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Sur Face Quarries: Types of Quarries.—The greatest tonnage of stone is from Sur face quarriesface quarries but there is an increasing number of underground mining operations. Sur face quarriesface workings are of the bank and pit types. Quarries developed below grade require the removal of overburden to expose the stone as do most bank deposits. Overburden may vary in thickness from a foot or two to 40 feet or more. Mining operations are scattered geographically and are mainly in limestone deposits, notably in Kentucky, Pennsylvania, Missouri and Tennessee.
Mines generally have entries on the horizontal, many times from an outside quarry Floor and many workings continue on underground at that level. Some mines are inclined to follow a dipping stratum of rock. Sur face quarriesface quarries and underground mining are sometimes worked at the same location, winning high-grade stone from underground for special markets, while quarrying lower chemical-grade stone for use as aggregates.
Types of Quarries.—Quarrying of dimension stone is usually accomplished in open pits but there are several tunnel operations. High explosives are not used and the stone is removed from the mass in rectangular blocks which are quarried down to specific dimensions. Quarries range from a few to several hundred feet in depth and the quarry floors may be horizontal or may slope up to 45 degrees. Quarrying practices have not changed radically, industry-wide, for many years but there have been improvements in equipment that have contributed to efficiency generally and there have been substantial changes in methods among some larger operations since 1940. |
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