Glossary

acid	Igneous rocks with over 66% silica (quartz).
acid rock	Igneous rock in which high-silica minerals dominate (also “felsic”).
Adelaidean	A time period from 870 to 570 million years ago.
aeolian	Deposited by wind action.
aeromagnetic	A survey of the Earth’s magnetic field conducted by an aircraft.
aeromagnetic survey	A survey made from the air for the purpose of recording magnetic survey data on rocks.
AGSO	Australian Geological Survey Organisation, formerly the Bureau of Mineral Resources, now Geoscience Australia.
aircore	A rotary drilling technique that uses compressed air to cut a core sample and return fragments to surface inside the drill rods.
alkaline rock	An igneous rock containing more sodium and/or potassium than is required to form feldspar with the available silica.
alluvium	An unconsolidated sediment deposited by water.
alunite	A hydrated sulphate of potassium and aluminium, generally occurring as a product of hydrothermal alteration in feldspathic igneous rocks.
amphibolite	A metamorphic rock consisting of amphibole and plagioclase, formed from basic igneous rocks such as dolerites or basalts.
andesite/andesitic	A volcanic rock intermediate in composition between basalt and rhyolite.
anomaly	An area where exploration has revealed results higher (or sometimes lower) than the local background level.
Archaean	The oldest rocks of the Precambrian era, older than 2,500 million years.
argillic alteration	A type of alteration in which certain rock minerals are converted to minerals of the clay group.
arkose	A form of sandstone composed to detrital grains of feldspar and quartz.
arsenopyrite	Arsenical pyrites.
As	The chemical symbol for the element arsenic.
Au	The chemical symbol for the element gold.
auger drilling	A drilling method where the sample rises up the outside of spiral drill rods.
auriferous	Gold-bearing.
banded iron formation	A sedimentary rock composed largely of iron minerals and chert and showing distinct banding.
basalt	A dark and fine grained basic volcanic igneous rock.
base metal	A metal inferior in value to precious metals; e.g. copper, lead, zinc, nickel.
basement	A much older harder rock surface underlying more recent deposits.
basic rocks/volcanics	Igneous rocks containing between 45 and 52% silica, distinct from acid or intermediate rocks.
basic	An igneous rock which is low in silica, generally less than 55%, eg basalt.
batholith	A very large mass of intrusive plutonic igneous rock, often granitic.
Bi	The chemical symbol for the element bismuth.
BIF	Banded iron formation
biotite	A dark mica mineral.
BLEG	Bulk leach extractable gold analysis; an analytical method for accurately determining low levels of gold.
breccia	A coarse grained rock of angular broken rock fragments cemented together.
bulk sample	A large, representative sample.
Cainozoic	Latest of the four eras of geological time; dating from 65 million years to the present.
calcite	A common mineral, calcium carbonate.
calcrete	A calcareous desert soil, or in soil precipitate, formed from crystallisation of calcite and associated carbonates by evaporation of upward moving solution.
caldera	A large, basin-shaped, volcanic depression within which smaller vents may be present.
carbonaceous	Containing fine particles of carbon distributed through the rock.
chalcopyrite	A copper-iron sulphide mineral, an important ore of copper CuFeS₂.
chlorite	A platy mica mineral rich in iron & magnesium, often formed by alteration.
co-magmatic	Igneous rocks derived from the same parent magma.
colluvium	A loose, heterogeneous and incoherent mass of soil and regolith deposited by down-slope processes.
conglomerate	A sedimentary rock composed predominantly of rounded pebbles, cobbles or boulders deposited by the action of water.
costean	A trench cut in order to collect a sample across a mineral prospect.
covellite	An ore of copper: CuS
cover	Applied to rocks or a sequence of rocks that overlie older rocks, usually basement.
craton	A large, stable and generally old part of the Earth’s crust.
crust/crustal	The outermost part of the earth adj. Crustal.
Cu	The chemical symbol for the element copper.
dacite	An extrusive intermediate volcanic rock composed mainly of plagioclase, quartz, pyroxene or/or hornblende.
Devonian	A time period from approximately 400 to 345 million years ago.
diamond drilling	Drilling method where a diamond impregnated bit cuts a cylindrical hole to recover a continuous rock core sample.
dip	The angle at which a layer or bed is inclined from the horizontal.
dolerite	A medium grained basic intrusive rock composed mostly of the minerals pyroxene and sodium-calcium feldspar.
downhole gamma logging	Measurement of rock radioactivity, indicative of radioactive elements including but not exclusively uranium, by lowering a probe down a drillhole.
dry-blowing	A means of recovering gold from soil via the use of wind to winnow and concentrate denser material.
dunite	A peridotite consisting essentially of olivine and chromite.
dyke	A tabular body of intrusive igneous rock, crosscutting the host strata.
EL	Exploration Licence.
ELA	Exploration Licence Application.
electromagnetics, EM survey	A method of measuring the alternating magnetic fields associated with electrical currents artificially or naturally maintained in the subsurface.
eluvial	A term for loose sediments on a slope close to their area of origin.
Eocene	The period of geological time between 55 and 34 Ma.
epidote	A yellow-green hydrated iron, aluminium, calcium silicate often a product of metamorphism or hydrothermal alteration.
epithermal	Hydrothermal activity within one kilometre of the earths surface in a temperature range 50 to 200 degrees Celsius, usually forming veins.
eruptive	Volcanic rocks that have burst through other rocks in a molten state.
extrusive	An igneous rock that has been erupted on to the earth’s surface.
facing	Applied to the original direction of a layer.
fault	Fracture in a rock sequence where one side has moved relative to the other.
feldspar	One of the commonest minerals, consisting of alkali aluminium silicates.
felsic	Descriptive term for a light coloured igneous rock rich in silica.
ferricrete	Surficial layer more or less cemented with iron oxide.
ferruginous	Containing iron.
fluorite	A mineral formed of calcium and fluorine which forms cubic crystals.
fluviatile	Refers to the results of river action.
foliated	Showing planar mineral alignment, usually as a result of metamorphic processes.
fuchsite	Bright green chromium-rich variety of muscovite.
g/t	An abbreviation for grams per tonne, a standard unit for reporting the concentration of precious metals in a rock, equivalent to parts per million (ppm).
gabbro	A coarse grained intrusive rock that is low in silica and has relatively high levels of iron and magnesium minerals.
galena	Lead sulphide, PbS.
gangue	The non-metalliferous or non-valuable components of ore.
garnet	A commonly red to brown euhedral mineral found in metamorphic rocks.
geochemical survey	A systematic study of the variation of chemical elements in rocks or soils.
geomorphology	Study of the form and origin of natural land surface features.
geophysics	Study of the earth by quantitative physical methods.
GEOTEM	A fixed-wing airborne electromagnetic (EM) geophysical survey system.
GIS	Abbreviation for Geographic Information System
gneiss	A metamorphic rock with compositional banding.
gossan	A ferruginous deposit remaining after the oxidation of the original sulphide minerals in a vein or ore zone.
granite	A plutonic felsic igneous rock composed of quartz, feldspar and mica.
granitoid	A general term to describe course grained felsic intrusive igneous rocks, resembling granite.
granodiorite	A course grained intermediate igneous intrusive rock composed of quartz, feldspar and hornblende and/or biotite.
granulite facies	Metamorphic conditions of high temperature and/or pressure.
graphitic	Containing graphite, a native form of elemental carbon generally found in meta-sedimentary rocks.
gravity survey	A geophysical survey technique using a gravimeter to measure the force of gravity at locations within an area.
greenschist facies	Metamorphic conditions of moderate temperature and pressure, characterised by the presence of the minerals chlorite, amphibole and sodium plagioclase.
greenstone	Term commonly applied to low metamorphic grade rocks of basic composition and comprised largely of the minerals albite, chlorite and amphibole. Commonly applied to Archaean rock sequences dominated by these rock types.
groundwater	Subterranean water held in fractures and porous rock or sand beneath the earth’s surface
haematite	Iron oxide mineral, Fe₂O₃ (hematite).
high-Mg basalt	A basalt with a higher proportion of magnesium than thoeleiitic basalts, but less than that usually attributed to komatiitic basalts.
HoistEM	A helicopter-towed time domain electromagnetic survey system.
hornfels	A fine grained metamorphic rock recrystallised by the heat of an intrusion.
hydrothermal	A process when hot water-rich solutions transfer materials or alter rocks.
igneous	Rocks formed by crystallisation from molten material.
indicator minerals	In connection with kimberlite exploration, indicator minerals include: pyrope garnet, picroilmenite, chrome-diopside, kimberlitic zircon, chromite and diamond.
Inferred Resource	The least assured category of mineral resource.
inlier	An area of rocks surrounded by rocks of younger age. Cf: outlier
intrusive	A body of igneous rock that was intruded whilst molten in to the earth’s crust.
IOCG deposit	Abbreviation for Iron-Oxide-Copper-Gold deposit, e.g. Olympic Dam orebody.
IOCGU deposit	Abbreviation for Iron-Oxide-Copper-Gold-Uranium deposit, e.g. Olympic Dam orebody.
IP survey	Induced Polarisation survey, an electrical geophysical method used to detect buried deposits formed by disseminated sulphide minerals.
K-feldspar	A potassium rich variety of feldspar.
kg/t U₃O₈	Measure of uranium content in rocks e.g. 0.640 kg/t U₃O₈ is equivalent to 0.064% U₃O₈
kimberlite	A type of ultramafic rock and the major primary source of diamonds.
komatiite	Magnesium-rich mafic to ultramafic extrusive rock.
lacustrine	Produced by or belonging to lakes.
lag sample	Sample of coarser or heavier residual material which accumulates by deflation on the ground surface.
lamprophyre	A mafic igneous rock containing a high percentage of biotite, hornblende and pyroxene as phenocysts and a fine-grained groundmass including feldspars.
Landsat	An unmanned satellite designed to provide multi-spectral imagery of the earth’s surface.
late tectonic	An event occurring towards the end of a tectonic event, or a rock or feature so formed.
laterite	A cemented residuum of weathering, generally leached in silica with a high alumina and/or iron content.
lava	Igneous rock that was extruded onto the Earth’s surface before solidifying.
leucogranite	Light coloured granite, lacking mafic minerals.
lignite	A soft brown coal intermediate between peat and sub-bituminous coal.
lineament	A naturally occurring major linear feature in the earth’s crust often associated with mineral deposits.
lode	A separate, tabular part of an orebody with well defined walls.
Ma	Millions of years before present.
mafic	Dark coloured igneous rocks composed dominantly of magnesian and iron rock-forming silicates.
magnetic survey	A survey of the Earth’s magnetic field either from the ground or the air.
magnetite	Magnetic ferrous iron oxide (Fe₃O₄); principal cause of magnetic anomalies.
magnetometer	An instrument used for measuring the intensity of the earth’s magnetic field.
malachite	Bright green mineral-hydrated copper carbonate, often in weathered Cu ore.
manganiferous	Containing abundant manganese.
matrix	The rock or earthy material containing a mineral or metallic ore.
MESA	Former Department of Mines and Energy, South Australia.
Mesoproterozoic	A period of geological time from 1600 to 1000 Ma.
Mesozoic	A time period from approximately 225 to 65 million years ago.
meta	A prefix meaning that the rock type has undergone metamorphism.
metamorphic	A rock that has modified texture, mineralogy and composition due to the effects of pressure, heat and fluids within the crust.
metasediment	Sedimentary rock that has been re-crystallised by metamorphism.
miarolitic	Term applied to small irregular cavities in igneous rocks (especially granites), into which small crystals of the rock-forming minerals protrude.
micaceous	Contains micas, a common hydrated silicate with a platy structure.
micro-gravity	A high-sensitivity geophysical gravity survey technique.
microgranite	A fine-grained granitic rock.
milligal	A unit of acceleration used with gravity measurements.
MIMDAS	An induced polarisation electrical geophysical survey technique developed by Mount Isa Mines Limited.
mineralisation	An anomalous concentration of metals of economic interest.
MMI	Mobile Metal Ion: A sensitive analytical technique for detecting ions that have moved some distance from oxidising mineralisation.
Mn	The chemical symbol for the element manganese.
Mo	The chemical symbol for the element molybdenum.
monzogranite	A granular plutonic rock containing approximately equal amounts of orthoclase and plagioclase feldspar, but usually with a low quartz content.
mylonite	deformation of a rock by pressure applied in a definite direction without chemical changes to the materials.
Neoproterozoic	A period of geological time from 1000 to 545 Ma.
nickel laterite	Nickel ore hosted within the laterite profile, usually derived from the weathering of olivine-rich ultramafic rocks.
NOAA	National Oceanic and Atmospheric Administration, a type of satellite imagery with resolution of around one kilometre.
olivine	An olive green magnesium-iron silicate (Mg, Fe)₂SiO₄, common in mafic and ultramafic igneous rocks.
onlap	Extension of successive sedimentary units beyond the limits of their predecessors as they transgress onto older rocks at the margins of a depositional basin.
open file	A category of reports at a Mines Department Library which are available for public perusal after a title has been relinquished; contrast with closed file.
Ordovician	A time period from 500 to 440 million years ago.
orogen/orogenic	A linear or arcuate region that has been subjected to folding and other deformation.
outcrop	The surface expression of a rock layer, verb to crop out.
outlier	An isolated area of rock surrounded by older rocks.
oz	Abbreviation for Troy ounce (31.103477 grams), an Imperial unit of weight used widely in the gold mining industry.
PACE	The Plan for Accelerating Exploration, whereby the South Australian government offers an incentive for companies to drill holes that will add to the knowledge of the geology of various regions.
palaeochannel	An ancient preserved stream or river.
Palaeoproterozoic	A period of geological time from 2500 to 1600 Ma.
Palaeozoic	A time period from approximately 590 to 248 million years ago.
Pb	The chemical symbol for the element lead.
pedogenic	Pertaining to soil formation.
pegmatite	A very course grained igneous rock formed at a late stage of magmatic differentiation.
percussion drilling	Rock drilling carried out by the hammering action of a pneumatically driven drill bit.
peridotite	A coarse grained igneous rock composed essentially of olivine, with or without other mafic minerals, and little or no feldspar.
Permian	A time period from approximately 280 to 225 million years ago.
petrology	The study of rocks in the fullest sense, adj. Petrographic.
Phanerozoic	Period of the earth’s history represented by rocks in which the evidence of life is abundant, from about 570Ma to the present.
phyllite	A metamorphic rock with abundant mica and a strong fabric.
PIRSA	Department of Primary Industry and Resources South Australia.
Playa	A dry or ephemeral lake or salina.
plug	A vertical pipelike body of magma representing the conduit to a former volcanic vent.
pluton/ plutonic	An igneous rock that has solidified slowly at depth in the Earth’s crust.
porphyry	A felsic intrusive or subvolcanic rock with larger crystals set in a fine groundmass.
potassic alteration	A variety of alteration with anomalous concentrations of potassium.
ppb	Parts per billion; a measure of low level concentration.
ppm	Parts per million; quantitative equivalent of g/t.
Precambrian	Era of geological time before the Cambrian, from about 4600 to 545 Ma.
precious metals	General term for gold, silver or minerals of the platinum group.
prospect	Location of perceived mineral potential
prospectivity	Qualitative estimate of the potential for undiscovered mineral resources
Proterozoic	The second eon of the Precambrian, spanning the period from 2,500 to 545 million years before the present.
pseudomorph	A mineral whose outward crystal form is that of another mineral species, which it has replaced.
Pt	The chemical symbol for the element platinum.
pyrite	An iron sulphide mineral, FeS₂.
pyroclastic	Clastic rocks that result from explosive volcanic activity.
quartz	The mineral silicon dioxide, the commonest mineral in the Earth’s crust.
quartzite	A rock composed predominantly of quartz.
Quaternary	A time period from 1.8 million years ago to the present.
RAB	Rotary Air Blast, a rotary drilling technique that uses compressed air to clear the drill bit of cuttings and return them to the surface.
radiogenic	Derived from a radioactive process.
radiometric survey	A geophysical survey technique whereby measurements are made of ambient radiation that may be indicative of different rocks, ores, etc.
RC drilling	Reverse circulation drilling, a rotary percussion drilling technique in which the samples are returned to the surface inside the drill rods minimising contamination.
Recent	Geological age from about 20,000 years ago to the present.
redbed	A sedimentary sequence predominantly red due to the presence of iron oxide.
redox boundary	Chemical reduction-oxidation boundary.
regolith	The layer of weathered and transported material overlying fresh rock.
remote sensing	The process by which satellite images are created by scanning the earth’s surface using sensors on satellites.
resistivity	A means of detecting buried features and areas of disturbance by measuring the resistance of an electrical current passed through the ground.
resource	That part of a mineral occurrence that is estimated to be of potential economic merit.
retrograde	Process of adjustment of mineral assemblage to lower grade metamorphism.
rhyodacite	Igneous rocks intermediate between rhyolite and dacite.
rhyolite	A fine grained acid volcanic rock having a similar chemical composition to granite.
roll front uranium	A type of uranium deposition localized as a roll or interface separating an oxidized interior from a reduced exterior. The reduced side of this interface is significantly enriched in uranium.
roof pendant	A downward projection of country rock into an igneous intrusion.
rotary percussion	A drilling technique involving simultaneous hammering and rotation action by a bit.
rotary mud drilling	A drilling process using a rotating bit to cut the rock and a solution of heavy mud to recover the cuttings.
SADME	The former South Australian Department of Mines and Energy.
SAEI	The South Australian Exploration Initiative, which ran from July 1992 to June 1996, whereby $23.5m was allocated by the State Government to mineral and petroleum geoscientific programs.
saprock	Zone of partially weathered towards the base of the weathered profile, in which the original textures have been preserved.
saprolite	Disintegrated, in-situ rock, partially decomposed by the chemical and physical processes of oxidation and weathering.
Sb	The chemical symbol for the element antimony.
scavenging	A geochemical process involving adsorption of trace elements onto Fe, Mn and Al-hydroxide.
schist	A micaceous metamorphic rock with parallel orientation of its minerals.
scintillometer	An instrument for measuring the natural radiation of rocks.
sediment	A rock formed of particles which were deposited from suspension in water, wind or ice.
sedimentary uranium	A type of uranium deposit found in sedimentary rocks of palaeodrainage channels.
sedimentary	A term describing a rock formed by the accumulation of biogenic or chemically formed minerals, and/or transported rock or mineral particles.
seismic reflection	The return of part of the energy of seismic waves to Earth’s surface after the waves bounce off a rock boundary.
seismic refraction	The bending of seismic waves as they pass from one material to another.
sericite	A fibrous form of muscovite, often resulting from the alteration of feldspar.
shale	A laminated sediment in which most particles are clay grade (<0.0039mm).
shear (zone)	A zone in which shearing has occurred on a large scale so that the rock is crushed and brecciated.
Shuttle Radar	The Shuttle Radar Topography Mission (SRTM) obtained elevation data on a near-global scale to generate a high-resolution digital topographic database of Earth.
silcrete	A surficial layer more or less cemented with silica.
silicified	Partially replaced by silica.
sill	A tabular intrusive body of igneous rock that is conformable with the layers it intrudes.
Silurian	A time period from 440 to 400 million years ago.
Sirotem	An electromagnetic geophysical exploration system developed by CSIRO.
skarn	A type of mineralisation occurring in the contact zone of an intrusion.
slate	A finely foliated metamorphic rock that results from the metamorphism of rocks such as shale under stress.
sphalerite	The principal ore of zinc: (Zn,Fe)S.
spinifex texture	Interpenetrating lacy elongate olivine crystals in komatiite, commonly thought to have formed by quenching.
splay	A small secondary fault diverging from a major fault at a low angle.
stockwork	A three-dimensional network of veinlets.
stratabound	A mineral deposit confined to a single stratigraphic unit.
stratiform	A type of stratabound deposit in which the ore minerals appear to have been deposited at the same time as the enclosing sediments.
stratigraphy	The succession or superimposition of rock strata.
stream sediment sampling	A geochemical exploration technique where stream sediments are the sampling medium.
strike	The direction or trend of bedding, cleavage or a fault on a horizontal plane.
structural lineament	A linear structural feature of regional extent.
structural corridor	Large scale linear zone or belt recognised by geological feature alignment.
sub-volcanic	Referring to an igneous intrusion whose depth is intermediate between that of plutonic and the surface.
sub crop	The near surface presence of a concealed rock layer.
sub-economic	Describing a resource that is not economic under the prevailing economic conditions.
subduction zone	A long narrow belt where one tectonic plate is descends beneath another.
sulphidic	Rich in sulphide minerals.
supergene	Process of ore enrichment or depletion by descending oxidising solutions.
supergene enrichment	Solution of metal by oxidised surface waters from the upper part of an ore deposit and its precipitation below, usually in response to reduction, creating a zone of enrichment.
surficial	Pertaining to the surface of the earth.
syncline	A fold in rocks in which the strata dip inward from both sides towards the axis.
syntectonic	An event occurring during tectonic activity, or a rock or feature so formed.
talus	Loose rock transported downhill by gravity.
targets	Exploration targets consist of a location that can be tested by drilling. They generally represent an anomaly from a survey or a geological concept.
tectonic	The forces involved in major structural processes forming faults and folds in the earth’s crust.
TEM	Transient electro-magnetic, a type of EM survey.
TEMPEST	An advanced fixed-wing airborne electromagnetic survey system.
tenement	Exploration or mining land title allowing various actions, eg an EL.
tennantite	An ore of copper: (Cu,Fe)₁₂As₄S₁₃.
Tertiary	The geological period prior to the Quaternary from 1.8 to 65 Ma.
tetrahedrite	An ore of copper: (Cu,Fe)₁₂Sb₄S₁₃.
thematic mapper	A type of Landsat imagery with resolution of around 30 metres.
tholeiitic basalt	A variety of basalt containing little or no olivine and in which the proportion of silica at a particular magnesium content is high.
thorium	A radioactive element.
tremolite	Calcium magnesium amphibole.
tuff	Volcanic ash strata.
turbidite	A sediment deposited by a turbidity current.
ultramafic	Mafic rock type composed of minerals rich in magnesium and iron silicates.
unconformity	A position in a sedimentary sequence where there is a lack of continuity in adjacent rock strata caused by a time break in sedimentation.
uraniferous	Containing uranium.
vein	A tabular or sheet like mineral-filled fracture.
VLF-EM	Very low frequency electromagnetic; a geophysical prospecting technique.
volcanic vent	An opening through which lava and rock fragments erupt.
volcanic, volcanogenic	Formed or derived from a volcano.
weathering	A process of change to rocks brought about by their exposure to oxygen and water.
Zn	The chemical symbol for the element zinc.

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