The specified maximum number of feet of borehole a single diamond- or
other-type bit may be allowed to drill in a specific-type rock, as
predetermined by the drill supervisor. Long
See:controlled velocity roller conveyor
A mosaic in which aerial photographs or images have been adjusted,
oriented, and scaled to horizontal ground control to provide an accurate
representation with respect to distances and distortions. It is usually
assembled from photographs that have been corrected for tilt and for
variations in flight altitude. See also:mosaic
A paradigm of mine waste management (based upon the eventual oxidation of
exposed sulfidic rock and mine wastes) that states that a slow release of
contamination over time may be superior to complete containment.
Connolly
When airways are arranged in parallel and a prescribed quantity of air is
made to flow through each branch. CF:natural splitting
Hartman, 2
controlled velocity roller conveyor
A roller conveyor having means to control the velocity of the objects
being conveyed. Syn:controlled gravity conveyor
See also:roller conveyor
Any mechanical or electrical device that is part of or added to a machine
or device for automatic regulation or control.
That at which the key machine in a series arranged for continuous ore
processing is set to work. The control function may be for quantity
passing per time, ratio of size reduction from feed to discharge, or for a
necessary physical or chemical change of state of solid or liquid phase of
the process. Pryor, 3
In flotation, that portion of an automatic feedback control system that
compares functions of a controlled variable and a command and adjusts a
manipulated variable as a function of the difference. It includes the
reference input elements, summing point, forward and final controlling
elements, and feedback elements. Fuerstenau
Person who maintains depth and composition of cryolite bath in aluminum
reduction pots within limits favorable to efficient aluminum production.
DOT
In quarrying, control on fracture is based on the experimental
determination of the type and the grade of explosive, the loading ratio,
and the pattern of boreholes. Streefkerk
Any station in a horizontal and/or vertical control system that is
identified on a photograph and used for correlating the data shown on that
photograph. AGI
In any continuous process, samples taken often enough (whether by hand or
mechanically) so that the operation process may be guided by the samples
and weights of the materials involved. Newton, 2
a. A process of mass movement of portions of any fluid medium (liquid or
gas) in a gravitational field as a consequence of different temperatures
in the medium and hence different densities. The process thus moves both
the medium and the heat, and the term convection is used to signify either
or both.
b. In hydrothermal systems, the flow of water around and through heated
zones adjacent to plutons in response to thermal gradients and controlled
by porosity-permeability, salinity, fluid viscosity, and allied factors.
The flow is generally down along the periphery, toward the system at
depth, and upward along and through its central portions, possibly
completing more than one loop. AGI
a. A thermally produced fluid flow.
b. A closed circulation of material sometimes developed during convection.
Convection currents normally develop in pairs; each pair is called a
convection cell. Leet, 1
A system of mining established for many years in British coal mines. The
longwall face is undercut, blasted, and loaded by hand to a face conveyor.
The conveyor is then moved forward ready for the next day, the packs are
built and the back props withdrawn. Such faces still produce about 60% of
the total output and is known as conventional machine mining. It has the
disadvantage that there are limits to production because it is cyclic
mining, e.g., it involves separate operations as enumerated above.
See also:turnover; continuous mining. Nelson
The cycle of operations that includes cutting the coal, drilling the shot
holes, charging and shooting the holes, loading the broken coal, and
installing roof support. Also known as cyclic mining. Woodruff
A drilling fluid containing essentially clay and water. Brantly, 1
a. The gradual decrease in the vertical distance or interval between two
specified rock units or geologic horizons as a result of the thinning of
intervening strata; e.g., the reduction in thickness of sedimentary beds
(as measured in a given direction and at right angles to the bedding
planes), caused by variable rates of deposition or by unconformable
relationship. AGI
b. Loss of height when a coal seam is extracted on a longwall face, as the
roof lowers and the floor lifts. Convergence is an important factor in
thin-seam mining.
c. Applied to the diminishing interval between geologic horizons. In some
instances, this is due to an unconformable relationship and in other
instances to variable rates of deposition. AGI
d. The line of demarcation between turbid river water and clear lake
water, which denotes a downstream movement of water on the lake bottom and
an upstream movement of water at the surface. AGI
e. In refraction phenomena, the decreasing of the distance between
orthogonals in the direction of wave travel. This denotes an area of
increasing wave height and energy concentration. AGI
f. In paleontology, resemblance that cannot be attributed to a direct
relationship or to genetic affinity. AGI
g. In oceanography, an area or zone in which the water sinks slowly
downward from the ocean surface. Schieferdecker
See:isochore map
¾ > 4@ –àÑ (DICTIONARY TERMS:convergence recorder An appliance for measuring cha
[\B]convergence recorder[\N]
In optical microscopy, a condensing lens causes light to converge at a
point within a sample to display optical interference patterns or to
enhance the Becke line.