Production Glossary
Glossary
A glossary of common mining terms.
| a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z |
Acid Rock Drainage (ARD)
Acid Rock Drainage (ARD) is a natural weathering process where sulphide minerals exposed to water and air react to produce acid. ARD occurs where large quantities of sulphur-containing rock minerals are produced, and can be observed in road and airport construction and at mines(mine rock piles, tailings, rock walls in open pits). Resultant acidic water dissolves other minerals, potentially increasing the metal content in the water to levels that are deleterious to aquatic habitat.
Activated carbon
Activated carbon has the ability to capture and extract gold from a gold solution. Small granules of carbon between 1/16 and 1/8 of an inch across are normally made from coconut shells for use in metallurgical plants. After heating to red heat in an oxygen-free atmosphere, the carbon is activated, and among other characteristics it attracts and binds with gold, releasing it from a cyanide solution.
Adit
A tunnel driven horizontally into a mountainside, providing bottom access to a mineral deposit and/or helping to drain water.
Agglomeration
Process whereby the mined ore is mixed with cement or lime prior to loading on the leach pad in order to group fine particles into larger pieces. This process also improves percolation of leaching fluids, and is often used when clay in the ore threatens to block percolation of leach fluids that are otherwise suitable for heap leaching.
Amalgamation
The primitive process where mercury is used to extract gold from gold-bearing ores. The mercury binds with gold to form an amalgam not dissimilar from old style tooth fillings. The amalgam is roasted to drive off the mercury, leaving a small bead of gold. If the mercury is not carefully captured its use by small miners often leads to health problems and environmental degradation.
Anomaly
A statistical abnormality discovered by surveying and plotting geochemical or geophysical patterns. "Anomalies" are easily found or generated, and investing on the basis of such an anomaly is highly speculative. If a geophysical and geochemical anomaly coincide, the probabilities are improved, but even if mineralization is discovered this in no way guarantees it will be economic.
Assay
The term given to the chemical analysis of rock samples and metals.
Autoclave System
Oxidation process in which high temperatures and pressures are applied to convert refractory sulphide mineralization into more amenable oxide ore. NB this is a particularly good system if the ore contains arsenic, since it traps this element in an environmentally benign compound. Autoclaves are not normally good if the ore contains carbon or carbonates.
Backfilling
Waste material used to fill the void created by mining an ore body. This can simply be broken rock from tunnelling that is tipped into a stope, or it can be crushed ore from which gold has been extracted that is pumped back underground. In California, mining rules require the backfilling of open pits, making most mining in that state uneconomic.
Ball Mill
A steel cylinder loaded with steel balls into which crushed ore is fed. The ball mill is rotated, causing the balls to cascade and grind the ore.
Bench
Successive steps/horizontal increments mined as an open pit progresses deeper. Bench heights of 30 feet are typical but can vary to suit required selectivity of mining.
Bioleaching
The process of using naturally occurring bacteria to accelerate the oxidation of sulfidic minerals that encase some forms of gold mineralization and prevent leaching chemicals from reaching the gold. When ore is exposed to large concentrations of these sulphide-consuming organisms, enough of the sulfidic material can be removed to recover the gold using the normal leaching process. This process can be done on leach pads or in aerated tanks.
By-product
A secondary metal or mineral product of economic value recovered in the extraction process. Typical gold mine by-products are silver, copper and zinc.
Carbonaceous Ore
Ore containing particles of carbon material can reduce gold recoveries. Natural carbon can compete with the activated carbon introduced in the treatment process for gold which has been liberated by the cyanide leach. Activated carbon introduced in the process has a large grain size and is captured on screens. After the ore is crushed and ground, natural carbon will be much finer and is lost to the tailings together with any gold which has attached to it. Roasting carbonaceous ore is one route to improve recoveries.
Carbon-in-leach (CIL)
A recovery process in which a slurry of gold ore, activated carbon granules and cyanide are mixed together. The cyanide dissolves the gold content and the gold is absorbed on the carbon. The carbon is subsequently separated from the slurry for further gold removal.
Carbon-in-pulp (CIP)
Similar to carbon-in-leach process, but initially the slurry is subjected to cyanide leaching in separate tanks followed by carbon-in-pulp. Carbon-in-leach is a simultaneous process. This is a better process if there is some carbon in the ore.
Cash Costs
Includes site costs for all mining, processing, administration, resource taxes, and royalties but does not include capital, exploration, depreciation, and financing costs. Total cash costs are reduced using by-product credits, and are then divided by payable gold ounces to arrive at net cash cost of production per ounce. This is a non GAAP measure.
Contained Ounces
Represents ounces in the ground without the reduction of ounces not recovered by the applicable metallurgical process.
Concentrate
If gold is intimately mixed with, for example, copper sulphides, it may be most economic to create a concentrate containing both metals, for further treatment at a smelter. The concentrate is a powdery product containing the valuable ore mineral from which most of the waste material has been eliminated.
Concentrator/Float plant
A particular type of milling plant that produces a concentrate of the valuable minerals or metals. The concentrate must then be treated in some other type of plant, such as a smelter, to effect recovery of the metal.
Contango
The normal futures curve for gold (certainly over the last two decades) where future gold prices are higher than spot prices.
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.
Cutting assays
In some gold mines very high grades are detected periodically, but if the actual result is included in the grade calculation for large blocks of ore it often overestimates the gold content of the block. Hence it's common in greenstone mines to "cut" high grade assays back to a standard level to limit the impact of small tonnages of very high grade gold in larger ore blocks.
Cyanide (cross reference to also see Cyanide discussion?)
This is a naturally occurring compound, which is very effective in taking gold into solution.
Cyanidation (cyanide leaching)
A method of extracting gold or silver from ore by dissolving it in a weak solution of sodium cyanide. After the precious metal is dissolved, the ground rock is separated from the solution and then the gold is precipitated from the solution, normally using zinc powder. If there is little silver in solution precious metals can be extracted from the leachate using activated carbon.
Deposit
A mineralized body, which has been physically delineated by sufficient drilling, trenching, and/or underground work, and found to contain a sufficient average grade of metal or metals to warrant further exploration and/or development expenditures. Such a deposit does not qualify as commercially mineable tons or as containing material reserves until final technical and economic factors have been resolved.
Dilution
The effect of waste or low grade ore being included unavoidably in the mined ore, lowering the recovered grade. However, it should be checked with the gold producer whether the grade of the quoted reserves is before or after dilution as this can have a significant effect on cash costs.
Dip
The inclination of a planar surface, measured in the vertical plane perpendicular to its strike. A steeply dipping orebody is generally easier to mine than a flatter one since gravity helps move ore.
Direct shipping ore
Sometimes a mine has very high grade ore that requires treatment in a smelter, and the cost of building a treatment plant is unnecessary. In this case this direct shipping ore goes directly to the smelter.
Disseminated Ore
Ore carrying small particles of valuable minerals, spread more or less uniformly through the gangue matter; distinct from massive ore, wherein the valuable minerals occur in almost solid form with very little waste mineral included.
Doré
Unrefined gold and silver bullion bars usually consisting of various percentages of precious metals which will be further refined to almost pure metal.
Drift
Horizontal underground tunnel driven alongside or through an ore deposit, from either an adit or shaft, to gain access to the deposit.
Drilling Terms
Blasthole Drilling holes into rock to place an explosive charge that breaks up the rock.
Diamond Drilling with a hollow bit with a diamond cutting rim, to produce a cylindrical core of rock or chippings used for geological study and assays. A Diamond Drill is a rotary type of rock drill that cuts a core of rock that is recovered in long, cylindrical sections. It's more costly on a per foot of drilling basis, but generally delivers more reliable results than reverse circulation (RC) drills.
Infill Diamond Drilling at shorter intervals between existing holes, used to provide greater geological detail and to help establish reserve estimates.
Reverse Circulation Drilling produces rock chips rather than core. Faster and cheaper than diamond drilling, it can be used for reconnaissance drilling. The chips are forced by air to surface for examination. RAB or reverse Air Blast drilling is similar.
Electro-winning
Recovery of a metal from solution by means of electrochemical processes. This is often used as a penultimate step in capturing gold from the CIP/CIL process.
Elution
The process used to recover gold from activated carbon. Normally the gold is recovered from loaded activated carbon using a hot concentrated cyanide solution. This generates a concentrated gold solution from which gold can be precipitated using electro-winning. Precipitated gold is melted into doré bars, and the carbon is re-activated in a furnace and re-cycled.
Epithermal Deposit
An epigenetic deposit formed at low temperatures (50-200°C) near the earth's surface (1,500 m).
Fault
A break in the earth's crust caused by tectonic forces which have moved the rock to one side with respect to the other. Faults can often be favourable hosts for orebodies or may have channelled ore-bearing fluids to more favourable horizons.
Flotation
A process by which mineral particles are induced to become attached to bubbles and float, and other particles to sink, so that the valuable minerals can be collected at the top of the float tanks and separated from waste rock. Flotation is an attractive treatment route since it doesn't normally attract as much environmental regulation.
Foot Wall
The wall or the rock on the underside of a vein or ore deposit.
Geostatistics
A sub sector of statistical theory that specializes in natural materials.
Geophysics
A term to describe exploration methods that use the physical (seismic, gravimetric) or electro resistive characteristics of potential orebodies. Geophysical methods are used to attempt to discover new ore or extensions to known orebodies.
Grade
The amount of valuable mineral in each ton of ore, expressed as troy ounces per ton or grams per tonne for precious metals and as a percentage for other metals.
Cut-off Grade: the minimum metal grade at which an ore body can be economically mined.
Mill Head Grade: metal content of mined ore going into a mill for processing. Usually lower than reserve grade because of dilution.
Recovered Grade: actual metal content of ore determined after processing.
Reserve Grade: estimated metal content of an ore body, based on reserve calculations. I
Hanging Wall
The wall or the rock on the upper side of a vein or ore deposit.
Heap/Dump Leaching
A process whereby gold is extracted by "heaping" broken ore on sloping impermeable plastic pads and spraying the heaps with a weak cyanide solution, which dissolves the gold content. The gold-laden (pregnant) solution is passed through activated carbon which collects the gold before it is passed back though the leach pad.
Heap Leach Pad
A large impermeable foundation or pad used as a base for ore during heap leaching. These are now often double lined with 1/8 inch thick plastic sheet to make certain cyanide solutions don't leak into ground water.
Hedge Book
A term used to describe a firm's full array of agreements and derivative products in place to guard against declines in the sales price of gold the company produces. These may include forward sales, puts, calls, or lease rate swaps.
Hoist
The machine used for raising and lowering the cage or other conveyance in a shaft.
Kriging
A method developed by a French statistician called Matheron using ideas developed
by South African Danie Krige to estimate ore reserves.
Layback
A term to describe phases of mining in an open pit required to access open pit ore, while at the same time maintaining a safe pit slope.
Leach Pad
See heap leach pad.
Long-hole Open Stope
A method of mining involving the drilling of holes up to 90 feet long into an ore body and then blasting a slice of rock which falls into an open space. The broken rock is extracted and the resulting open chamber may be backfilled with waste rock.
Low sulfadation ore
Gold ore with a low sulphur content. This is helpful in that the resulting tailings are unlikely to contribute acidic waters leading to acid rock drainage.
Mark-to-Market (MTM)
A term used to refer to the unrealized gain or loss of a company's hedge book.
Measured and Indicated Resource
See resources.
Merrill-Crowe
A precipitation process to recover precious metals using zinc dust to treat a deoxygenated precious metals-cyanide solution. This is most applicable to ores with higher silver content.
Metallurgy
A general term embracing the practice and science of extracting metals from their ores and the refining of crude metal.
Mill/Milling Circuit/Treatment plant/Met plant
A plant where ore is crushed, then ground fine and submitted to a process whereby it undergoes physical or chemical treatment to extract the valuable metals.
Mineralization
Rock containing an undetermined amount of minerals or metals, with as yet unknown economics.
Mining Claim
That portion of public mineral lands which a party has staked or marked out in accordance with federal, provincial, or state mining laws to acquire the right to explore for and exploit the minerals under the surface.
Ore Pass
A vertical or sub-vertical hole in which ore is tipped normally through a large grid or "grizzly". Ore falls down this hole and is collected sometimes after crushing for hoisting to surface.
Open Pit (Open Cut)
A mine that is entirely on the surface.
Ore/Ore Reserves
Rock, generally containing metallic or non-metallic minerals, that can be mined and processed at a profit, and has been engineered and permitted so that the only impediment to mining is scheduling.
Oxide Ore
Ore in which some or all of the original minerals have been oxidized. Oxidation tends to make the ore more porous and permits a more complete permeation of cyanide solutions so that minute particles of gold in the interior of the minerals will be readily dissolved. Oxidation tends to improve gold recovery.
Placer
A sedimentary deposit of minerals concentrated by natural mechanical processes, usually involving moving water in which the dense minerals sink.
Porphyry
Igneous rock composed of large, conspicuous crystals (phenocrysts) and a groundmass in which the phenocrysts are embedded. This rock can be a host for large copper and gold deposits. Porphyry gold and copper gold deposits tend to be big and amenable to large-scale mechanized mining.
Pregnant Pond
Pond containing gold solution; the solution is impregnated with gold and silver removed from the ore. This pond is normally a green colour, the darker green the more contained gold.
Proven and Probable Reserves
That part of a mineral deposit which could be economically and legally extracted or produced at the time of the reserve determination. Reserves are customarily considered ore when dealing with metalliferous minerals.
Raise
A vertical hole between mine levels used to move ore or waste rock or to provide ventilation.
Ramp
An inclined underground tunnel which provides access for exploration or a connection between levels of a mine.
Reclamation
The process by which lands disturbed as a result of mining activity are reclaimed back to a beneficial land use. Reclamation activity often includes the removal of buildings, equipment, machinery and other physical remnants of mining, closure of tailings impoundments, leach pads and other mine features, and contouring, covering and revegetation of waste rock piles and other disturbed areas.
Recovery Rate
A term used in process metallurgy to indicate the proportion of valuable material obtained in the processing of an ore. It is generally stated as a percentage of the material recovered compared to the total material present.
Reef
See vein.
Refining
The final stage of metal production in which impurities are removed from crude metal from the smelting process.
Refractory Ore
Gold ores in which the gold is not amenable to recovery by conventional cyanide methods without any pre-treatment. The refractory nature can result from either silica or sulphide encapsulation of the gold. Alternatively it can result from the presence of naturally occurring carbon, which reduces gold recovery.
Reserves
That part of a mineral deposit, which could be economically and legally extracted or produced at the time of the reserve determination. Reserves are customarily stated in terms of ore when dealing with metalliferous minerals. There are two categories of reserves:
Proven Ore: Material for which tonnage and grade are computed from dimensions revealed in outcrops, trenches, underground workings or drill holes; grade is computed from the results of adequate sampling; and the sites for inspection, sampling and measurement are so spaced and the geological character well enough defined that size, shape and mineral content are established.
Probable Ore: Material for which tonnage and grade are computed partly from specific measurements, samples, or production data and partly from projection for a reasonable distance on geological evidence, and for which the sites available for inspection, measurement and sampling are too widely or otherwise inappropriately spaced to outline the material completely or to establish its grade throughout.
Resources
Resources are composed of mineralized material which is either not sufficiently quantified, or doesn't qualify as ore because it is uneconomic or is not engineered or is lacking permits. Resources are now typically reported in two categories
Measured and indicated: This is material for which tonnage and grade are known with reasonable confidence. This material is likely to be excluded from reserve categories because the ore has not been engineered into the mine plan or it awaits permits.
Inferred: This material is less well quantified. It will normally require infill drilling to raise confidence in the tonnage and grades before a decision on whether it is economic can be made.
Roasting
The treatment of ore by heat in air, or an oxygen-enriched atmosphere. This process destroys the structure of the (typically) sulphide minerals that could have been trapping gold and reducing recoveries in a refractory ore. This process is very good if the ore is carbonaceous, it is not good if the ore contains arsenic. NB although the plant itself is not normally expensive, environmental treatment of the off gasses can be very costly.
ROM (Run of Mine)
Ore is normally treated in some way, but in some low-grade operations the cost of crushing or otherwise preparing the ore ahead of treatment is not beneficial to the project's economics, and the ore goes to ROM leach pads.
Semi-autogenous Grinding (SAG)
A method of grinding rock into fine powder whereby the grinding media consist of larger rocks, sometimes assisted by steel balls.
Shaft
A vertical passageway to an underground mine for moving personnel, equipment, supplies, and material, including ore and waste rock.
Smelting
A metallurgical operation in which metal is separated from impurities by a process that includes fusion. This is a common intermediate process where an ore concentrate is produced.
Social license
A term used to describe the relationship a mining company has with its neighbours in countries where it operates. This has come to include the miners' responsibility to minimize the environmental impact of a mining project, and to maximize the economic/social benefit of the project for its in-country partners.
Stope
A term used to describe a block of ore in an underground mine.
Strike
The strike of a linear orebody is the direction of the longest dimension of the orebody, for example northeast to southwest.
Strike Length
The longest horizontal dimension of an ore body or zone of mineralization.
Stripping Ratio
The ratio of the number of tons of waste material removed to the number of tons of ore removed, or sometimes the number of tons of rock to be moved per ounce of gold, used in connection with open pit mining.
Sulphide
A compound of sulphur and some other metallic element.
Sulphide Ore
Sulphide ore will normally represent primary ore. Gold can be simple coatings on sulphide granules and amenable to simple cyanide leaching. Or gold can be intimately mixed with, for example, iron sulphides requiring autoclaving or roasting to extract gold.
Tailings
The material that remains after all metals considered economic have been removed from ore during milling or heap leaching.
Tailings Dam
A natural or man-made area suitable for depositing the material that remains after the treatment of ore.
Troy Ounce
Troy ounce of a fineness of 999.9 parts per 1,000 parts, equal to 31.1034 grams.
Vein
A tabular geological feature, normally much longer than its width, where chemical or physical differences between it and the surrounding rock have caused economic mineral to concentrate. The vein or reef can be a little or extremely discontinuous and can contain higher-value payshoots.
Waste Pass
A vertical or subvertical hole in which rock is tipped normally through a large grid or "grizzly". Waste falls down this hole and is collected sometimes after crushing for hoisting to surface.
Water Management
The process whereby the groundwater table in the mining area is lowered by pumping water from wells; and the water is conveyed and used or recharged to the groundwater system through infiltration, re-injection or irrigation return.
