Hand steel:  Referring to the use of a star drill and hammer to drill blastholes into rock.
Halite:  Rock salt.
Hanging wall:  The mass of rock overlying a geological structure such as an orebody or fault.
Hardpan:  Cemented or compacted gravels and clays.
Haulage Units:  Trucks of other mobile equipment used to transport ore and waste.
Header:  In hardrock mining it is a large timber placed horizontally on top of vertical posts to form a set. In placer stream mining, it is the leading box, trough, or sluice. The top or head end.
Header box:  Used on beginning end of sluice or long tom. Same as “Grizzly”.
Head-frame:  Structure erected over the mouth of a shaft.
Head grade:  The average grade of ore fed into a mill.


Value of an ore before being milled; also the ore itself.
Heap:  Pile of ore stacked for leaching.
Heap leaching:  A low-cost process whereby valuable metals (usually gold and silver) are leached from a heap, or pad, of crushed ore by leaching solutions percolating down through the heap and are collected from a sloping, impermeable liner below the pad. Very popular in the southwestern U.S.
Heap Leach pad:  A large impermeable foundation or pad used as a base for ore during heap leaching. The leach solution is collected and does not escape the circuit.
Hectare:  An area of land equivalent to 10,000 square meters or 2.47 acres.
Hematite:  An iron oxide mineral, one of the commonest ores of iron.
High grade:  Rich ore. As a verb, it refers to selective mining of the best ore in a deposit.
High-grader:  One who steals rich ore, especially gold, from a mine.
Hitch:  Hole in rock to support timbers; also connecting objects together.
Hoist:  The machine used for raising and lowering the cage or other conveyance in a shaft.
Hoist room:  An area in a mine where a hoist is operated from.
Homblende:  An amphibole mineral.
Homogeneous:  Generally uniform throughout; well mixed.
Hookah:  Similar to scuba but instead of wearing air tanks, a breathing hose is connected to an air compressor at the surface.
Hornfels:  A fine-grained metamorphic rock composed of quartz, feldspar, mica, and other minerals, formed by the action of intrusive rock upon sedimentary rock, especially shale.
Horse:  A mass of waste rock lying within a vein or orebody.
Horst:  An upfaulted block of rock.
Host rock:  The rock surrounding an ore deposit. Hydraulics - A method of doing mechanical work in machines whereby energy is transmitted by a fluid such as oil, as opposed to pneumatic machines which operate on compressed air.
Hydrated:  Contains water in chemical combination.
Hydraulic:  Related to water in motion, especially under pressure. Also refers to force exerted by liquids under pressure, including oils.
Hydrochloric acid:  Acid composed of hydrogen and chlorine.
Hydrographic basins:  One of 260 Hydrographic Areas recognized within the Great Basin by the United States Geological Survey. These areas are used for management of water resources. The hydrographic areas are defined by watershed boundaries that generally correspond to geographic features.
Hydrometallurgy:  The treatment of ores by wet processes (e.g., leaching) resulting in the solution of some component and its subsequent recovery.


The water part of the Earth's surface.


Relating to hot fluids circulating within the Earth's crust.

Igneous rocks: 

Rocks formed by the solidification of molten material that originated within the Earth.


A lustrous black to brownish titanium ore, being an iron-titanium oxide.


Rocks or minerals saturated with some other substance.

In-fill drilling: 

Drilling within a group of previously drilled holes to provide a closer spaced pattern to define more accurately the parameters of the orebody


A rising slope.


A coating or crust on a rock.

Indicated value: 

The prehinluary value determined for a placer sample, before it is adjusted or corrected for known variables.

Induced polarization: 

A method of ground geophysical surveying employing an electrical current to determine indications of mineralization.

Industrial minerals: 

Non-metallic, non-fuel minerals used in their natural state in the chemical and manufacturing industries; they require some beneficiation. Examples: asbestos, gypsum, salt, graphite, mica, gravel, building stone and talc.


Occurring between distinct rock layers or strata.

Intermediate rock: 

An igneous rock containing 52% to 66% quartz.


A place where different veins or stringers intersect.


A mass of rock that has been forced into or between other rocks.


A body of igneous rock formed by the consolidation of magma intruded into other rocks, in contrast to lavas, which are extruded upon the surface.

Intrusive-Hosted Mineralization: 

Mineralization within a rock type that was once molten and has "intruded" into other rocks in that state, after which it cools.

Ion exchange: 

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


Display of colors by diffraction of light.


Term for rock-breaking pneumatic hammer or rock drill.


A device which a rock drill sits on that forces the drill forward as it turns.

Jaw crusher: 

A machine in which rock is broken by the action of steel plates.


Device for spraying water, also the water spray itself.


A piece of milling equipment used to concentrate ore on a screen submerged in water, either by the reciprocating motion of the screen or by the pulsation of water through it.


A large vat.


A series of rocks consisting mostly of lavas, but including some sediments; the oldest recognized Precambrian rock unit.


A variety of peridotite; the host or source rock for diamond deposits, originating from deep in the earth’s crust where temperature and pressure conditions permit the creation of diamonds.


An isolated, projecting hill or butte.