocks hidden below the city. In the background is an abandoned tunnel within the quarry pit. Click for a larger image. (Photo: IUPUI Earth Sciences.)
Underground mines are more expensive to operate. Risks of injury are higher, and less material can be removed because "pillars" of the desired rock must be left behind to prevent the mine shaft from collapsing. Underground quarries have huge mine shafts, large enough to drive heavy equipment down into them. Smaller amounts of explosives are used in underground mines to prevent collapse, injury, or damage to the surface.
Sand and Gravel Quarries
Another dominate form of quarrying in Indiana is sand and gravel operations. These operations are actually mining materials deposited by the several periods of glaciation within Indiana. When the glaciers melted, their outwash deposited large amounts of sand and gravel once trapped within the ice. Many of these sand and gravel deposits were trapped in these outwash areas, some of which follow present day rivers; others are located away from present day rivers.
In central Indiana, several sand and gravel operations are located along the White River, which served to drain glacial melt water. Extracting this material is easy, since it is the top most layer of material.