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Glossary Print

Here is a glossary of terms relevant to uranium mining. 

This glossary was compiled from these sources:

Uranium Miner Glossary
SEA-US: The Sustainable Energy and Anti-Uranium Service Inc.
Uranium In Situ Leaching: The Case Against Solution Mining



Acid mine drainage - Acidic run-off water from mine waste dumps and mill tailings ponds containing sulphide minerals. Also refers to ground water pumped to surface from mines.

Actinide -  Fifteen radioactive elements of which only thorium and uranium occur naturally in the earth's crust in anything more than trace quantities.

Aquifer - An underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well.

Arsenic - A chemical element that is notoriously poisonous.

Assay - A chemical test performed on a sample of ores or minerals to determine the amount of valuable metals contained.

Assessment work - The amount of work, specified by mining law, that must be performed each year in order to retain legal control of mining claims.


Backfill - Waste material used to fill the void created by mining an orebody. 

Barren Solution - A solution in hydrometallurgical treatment from which all possible valuable constituents have been removed.

Bleed Solution - Solution drawn to adjust production or to restore groundwater by pumping more fluids from the production zone than are injected, creating an inflow of fresh groundwater into the production area.


Brine Solution - A concentrated solution containing dissolved minerals (usually greater than 100,000 mg/liter), especially chloride salts.

Byproduct - A secondary metal or mineral product recovered in the milling process.


Claim - A portion of land held either by a prospector or a mining company.

Clarification - Process of clearing dirty water by removing suspended material.

Conventional mill (uranium) - A facility engineered and built principally for processing of uraniferous ore materials mined from the earth and the recovery, by chemical treatment in the mill's circuits, of uranium and/or other valued coproduct components from the processed ore.

Cut-and-fill - A method of stoping in which ore is removed in slices, or lifts, and then the excavation is filled with rock or other waste material (backfill), before the subsequent slice is extracted.


Dilution (mining) - Rock that is , by necessity, removed along with the ore in the mining process, subsequently lowering the grade of the ore.

Domestic uranium industry - Collectively, those businesses (whether U.S. or foreign-based) that operate under the laws and regulations pertaining to the conduct of commerce within the United States and its territories and possessions and that engage in activities within the United States, its
territories, and possessions specifically directed toward uranium exploration, development, mining, and milling; marketing of uranium materials; enrichment; fabrication; or acquisition and management of uranium materials for use in commercial nuclear power plants.

Dump - A pile of broken rock or ore on surface.


Elution - Activities of removing "elutes" a material (uranium) adsorbed on ion exchange resin from the "eluant" solution. 

Enriched uranium - Uranium in which the 235U isotope concentration has been increased to greater than the 0.711 percent 235U (by weight) present in natural uranium.

Enrichment feed deliveries - Uranium that is shipped under contract to a supplier of enrichment services for use in preparing enriched uranium product to a specified 235U concentration and that ultimately will be used as fuel in a nuclear reactor.

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.

Erosion - The breaking down and subsequent removal of either rock or surface material by wind, rain, wave action, freezing and thawing and other processes.

Evaporation Pond - A containment pond (that should have an impermeable lining of clay or synthetic material such as hypalon) to hold liquid wastes and to concentrate the waste through evaporation.

Exploration - Prospecting, sampling, mapping, diamond drilling and other work involved in searching for ore.

Exploration drilling - Drilling done in search of new mineral deposits, on extensions of known ore deposits, or at the location of a discovery up to the time when the company decides that sufficient ore reserves are present to justify commercial exploitation. Assessment drilling is reported as exploration drilling.

Extraction Well (Production) - A well or a drill hole in an in situ leach operation through which the solutions (or groundwater) are extracted to the surface treatment plant. Typically surrounded by injection wells. 


Groundwater - Water beneath the surface in the saturated zone that is under atmospheric or artesian pressure. 


Heap leaching - A process whereby valuable metals are leached from a heap, or pad, of crushed ore by leaching solutions percolating down through the heap and collected from a sloping, impermeable liner below the pad.

Heap leach solutions - The separation, or dissolving-out, from mined rock of the soluble uranium constituents by the natural action of percolating a prepared chemical solution through mounded (heaped) rock material. The mounded material usually contains low grade mineralized material and/or waste rock produced from open-pit or underground mines. The solutions are collected after percolation is completed and processed to recover the valued components.

Heavy metal - any of a number of higher atomic weight elements, which has the properties of a metallic substance at room temperature. Living organisms require trace amounts of some heavy metals, including iron, cobalt, copper, manganese, molybdenum, vanadium, strontium, and zinc, but excessive levels can be detrimental to the organism. Other heavy metals such as mercury, lead and cadmium (with one exception for the latter) have no known vital or beneficial effect on organisms, and their accumulation over time in the bodies of mammals can cause serious illness. Two pathways or toxic effects on humans is to enter the soil as a soil contaminant or to enter groundwater as a water pollutant.

Hydraulic conductivity - Factor of proportionality in Darcy's equation relating flow velocity to hydraulic gradient having units of length per unit of time. A property of the porous medium and the fluid (water content of the medium).

Hydrometallurgy - The treatment of ore by wet processes, such as leaching, resulting in the solution of a metal and its subsequent recovery.


Injection Well - A well or a drill hole in an in situ leach operation through which barren solutions are entered into an underground stratum or ore body by gravity or under pressure. Typically surrounded by monitoring wells.

In Situ Leaching - The in-place mining of a mineral without removing overburden or ore, by installing a well and mining directly from the natural deposit thereby exposed to the injection and recovery of a fluid that causes the leaching, dissolution, or extraction of the mineral.

In Situ Leach mining (ISL) - The recovery, by chemical leaching, of the valuable components of an orebody without physical extraction of the ore from the ground. Also referred to as "solution mining" or In Situ Recovery. 


Injection Well - A well or a drill hole in an in situ leach operation through which barren solutions are entered into an underground stratum or ore body by gravity or under pressure. Typically surrounded by monitoring wells.

Ion exchange - An exchange of ions in a crystal with irons in a solution. Used as a method for recovering valuable metals, such as uranium, from solution.



Leachable - Extractable by chemical solvents.

Leachate - The liquid that has percolated through the soil or other medium.

Leaching - A chemical process for the extraction of valuable minerals from ore; also, a natural process by which ground waters dissolve minerals, thus leaving the rock with a smaller proportion of some of the minerals than it contained originally.

Lixiviant - Leachate solution pumped underground to a uranium ore body; it may be alkaline or acidic in character.


Mill - A plant in which ore is treated and metals are recovered or prepared for smelting; also a revolving drum used for the grinding of ores in preparation for treatment.

Milling ore - Ore that contains sufficient valuable mineral to be treated by milling process.

Milling of uranium - The processing of uranium from ore mined by conventional methods, such as underground or openpit, to separate the uranium from the undesired material in the ore.

Molybdenum - A chemical element found in trace amounts in plants and animals, and in some animals, excess molybdenum can be toxic.


Nonconventional plant (uranium) - A facility engineered and built principally for processing of uraniferous solutions that are produced during in situ leach mining, from heap leaching, or in the manufacture of other commodities, and the recovery, by chemical treatment in the plant's circuits, of uranium from the processed solutions.

Nuclear Energy - Nuclear energy originates from the splitting of uranium atoms in a process called fission. At the power plant, the fission process is used to generate heat for producing steam, which is used by a turbine to generate electricity. Because nuclear power plants do not burn fuel, they do not emit air pollutant emissions. All of the nuclear power plants in the United States collectively produce about 2,000 metric tons per year of radioactive waste. Abandoned uranium mines contaminated with high-level radioactive waste can continue to pose radioactive risks for as long as 250,000 years after closure. There are more than 60 nuclear power plants currently in operation in the U.S., which accounts for approximately 20 percent of the country’s electricity production. No nuclear power plants have been built since 1996, mostly due to economic factors and environmental concerns.


Open pit - A mine that is entirely on surface. Also referred to as open-cut or open-cast mine.

Oxidation - A chemical reaction caused by exposure to oxygen that results in a change in the chemical composition of a mineral.


Permeability - The ease with which fluid flows through a porous medium.

Pitchblende - An important uranium ore mineral. It is black in color, possesses a characteristic greasy lustre and is highly radioactive.

Plutonium - is a radioactive, metallic chemical element.  It is the element used in most modern nuclear weapons.

Polishing pond - The last in a series of settling ponds through which mill effluent flows before being discharged into the natural environment.

Porous (Pore Space) - The open spaces or voids within a soil or rock. It is a measure of the amount of liquid or gas that may be absorbed or yielded by a particular formation.

Pregnant Solution - A solution containing dissolved extractable mineral that was leached from the ore; uranium leach solution pumped up from the under-ground ore zone though a production hole.



Radioactive decay - the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves.

Radioactivity - The property of spontaneously emitting alpha, beta or gamma rays by the decay of the nuclei of atoms.

Radium-226 - Radium is an alkaline earth metal that is found in trace amounts in uranium ores. It is extremely radioactive. Its most stable isotope, 226Ra, has a half-life of 1602 years and decays into radon gas.

Radon - A radioactive noble gas that is formed by the decay of radium, radon is one of the heaviest gases and is considered to be a health hazard. Radon is a significant contaminant that affects indoor air quality worldwide. Radon gas from natural sources can accumulate in buildings and reportedly causes 21,000 lung cancer deaths per year in the United States alone.

Reclamation - The restoration of a site after mining or exploration activity is completed. Includes surface contouring, equipment removal, well plugging, revegetation, etc.

Renewable Energy -The term renewable energy generally refers to electricity supplied from renewable energy sources, such as wind and solar power, geothermal, hydropower, and various forms of biomass. These energy sources are considered renewable sources because they are continuously replenished on the Earth.

Replacement ore - Ore formed by a process during which certain minerals have passed into solution and have been carried away, while valuable minerals from the solution have been deposited in the place of those removed.

Restoration - The returning of all affected groundwater to its premining quality for its premining use by employing the best practical technology.

Reverse Osmosis - The act of reversing a diffusion through a semipermeable membrane, typically separating a solvent and a solution, that tends to equalize their concentrations.

Roll Front - A type of uranium deposition localized as a roll or interface separating an oxidized interior from a reduced exterior. The reduced side of this interface is significantly enriched in uranium.


Saturated Zone - The zone of a soil or rock formation where the pore space is completely filled with water. This would be called an aquifer at depth or the water table if immediately below the surface sediments.

Selenium - see Impacts: Selenium Contamination

Sedimentary rocks - Secondary rocks formed from material derived from other rocks and laid down under water. Examples are limestone, shale and sandstone.

Slash - The process of blasting rock from the side of an underground opening to widen the opening.

Solution Mining - Another term used for In Situ Leaching.

Stratigraphy - Strictly, the description of bedded rock sequences; used loosely, the sequence of bedded rocks in a particular area.

Strip - To remove the overburden or waste rock overlying an orebody in preparation for mining by open pit methods.

Stripping ratio - The ratio of tonnes removed as waste relative to the number of tonnes of ore removed from an open-pit mine.

Strip mine - An open-pit mine, usually a coal mine, operated by removing overburden, excavating the coal seam, then returning the overburden.

Sump - An underground excavation where water accumulates before being pumped to surface.


Tailings - Material rejected from a mill after most of the recoverable valuable minerals have been extracted.

Tailings pond - A low-lying depression used to confine tailings, the prime function of which is to allow enough time for heavy metals to settle out or for cyanide to be destroyed before water is discharged into the local watershed.

Trench - A long, narrow excavation dug through overburden, or blasted out of rock, to expose a vein or ore structure.


Uranium - A heavy, naturally radioactive, metallic element (atomic number 92). Its two principally occurring isotopes are 235U and 238U. The isotope 235U is indispensable to the nuclearindustry because it is the only isotope existing in nature to any appreciable extent that is fissionable by thermal neutrons. The isotope 238U is also important because it absorbs neutrons to produce a radioactive isotope that subsequently decays to the isotope 239Pu, which also is fissionable by thermal neutrons.

Uranium concentrate - A yellow or brown powder obtained by the milling of uranium ore, processing of in situ leach mining solutions, or as a byproduct of phosphoric acid production.

Uranium deposit - A discrete concentration of uranium mineralization that is of possible economic interest.

Uranium endowment - The uranium that is estimated to occur in rock with a grade of at least 0.01 percent U3O8. The estimate of the uranium endowment is made before consideration of economic availability and any associated uranium resources.

Uranium hexafluoride (UF6) - A white solid obtained by chemical treatment of U3O8 and which forms a vapor at temperatures above 56 degrees Centigrade. UF6 is the form of uranium required for the enrichment process.

Uranium ore - Rock containing uranium mineralization in concentrations that can be mined economically, (typically 1 to 4 pounds of U3O8 per ton or 0.05 to 0.20
percent U3O8).

Uranium oxide - Uranium concentrate or yellowcake. Abbreviated as U3O8.

Uranium property - A specific tract of land with known uranium reserves that could be developed for mining.

Uranium reserves - Estimated quantities of uranium in known mineral deposits of such size, grade, and configuration that the uranium could be recovered at or below a specified production cost with currently proven mining and processing technology and under current law and regulations. Reserves are based on direct radiometric and chemical measurements of drill hole and other types of sampling of the deposits. Mineral grades and thickness, spatial relationships, depths below the surface, mining and reclamation methods, distances to milling facilities, and amenability of ores to processing are considered in the evaluation. The amounts of uranium in ore that could be exploited within the chosen forward-cost levels are estimated utilizing available sampling, engineering, geologic, and economic data in accordance with conventional engineering practices.

Uranium resources categories - Three categories of uranium resources are used to reflect differing levels of confidence in the resources reported. Reasonably assured resources (RAR), estimated additional resources (EAR), and speculative resources (SR) are described below.

  • Reasonably assured resources (RAR) - The uranium that occurs in known mineral deposits of such size, grade, and configuration that it could be recovered within the given production cost ranges, with currently proven mining and processingtechnology. Estimates of tonnage and grade are based on specific sample data and measurements of the deposits and on knowledge of deposit characteristics. RAR correspond to DOE's uranium reserves category.       
  • Estimated additional resources (EAR) - The uranium in addition to RAR that is expected to occur, mostly on the basis of direct geological evidence, in extensions of well-explored deposits, little explored deposits, and undiscovered deposits believed to exist along well-defined geological trends with known deposits, such that the uranium can subsequently be recovered within the given cost ranges. Estimates of tonnage and grade are based on available sampling data and on knowledge of the deposit characteristics, as determined in the best-known parts of the deposit or in similar deposits. EAR correspond to DOE's probable potential resources category.
  • Speculative resources (SR) - Uranium in addition to EAR that is thought to exist, mostly on the basis of indirect evidence and geological extrapolations, in deposits discoverable with existing exploration techniques. The locations of deposits in this category can generally be specified only as being somewhere within givenregions or geological trends. The estimates in this category are less reliable than estimates of RAR and EAR. The category of SR corresponds to DOE's possible potential resources plus speculative potential resources categories combined.



Waste - Unmineralized, or sometimes mineralized, rock that is not minable at a profit.

Wellfield - The area of an in situ leach operation that encompasses the array of injection and extraction wells and interconnected piping employed in the leaching process.



Yellowcake - A natural uranium concentrate that takes its name from its color and texture. Yellowcake typically contains 70 to 90 percent U3O8 by weight. It is used as feedstock for uranium fuel enrichment and fuel pellet fabrication. Yellow cake is also known as "uranium oxide" (see uranium oxide).


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