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Glossary of Geological Terms and Abbreviations
Aeromagnetic Survey Traverses carried out along equally spaced lines that measure the strength of the earth's magnetic field
Ag Silver
Air Core Drilling Rotary drilling technique in which sample is returned to surface inside the rod string by compressed air.
Alkaline Relating to or containing an alkali; having a pH greater than 7.
Alluvium A general term for unconsolidated material deposited during comparatively recent geologic time by a stream or other form of running water.
Amphibole Any of a large group of structurally similar hydrated double silicate minerals, such as hornblende, containing various combinations of sodium, calcium, magnesium, iron, and aluminium. General formula of XY2Z5(Si, Al, Ti)8O(22(OH, F)2. (needs checking)
Anomaly A departure from the expected norm. In mineral exploration this term is generally applied to either geochemical or geophysical values higher or lower than the norm.
Anorogenic Magmatic rocks formed outside orogenic belts, in continental setting.
Anorthosite A group of essentially monomineralic plutonic rocks composed almost entirely of plagioclase feldspar and little or no dark-coloured minerals (<10%).
Apatite A common complex mineral consisting of calcium fluoride phosphate or calcium chloride phosphate; a source of phosphorus.
Archaean A geological eon of time before 2,500 Ma.
A-type granite Group of granitis rocks usually, though not exclusively, formed in rift related environments in continental crustal regions. Most A-type granites are Ca-poor: syenogranites and alkali feldspar-granites, including rapakivi granites.
Au Gold
Basement The igneous and metamorphic rocks that exist below the oldest sedimentary cover. In some areas such as shields the basement rocks may be exposed at the surface.
Base-metal A metal which oxidises when heated in air, e.g. lead, copper, tin, zinc, as opposed to noble metals such as gold and platinum.
Biotite A dark-brown or dark-green to black mica, K2(Mg,Fe,Al)6(Si,Al)8O20(OH)4, found in igneous and metamorphic rocks. (needs checking)
Bornite A brownish-bronze, lustrous copper ore with the composition Cu5FeS4 that tarnishes to purple when exposed to air.
Breccia A coarse-grained clastic rock composed of angular and/or sub-angular broken rock fragments held together by a mineral cement or in a fine-grained matrix.
Bull's eye Elliptical feature with concentrical bands.
Calcrete A layer where cemented carbonate precipitation has occurred.
Calc-silicate rock A rock containing mainly calcium-bearing silicate minerals such as diopside and wollastonite.
Chalcocite A metallic dark gray mineral, essentially Cu2S, that is an important ore of copper.
Chalcopyrite A yellow mineral, essentially CuFeS2, that is an important ore of copper. Also called copper-pyrite.
Chalcophile Chemical elements that have a strong affinity for sulphur.. They tend to concentrate in sulphide minerals.
Chert A hard, extremely dense or compact, dull to semi-vitreous, microcrystalline or cryptocrystalline sedimentary rock consisting of interlocking crystals of quartz less than about 30 microns in diameter.
Chromitite An ultramafic rock containing more than 20% chromite (chromium spinel).
Chrysocolla A hydrated copper silicate common in oxidized zone of copper deposits.
Chrysoprase A green gem variety of chalcedony, where the green color is related to the presence of nickel minerals.
Co Cobalt
Colluvium A loose deposit of rock debris accumulated through the action of gravity.
Conglomerate A sedimentary rock consisting of other variably rounded rocks and quartz fragments that have been cemented together.
Covellite An indigo-blue copper sulphide, CuS
Craton A craton is an old and stable part of the continental crust that has survived the merging and splitting of continents and supercontinents for at least 500 million years.
Cu Copper
Cubanite A brassy golden yellow rare copper mineral, essentially CuFe2S3 that does not contribute much to the supply of copper.
Cuprite Copper oxide (Cu2O) found in oxidized zone of copper deposits.
Diatreme A general term for a volcanic vent or pipe drilled through enclosing rocks (usually flat-lying sedimentary rocks) by the explosive energy of gas-charged magmas.
Dike Tabular body of intrusive igneous rock which cuts across the layering or structural fabric of the host rock.
Disseminated sulphide Sulphide mineralisation where sulphide grains are dispersed widely between other mineral grains in the rock.
Dolerite A comparatively coarse grained basaltic rock composed of calcic plagioclase and pyroxene together with minor amounts of accessory minerals such as olivine.
Dunite Rock composed almost entirely of the mineral olivine (>90%).
Electromagnetic Survey Traverses carried out along equally spaced lines that input an electrical field to the ground, and measure the measure the changes in the earth's magnetic field at different times after the application of the electrical field.
Epithermal A kind of epizonal mineralisation related to volcanic activity.
Fe iron.
Feldspar A group of rock-forming silicate minerals that are essential constituents of igneous rocks, and are also common in sedimentary and metamorphic rocks.
Felsic volcanic rock A generally finely crystalline or glassy igneous rock having abundant light-coloured minerals (quartz, feldspar, muscovite) resulting from volcanic action at or near the surface of the earth.
Fluorite A mineral composed of calcium fluoride (Ca2).
Gabbro A group of dark-coloured, mafic intrusive igneous rocks composed principally of calcic plagioclase and clinopyroxene with or without olivine and orthopyroxene.
Gabbronorite Is a member of the Gabbro family that has both orthopyroxene and clinopyroxene.
Gneiss A coarse-grained, imperfectly foliated, or layered, metamorphic rock. Gneiss is characterized by alternating light and dark bands differing in mineral composition and usually having coarser grains than those of schist. The light bands of gneiss are generally composed of quartz and feldspar. Hornblende, biotite mica, garnet, or graphite commonly form the dark bands. Gneisses result from the metamorphism of many igneous or sedimentary rocks, and are among the most common types of rocks found in Precambrian regions.
Gossan An intensely oxidized, weathered or decomposed rock, usually the upper and exposed part of an ore deposit or mineral vein. In the classic gossan or iron cap all that remains is iron oxides and quartz often in the form of box-works, quartz lined cavities retaining the shape of the dissolved ore minerals.
Granite A plutonic rock in which quartz constitutes 10 to 50 percent of the felsic components and in which the alkali feldspar / total feldspar ratio is restricted to the range of 65 to 90%.
Granophyre Is a felsic rock having a fine matrix of composed by quartz and K-feldpsar intergrowth.
Granulite A high-grade metamorphic rock in which mafic minerals are hydroxyl-free. Feldspar is always present and muscovite absent. Cordierite and garnet are other common minerals. (note that this is the updated definition of granulite from the IUGS subcommission on the nomenclature of metamorphic rocks).
Hematite An oxide mineral with the general formula alpha Fe2O3
Hydrothermal Heated water and its actions.
Induced Polarisation The production of a double layer of charge at a mineral interface, or production of charges in double-layer density of charge, brought about by application of an electric or magnetic field.
IOCG Iron Oxide-Copper-Gold.
K-feldspar A group of feldspar minerals (Si- and Al-rich), where the third element in abundance is K. This group includes orthoclase, microcline, and sanidine.
Kaolinite Is a K-rich clay commonly formed by the alteration of K-feldspar.
Laterite A reddish residual soil or rock formed in tropical and subtropical regions that is leached of soluble minerals and enriched in iron, aluminium or manganese oxides. Laterites formed over ultramafic rocks may be enriched in Ni-minerals, such as garnierite.
Leucogabbro Is a member of the gabbro family between a gabbro and an anorthosite, having a colour index between 10 and 35.
Limonite Limonite is a hydrated iron+3 oxide hydroxide of varying composition. The generic formula is frequently written as FeO(OH)onH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.
Lopolith A large, concordant, typically layered igneous intrusion, of plano-convex or lenticular shape, that is sunken in its central part owing to sagging of the underlying country rock.
Ma Million years.
Mackinawite A metastable iron-sulphur phase important as a precursor to pyrite formation in sedimentary and hydrothermal systems. It is the first-formed iron sulphide phase following reaction of ferrous ions with sulphide ions. (Fe,Ni)9S8
Mafic volcanic rock A volcanic rock composed chiefly of one or more ferromagnesian, dark-coloured minerals.
Magma Naturally occurring molten and mobile rock material, generated within the Earth and capable of intrusion or extrusion, from which igneous rocks are thought to have been derived through solidification and related processes.
Magnetite An oxide mineral with the general formula Fe2+Fe3+2O4
Malachite Emerald-green hydrated copper carbonate, usually banded and formed in oxidation zones of copper mineralisation.
Massive sulphide Sulphide mineralisation where a large number of sulphide grains are in contact with each other.
Mesoproterozoic A geological era of time from 1,600 Ma - 1,000 Ma.
Mesozoic A geological period of time from 251 Ma to 65 Ma.
Metamorphism The mineralogical, chemical and structural adjustment of solid rocks to physical and chemical conditions which have generally been imposed at depth below the surface zones of weathering, and which differ from the conditions under which the rocks in question originated.
Mylonite A fault rock which is cohesive and characterized by a well developed schistosity resulting from tectonic reduction of grain size, and commonly containing rounded porphyroclasts and lithic fragments of similar composition to minerals in the matrix.
Neoarchaean A geological era of time, from 2,800 Ma to 2,500 Ma.
Neoproterozoic A geological era of time, from 1,000 Ma - 542 Ma.
Ni Nickel.
Olivine A mineral with the chemical formula (Mg,Fe)2SiO4.
Palaeozoic A geological eon of time, from 542 Ma - 251 Ma.
Pb Lead.
Pd Palladium.
Pelite A fine-grained, aluminous sedimentary rock.
Pentlandite A yellowish-bronze, opaque mineral, a sulphide of iron and nickel, (Fe,Ni)9S8. It is found in masses nearly always associated with the iron sulphide pyrrhotite. The largest deposit of this important ore of nickel is at Sudbury, Ontario, Canada. Important deposits are mined in Manitoba, Russia, and Western Australia.
PGE Platinum Group Elements.
Phanerozoic A geological period of time or era, from 542 Ma to present day.
Pisolite A spheroidal crystalline particle larger than 2 millimetres in diameter. A massive form of some carbonates, consisting of small globular concretions.
Plug Small and shallow intrusion with near-cylindrical shape, less than 1 km in diameter.
ppb Parts per billion.
ppm Parts per million.
Precambrian A geological eon of time from ~4,500 Ma to 542 Ma
Proterozoic A geological eon of time from 2,500 Ma to 542 Ma
Protolith Refers to the precursor rock of a given lithology. Granitoids can for instance be derived through melting of a sedimentary rock, and thus have a sedimentary protolith, or be derived from a magmatic precursor, and thus have a magmatic protolith.
Psammite A clastic sedimentary rock composed of sand-sized particles.
Pseudotachylite Ultrafine-grained vitreous-looking material, usually black and flinty in appearance, occurring as thin planar veins, injection veins or as a matrix to pseudo-conglomerates or breccias, which infills dilation fractures in the host rock.
Pt Platinum.
Pyrite A brass-coloured mineral, FeS2, occurring widely and used in producing sulfur dioxide for sulfuric acid. Also called fool's gold, iron pyrites.
Pyroxenite An intrusive igneous rock composed almost entirely (>90%) of one ore more pyroxenes.
Pyrrhotite A brownish-bronze iron sulphide mineral, FeS, characterized by weak magnetic properties and used in the manufacture of sulphuric acid. Also called magnetic pyrite.
Rare Earth Element Also referred to as Lanthanides, is a relatively abundant group of 15 chemical elements (lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium).
Quartz Silica oxide, and is the most abundant mineral in the crust.
RC Reverse Circulation.
Regolith All the material at the earth's surface that lies above fresh, unweathered rocks.
Rhyolite An igneous, volcanic rock of felsic composition, with aphanitic to porphyritic texture. Mineral assemblage is usually quartz, alkali feldspar and plagioclase (in a ratio > 1:2). Biotite and pyroxene are common accessory minerals.
Sandstone A sedimentary rock, composed mostly of grains (typically quartz, but also other minerals and rock fragments). Grain size varies from 1/16mm to 2mm in diameter.
Saprolite An in situ deeply weathered rock, clay-rich, more common in tropical environment.
Schist A metamorphic rock displaying schistose structure. Schistosity is a preferred orientation of inequant minerals grains or grain aggregates produced by metamorphic processes. Actually the IUGS (International Union for Geological Sciences) includes the metamorphic rocks named slate and phyllite in the schist group of rocks.
Sedimentary Basin A low area in the earth's crust, of tectonic origin, in which sediments have accumulated.
Serpentinisation A geological metamorphic process involving heat and water in which low-silica mafic and ultramafic rocks are oxidized and hydrolysed with water into serpentinite.
Shear zone A tabular zone of rock that has been crushed and brecciated by many parallel fractures due to shear strain.
Skarn Contact metamorphic rock derived from carbonate rock.
Strike-slip fault A fracture or a zone of fractures along which there has been displacement of the sides relative to one another and parallel to the strike trend of the fault.
Syenite (itic) Felsic plutonic rock having less than 5% quartz and up to 1/3 plagioclase among the feldspars.
Ti Titanium.
Thrust fault A fault with a dip of 45 degrees or less over much of its extent with overriding movement of one crustal unit over another.
Troctolite troctolite is a gabbroic rock where the main mafic mineral is olivine.
Ultramafic Rock Igneous rocks with no quartz, more than 90% mafic minerals (olivine, pyroxene or hornblende) and up to 10% feldspar.
Unconformity A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic succession, such as an interruption in the continuity of a depositional sequence of sedimentary rocks or a break between eroded igneous rocks and younger sedimentary strata.
Weathering The process of alteration of fresh rock at the earth's surface.