Appendix:Dictionary of Mining, Mineral, and Related Terms/P/6

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practical shot

In coal mining, a shot for which a hole has been drilled in a direction selected with reasonable care and filled with powder and tamped with the same degree of care.

prairie soil

Soil transitional between a pedalfer and a pedocal.


a. A translucent dull green or yellow-green variety of chalcedony.

b. Crystalline quartz containing abundant hairlike crystals of actinolite. Syn: edinite; mother-of-emerald.

praseodymium oxide

A rare earth that, together with zirconia and silica, produces a distinctive and stable yellow color for pottery decoration.


a. A green alteration product of iolite.

b. A greenish foliated alteration product of cordierite.


A green chromium variety of common opal from Australia, Hungary, and Brazil. Also spelled prase opal.

Pratt hypothesis

A suggested type of hydrostatic support for the Earth's solid outer crust in which crustal density is supposed to be greater under mountains than under oceans. CF: isostasy; Airy hypothesis.

Pratt truss

See: N-truss.

Prayon process

The most common phosphoric acid dihydrate process for phosphoric acid production using sulfuric acid with naturally occurring phosphate rock.


Aeration of water or ore pulp before treatment, notably by froth flotation where deoxygenated water is used (e.g., from under a frozen lake). Also used to stabilize ore pulp containing unstable sulfides before cyanidation.

prebaked anode

Anode produced by binding together crushed petroleum coke and coal-tar pitch in a mold under pressure; subsequently baked to 1,000 to 1,200 degrees C; used in a metallurgical electrical furnace and replaced as a unit when consumed; in the production of aluminum metal, the anode is attached to a metal rod.


Pertaining to the time period prior to the initiation of a blast.

preblast survey

Documentation of the existing condition of a structure prior to exposure to blasting vibrations.

Precambrian shield

Rocks older than the Cambrian age. Name refers to the great shield-shaped areas of ancient mineral-bearing rocks. These ancient rocks occur in many parts of the world.

precementation process

Grouting the strata to control ground water prior to the start of construction or excavation, such as shaft sinking. Precementation has been used in South Africa to depths of 4,000 ft ( 1,200 m) and considerable savings have resulted. See also: cementation sinking.


Descriptive of the finest variety of a gem or mineral. Syn: oriental; precious stone.

precious garnet

Brilliantly purple almandine.

precious metal

Any of several relatively scarce and valuable metals, such as gold, silver, and the platinum-group metals.

precious olivine

See: peridot.

precious opal

A gem variety of opal that exhibits a brilliant play of delicate colors by diffraction of light from close-packed 150- to 300-mm spheres of cristobalite-tridymite. The color of the bulk material may be black or white. CF: common opal.

precious serpentine

A pale or dark oil-green, massive, translucent serpentine.

precious stone

See: gemstone.

precious topaz

a. Genuine topaz as distinguished from topaz-colored quartz (jewelers' topaz).

b. An incorrect term for yellow to brown sapphire.

precious tourmaline

Dark-colored gem variety of tourmaline.


Any agent, as a reagent, that when added or applied to a solution causes a precipitate of one or more of its constituents.


a. The operation, act, or process of adding a chemical or chemicals to an aqueous solution to react with a dissolved material in the solution and remove the resulting new solid matter by settling.

b. The solids resulting from the precipitation process.

precipitated sulfur

Sulfur precipitated from calcium polysulfide solutions by hydrochloric acid and washed to remove all calcium chloride.


a. The process of separating mineral constituents from a solution; e.g., by evaporation (such as halite or anhydrite) or by cooling of magma (to form an igneous rock).

b. Exsolution. c. Water that falls to the surface from the atmosphere as rain, snow, hail, or sleet. It is measured as a liquid-water equivalent regardless of the form in which it fell.

precipitation barrier

Metal-rich water, as it moves away from the source of the metal, ordinarily comes into an environment where changing conditions of some kind cause precipitation of part or all of the metal from the water. Precipitation barriers account for the more than normal decay of hydrochemical anomalies than can be accounted for by simple dilution. They characteristically occur in spring and seepage areas where groundwaters coming to the surface encounter an environment of increased availability of oxygen, sunlight, and organic activity.

precipitation hardening

Hardening caused by the precipitation of a constituent from a supersaturated solid solution. See also: aging; hardening.

precipitation heat treatment

Artificial aging in which a constituent precipitates from a supersaturated solid solution. See also: artificial aging; progressive aging.

precipitation process

a. The manipulation of physical and/or chemical properties of a solution to cause one of the constituents of that solution to become insoluble.

b. The treatment of lead ores by direct fusion with metallic iron or slag, or ore rich in iron; performed generally in a shaft furnace, rarely in a reverberatory. It is often combined with the roasting and reduction process. See also: iron-reduction process.


In beneficiation, smelting, and refining, a person who (1) tends zinc boxes in which gold or silver that has been dissolved in a cyanide solution is precipitated; and (2) precipitates gold from cyanide solution, except that the cyanide solution is agitated with zinc dust in a mixing cone and precipitate, then turned into a filter press where the precipitate is recovered prior to the drying and refining to secure the gold.


The degree of agreement or uniformity of repeated measurements of a quantity; the degree of refinement in the performance of an operation or in the statement of a result. It is exemplified by the number of decimal places to which a computation is carried and a result stated. Precision relates to the quality of the operation by which a result is obtained, as distinguished from accuracy, but it is of no significance unless accuracy is also obtained.

precision depth recorder

A device for recording a sonic depth trace. Abbrev., PDR.

precision idler bearing

A bearing having ground races and in which the bore and outside diameter tolerances are held to ten-thousandths of an inch and the width tolerance to thousands of an inch.

precooler load

The amount of sensible heat, removed from the air in precooling.


Method used in machine mining where a coal cutter makes a cut along the face in front of a cutter loader. It may be adopted in hard coal seams or where an improvement in the +2-in (+5.1-cm) coal product is required.

precutting blade

A special blade attached to a plow that operates a little in advance of the main blades of the machine. It may be used in hard coals or to prevent the climbing of the machine, which would leave a layer of coal on the floor.

predicted 4-hour sweat rate

An index devised by the Medical Research Council of Great Britain which is based on the rate of loss of sweat from the body. It is designed to measure the physiological effect of work in near limiting conditions in hot working places, and is based on the assumption that heat stress is a function of the rate of sweating.

predictive metallogeny

See: mineral assessment.

preemption act

An act providing for a patent to agricultural lands. The act does not include mineral deposits, as they are expressly reserved.


A familiar term under the public land laws meaning exclusive.

preferential flotation

a. A name applied to a special type of differential flotation in which a mixture of two flotative, sulfide minerals is given a slight roast so that one may be oxidized, and therefore not float, and the other remain unchanged.

b. Preferential flotation may also be achieved by control of pH or by addition of an activating agent or depressant to the flotation mixer, conditioner, or cell.

preferential wetting

Applied to froth flotation when separating fine coal from coal washery slurries. The slurry or mixture is treated with a reagent that has an affinity for the material to be recovered and that will lend itself to subsequent stages in the separation process.

preferred orientation

Feature of a rock in which the grains are more or less systematically oriented by shape. A schist in which the mica plates are parallel to one another shows a preferred orientation; so does a hornblende schist in which the long axes of the hornblende crystals are parallel. See also: orientation; unoriented.

preformed rope

Wire rope in which the strands are bent to their correct lay before being laid up, so that the rope is unlikely to spin or kink.

pregnant solution

A value-bearing solution in a hydrometallurgical operation.

pregnant solvent

In solvent extraction, the metal-bearing solvent produced in the solvent extraction circuit.


The liquor resulting from leaching of ore to dissolve a valuable constituent. Term connotes such a solution when it has reached a loading sufficient to justify its removal from contact with the ore, for separate treatment to reclaim the contained values (by precipitation, ion exchange, or stripping). After this treatment, the now barren solution is returned to work, or if foul, is run to waste or regenerated. Also called pregnant solution; royals.


To heat beforehand; as: (1) to heat (an engine) to an operating temperature before operation; and (2) to heat (metal) prior to a thermal or mechanical treatment.

preheat zone

That portion of a continuous furnace through which the ware passes before entering the firing zone.


An orthorhombic mineral, Ca (sub 2) Al (sub 2) Si (sub 3) O (sub 10) (OH) (sub 2) , in which Fe replaces Al; forms botryoidal or mammillary and radiating aggregates. Occurs in: hydrothermal veins, cavities, and amygdules in basalt; veins in felsic plutonic rocks; and low-grade metamorphic rocks. Commonly associated with zeolites. Syn: aedelite.


a. A variety of mizzonite resembling prehnite.

b. Impure prehnite.

preliminary exploration

An investigation carried out along certain broad features of a coal or mineral area, with the object of deciding whether the proposition is such as to warrant a detailed or final exploration, which is often costly.

preliminary prospecting

Prospecting undertaken after scout prospecting has disclosed the existence of values. Preliminary prospecting helps to determine approx. the extent of the payable ground.

preliminary soil survey

A quick investigation of surface or near-surface conditions; no special equipment is employed. Tests are carried out on site for approximate classification of soil and are limited to visual or other simple tests. See also: detailed soil survey; general soil survey.

premature blast

The detonation of an explosive charge earlier than warranted. Premature explosion may be due to carelessness, accidental percussion, a faulty fuse, or degenerated explosives. See also: safety fuse; hangfire.

premature block

An obstruction or block in a core barrel or bit that prevents the entry of core into the barrel before the bit can be advanced far enough to cut a length of core to fill the barrel.

premature firing

The detonation of an explosive charge or the initiation of a blasting cap before the planned time.

premature set

a. The hardening of cement in a shorter time than normal or estimated.

b. This may be caused by the addition of catalysts to cement to increase setting time or by downhole temperatures and pressure that cause cement to set prematurely.

premium tin

Tin of such high purity as to rate a special bonus in the metal market.


Aggregate that has been coated with bituminous binder before spreading. See also: penetration macadam; tarmacadam.


a. The treatment of ore or coal to reject waste. See also: concentration; ore dressing; preparation plant.

b. The process of preparing run-of-mine coal to meet market specifications by washing and sizing.

preparation boss

In bituminous coal mining, a foreman who is in charge of the operations of washing and sizing coal for market at the washery plant.

preparation plant

Strictly speaking, a preparation plant may be any facility where coal is prepared for market, but by common usage it has come to mean a rather elaborate collection of facilities where coal is separated from its impurities, washed and sized, and loaded for shipment. Syn: cleaning plant. See also: coal-preparation plant; coal washer.

preparatory work

Mining operations to facilitate mining proper after having explored a deposit and having made it accessible both in strike and dip. This work is executed almost entirely within the deposit and includes making: (1) inclines and transfer stations with manways; (2) sublevel drives between the levels; and (3) various crosscuts, chutes, minor shafts, raises, winzes, and other works.


a. To shear or undermine coal so that it can be readily blasted loose.

b. Arkansas. To make a cartridge for a blast. c. Arkansas. To charge a blasthole.


The lead or stagger that exists between planing blades in the same vertical plane of a plow.

prereduced iron-ore pellet

A semimetallized pellet developed by the U.S. Bureau of Mines from taconite concentrates. The process involves rolling the concentrates into pellets, then drying, calcining, and roasting the pellets in a reducing (oxygen-deficient) atmosphere. During the heat-hardening stage, the pellets are partly converted to metal. Use of these pellets causes a considerable increase in pig-iron production. See also: iron ore.


An arrangement by which a gear level can be moved, but the resulting speed shift will not take place until the clutch or the throttle is manipulated.


Eng. Stone of suitable thickness for shaping into a tile stone without frosting; occurs in Stonesfield slate series and Chipping Norton limestone of the Cotswolds.

present value

a. The present value of a mine may be considered to be a sum of money that may be allowed for the purchase, development, and equipment of a mine, with the expectation of receiving for this capital expenditure, during the estimated life of the mine, the return of this capital plus a substantial profit commensurate with the risk involved in the venture.

b. The present value of a property is the amount that, if invested now in its purchase, would find its repayment with commensurate profit in the estimated series of annual dividends. Actuarially, it is the discounted sum of each and all those dividends, after allowance for any estimated further capital expenditure on necessary works and equipment.


For mine timbers that are exposed to severe conditions of damp, ventilation, and stress, any of several chemicals used to impregnate them to resist dry or wet rot. These include copper sulfate, creosote, salt, sodium fluoride and silicofluoride, and zinc as chloride or sulfate.


a. A smooth blasting method in which cracks for the final contour are created by blasting prior to the drilling of the rest of the holes for the blast pattern. Once the crack is made, it screens off the surroundings to some extent from ground vibrations in the main round.

b. See: controlled blasting.

press cloth

See: filter cloth.

pressed amber

Synthetic amber produced by consolidating amber fragments under pressure with an oil binder. Syn: reconstructed amber; amberoid.

pressed cameo

Similar to molded cameo, but pressed. CF: molded cameo.

pressed copal

Synthetic copal produced by consolidating copal fragments under pressure with an oil binder.


In ceramics, a worker who molds the handle, ears, and decorative reliefs to be applied to a pottery vessel before firing.

pressing machine

a. A machine that forms ceramic shapes by forcing plastic or semiplastic raw materials into a die or mold.

b. A machine in which the whole forming operation is carried out by pressing the plastic glass by a plunger forced into a die or mold. The machine may be operated by hand or it may be fully automatic.


a. The force exerted across a real or imaginary surface divided by the area of that surface; the force per unit area exerted on a surface by the medium in contact with it.

b. A commonly used short form for geostatic pressure. c. As used in mine ventilation terminology, it is sometimes defined as the available energy content of the air and as the pressure difference between two points in a ventilation current as the energy lost due to friction between two points. d. Force exerted by air per unit area, either gage or absolute. Atmospheric pressure is measured by a barometer. Measured in pounds per square inch, kilopascals, or inches of mercury.

pressure anemometer

a. An instrument for measuring the velocity of ventilating air currents in mines.

b. An anemometer indicating wind velocity by means of the velocity head exerted.

pressure arch

The driving of a narrow roadway results in the development of a pressure arch over the excavation. The strata within the arch bend slightly and cease to support the overlying beds, and the load is transferred to the solid or rock along the sides. The wider the roadway, the greater the span of the arch and its height at the crown. A similar but larger pressure arch is formed across a longwall face, with one leg resting on the solid coal and the other on the solid pack behind the coal face. See also: abutment; arch structure; load transfer.

pressure arch theory

The pressure arch theory in roof action suggests that, when a narrow heading is advanced, the layers of rock in the immediate roof deflect slightly and relieve themselves of the load of the overlying strata by transferring it to the sides of the opening by means of a pressure arch. The arch width just short of that which the higher strata cannot span and transfer the load to the sides of the opening is called the maximum-pressure arch. The depth mainly influences the minimum width of the pressure arch, although the type of overburden also plays a part. The following formula has been developed for approximating the minimum width of the maximum-pressure arch (W = minimum width of arch, in feet; D = depth of coal from surface, in feet): W = 3[(D / 20) + 20]. The equation does not apply for overburden less than 400 ft (122 m) or more than 2,000 ft (610 m) thick.

pressure balancing

When an area of a mine has been sealed off from the remainder of the workings by barriers or stoppings inserted at suitable points, it is important to prevent the circulation of air within the sealed area. This means that external air pressures must be equalized on all the seals. The object of equalizing the atmospheric pressures on the seals is attained by inserting or removing doors or brattice cloths at appropriate places. It is possible to make all the seals contiguous with a common airway by this means, so that, if they are not widely separated, they will be subjected to the same external atmospheric pressure.

pressure block

Pressure formed over the workings by masses of rock being severed from the surrounding formations, creating pressure on the pillars, walls, or other supports. Pressure blocks of large size may result from natural geological phenomena, such as faults, or may occur as a result of mining operations.

pressure blower

A machine or blower having either pistons, cams, or fans for furnishing an airblast above atmospheric pressure.

pressure bump

An occurrence when a coal pillar suddenly fails on becoming overloaded by the weight of the rocks above it. Generally, the coal is forced with some violence into the roadways and other open spaces. See also: rock bump; rock burst; shock bump; bumps.

pressure chamber

seals off an area and is furnished with means of raising or lowering the air pressure within it.

b. If the mine area to be sealed off is extensive, and the seals are widely scattered, the fact that they are subject to different pressures may be unavoidable. In this event, pressure chambers may be required on the outby side of seals. Pressure chambers are also of value when the seals cannot be made tight, because of broken or fissured ground. The principle consists of building an outer chamber by erecting a second stopping on the outby side of the seal. The air pressure in the intervening space is then controlled to prevent movement of air across the seal. c. A method of driving tunnels and sinking shafts through running sand by holding back the loose material by compressed air. The technique is no longer applied to any great extent in mining. See also: caisson sinking.

pressure creosoting

The most effective method of preserving timber by impregnation with creosote under pressure in tanks.

pressure detector

See: hydrophone.

pressure die casting

The usual die casting process in which the molten metal is forced into highly finished molds under heavy pressure by plungers, compressed air, or combined methods.

pressure dome

a. See: air dome.

b. The bonnet on a steam boiler.

pressure drilling

A process of rotary drilling in which the drilling fluid is kept under pressure in an enclosed system.

pressure drop

The decrease in pressure at which a liquid or gas is made to move between the intake and discharge of a pipeline or drill stem.

pressure equalizer

In drilling, a diaphragm connected to the fluid column by a series of ports incorporated in the design of some core barrels and preventing the entry of drilling fluids into the core-barrel-head bearings.

pressure fan

a. A fan supplying air under pressure.

b. A fan that forces fresh air into a mine as distinguished from one that exhausts air from the mine.

pressure figure

The indistinct six-rayed star produced on a mica plate after pressing with a dull point. CF: percussion figure.

pressure filter

a. A machine for removing solids from tailings; the effluent can be reused in the washery or plant. The tailings are pumped into the filter under pressure; filtration takes place and solids are deposited in the chambers. Gradually the resistance increases until a pressure of 100 psi (690 kPa) is necessary to force more tailings into the press. At this stage, the chambers are almost full of solids. The feed is cut off and the press opened to allow the cakes to fall onto the conveyor beneath the chambers. The output of the pressure filter is low.

b. A filter in which pressure is applied to increase the rate of filtration. c. A filter in which the liquid to be filtered is forced through filtering material by a pressure greater than its own weight in the filter.

pressure forging

Forging done by a steady pressure, as in a hydraulic press.

pressure gage

An instrument used to measure the force per unit area exerted by a confined fluid or gas.

pressure grouting

a. The act or process of injecting, at high pressures, a thin cement slurry or grout through a pipeline or borehole to seal the pores or voids in rock or to cement fragmented rocks together.

b. Forcing a slurry of cement and sand into subgrade or an embankment either by use of compressed air or by hydraulic pressure.

pressure head

The height of a column of liquid supported, or capable of being supported, by the pressure at a point in the liquid. See also: static head; total head.

pressure leaching

In chemical extraction of valuable ore constituents, use of an autoclave to speed processing by means of increased temperatures and pressures.

pressure per diamond

The feed pressure or load applied per diamond in a bit. The total load supported by the bit divided by the number of stones set in the bit face expresses the pressure per stone in numerical values. Also called diamond pressure; stone pressure.

pressure plate

In a clutch, a plate driven by the flywheel or rotating housing, which can be slid toward the flywheel to engage the lined disk or disks between them.

pressure process

Treatment of mine timber to prevent decay by forcing a preservative, such as creosote, zinc chloride, sodium fluoride, and other chemicals, into the cells of the wood. See also: timber preservation.

pressure-quantity survey

See: ventilation survey.

pressure ring

A ring about a large excavated area, evidenced by distortion of the openings near the main excavation. Shear cracks appear and minor slabbing of the rock takes place.

pressure shadow

The name sometimes applied to a fringe or halo differing from the groundmass that often accompanies a porphyroblast in a schistose rock.

pressure stripping

The predominant means of extracting precious metal values from loaded activated carbon in the cyanidation process. Loaded carbon is placed in a pressure column along with a solution containing about 1% NaOH. This solution is circulated through the column at 150 degrees C until the precious metal values have been removed from the carbon absorbant. The loaded strip solution serves as the electrolyte for a subsequent electrowinning step for recovery of the precious metals.

pressure surface

See: potentiometric surface.

pressure survey

An investigation to determine the pressure distribution or pressure losses along consecutive lengths or sections of a ventilation circuit. See also: ventilation planning; ventilation survey.

pressure testing

An indirect method of testing porosity and permeability of formations at elevations of proposed structures.

pressure water loader

A cartridge loader in which compressed water, rather than compressed air, is used for loading underwater.

pressure wave

A pressure produced by expanding gases moving at high velocity, the side component of which, equivalent to static pressure, may be recorded by a manometer at the side of the entry or mine passage. Syn: P wave; compressional wave.

pressure wire

Wire leading from any of various points of an electric system to a central station, where a voltmeter indicates the potential of the system at the point.


a. Said of any structure, area, or zone fitted with an arrangement that maintains nearly normal atmospheric pressure.

b. Said of any structure or area in which the pressure within is held higher than the outside pressure.


The application of load to a structure so as to deform it in such a manner that the structure will withstand its working load more effectively or with less deflection.


The Hoyer method of prestressing concrete beams, precast in a workshop with the tensioned wires embedded in them and firmly anchored.

preventive maintenance

A system that enables breakdowns to be anticipated and arrangements made to perform the necessary overhauls and replacements in good time.


The dense woody lenses in lignite that are equivalent to the vitrain in coal of higher rank.


A triclinic mineral, Ca (sub 4) B (sub 10) O (sub 19) .7H (sub 2) O(?) ; earthy to porcelainous white; conchoidal fracture. Syn: pandermite.

pricking bar

a. A bar used in opening the taphole of a furnace.

b. A rod used for removing obstructions from tuyeres and blowpipes.


A tetragonal mineral, (K,Ba)(Ti,Fe) (sub 8) O (sub 16) ; cryptomelane group; red; easily mistaken for rutile in leucite rocks; occurs at Kimberley, Western Australia.


See: iriginite.


In assaying, the bullion bead resulting from cupellation of an auriferous or argentiferous lead button.


Tin extracted from slag. Also spelled prillon.


A fuse composed of an explosive core within a textile or plastic covering. It detonates every explosive that is in direct contact with it.

Primacord-Bickford fuse

A detonating fuse having an explosive of pentaerythritetetranitrate (PETN). Used in large-scale blasting work, esp. in quarries.


a. Characteristic of or existing in a rock at the time of its formation; pertains to minerals, textures, etc.; original. Ant: secondary.

b. Said of a mineral deposit unaffected by supergene enrichment. c. Said of a metal obtained from ore rather than from scrap. Syn: virgin.

primary anomaly

An anomaly formed by primary dispersion.

primary basalt

A presumed original magma, from which all other rock types are obtained by various processes of fractional crystallization.

primary blast

A blast used to fragment and displace material from its original position to facilitate subsequent handling and crushing.

primary blasting

The blasting of solid rock, ore, or coal; blasting in situ. See also: secondary blasting.

primary breaker

A machine that takes over the work of size reduction from blasting operations; may be a gyratory or jaw breaker. Its capacity must be greater than the overall crushing plant capacity. In mines, primary ore crushing to about 7 in (18 cm) may be performed underground. See also: reduction ratio; tertiary crushing.

primary breaking

A stage in bituminous coal crushing that occurs at the entrance to a plant and consists of raw feed flowing into the primary breaker for reduction to a maximum top size of 4 in, 5 in, 6 in, or 8 in (10.2 cm, 12.7 cm, 15.2 cm, or 20.3 cm) either for washing or for other preparation purposes.

primary cell

a. A group or bank of flotation cells in which the raw feed is given a preliminary treatment, either or both of the products being subsequently retreated.

b. A cell that generates or makes its own electrical energy from the chemical action of its constituents; e.g., the voltaic cell, Deaniell cell, LeClanche cell, and dry cell.

primary clay

A clay found in the place where it was formed. CF: residual clay; secondary clay.

primary coil

a. The coil through which the inducing current passes in an induction coil or transformer.

b. A coil, forming part of an electrical machine or piece of apparatus, in which a current flows, setting up the magnetic flux necessary for the operation of the machine or apparatus.

primary creep

Elastic deformation that is time-dependent and results from a constant differential stress acting over a long period of time. CF: secondary creep.

primary crusher

a. The first crusher in a series for processing shale or other rocks. See also: secondary crusher.

b. In comminution of ore, a heavy-duty dry crushing machine capable of accepting run-of-mine coarse ore and reducing it in size to somewhere between 4 in and 6 in (10 cm and 15 cm). Heavy-duty connotes the ability both to handle large tonnages daily and to withstand very rough treatment.

primary crushing

In ore dressing, the first stage in which crushers take run-of-mine ore and reduce it to a size small enough to be taken by the next crusher in the series. Ordinarily, the Blake jaw crusher or a gyratory crusher is used.

primary crystal

The first type of crystal that separates from a melt on cooling.

primary current distribution

The current distribution in an electrolytic cell that is free of polarization.

primary dip

See: original dip.

primary dispersion

Geochemical dispersion of elements by processes operating within the Earth. CF: secondary dispersion.

primary drilling

The process of drilling holes in a solid rock ledge in preparation for a blast by means of which the rock is thrown down.

primary environment

See: geochemical environment.

primary excavation

Digging in undisturbed soil, as distinguished from rehandling stockpiles.

primary flat joint

See: L-joint.

primary flow structure

Structure of either linear or platy nature developed in igneous rocks prior to or during consolidation.

primary fluid inclusion

A fluid inclusion containing fluid trapped during original crystallization of its host mineral.

primary foliation

The variety of platy flow structure that forms during crystallization of a magma and is due to the parallelism of platy minerals.

primary gneiss

A rock that exhibits planar or linear structures characteristic of metamorphic rocks, but lacks observable granulation or recrystallization, and is therefore considered to be of igneous origin.

primary gneissic banding

Banding exhibited by certain igneous rocks of heterogeneous composition; produced by the admixture of two magmas only partly miscible or, in other cases, by magma intimately admixed with country rock into which it has been injected along bedding or foliation planes.

primary haulage

A short haul in which there is no secondary or mainline haulage; e.g., a mine is started into a hillside, using mine cars, track, and hand loaders. An empty car is placed for the loader, and the loaded car is taken to the dump manually or by machine, repeating the process for each loader. See also: face haulage.

primary metal

a. Metal produced: by direct smelting of ore; from a mine product, such as that extracted from mined ore; from reprocessing mine tailings; or from reprocessing smelter or refinery slags or residues.

b. Metal extracted from ores, natural brines, or ocean water. Also called virgin metal. c. Ingot cast from reduced and perhaps refined metal as distinct from ingot containing recovered scrap metals. d. Metal recovered as a principal or byproduct material from the processing of ores; includes metal recovered from ore processing wastes such as tailings, and downstream processing wastes such as slags and residues from the smelting and refining of the metal. Excludes metal recovered from scrap or its processing wastes (secondary metal).

primary mill

A mill for rolling ingots or the rolled products of ingots to blooms, billets, or slabs. This type of mill is often called a blooming mill and sometimes a cogging mill.

primary mineral

A mineral formed at the same time as the rock enclosing it, by igneous, hydrothermal, or pneumatolytic processes, and that retains its original composition and form. CF: secondary mineral. Syn: original mineral.

primary mineral deposit

Syngenetic ore deposit.

primary ore

Ore that has remained practically unchanged from the time of original formation.

primary ore mineral

An ore mineral that was deposited during the original period or periods of metallization. The term has also been used to designate the earliest of a sequence of ore minerals, as contrasted with later minerals of the same sequence, which some writers have called secondary. To avoid confusion, Ransome proposed the terms hypogene and supergene. Hypogene, as the word implies, indicates formation by ascending solutions. All hypogene minerals are necessarily primary, but not all primary ore minerals are hypogene; e.g., sedimentary hematite is of primary deposition even though it formed as a low-temperature precipitate.

primary phase

The only crystalline phase capable of existing in equilibrium with a given liquid; it is the first to appear on cooling from a liquid state and the last to disappear on heating to the melting point.

primary reject elevator

A refuse elevator that extracts the first or heavier reject; usually situated at the feed end of a washbox.

primary relict

A relict mineral that was a constituent of the original rock, whether igneous or sedimentary.

primary screen

A screen used to divide coal (usually raw coal) into sizes more suitable for the subsequent cleaning of some or all of them.

primary settling

The surface subsidence that manifests itself a few months after mineral extraction and that usually constitutes 60% to 90% of the total subsidence. It varies according to the depth and thickness of the seam, the nature of the overburden, the mining method, and the thoroughness of the filling in the mined-out areas. The primary period is followed by the secondary period, in which the surface subsides gradually for a period of many years or even decades.

primary shaft

The shaft from the surface in which the first stage of hoisting is carried out.

primary solid solution

A constituent of alloys that is formed when atoms of an element B are incorporated in the crystals of a metal A. In most cases, solution involves the substitution of B atoms for some A atoms in the crystal structure of A, but there are cases in which the B atoms are situated in the interstices between the A atoms.

primary source

An operation that produces or creates new dust.

primary structure

a. A structure in an igneous rock that originated contemporaneously with the formation or emplacement of the rock, but before its final consolidation; e.g., layering developed during solidification of a magma.

b. A primary sedimentary structure, such as bedding or ripple marks. c. The structure preexisting the deformation and reequilibration associated with the emplacement at shallow depth of a metamorphic body of deep origin during an orogeny. CF: secondary structure.

primary washbox

The first of a series of washboxes, which receives the feed and from which one product at least is given further treatment.

primary washer

The first of a series of washers, receiving raw feed, from which at least one product is retreated.

primary water supply

The principal or original source from which drilling water is obtained, as opposed to recirculated water.

primary wave

See: longitudinal wave.

primary zone

Portion of a lode below that changed by leaching and secondary enrichment, and characteristic of the type of ore most likely to persist into the deeper levels of a mine.

prime mover

a. A machine that converts fuel or other natural energy into mechanical power.

b. A tractor or other vehicle used to pull other machines. c. Any machine capable of producing power to do work.


a. A contrivance, such as a cap, tube, or wafer, containing percussion powder or other compound for igniting an explosive charge; ignited by friction, percussion, or electricity. Syn: percussion cap.

b. The cartridge or that portion of a charge that carries a detonator or is coupled to Cordtex fuse and that detonates or sets off the remainder of the charge. The primer cartridge is placed at one end of the charge with the detonator pointing toward the charge. See also: direct initiation. c. In blasting, the cartridge in which the cap is placed. d. Usually the combination of a dynamite cartridge and a detonating cap.

primer cartridge

The explosive cartridge into which a detonator has been inserted.

primer charge

A boosting charge placed in contact with a detonator to ensure detonation of the main charge.

prime virgin mercury

A term used for mercury produced by mines.

prime western spelter

See: prime western zinc.

prime western zinc

Low grade of virgin zinc containing about 98% zinc, 1.60% lead, 0.08% iron, with no limitations on cadmium or aluminum.


a. The act of placing a detonator in an explosive charge.

b. The act of adding water to displace air, thereby promoting suction, as in a suction line of a pump. Water used to promote initial suction in a centrifugal or reciprocating pump.

priming cartridge

See: primer.

priming coat

A coating of binder applied to a surface of natural compacted or stabilized soil before surface dressing.

priming tube

A tube containing fulminating powder for firing a charge. A detonator.

priming valve

a. A safety valve on the working cylinder of a steam engine to discharge the priming.

b. A valve connected with the discharge pipe of a force pump through which the pump may be primed.


See: primitive circle.

primitive circle

In crystallography, the great circle on a stereographic projection that represents the equator of the spherical projection. The poles of all vertical crystal planes plot on the primitive. Syn: primitive.

primitive form

A crystal form from which other forms may be derived; e.g., a hexoctahedron has six faces replacing each octahedral face.

primitive unit cell

See: unit cell.


Roofing slate sized 24 in by 14 in (61 cm by 36 cm).


Primary, or leading function. A principal axis is the longest one in a crystal. The principal valence is that at which an element forms the greatest number of stable compounds.

principal axis

a. In the tetragonal and hexagonal systems, the vertical crystallographic axis; hence what is the same thing in uniaxial crystals, the optic axis. In the orthorhombic and triclinic crystals, the axis of the principal zone; the axis with the shortest period, often the axis of the principal zone. In monoclinic crystals, the axis c, usually the axis of the principal zone excluding the symmetry axis; the symmetry axis b.

b. That crystallographic axis with unique symmetry in a crystal system, designated c, except in the monoclinic system where the second setting is used by mineralogists making b the unique axis. c. In a transducer used for sound emission or reception, a reference direction for angular coordinates used in describing the directional characteristics of the transducer. It is usually an axis of structural symmetry or the direction of maximum response, but if these do not coincide, the reference direction must be described explicitly. d. In experimental structural geology, a principal axis of stress or a principal axis of strain.

principal axis of strain

One of the three mutually perpendicular axes of the strain ellipsoid.

principal axis of stress

One of the three mutually perpendicular axes that are perpendicular to the principal planes of stress. See also: principal axis.

principal meridian

A central meridian on which a rectangular grid is based; specif. one of a pair of coordinate axes (along with the base line) used in the U.S. Public Land Survey system to subdivide public lands in a given region. It consists of a line extending north and south along the astronomic meridian passing through the initial point and along which standard township, section, and quarter-section corners are established. The principal meridian is the line from which the survey of the township boundaries is initiated along the parallels.

principal moment of inertia

The moment of inertia of an area about either principal axis.

principal point

The geometric center of an aerial photograph, or the point where the optical axis of the lens meets the film plane in an aerial camera. Symbol: p. See also: fiducial mark.

principal section

a. In crystallography, the plane passing through the optical axis of a crystal.

b. The optical indicatrix of a biaxial mineral is a triaxial ellipsoid with semiaxes proportional to the refractive indices alpha, beta, and gamma. A principal section is an ellipse containing any two of these semiaxes. The indicatrix of a uniaxial mineral is an ellipsoid of revolution; its principal sections contain the axis of revolution which is proportional to the refractive index epsilon.

principal stress

The stress normal to one of three mutually perpendicular planes that intersect at a point in a body on which the shearing stress is zero.

principle of superposition

To determine the stress in a member due to a system of applied forces, the system can be split up into several component forces and their moments and reactions added in order to calculate the total stress.

principle of uniformity

See: uniformitarianism.

Prins washer

A dense-media process in which large-size coal is separated from the refuse in a flowing bed of small coal in a reciprocating launder. Refuse sinks to the bottom. The small coal is screened from the coarse refuse and returned to the head of the launder by a drag conveyor. The floating large coal passes over skimmers in the trough to the discharge chute. zK �tc �xc '���� � ��DICTIONARY TERMS:Prins washer A combination trough washer and jig in A combination trough washer and jig in which the feed enters the unit through the central launder, where stratification takes place. The stratified material overflowing the stationary trough is divided at the first opening in the shaking jig, allowing the upper stratum of the material to flow onto the top deck of the jig while the lower stratum enters the jig reclean chamber.


An orthorhombic mineral, (Y,Ca,Fe,Th)(Ti,Nb) (sub 2) (O,OH) (sub 6) ; now formally named aeschynite-(Y); forms series with aeschynite-(Ce) and with tantalaeschynite-(Y); black; forms with other rare-earth minerals in granite pegmatites and placers. Syn: blomstrandine.


a. The volume of a length of embankment or excavation.

b. The liquid mobile volume of a stream. c. An open crystal form with faces and their intersecting edges parallel to the principal crystallographic axis. Prisms have three (trigonal), four (tetragonal), six (ditrigonal or hexagonal), eight (ditetragonal), or twelve (dihexagonal) faces. The nine-sided prisms of tourmaline are a combination of trigonal and hexagonal prisms. d. A long, narrow, wedge-shaped sedimentary body with width:thickness between 5:1 and 50:1; e.g., a bajada adjacent to an escarpment. It is typical of orogenic sediments formed during periods of intense crustal deformation; e.g., the arkoses found in fault troughs. CF: tabular. Syn: wedge.


a. Descriptive of a clast with length to width ratio between 1.5:1 and 3:1. CF: tabular.

b. Pertaining to a sedimentary prism. c. Pertaining to a crystallographic prism. d. Descriptive of a crystal with one dimension markedly longer than the other two. e. Descriptive of two directions of cleavage. f. Descriptive of a metamorphic texture in which a large proportion of grains are prismatic and have approx. parallel orientation, giving a lineated appearance in hand specimens and thin sections. CF: equant. See also: columnar.

prismatic compass

A small magnetic compass held in the hand when in use and equipped with peep sights and a glass prism so arranged that the magnetic bearing or azimuth of a line can be read (through the prism) from a circular graduated scale at the same time that the line is sighted over.

prismatic plane

Any crystallographic plane that is parallel to the principal axis of a crystal.

prismatic quartz

Collectors' name for cordierite.

prismatic system

See: orthorhombic system.

prismatic telescope

A telescope having an eyepiece fitted with a prism that reflects at 90 degrees .


Any solid, bounded by planes, whose end faces are parallel. Usually understood to include also figures whose bounding surfaces are warped surfaces.


Adj. of prismoid; used in sedimentary petrology (not prismatic, which is a crystallographic term).

prismoidal formula

A formula used in the calculation of earthwork quantities. It states that the volume of any prismoid is equal to one-sixth its length multiplied by the sum of the two end-areas plus four times the mid-area.


A statistical measure (where zero is impossibility and one is certainty) of the likelihood of occurrence of an event.

probable ore

a. Indicated reserves. See: reserves.

b. A mineral deposit adjacent to developed ore but not yet proven by development. CF: extension ore.

probable performance curve

A performance curve showing the expected results of a coal-preparation treatment.

probable reserves

Areas of coal or mineral believed to lie beyond the developed reserves but not yet proven by development. See also: economic coal reserves. Syn: theoretical tonnage.


a. A small tube containing a sensing element of electronic equipment, which can be lowered into a borehole to obtain measurements and data.

b. To conduct a search for mineral-bearing ground by drilling or boring. c. To lower drill rods, etc., to locate obstructions and/or to determine the attitude of a piece of junk in a borehole.


A monoclinic mineral, NaCaB (sub 5) O (sub 7) (OH) (sub 4) .3H (sub 2) O ; colorless; forms radiated columnar crystals; in Kern Country, CA. Syn: kramerite; boydite.


Thrusting a pointed steel rod down through sand or soft clays to contact a seam or orebody. The point of the rod is examined for traces of coal or mineral. See also: auger.


The term proceedings is broader than the term action, yet in the mining law it is used in the sense of action and refers to the commencement of an action. It is used to enable a party to institute such proceedings under the different forms of actions allowed by the State and Federal courts.


A series of operations conducted to achieve a result.

process company

Company formed for the purpose of exploiting a patented process.

process flowsheet

A basic flowsheet indicating the main operational steps within a plant, the movement of the various materials between the steps, and the final products obtained, and often also the quantities of material with which the plant must be capable of dealing at various points.


a. The methods employed to clean, process, and prepare coal and metallic ores into the final marketable product.

b. The various artificial methods adopted for strengthening a soil, such as compaction, treatment with bitumen, lime, cement, etc. See also: stabilizer; soil stabilization.


An official land surveyor.

process lag

In mineral processing, the delay or retardation in the response of the controlled variable at a point of measurement to a change in value of the manipulated variable.

process metallurgy

Branch of metallurgy that deals with the recovery or extraction of metals from their ores. See also: extractive metallurgy.

process scrap

The scrap arising during the manufacture of finished articles from iron and steel, and usually returned to steelworks after sorting and processing by scrap merchants. See also: capital scrap; circulating scrap.

Proctor penetration needle

A quick and convenient method for testing the resistance of a fine-grained soil to penetration at a standard rate of 1/2 in/s (1.27 cm/s). Needles from 1 to 0.05 in (super 2) (6.5 to 0.3 cm (super 2) ) area are used, and a spring balance indicates the pressure required for the needle to penetrate the soil. See also: penetration resistance; penetrometer; soil.

prod cast

See: impact cast.

prod mark

a. An indicator of slip direction on a slickensided fault surface, consisting of a groove made by a clast.

b. A short tool mark oriented parallel to the current of a stream and produced by an object that plowed into and was then raised above the bottom; its longitudinal profile is asymmetric. The mark deepens gradually downcurrent where it ends abruptly (unlike a flute). CF: bounce cast. Syn: impact cast.


a. The marketable ores or minerals produced by mining and dressing.

b. Corn. The amount of fine copper in one hundred parts of ore.


a. Person who extracts ore or coal from mines, rock from quarries, metals from ore by metallurgical processes, etc. See also: production.

b. A producing well. c. A furnace or apparatus that produces combustible gas to be used for fuel; usually of the updraft type, which forces or draws air or a mixture of air and steam through a layer of incandescent fuel (such as coke) with the resulting gas consisting chiefly of carbon monoxide, hydrogen, and nitrogen. d. An organism (e.g., most plants) that can form new organic matter from inorganic matter such as carbon dioxide, water, and soluble salts.


Percent of metal in ore.


That which is produced or made; any tangible result of industrial or other labor. The yield or output of a mine, metallurgical plant, or quarry. See also: producer.

production checker

In metal mining, a person who keeps a record of the number of containers (cars, buckets, or skips) raised to the surface, and the amount of ore contained in each, estimating or weighing the contents.

production gang

A team of workers employed at the face on production, covering all face operations, maintenance, and supplies.


Yielding payable ore.

productive development

The headings and levels excavated in a coal seam, preparatory to opening out working faces. These drivages are planned to prove and render accessible the maximum area of coal for the minimum yardage of development work. The modern trend is to make in-the-seam development as productive as possible with the aid of machines. See also: unproductive development.

productive land

Land that has produced farm crops within the previous 5 years.


a. A term closely allied with, and that may be expressed as, the output per manshift of a face or colliery or metal mine. Productivity will vary with the degree of mechanization and multishift working; it is also a function of the horsepower, of a suitable nature, at the disposal of each miner. See also: output.

b. The efficiency with which economic resources (workers, materials, and machines) are employed to produce goods and services.


a. The outline produced where the plane of a vertical section intersects the surface of ground; e.g., the longitudinal profile of a stream, or the profile of a coast or hill. Syn: topographic profile.

b. A graph or drawing that shows the variation of one property such as elevation or gravity, usually as ordinate, with respect to another property, such as distance. c. Cross section of a region of cylindrical folds drawn perpendicular to the fold axes. d. In seismic prospecting, the data recorded from one shot point by a number of groups of detectors. e. See: soil profile. f. A vertical section of a water table or other potentiometric surface, or of a body of surface water. g. A drawing used in civil engineering to show a vertical section of the ground along a surveyed line or graded work.

profile flying

The technique of flying at a constant height above the ground during airborne mineral exploration. Generally, the aircraft maintains a height of 300 ft or 500 ft (91 m or 152 m) above the ground. This often involves a series of skillfully controlled climbs and dives over rolling ground. See also: vertical aerial photograph.

profile shooting

A type of seismic refraction in which the shots and detectors are laid out on long straight lines. Successive shots are taken at uniform or almost uniform intervals along each line, and successive detector spreads are shifted about the same distance as the corresponding shot points so as to keep the range of shot-detector distances approx. the same for all shots. Generally, shots are received from opposite directions on each detector spread. The distance range is chosen so that the first, or where desired the second, arrivals will be refracted from a particular formation such as the basement or a high-speed limestone marker. The proper distance is usually determined from time-distance plots based on experimental shooting at the onset of the program.


An instrument for plotting the perimeter profile of an airway on a reduced scale, and primarily used when taking air measurements underground.


When one speaks of the interest on a mining investment, the rate mentioned ordinarily consists of the normal rate plus a substantial additional rate that represents the profit that should accrue in proportion to the hazardous nature of the mining business. In this sense, the rate of interest in most forms of mining should be high; to be satisfied with less than 10% annually would show a lack of acumen.

profit in sight

Probable gross profit from a mine's ore reserves, as distinct from the ground still to be blocked out.

proforma invoice

Invoice that does not charge for goods marked, but shows cost details.

prograde metamorphism

Metamorphic changes in response to a higher pressure or temperature than that to which the rock last adjusted itself. CF: retrograde metamorphism.

progress chart

A chart or graph forming a continuous record, which is kept up to date, of the amount of work done on a major project. It may take the form of a bar graph, divided into sections representing different jobs to be done, estimated and actual completion dates, etc. The chart covers the entire project from the initial site preparation or drivage to completion.

progressing cavity pump

See: Mono pump.

progressive aging

In heat treatment, aging by increasing the temperature in steps or continuously during the aging cycle. See also: precipitation heat treatment.

progressive failure

Rock or material failure in which the ultimate shearing resistance is progressively mobilized along the failure surface.

project data

Basic information needed by engineers concerned with design, site development, machine and housing assembly, plant erection, contract supervision, and coordination when planning, erecting, and bringing into operation a new mine and its attendant services, including the ore treatment plant.

projected pipe

A pipe laid on the surface before building a fill that buries it.


a. In underground mining, a plan showing the proposed direction and location of entries, rooms, shafts, fans, and watercourses. Such projections commonly cover the entire property to be worked.

b. A systematic, diagrammatic representation on a plane (flat) surface of three-dimensional space relations, produced by passing lines from various points to their intersection with a plane; esp. a map projection. c. Any orderly method by which a projection is made; the process or operation of transferring a point from one surface to a corresponding position on another surface by graphical or analytical means, so that each point of one corresponds to one and only one point of the other. d. See: exposure. e. See: outcrop. f. In mapping, a geometric (or mathematical) system of constructing the true meridians and parallels, or the plane rectangular coordinates on a map. g. A geometrically or mathematically derived portrayal of the surface of the geoid on a plane surface. The requirement for a particular projection is that it show the features of the surface of the Earth with a minimum of distortion of distances, directions, shapes, and areas. h. The act or result of constructing a figure upon a plane or other two-dimensional surface that corresponds point for point with a sphere, a spheroid, or some other three-dimensional form.

projection balance

Shows movement of a pointer by means of an illuminated scale.

project plans

A series of plans of a proposed new mine or reconstruction, which are drawn up for the purpose of obtaining approval of a project.

prolapsed bedding

A series of flat folds with near-horizontal axial planes contained entirely within a bed with undisturbed boundaries.


Secondary condenser used in the zinc industry.


Eng. The forked end of a bucket-pump rod; used for attachment to the traveling valve and seat.

Prony's dynamometer

A dynamometer for obtaining data for computing power delivered by turbines and other water wheels, or from the flywheel of an engine, or transmitted by shafting.

proof stress

a. The stress that will cause a specified small permanent set in a material.

b. A specified stress to be applied to a member or structure to indicate its ability to withstand service loads.


To transmit or spread from place to place; as coal dust propagates a mine explosion.

propagated blast

A blast consisting of a number of unprimed charges of explosives and only one hole primed, generally for the purpose of ditching, where each charge is detonated by the explosion of the adjacent one, the shock being transmitted through the wet soil. In this method, one detonator fired in the middle of a line of holes is capable of bringing about the explosion of several hundred such charges.


a. The transfer of a signal through a medium; e.g., sound in air, seismic waves in fluids and solids, electromagnetic waves in a vacuum.

b. In general, propagation is said to occur when the flame of an explosion travels over considerable areas of a mine in such manner as might result in loss of life of workers in the mine.

propagation velocity

The speed of a wave in the material concerned, such as the propagation velocity of a detonation wave front traveling through an explosive or the propagation velocity of a seismic wave from a blast traveling through the ground.

prop-crib timbering

Shaft timbering with cribs kept the proper distance apart by means of props.

prop cutter

In mining, a person who operates a power saw to cut to designated- and standard-length timbers and props used to support the walls and roofs of underground passageways and workplaces. Also called: prop sawyer; timber cutter.

prop drawer

a. A sylvester or other appliance for withdrawing props from the waste area in coal mining. See also: monkey winch.

b. A worker who withdraws props and allows the roof to collapse. Props are withdrawn when caving of the roof is adopted. See also: timber robber.

propeller fan

a. Axial-flow ventilating fan used to blow fresh air into mine workings or to extract foul air.

b. A fan having an impeller, other than of the centrifugal-type, rotating in an orifice, the air flow into and out of the impeller not being confined by any casing.

propeller pump

This type of pump, often called axial-flow, develops most of its head by the propelling or lifting action of the vanes upon the liquid. These pumps are built in horizontal or vertical casings and are primarily used in handling sludge, dewatering pits, sewage pumping, and similar duties requiring large capacities and heads under 100 ft (30 m).

propeller shaft

Usually a main drive shaft fitted with universal joints.

propel shaft

In a revolving shovel, a shaft that transmits engine power to the walking mechanism.


In crystallography, any symmetry rotation which does not change the chirality (handedness) of an asymmetric unit; e.g., not involving reflection or inversion. CF: improper.

proper proportion

In a transparent gemstone, the proportion of the mass above and below the girdle, as well as the angles of the facets in relation to the girdle, that produces the greatest brilliancy from the particular species. These proportions vary with the refractive index of the gem species.

properties of sections

These include the cross-sectional area of a structural member, its moment of inertia, section modulus, and other geometrical properties essential for accurate design calculations.


One of the physical and chemical characteristics of a material.

property man

In bituminous coal mining, formerly one who kept record of location and has charge of distribution of coal cutting machines, drills, loaders, and other mechanical equipment in and about a mine. Now, one who oversees surface lands and structures.


In longwall mining of a coal seam, a face with no posts between the coal and the conveyor used to remove it.

prop-free front

a. In coal mining, longwall working in which support to the roof is given by roof beams cantilevered from behind the working face. This leaves unobstructed room for digging and conveying equipment in a mechanized working.

b. Such a face is necessary where armored flexible conveyors are used to carry a coal cutter or power loader. See also: link bar; self-advancing supports.

prophylene-glycol dinitrate explosive

An explosive containing the liquid ingredients named, in contradistinction to dynamite, which contains nitroglycerin. In commerce, the term dynamite is loosely used to include any mixture containing a liquid explosive.


A statement of equality between two ratios. When one ratio is equal to another ratio, they are said to be in proportion.

proportional control action

As used in mineral processing, action in which there is a continuous linear relation between the output and the input.

proportional counter

A gas-filled, radiation-detection tube in which the pulse produced is proportional to the number of ions formed in the gas by the primary ionizing particle.

proportional limit

The greatest stress that a material is capable of withstanding without deviation from proportionality of stress to strain (Hooke's law). In the case of rocks, this term and "elastic limit" are restricted to short-time tests; rocks may slowly and permanently deform in periods of long duration, even at stresses below the short-time proportional limit.

proportional plus integral control action

As used in mineral processing, action in which the output is proportional to a linear combination of the input and to the time integral of the input.

proportional plus integral plus derivative control action

As used in mineral processing, action in which the output is proportional to a linear combination of the input, the time integral of input, and the time rate of change of input.


Measuring by weight or by volume the constituents, before mixing of concrete, mortar, or plaster.


Hydraulic fracturing and propping agent employed in the gas and oil industry to enable production from deep petroleum reservoirs.


The setting of timber props in mine workings.

prop retriever

See: prop drawer.

prop sawyer

See: prop cutter.

prop setter

In anthracite and bituminous coal mining, a worker who installs props (posts) to support the roofs of underground working places, placing and wedging them at the most effective points.

prop wall

Props that are fastened together in a group, like a fence, and placed against the walls to prevent the roof from caving into the stope.


A hydrothermally altered andesite resembling a greenstone and containing calcite, chlorite, epidote, serpentine, quartz, pyrite, and iron oxides. The term was first used by Richthofen in 1868. Propylite is common in mining districts of the Western United States, generally in the outermost subzone of hydrothermal alteration. See also: propylitization.

propylitic alteration

See: propylitization.


The result of low-pressure-temperature alteration around many orebodies. The propylitic assemblage consists of epidote, chlorite, Mg-Fe-Ca carbonates, and sometimes albite-orthoclase, all involved in partial replacement of wall-rock minerals. Syn: propylitic alteration. See also: phyllic alteration.


A monoclinic mineral, CaAl (sub 2) (F,OH) (sub 8) ; forms tabular crystals or granular masses.


a. An area that is a potential site of mineral deposits, based on preliminary exploration.

b. Sometimes, an area that has been explored in a preliminary way but has not given evidence of economic value. c. An area to be searched by some investigative technique, such as geophysical prospecting. d. A geologic or geophysical anomaly, esp. one recommended for additional exploration. A prospect is distinct from a mine in that it is nonproducing. See also: prospecting. e. A mineral property, the value of which has not been proved by exploration. f. To search for minerals or oil by looking for surface indications, by drilling boreholes, or both. g. A plot of ground believed to be mineralized enough to be of economic importance. h. Territory under examination for its mineral wealth. Prospecting is the search for deposits and is performed by aerial survey, magnetometry, surface examination, pitting, trenching, use of a prospector's pan, geochemical testing of soil, drilling (shallow or deep), seismic probe, and resistivity survey. i. The gold or other mineral obtained by working a sample of ore. j. A formation that may be capable of development into a mine, but which is untested. See also: favorable locality. k. A sample of gold obtained in panning. l. A specimen or sample of mineral obtained from a small amount of paydirt or ore. m. To work (a mine, ledge, etc.) experimentally in order to ascertain its richness in precious minerals.

prospect drilling

The exploratory drilling of boreholes in the search for minerals and petroleum.

prospect drill panner

In metal mining, a person who, with a cable drill rig, drills down through gravel to bedrock along a present or an old creek bed that usually has been prospected by a hand-dug hole. The panner saves the drillings and pans them to discover the possible presence of paydirt (gold-bearing gravel), and weighs gold particles recovered. In the event of the discovery of gold in quantities sufficient for profitable removal, the panner moves drill and continues operations to determine the boundaries of the gold-bearing strata.

prospect entry

See: prospect tunnel.


a. The search for outcrops or surface exposure of mineral deposits.

b. Searching for new deposits; also, preliminary explorations to test the value of lodes or placers already known to exist. c. The surface discovery of coal or mineral only proves its superficial existence and further work is necessary to establish its quality and extent. The term exploration is sometimes applied to this extension of the discovery work. See also: exploration.

prospecting and mining

Generic terms which include the whole mode of obtaining metals and minerals.

prospecting claim

Aust. A claim larger than the average; allotted to the miner who is the first in a district to discover the presence of gold.

prospecting dish

A simple appliance used in the search for gold and other heavy minerals. By means of water washing, the lighter, worthless material is separated from the valuable, heavier minerals, which are made visible by concentration and retention in the dish. Standard dishes with sloping sides are made in sizes ranging from top diameter 10 to 18 in (25 to 46 cm) and from 2 to 4 in (5 to 10 cm) deep, with riffles or grooves to retain the heavy minerals. Syn: pan.

prospecting license

Authorization granted by a government to an individual in some countries, permitting the person to prospect for minerals and to register (stake) a claim.

prospecting pan

See: pan.

prospective ore

Ore that cannot be included as proved or probable, nor definitely known or stated in terms of tonnage. See also: possible ore; ore expectant.


A person engaged in exploring for valuable minerals or in testing supposed discoveries of the same.

prospect shaft

A shaft sunk in connection with prospecting operations.

prospect tunnel

A tunnel or entry driven through barren measures, or a fault, to ascertain the character of strata beyond. Syn: prospect entry.


A preliminary printed statement describing a business or other enterprise, and distributed to prospective buyers, investors, or participants, giving detailed information concerning the company's business and financial standing. Common in mining.

protecting magnet

Electromagnet or permanent magnet installed ahead of crushing machinery to remove tramp iron that otherwise might enter and damage the appliances.

protection screen deck

A screen plate with large apertures mounted over the screening deck in order to reduce the load and wear thereon.

protective alkali

In the cyanide process, the use of dissolved lime to maintain a slightly alkaline pulp, therefore ensuring that the cyanide salt retains its potency and does not acidify to hydrocyanic acid, which cannot dissolve gold or silver. See also: cyanide process.

protective alkalinity

Lime added to auriferous pulp to ensure alkalinity. Important in the cyanidation process for precious metals.


An objection to the patent proceeding; when made, it calls for a hearing on the matter in the local land office.


A name for a series of artificial orthorhombic fluoramphiboles having only half the a-dimension of anthophyllite. The presence of lithium and absence of calcium appear to be essential to their formation. Named because of a structural relation to protoenstatite.


Leith's term for a rock possessing what he considered to be primary cleavage; e.g., bedding planes in sedimentary rock, formed concurrently with the rock. CF: metaclase.


a. Said of igneous rocks in which the earlier formed crystals have been broken or deformed because of differential flow of the magma before complete solidification.

b. Said of an igneous rock containing deformed xenocrysts. c. Said of the texture characteristic of an early stage of cataclasis, with a very small amount of finite strain.


a. Dolomite with calcium and magnesium disordered within layers rather than ordered by layer.

b. An imperfectly crystallized synthetic material of composition near CaMg(CO (sub 3) ) (sub 2) .


See: protogine.


Said of original rocks as opposed to derived rocks, and including saline deposits, coal, igneous rocks, and ore deposits. The term is no longer used.


A granitic rock, occurring in the Alps, that has gneissic structure, contains sericite, chlorite, epidote, and garnet, and shows evidence of a composite origin or of crystallization (or partial recrystallization) under stress after consolidation. Also spelled protogene. The term, dating from 1806, is obsolete.


a. A mylonitic rock produced from contact-metamorphosed rock, with granulation and flowage being due to overthrusts following the contact surfaces between intrusion and country rock.

b. A coherent crush breccia whose characteristically lenticular, megascopic particles faintly retain primary structures. It is a lower grade in the development of mylonite and ultramylonite. CF: ultramylonite.


An elementary particle with a single positive electrical charge and a mass approx. 1,847 times that of an electron. The atomic number of an atom equals the number of protons in its nucleus.


A well-sorted, quartz-enriched sandstone that lacks the well-rounded grains of an orthoquartzite; specif. a lithic sandstone intermediate in composition between subgraywacke and orthoquartzite.


In older writings, any primary mineralized material too low in tenor to constitute ore but from which ore may be formed through secondary enrichment. As commonly employed today, the rock below the sulfide zone of supergene enrichment; the primary material that cannot be produced at a profit under existing conditions but that may become profitable with technological advances or price increases. See also: oxidized zone; sulfide zone.


An instrument used in drawing and plotting, designed for laying out or measuring angles on a flat or curved surface, and consisting of a plate marked with units of circular measure. See also: goniometer.


A trigonal mineral, Ag (sub 3) AsS (sub 3) ; dimorphous with xanthoconite; rhombohedral cleavage; soft; ruby red; occurs in low-temperature or secondary-enrichment veins; a minor source of silver. Syn: light ruby silver; light red silver ore.


a. To determine, by boring from the surface or driving a passageway underground, the location and character of a coalbed or the nature of rock strata.

b. To establish, by drilling, trenching, underground openings, or other means, that a given deposit of a valuable substance exists, and that its grade and dimensions equal or exceed some specified amounts. See also: proved reserve.

proved ore

See: proved reserve.

proved reserve

An ore deposit that has been reliably established as to its volume, tonnage, and quality by approved sampling, valuing, and testing methods supervised by a suitably qualified person. The proved reserve is the overridingly important asset of a mine, and by its nature is a wasting one from the start of exploitation unless it is increased by further development. Syn: proved ore.


A place of origin; specif. the area from which the constituent materials of a sedimentary rock or facies are derived. Also, the rocks of which this area is composed. CF: distributive province. Syn: source area.

prove up

a. To show that the requirements for receiving a patent for government land have been satisfied.

b. Can. To establish economic value of a property.

proving hole

a. A borehole drilled for prospecting purposes.

b. Advance bore or heading into a mineral deposit, made either to check the quality of the ore being approached or to relocate a deposit that has been distorted or dislocated by faulting.

proving ring

A steel ring that has been accurately turned, heat treated, and polished. It is precisely calibrated in a testing machine by measuring its deflection for different loads and can be used for measuring applied loads on a structure.

proving the area

The establishment of the quantity and grade of coal or ore available for working by means of geological surveys, exploratory drilling, or exploring headings.

proximate analysis

a. The determination of the compounds contained in a mixture as distinguished from ultimate analysis, which is the determination of the elements contained in a compound. Used in the analysis of coal.

b. The determination, by prescribed methods, of moisture, volatile matter, fixed carbon (by difference), and ash. The term proximate analysis does not include determinations of chemical elements or determinations other than those named. See also: chemical constitution of coal.

proximity log

A Schlumberger log based on the principle of shallow investigation; as its name implies it is markedly affected by material that lies in its immediate proximity. It depends for its operation on the forcing of a more or less horizontal beam of current into the formation. Its vertical resolution is about 6 in (15 cm) and it is almost impervious to the presence of a mud cake on the formation wall.

prudent-man (person) test

The basic legal standard for discovery under the mining law that states: Where minerals have been found and the evidence is of such a character that a person of ordinary prudence would be justified in the further expenditure of his labor and means, with a reasonable prospect of success in developing a valuable mine, the requirements of the statute have been met.

P.R.U. hand pump and densitometer

A dust sampling instrument comprising a D.V.P. Mark 11 pump with a swept volume of 90 cm (super 3) . A filter paper is inserted into a bridge behind the inlet nozzle of the pump such that a circle of 1-cm diameter of the filter paper is exposed to the dust. The dust, while passing through the filter paper, produces a stain. The optical density of the stain is determined photoelectrically in a densitometer by the light that falls upon a galvanometer. The dust particle concentration is evaluated by a calibration factor. Its main disadvantage is that it underestimates the number of fine particles.

Prussian blue

See: vivianite.

prussic acid

See: hydrocyanic acid.


Eng. Cornish miners' term for soft white clay. Also spelled pryan.

pryany lode

A lode in which the ore is mixed with gossan or flucan.


A pole that forms the prop of a hoisting gin and stands facing the windlass.