unconsolidated surface deposits
Surface deposits such as moss, peat, sand, gravel, silt, or mud.
BS, 7
unconventional mineral deposit
A mineral deposit of such unusual grade, mineralogy, or geologic setting
that experienced mining personnel would not consider it to be similar to
any known deposit type. Barton
Greasy or soapy to the touch, as certain magnesian minerals.
Standard, 2
a. A diamond the original shape of which has not been altered
artificially. Long
b. Unadulterated.
A theory proposed by Van Bemmelen (1933) that explains the structural and
tectonic features of the Earth's crust by vertical upward and downward
movements caused by waves that are generated by deep-seated magma.
AGI
See:undermanager
Sprays located on the rear corners of the shovel at the sides of the
continuous miner and aimed towards the front of the gathering arms to
suppress dust by wetting the coal. SME, 1
Rock that remains unbroken inside the neat lines in a tunnel or shaft
after firing a round of explosive shots. CF:overbreak
Insufficient burden of rock in relation to the explosive charge, resulting
in a blown-out shot or a premature shot through shock of a neighboring
charge of a blast pattern, often yielding less work than expected.
a. An air crossing in which one airway is deflected to pass under the
other. BS, 8
b. The lower airway of an air crossing. See also:air crossing
BS, 8
c. An undercast is nothing more than an inverted overcast. Undercasts are
not considered to be as efficient as overcasts, owing to the tendency of
water to collect in them. CF:overcast
Haulage in which the chains are placed beneath a mine car at certain
intervals with suitable hooks that thrust against the car axle.
Stoces
A drive is underchained when it incorporates a chain of substantially
lower rating than that indicated by normal selection procedures.
Jackson, 1
a. A layer of fine-grained detrital material, usually clay, lying
immediately beneath a coalbed or forming the floor of a coal seam. It
represents the old soil in which the plants (from which the coal was
formed) were rooted, and it commonly contains fossil roots (esp. of the
genus Stigmaria). It is often a fireclay, and some underclays are
commercial sources of fireclay. Syn:underearth; seat earth; seat clay;
root clay; thill; warrant; coal clay; warrant clay. AGI
b. A bed of clay, in some cases highly siliceous, in many others highly
aluminous, occurring immediately beneath a coal seam, and representing the
soil in which the trees of the Carboniferous swamp forests were rooted.
Stigmarian roots commonly occur as fossils in underclays, many of which
are used as fireclays. See also:fireclay
A thin, dense, nodular, relatively unfossiliferous fresh-water limestone
underlying coal deposits, so named because it is closely related to
underclay. AGI
S. Wales. An argillaceous shale forming the floor of many coal seams.
underconsolidated soil deposit
A deposit that is not fully consolidated under the existing overburden
pressure. Not yet in equilibrium with existing physical environment. Still
being compacted. ASCE
A short sluice much wider than the main sluice and set on a steeper grade,
generally at right angles to the main sluice. It is designed to save fine
gold that does not readily settle. See also:table
a. To remove a horizontal section of kerf in the bottom of a block of coal
to facilitate its fall. See also:underhole; undercutting. BCI
b. To undermine, to hole, or to mine. To cut below or in the lower part of
a coalbed by chipping away the coal with a pick or mining machine.
Undercutting is usually done on the level of the floor of the mine.
See also:cut; undermine. Fay
c. A machine cut along floor level in a coal seam to ease its removal by
hand, machine, or shotfiring. See also:holding
d. Excavation of ore from beneath a larger block of ore to induce settling
under its own weight. Nelson
e. In stoping, removal either of footwall or of the lower part of a a
flattish lode, bed, or seam of ore or coal, thus facilitating detachment
of the portion left hanging. Method used in block caving to induce caving
in. Pryor, 3
f. To enlarge a drillhole at a depth that has been previously drilled.
A device for passing a fine spray of compressed air and water to dilute
the combustible gases and allay the coal dust in the track of a
coal-cutter jib. The spray is passed through a modified whale-type jib.
Nelson
The ignition of an explosive mixture of combustible gases and air in the
undercut of a coal cutter due to frictional sparking. Combustible gases in
dangerous quantities often exist in a machine undercut.
See also:whale-type jib