Mining Glossary

• Adit – A horizontal passage from the surface into a mine. It is commonly called a tunnel, though in strict usage a tunnel is open at both ends.
• Alteration – Changes in the chemical or mineralogical composition of a rock, generally produced by weathering or hydrothermal solutions.
• Andesite – A dark-colored, fine-grained extrusive rock.
• Anomaly - A geological feature, especially in the subsurface, distinguished by geological, geochemical or geophysical means, which is different from the general surroundings and is often of potential economic value, e.g. a magnetic anomaly.
• Calcite – A common rock-forming mineral, CaCO3 (calcium carbonate). Commonly white or gray, calcite is the chief constituent of limestone and most marble.
• Conglomerate – A course-grained clastic sedimentary rock, composed of rounded to subangular fragments larger than 2mm in diameter (granules, pebbles, cobbles, boulders) set in a fine-grained matrix of sand or silt, and commonly cemented by calcium carbonate, iron oxide, silica or hardened clay; the consolidated equivalent of gravel.
• Detachment fault – A near-horizontal fault of great displacement, frequently over 10 miles, caused by regional extension of the affected terranes. Heat generated by the process of detachment faulting may result in hydrothermal alteration of the upper plate, the lower plate, or both, and the consequent deposition of minerals such as gold, silver, copper, lead, zinc or manganese.
• Dump – An area adjacent to a shaft, adit or other mine working where mined material has been stored or dumped.
• Extrusive – Said of igneous rock that has been erupted onto the surface of the earth. Extrusive rocks include lava flows and pyroclastic material such as volcanic ash.
• Fault – A fracture or fracture zone along which there has been displacement of the sides relative to one another.
• Foliated – A rock that has been subject to foliation, which is a planar arrangement of textural or structural features in any type of rock, especially the planar structure that results from flattening of the constituent grains of a metamorphic rock.
• Geochemical exploration – The search for economic mineral deposits by detection of abnormal concentrations in surficial materials or organisms, usually by techniques that may be applied in the field.
• Geophysical exploration – The use of geophysical techniques – electric, gravity, magnetic, seismic or thermal – in a search for economically valuable mineral deposits.
• Gneiss – A foliated rock formed by regional metamorphism, often of granitic rocks, in which bands of granular materials alternate with bands of minerals with flaky or prismatic habit.
• Gravel – An unconsolidated natural accumulation of rounded rock fragments, mostly of particles larger than sand.
• Hanging wall – The overlying side of an ore body, fault, or mine workings; especially the wall rock above an inclined vein or fault.
• Hematite – A common iron mineral, it is the principal ore of iron.
• Hydrothermal alteration – Alteration of rocks and minerals by the reaction of hot water or steam with pre-existing solid rock.
• Igneous – Said of a rock or mineral that solidified from molten or partly molten material such as magma.
• Magnetic survey – A technique of applied geophysics: a survey is made with a magnetometer, on the ground or in the air, which yields local variations, or anomalies, in magnetic-field intensity. These anomalies are interpreted as to depth, size, shape, and magnetization of geologic features causing them.
• Metamorphic rock – Any rock derived from pre-existing rocks by mineralogical, chemical, and / or structural changes, essentially in the solid state, in response to marked changes in temperature, pressure, shearing stress, and chemical environment, generally at depth in the earth's crust.
• Mining District – A geographic area in which a number of mines are located. During the early days of the American West before effective local governments were established, the mining district enacted rules and enforced them.
• Mylonitic – Descriptive of a rock that has been subject to mylonitization, which is deformation by extreme microbrecciation, due to mechanical forces applied in a definite direction, without noteworthy chemical reconstitution of granulated minerals.
• Pediment – A broad gently sloping erosion surface or plain of low relief, typically developed by running water, in an arid or semi-arid region at the base of an abrupt and receding mountain front; it is underlain by bedrock that may be bare but is more often mantled with a thin discontinuous veneer of alluvium derived from the upland masses and in transit across the surface.
• Precambrian – All geologic time, and its corresponding rocks, before the beginning of the Paleozoic age approximately 570 million years ago.
• Regional metamorphism – A general term for metamorphism that extends continuously throughout an extensive region, as opposed to local metamorphism.
• Sedimentary rock – A layered rock resulting from the deposition of sediment, usually formed under water, e.g. a clastic rock such as sandstone, a chemical rock such as rock salt, or an organic rock such as coal.
• Shaft – A vertical or near – vertical mine working through which access is gained to levels of mine workings below the surface.
• Silicified – A rock that has been affected by silicification, which is the introduction of, or replacement by, silica, especially in the form of fine-grained quartz, which mat fill pores and replace existing minerals.
• Tertiary – The era of time beginning about 65 million years ago up to 2 million years before the present, and the corresponding system of rocks.
• Unpatented mining claim – In the United States of America, a claim to mineral rights on Federal lands open to mineral entry, obtained by staking and recordation with the County Recorder and the United States Bureau of Land Management (BLM).