Effervesce:  Forming and breaking gas bubbles by chemical reaction.
Effluent Discharge:  Excess water from a mining and milling operation that is discharged to the receiving environment.
El Oro:  Spanish for gold.
Electrolysis:  An electric current is passed through a solution containing dissolved metals, causing the metals to be deposited on to a cathode.
Electrolytic refining:  The process of purifying metal ingots that are suspended as anodes in an electrolytic bath, alternated with refined sheets of the same metal which act as starters or cathodes.
Electrostatic separator:  Machine employing static electrical charges to separate heavy mineral concentrates.
Electrum:  Native gold containing a large amount of alloyed silver.


Substance composed of atoms that cannot be broken down by ordinary chemical means; metals, nonmetals and certain gasses.
Eluvium:  Material produced by decomposing rock formations where water movement and abrasion are not present.
Emulsion:  A mixture of water and oily substances.
EM survey:  A geophysical survey method which measures the electromagnetic properties of rocks.
En echelon:  A geological term used to describe the geometric structure of minerals found in a roughly parallel but staggered fashion.
End line:  Line across the width of a lode chain.
Entry:  Refers to mining location; also opening to underground workings.
Environmental impact study:  A written report, compiled prior to a production decision, that examines the effects proposed mining activities will have on the natural surroundings of an exploration property.
Epigenetic: Orebodies formed by hydrothermal fluids and gases that were introduced into the host rocks from elsewhere, filling cavities in the host rock.
Epithermal:  Hydrothermal deposits formed at low temperature and pressure.
Epithermal deposit:  A hydrothermal mineral deposit formed at low temperature and pressure consisting of veins and replacement bodies, usually in volcanic or sedimentary rocks, containing precious metals, or, more rarely, base metals.
Era:  A large division of geologic time - the Precambrian era, for example.
Erosion:  The breaking down and subsequent removal of either rock or surface material by wind, rain, wave action, freezing and thawing and other processes.
Erratic:  Refers to either a piece of visible gold (or gold nugget in a core sample) or a large glacial boulder.
Eureka:  A term used by early miners meaning “I have found it!”.
Evaporate:  Drying out; also refers to the dry product.
Exothermic Reaction:  A chemical reaction which generates heat.
Exploration:  Prospecting, sampling, mapping, diamond drilling and other work involved in searching for ore.
Exposure:  An outcrop of ore or a rock alluvial; Sand and gravel laid down by water movement.
Extralateral right:  Right to minerals beyond side lines of mining claims.
Extrusive:  Igneous rocks that cooled at or above the earth's surface.
Exude:  To ooze out, or emit an odor.
Face:  The end of a drift, crosscut or stope in which work is progressing.
Fahrenheit:  A system of temperature measurement.
False set:  Temporary timbering in a mine.
Fault:  A break in the Earth's crust caused by tectonic forces which have moved the rock on one side with respect to the other; faults may extend for many kilometers, or be only a few centimeters in length; similarly, the movement or displacement along the fault may vary widely.
Feed Grade:  The grade (percentage of metal, or ounces per tonne in the case of precious metals) of materials supplied by a mine to the on-site processing plant (commonly known as a concentrator in the case of metal mines and a washing plant in the case of coal mines).
Feldspar:  A group of rock-forming minerals. Includes: microcline, orthoclase, and plagioclase.
Felsic:  Term used to describe light-colored rocks containing feldspar, fledspathoids and silica.
Ferrous:  Containing iron.
Fine gold:  Fineness is the proportion of pure gold or silver in jewelry or bullion expressed in parts per thousand. Thus, 925 fine gold indicates 925 parts out of 1,000, or 92.5%, is pure gold. A fine ounce is a troy ounce of 99.5% gold and 0.5% silver.
Fineness:  Gold content expressed in parts per thousand.
Fire assay:  The assaying of metallic minerals by use of a miniature smelting procedure with various fluxing agents.
Fissile:  Capable of being split or removed in sheets, as slate and mica.
Fissure:  An extensive crack, break or fracture in rocks.
Fixed Assets:  Possessions such as buildings, machinery and land which, as opposed to current assets, are unlikely to be converted into cash during the normal business cycle.
Flare jet:  A specific type of suction jet used on a dredge. It has a section which gradually tapers outward ahead of the sluice box in which surface tension of the water causes it to slow down as opposed to the collector box used on typical dredges.
Flake gold:  Heavy pieces of gold, smaller than nuggets.
Flour gold:  Very minute specks of gold, otherwise knows as gold dust.
Flask:  Unit and container for measuring mercury, equal to 76 pounds.
Float:  Pieces of rock that have been broken off and moved from their original location by natural forces such as frost or glacial action.
Floor:  The bottom of a mining level in underground mines.
Flotation:  A process for concentrating materials based on the selective adhesion of certain minerals to air bubbles in a mixture of water and ground-up ore. When the right chemicals are added to a frothy water bath of ore that has been ground to the consistency of talcum powder, the minerals will float to the surface. The metal-rich flotation concentrate is then skimmed off the surface.
Flour:  Extremely fine gold particles; also finely-ground ore.
Flow sheet:  An illustration showing the sequence of operations, step by step, by which ore is treated in a milling, concentration, or smelting process.
Flume:  A trough used to convey water. fluvial: Sand and gravel laid down by water movement.
Flux:  A chemical substance used in metallurgy to react with gangue minerals to form slags, which are liquid at furnace temperature and low enough in density to float on the molten bath of metal or matte; examples range in scale from large tonnages of limestone, silica, etc., in large furnaces, to small quantities of borax, soda, etc., used in laboratory assay ovens.
Fluxgate magnetometer:  An instrument used in geophysics to measure total magnetic field.


Any bending or wrinkling of rock strata.
Foliated:  Leaf-like formations of minerals.
Fool’s gold:  Pyrite or iron pyrite. Golden yellow color, and brittle.
Footwall:  The mass of rock beneath a geological structure such as an orebody or fault.
Formation:  The ordinary unit of geologic mapping consisting of a large and persistent stratum of rock.
Forward contract:  The sale or purchase of a commodity for delivery at a specified future date.
Fracture:  A break in the rock, the opening of which affords the opportunity for entry of mineral-bearing solutions. A "cross fracture" is a minor break extending at more-or-less right angles to the direction of the principal fractures.
Free gold:  Small particles of native gold.
Free milling:  Ores of gold or silver from which the precious metals can be recovered by concentrating methods without resort to pressure leaching or other chemical treatment.
Friction hoist:  A mine hoist in which conveyances are suspended from both sides of a simple friction pulley which imparts the desired motion; it is distinct from a drum hoist, in which the ropes are wound on to their individual drums.
Fumarole:  A site where hot smoke and gases are expelled in a volcanic area.
Furnace:  Equipment for roasting or smelting ores.
Fusion:  The melting of a substance.


A coarse-grained, dark, igneous rock.
Galena:  A sulfide mineral of lead, being a common lead ore mineral.
Gamma:  A unit of measurement of magnetic intensity.
Gangue:  The worthless minerals in an ore deposit.
Geiger counter:  An instrument used to measure radioactivity (e.g., that which emanates from certain minerals) by means of a Geiger- Mueller tube. It detects the gamma rays and indicates the frequency or intensity either visually (by dial or flashing light), audibly (by earphones) or both.
Gem stones:  Semi-precious stones hard enough to cut and polish.
Geochemistry:  The study of the chemical properties of rocks.
Geochemical sampling:  Samples of soils, stream sediments or rock chips taken to ensure the quantities of trace and minor elements.
Geology:  The science concerned with the study of the rocks which compose the Earth.
Geophysical Survey:  An exploration method which measures magnetic, electrical or other physical characteristics of the earth, the results of which can be interpreted and used to predict the possibility of economic mineral concentrations beneath the surface of the earth. Common properties investigated include magnetism, specific gravity, electrical conductivity and radioactivity.
Geophysicist:  A scientist who practices geophysics.
Geophysics:  The study of the physical properties of rocks and minerals.
Geothermal:  Pertains to the heat of the Earth's interior.
Glacial drift:  Sedimentary material, consisting of clay and boulders, that has been transported by glaciers.
Glacial striations:  Lines or scratches on a smooth rock surface caused by glacial abrasion.
Glory hole:  An open pit from which ore is extracted, especially where broken ore is passed to underground workings before being hoisted.
Gneiss:  A layered or banded crystalline metamorphic rock the grains of which are aligned or elongated into a roughly parallel arrangement.
Gold:  A precious metal of bright yellow color. The most ductile and malleable of all metals and one of the heaviest.
Gold nuggets:  Gold particles not passing through a 10 mesh screen.
Gold pan:  Heavy metal or plastic pan specially designed to assist in gold recovery.

Gold screw: 


A gold pan shaped device which has spiral groves and is rotated by a small electric motor in a manner that, if concentrates are added, gold will get separated and fall into a flask through a hold in the center.

Gold sniffer: 

Suction syringe type instrument used to suck gold from crevices.
Gold table:  Volume or weight of placer gravel or an ore.
Gophering:  Prospecting by means of hand-dug holes.
Gossan:  The rust-colored oxidized capping or staining of a mineral deposit, generally formed by the oxidation or alteration of iron sulfides.
Gouge:  Fine, putty-like material composed of ground-up rock found along a fault.
Graben:  A downfaulted block of rock.
Grab sample:  A sample taken at random; it is assayed to determine if valuable elements are contained in the rock. A grab sample is not intended to be representative of the deposit, and usually the best-looking material is selected.
Grade:  The relative quality or percentage of ore metal content.
Grading plate:  Steel plate punctured to grade the size of gravels.

Graduated cylinder: 

Flask marked with lines to indicate measured volumes.
Grain:  Unit of weight. There are 480 grains in a troy ounce.
Gram:  Metric unit of weight. There are 31.103 grams in a troy ounce.
Granite:  An coarse-grained (intrusive) igneous rock consisting of quartz, feldspar and mica.
Granular:  Composed of compacted mineral grains.
Graphitic:  Containing carbon or graphite.
Grassroots Exploration (Reconnaissance):  Exploration activities in search of mineral deposits in areas where no known economically viable mineral deposits are present.
Gravity/flotation:  In the gravity circuit, the heaviest particles are separated from the ground ore in a centrifugal concentrator. The gold is further concentrated on a shaking table by virtue of its high density. The remaining ore is processed in the flotation circuit where the mineral particles, including the balance of the gold and silver, are caused to become attached to bubbles, float and become concentrated.
Gravity meter, gravimeter:  An instrument for measuring the gravitational attraction of the Earth; gravitational attraction varies with the density of the rocks in the vicinity.
Gravity separation:  Recovery of gold from crushed rock or gravel using gold's high specific gravity to separate it from lighter material.
Greenstone belt:  A convenient field term used to describe any fine-grained greenish volcanic rock, most often applied to andesite.
Grinding media:  Material used to finely grind ore material to a size which allows recovery of the desired contained material.
Grizzly (or mantle):  A grating (usually constructed of steel rails) placed over the top of a chute or ore pass for the purpose of stopping large pieces of rock or ore that may hang up in the pass.
Gross value:  The theoretical value of ore determined simply by applying the assay of metal or metals and the current market price; it represents the total value of the contained metals before deduction for dilution, mill recovery losses, mining and smelting costs, etc.; it must be used only with caution and severe qualification.
Gross value royalty:  A share of gross revenue from the sale of minerals from a mine.
Grouting:  The process of sealing off a water flow in rocks by forcing thin cement slurry, or other chemicals, into the crevices; usually done through a diamond drill hole.
Grubstake:  Finances or supplies of food, etc., furnished to a prospector in return for an interest in any discoveries made.
Guides:  The timber rails installed along the walls of a shaft for steadying, or guiding, the cage or conveyance.
Gulch:  A narrow or deep ravine or canyon.
Gully:  A small ravine.
Gumbo:  Very sticky or clayey mud.


The lowest depression in the bottom of a stream channel.
Gypsum:  A sedimentary rock consisting of hydrated calcium sulfate.
Gyratory crusher:  A machine that crushes ore between an eccentrically mounted crushing cone and a fixed crushing throat. Typically has a higher capacity than a jaw crusher.