G

Ga – Gigaannum is equal to 10⁹ years, or one billion years.

Gabbro – Fine to coarse grained, dark coloured crystalline igneous intrusive rock composed mainly of calcic plagioclase, clinopyroxene and sometimes olivine. The deep intrusive equivalent of basalt or diabase. These rocks are plutonic, formed when molten magma is trapped beneath the Earth’s surface and cools into a crystalline mass.

Galena – Lead mineral, which occurs with sphalerite in hydrothermal veins, also in sedimentary rocks as replacement deposits; an important source of lead and silver.

Gamma – Common unit of magnetic field intensity, equal to one nano Tesla. The Earth’s magnetic field strength is about 50,000 gammas (g) in mid-latitudes.

Gamma Log – Log of the natural radioactivity of the rocks penetrated by a drillhole which also will detect gamma-emitting artificial radioisotopes.

Gamma Ray – Photon that has neither mass nor electrical ge that is emitted by the nucleus of an atom; measured in gamma logging and output from a source used in gamma-gamma logging.

Gangue – Worthless rock or other material in which valuable minerals are found.

Garnet – Silicate mineral that usually occurs as small, rounded, red or pink crystals mainly in metamorphic rocks but is rarely also found in granite veins.

Gastropod – Mollusk belonging to the class Gastropoda characterized by a distinct head with eyes and tentacles and in most by a single calcareous shell that is closed at the apex, sometimes spiraled, not chambered, and generally asymmetrical. A good example would be a snail.

Gastroliths – Fossilized gizzard stones, usually applicable in the fossil study of birds and reptiles.

Geochemical – Trace quantities of elements of a certain area.

Geochemistry/Geochemical – Study of variation of chemical elements in rocks or soil.

Geochronology – Science of absolute dating and relative dating of geologic formations and events, primarily through the measurement of daughter elements produced by radioactive decay in minerals.

Geologic Cycle – Sequence through which rock material passes in going from its sedimentary form, through diastrophism and deformation of sedimentary rock, then through metamorphism and eventual melting and magma formation, then through volcanism and plutonism to igneous rock formation, and finally through erosion to form new sediments.

Geologic Maps – Show the types and ages of rock of an area. These maps are used by paleontologists to find areas that are likely to contain fossils.

Geologic Time Scale – Categorization of geological events based on successively smaller time spans: eons, eras, periods, epochs, and ages. The division is accomplished through stratigraphy and paleontology.

Geology/Geological – Study of the earth’s history and life, mainly as recorded in rocks.

Geomagnetic Field – The earth’s magnetic field.

Geomorphic Cycle – Idealized model of erosion wherein a plain is uplifted epeirogenically, then dissected by rapid streams referred to as youth; then rounded by downslope movements into a landscape of steep hills known as maturity; and finally reduced to a new peneplain at sea level commonly referred to as old age.

Geomorphology – Science of surface landforms and their interpretation on the basis of geology and climate.

Geophones – Receivers used to record the seismic energy arriving from a source, in seismic geophysical methods.

Geophysics/Geophysical – Study of the earth by quantitative physical methods, either by surveys conducted on the ground, in the air (by fixed wing aircraft or helicopter) or in a borehole or drillhole.

Geophysical Mapping – Locating geophysical anomalies in space ; as opposed to time, which is geophysical monitoring.

Geophysical Model – Simplified concept of how one physical property is distributed within the earth. Geophysical models are generally an object, either a halfspace, or in 1D, 2D, or 3D. A model of earth can mean a geological model in which the subsurface is described in terms of rock types, structures, fluids, and so on, or alternatively it can mean a geophysical model defined here in terms of physical properties and physical property contrasts.

Geophysical Monitoring – Observation of the change in a geophysical measurement with time.

Geophysical Survey – Study conducted to measure the physical characteristics of a certain area-grade – the measure of concentration of a metal within mineralized rock.

Geosyncline – Major down-warp in the earth’s crust, often more than 1000 kilometers in length, in which sediments accumulate to thicknesses of many kilometers. The sediments may eventually be deformed and metamorphosed during a mountain-building episode.

Geotherm or Geothermal Gradient – Plot of the curve that indicates the temperature of the earth at various depths, such as a plot of temperature vs. depth.

Geyser – Hot spring that throws hot water and steam into the air; the heat thought to result from the contact of groundwater with magma bodies.

Glacial Rebound – Epeirogenic uplift of the crust that takes place after the retreat of a continental glacier in response to earlier subsidence under the weight of the ice.

Glacial Striation – Scratches left on bedrock and boulders by overriding ice and showing the direction of motion.

Glacial Valley – Valley occupied or formerly occupied by a glacier; most notably with a U-shaped profile.

Glacier – Large mass of ice and surficial snow that persists throughout the year and flows downhill under its own weight. Glaciers vary in size from small valley glaciers to huge ice sheets of continental dimensions.

Glacier Surge – A period of unusually rapid movement of one glacier, sometimes lasting more than a year.

Glass – Rock formed when magma is rapidly cooled too quickly to allow crystal growth.

Glassiness – Content of extent of glass in an igneous rock.

Gneiss – Coarse-grained foliated rock produced by regional metamorphism. The mineral grains within the gneiss show parallel alignment and the rock displays compositional banding where the minerals alternate into alternating bands of light and dark coloured materials.

Gneissic/Gneissose – Pertaining to the features of a gneiss.

Gocad Mining Suite – Customized mining extension to the Gocad (Geological Object Computer Aided Design) modelling engine. Features include highly sophisticated yet simple to understand geological modelling, powerfully interactive 3D editing, and enormous power in structural modelling, surface (wireframe) construction, stratigraphic and regular block modelling, and geostatistics.

Gold – A heavy, soft, ductile, malleable, yellowy-coloured precious metal used in jewelry, dentistry, electronics and investment purposes.

Gondwana – Ancient continental landmass comprising the present South America, Africa, India, Australia and Antarctica. It split apart during Mesozoic time.

Gossan – Iron-rich, rusty-coloured, weathering product formed over rocks commonly containing sulphide minerals, especially iron sulphides.

Graben – Downthrown block between two normal faults of parallel strike but converging dips; hence a tensional feature.

Grade – Amount of valuable metal or minerals in each tonne of ore, expressed as grams per tonne for precious metals and as a percentage for most other types of metals. The cut-off grade is the minimum metal grade at which a tonne of rock can be processed on an economic basis. The recovered or recoverable grade – is actual metal grade that can be realized by the metallurgical process and treatment of the ore usually established by specialized laboratory and process testing.

Graded Bedding – Type of bedding in which each layer is characterized by a progressive decrease in grain size from the bottom to the top of the bed. The coarsest particles are concentrated at the bottom and grade gradually upward into fine silt, the whole bed having been deposited by a waning current.

Graded Stream – Stream whose smooth profile is unbroken by resistant ledges, lakes, or waterfalls, and which maintains exactly the velocity required to carry the sediment provided to it.

Grain – Particles or discrete crystals which comprise a rock or sediment.

Grain Density – Density of a unit volume of rock matrix at zero porosity, in grams per cubic centimeter. Often referred to as matrix density.

Grain Size – Size of the particles or crystals that constitute a rock or sediment; hence fine, medium, or coarse-grained.

g/t – Grammes per metric tonne is a measurable unit utilized in geochemical prospecting techniques which measure the content of specified, usually precious metals, in soils and rocks for the purpose of defining anomalies.

Granite – Light-coloured, coarse-grained highly felsic igneous intrusive rock composed primarily of quartz, feldspar, orthoclase, plagioclase and ferromagnesium minerals such as mica and hornblende. Considered the intrusive equivalent of rhyolite.

Granitization – Formation of metamorphic granite from other rocks by recrystallization with or without complete melting.

Granular Snow – Snow that has been transformed into small granules of ice.

Granulite – Metamorphic rock with coarse interlocking grains and little or no foliation.

Graptolite – Extinct animal of which the fossil remains look like tiny, serrated black rods.

GRAV3D – Program developed by the Universality of British Columbia Geophysical Inversion Facility (UBC-GIF) for carrying out forward modelling and inversion of surface, airborne, and/or borehole gravity data in three dimensions. The program library carries out the following functions: 1) forward modelling of the vertical component of the gravity response to a 3D volume of density contrast, and 2) inversion of surface, and/or airborne gravity data to generate 3D models of density contrast.

Gravel – Coarsest of alluvial sediments, containing mostly particles larger than 2 mm in size and including cobbles and boulders.

Gravity Anomaly – Difference between the observed acceleration of earth’s gravity and a value predicted from a model.

Gravity Gradiometry – Study and measurement of variations in the acceleration due to gravity.

Gravity Recovery Circuit – Mechanical equipment used within a plant to recover gold from the ore using the difference in specific gravity between the gold and the host rock. Commonly used equipment are shaking tables, spirals, and so on.

Gravity Survey – Measurement of gravity at regularly spaced grid points with repetitions to control instrument drift.

Greenhouse Effect – Heating of the atmosphere by the absorption of infrared energy re-emitted by the earth as it receives light energy in the visible band from the sun.

Greenschist – Metamorphic schist containing green coloured chlorite and epidote and formed by low-temperature, low-pressure metamorphism.

Grinding – Powdering or pulverising of ore by pressure or abrasion to liberate valuable minerals for further metallurgical processing. Sometimes referred to as milling.

Ground Electrode – Surface electrode used for SP and resistivity logging.

Ground Moraine – Glacial deposit of till with no marked relief and interpreted as having been transported at the base of the ice.

Ground Penetrating Radar – GPR is a geophysical method in which bursts of electromagnetic energy are transmitted downwards from the surface to be reflected and refracted by velocity contrasts within the subsurface. Sometimes referred to as ground probing radar.

Groundwater – Mass of water in the ground below the phreatic zone which occupies the total pore space in the rock and moves slowly downhill where permeability allows.

Group – Unit in geological mapping that consists of two or more formations.

Guard Log – Focused resistivity log that gets its name from guard electrodes that are designed to focus the flow of current.

Gully – Small steep-sided valley or erosional channel ranging anywhere from 1 meter to about 10 meters across.

Guyot – Flat-topped, submerged mountain or seamount found in the ocean.

Gypsum – Soft, white mineral consisting mainly of calcium sulphate formed during the evaporation of sea water. It is primarily used in the manufacture of drywall.

Gyre – Circular rotation of the waters of each major sea that is driven by prevailing winds and the Coriolis Effect.