Definition of Terms

Acid Mine Drainage
Sulfuric acid is formed when rock that has been excavated in an open pit or underground mine, contains sulfide minerals that react with water and oxygen. The acid may leach from the rock for hundreds or thousands of years, and seep into nearby waterways, killing aquatic life.

Adit
Underground mining, a horizontal tunnel used to access the deposit.

Backfill
In open pit mining, the process of filling a pit either sequentially, or at the end of mining, with waste rock.

Barren Solution
Cyanide solution after the gold has been “stripped” from it.

Base Metal
A metal that is not considered part of the precious metals group, such as zinc, lead, copper, iron and aluminum.

Processing mill at Stillwater mine, MT © Northern Plains Resource Council

Bird
A tubular instrument used in geophysical surveys that is carried in a sling below a helicopter. Most often used where overburden and vegetation obscure bedrock, geophysical surveys, such as magnetic surveys, can detect changes in bedrock and geological structures which may be correlated to mineralization. Such surveys often trigger on-the-ground staking rushes, or can be used in advanced exploration to further delineate a mineral occurrence.

Cut-off grade
The grade (number of ounces per ton, in precious metals, or percentage, in base metals) below which material mined in a lode operation is considered “waste” rather than “ore”.

Cyanide Heap Leach
A technique for extracting microscopic gold ore through the process of saturating a pile (heap) of crushed and agglomerated gold-bearing rock with a weak cyanide solution and collecting the resulting gold-bearing solution.

Cyanide Vat Leach
Similar to the heap leach process for gold extraction, however, gold-bearing material is processed within vats, rather than in heaps.

Development Rock
Industry term for waste rock, which is the non-mineralized rock that is removed in an open pit operation to reach the ore deposit.

Flotation
Industry process that recovers minerals by using reagents to create a froth that collects target minerals. This froth is then skimmed off the top of the vat, and the minerals extracted from the solution.

Grassroots exploration
In hardrock "or lode" metal exploration – to conduct preliminary exploration activities in an area not previously known for hardrock mineral occurrences. Grassroots typically starts with literature searches, reviews of old maps and papers, land record searches, and then is followed by reconnaissance rock sampling by field geologists, geochemical sampling, and panning streams for visible gold.

Hardrock
Hardrock or “lode” mining refers to mining an ore body that is emplaced in bedrock. Hardrock mining is done either underground – where tunnels are dug to reach the deposit – or by open pit, where organic material and rock are stripped off to reach the ore. Open pits can be several miles long and several thousand feet deep.

Indicator element
In hardrock mining, a signature element (or mineral) that, as a result of geochemical processes, characterizes a specific lode deposit. For example, the Ft. Knox deposit is associated with anomalously high bismuth, while the nearby True North deposit is characterized by anomalously high antimony.

Junior
A relatively young, small mining company. Juniors are typically undercapitalized companies with perhaps one or two operating mines and a portfolio of undeveloped properties. By undertaking risky projects and conducting mostly grassroots exploration, juniors finance their operations through a combination of joint-ventures with better-capitalized companies, stock sales and investments by private investors and venture capitalists.

Leach Pad
The bench upon which agglomerated ore material is placed in a cyanide heap leach operation. The pad is lined with an impermeable liner, is surrounded by berms, and has leak detection wells installed in efforts to protect groundwater from accidental solution leaks.

Major
A large, well-capitalized mining company. In addition to typically being a company that has an established track record in mining, a major also controls a significant percentage of mineral wealth in the ground, and has a healthy portfolio of operating mines and advanced exploration properties. The top majors in gold mining are Newmont, Barrick, and Placer Dome. In base metals, Rio Tinto, Freeport McMoran and Teck-Cominco are among the top majors.

Net Income Royalty (NIR)
A royalty paid to a landowner based on profit that allows deductions for operating costs. Allowable deductions in calculating the NIR are negotiated between operator and landowner. Alaska has a 3% NIR on minerals mined on state lands.

Net Smelter Royalty (NSR)
A royalty paid to a landowner or claimholder that is a percentage of a minerals’ value at time of sale. This type of royalty is free of all development, operating and environmental liability costs. A Net Smelter Royalty returns more value to the landowner than does a Net Income Royalty.

Open
Most often “open at depth” is used by industry to indicate that the limit of an ore body has not yet been found in a particular direction.

Ore
Any mineral or metal that occurs in bedrock which is economically recoverable. The quantity of ore in an identified deposit fluctuates with the commodity price of the contained metal.

Tailings impoundment at Stillwater mine, MT © Northern Plains Resource Council

Overburden
Organic material and soil that overlie a mineral deposit.

Pit Lake
The water that fills an open pit after mining has finished. Almost all pits go below the water table; during mining, the pit is continually dewatered to keep it dry. After mining ceases, groundwater flows back into the pit, gradually returning to its former level within the surrounding bedrock.

Placer
Any mineral (although gold is the most common mineral associated with the term) that has been concentrated by erosion in stream, river, or glacial gravels. Placer minerals are most commonly mined by surface excavation, although underground placer mines (called drifts) do occur. In both cases, however, the target mineral is recovered using gravity – the gravels are sorted, washed and concentrated in a sluice box. Other common placer minerals are tin (wood tin), garnets, emeralds, rubies and diamonds.

Pond
Impoundment for the weak cyanide solution used in cyanide gold processing.

Pregnant Solution
The gold-bearing cyanide solution that is collected in a heap or vat leach process.

Precious metal
Gold, silver, platinum and palladium metals are the most common members of the precious metal grouping.

Prove Up
To convert a mineral prospect to an ore body – in other words, to locate a recoverable mineral discovery.

Recovery
The extraction of ore from its host rock.

Reserve
As a result of exhaustive exploration and geo-modeling, the predicted quantity of recoverable ore within a mineral deposit. In Security Exchange Commission filings and other financial documents, mining companies report their proven and probable reserves for each mine they operate.

Resource
The estimated amount of ore that potentially could be extracted from a mineral deposit, regardless of economic or operating conditions. Resources are reported not only for properties still under exploration, but also for operating mines with identified ore reserves.

Royalty
A landowner’s share of the value of minerals produced on their property.

Shaft
Underground mining, a vertical tunnel used to access the deposit, or to provide ventilation to the underground mine.

Stripping Ratio
The ratio of overburden or development rock that needs to be removed to the amount of ore removed. For example a stripping ratio of 4:1 means that 4 tons of development rock are removed to extract one ton of ore. An ideal stripping ratio for a mine is 1:1.

Sulfides
A general term for a group of sulfur-bearing minerals that are either potential ore minerals or are typically associated with ore deposits. Most common sulfides are: pyrite (iron), arsenopyrite (arsenic), galena (lead), chalcopyrite (copper-iron) and sphalerite (zinc).

Tailings
The material that is left after ore has been recovered from it. In hard rock mining, tailings are in a slurry form. In placer mining, tailings are gravel and rock.

Mine waste rock dump

Vat Leach
The process whereby disseminated ore is recovered using chemicals to bind with the metal in crushed rock. The Kennecott Copper Mine at Kennicott Alaska used an ammonia vat leach to recover copper; the old vats can still be seen at the abandoned mine.

Waste Rock
The non-mineralized rock that is removed in an open pit operation to reach the ore deposit.

Workings
Colloquial term for a mine, especially an underground mine.