Deck:  The area around the shaft collar where men and materials enter the cage to be lowered underground.
Decline:  A sloping underground opening, usually driven at a grade of about 15% to 20%, for machine access from level to level or from surface; also called a ramp.
Deferred charges:  Expenses incurred but not charged against the current year's operation.
Depletion:  An accounting device, used primarily in tax computations. It recognizes the consumption of an ore deposit, a mine's principal asset.
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 a commercially mineable ore body or as containing ore reserves, until final legal, technical, and economic factors have been resolved.
Depreciation:  In accounting, the practice of deducting annually a specified amount or percentage from the value of equipment and machinery representative of the deterioration suffered by the equipment or machinery during the year. The deduction reduces the amount of profit reported but is not an actual out-of-pocket expense.
Detritus:  A general term covering all unconsolidated sediments.
Development:  Underground work carried out for the purpose of opening up a mineral deposit. Includes shaft sinking, crosscutting, drifting and raising.
Development drilling:  Drilling to establish accurate estimates of mineral reserves.
Diabase:  A dark-gray to black, fine-textured igneous rock composed mainly of feldspar and pyroxene and usually occurring in dykes or sills.
Diamond:  The hardest known mineral, composed of pure carbon; low-quality diamonds are used to make bits for diamond drilling in rock.
Diamond drill:  A rotary type of rock drill in which the cutting is done by abrasion rather than percussion. The cutting bit is set with diamonds and is attached to the end of long hollow rods through which water is pumped to the cutting face. The drill cuts a core of rock that is recovered in long cylindrical sections, two centimeters or more in diameter.
Diamond driller:  A person who operates a diamond drill.
Diamond drilling (core drilling):  A drilling method whereby the rock is cut with a diamond bit, usually to extract cores.
Dilution:  Waste or low-grade rock that is unavoidably removed along with the ore in the mining process, subsequently lowering the grade of the ore.
Dilution (mining):  Rock that is, by necessity, removed along with the ore in the mining process, subsequently lowering the grade of the ore.
Diorite:  An intrusive igneous rock composed chiefly of sodic plagioclase, homblende, biotite or pyroxene.
Dip:  The angle at which a vein, structure or rock bed is inclined from the horizontal, measured at right angles to the strike.
Dip needle:  A compass with the needle mounted so as to swing in a vertical plane, used for prospecting to determine the magnetic attraction of rocks.

Directional drilling: 

A method of drilling involving the use of stabilizers and wedges to direct the orientation of the hole.
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.
Dome:  An uplifted structure with an inverted bowl shape.
Doré:  Unrefined gold and silver bullion usually consisting of approximately 90 percent precious metals which will be further refined to almost pure metal.
Doré bar: Doré which has been melted and poured into molds to form bars which are the final saleable product of a mine.
Double-Jack:  A large sledge hammer.
Drag fold:  The result of the plastic deformation of a rock unit where it has been folded or bent back on itself.


Equipment with a long boom and large digging bucket that is cast outward and dragged back toward the machine.
Drawpoint:  An underground opening at the bottom of a stope through which broken ore is extracted from the stope.
Dredge:  A mechanical device used to bring gold-bearing materials up from the water for recovery.
Drift:  A horizontal underground opening that follows along the length of a vein or rock formation as opposed to a crosscut which crosses the rock formation.


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 mined.
Drifter:  A hydraulic rock drill used to drill small-diameter holes for blasting or for installing rock bolts.

Drill core: 

The sand and gravel forced upward into the drill casing as it is driven into placer deposit.
Drill log:  A record of drilling results compiled as the work progresses.
Drill steel:  The long steel rod with a replaceable carbide cutting head at one end. It is inserted into a impact drill and used to drill holes into rock for blasting. The rod usually has a hole down the center for water which gets pumped to the cutting head to prevent dust and wash the debris from the drillhole.
Drill-indicated reserves:  The size and quality of a potential orebody as suggested by widely spaced drillholes; more work is required before reserves can be classified as probable or proven.
Drive pipe:  Another term for casing.
Dry room:  A room where underground miners can change out of their wet muddy close into clean dry close which they placed in a locker at the start of the shift.
Dry washing:  Extracting gold from dry gravels, usually by equipment which uses air bellows for separating lighter from heavier material.
Dry:  A building where the miner changes into working clothes.
Ductile:  Capable of being bent, drawn into wire, or pounded into sheets.
Due diligence:  In a professional evaluation, the degree of care and caution required before making a decision.


Refers to a mineral's luster; not colorful or shiny.
Dump:  A pile or heap of broken rock or ore on surface.
Dust:  Very fine ground gold, powdery.
Dutchman:  A trolley seat used to cross a stream or ravine.
Dyke:  A long and relatively thin body of igneous rock that, while in the molten state, intruded a fissure in older rocks.