Ichnology – Study of trace fossils.
Igneous – Rock formed by the cooling or solidification of molten material and lhas crystallized from molten material, known as magma. Igneous rock is called intrusive when formed below the surface, or extrusive when formed on the surface.
Ignimbrite – Igneous rock formed by the lithification of volcanic ash and volcanic breccia.
Ilmenite – Weakly magnetic crystalline iron titanium oxide mineral, symbol FeTiO3, which is iron-black or steel-gray.
Imaging Work Station – Location consisting of a microcomputer with a high-resolution color monitor and accompanying software which allows the manipulation, enhancement and visual display of digital data.
Imbricate – Process of depositing clastic sediments with a preferential orientation of the composing grains.
Impressions – Prints or marks made when an organism’s body has been compressed. Impressions are different from compressions because no thin organic material is left behind.
Inclination – Angle between a line in the earth’s magnetic field and the horizontal plane. Often known as a dip.
Index of Refraction – Ratio of the speed of light in a vacuum to the speed in a material. This ratio determines the amount that light is refracted as it passes into a crystal.
Indicated Mineral Resource – That part of a Mineral Resource for which quantity, grade or quality, densities, shape and physical characteristics can be estimated with a level of confidence sufficient to allow the appropriate application of technical and economic parameters, to support mine planning and evaluation of the economic viability of the deposit. The estimate is based on detailed and reliable exploration and testing information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes that are spaced closely enough for geological and grade continuity to be reasonably assumed.
Induced Magnetization – Magnetization caused by an applied magnetic field. This contrasts with remnant magnetization.
Induced Polarization – IP is used both to refer to a phenomenon and to the type of field survey that measures this phenomenon. Electric charges in the ground, and the way in which they interact with surfaces of mineral grains, are affected by application of an electric field. The effects can be measured by recording dynamictime or frequency behaviour of potentials caused by the application of the field.
Induction/Induce – EM is a process described by Faraday’s Law whereby a variable magnetic field generates an electric field (voltage) that in the presence of a conductor will produce electric currents.
Induction Log – Method for measuring resistivity or conductivity that uses an electromagnetic technique to induce a flow of current in the rocks around a borehole. It can be used in nonconductive-borehole fluids.
Induction Number – Quantitative measure of the quality of a target for EM methods. The formulation varies for different targets but in general it involves the product of target conductivity, magnetic permeability, frequency of the transmitter and a cross-sectional dimension of the target.
Inferred Mineral Resource – Part of a Mineral Resource for which quantity and grade or quality can be estimated on the basis of geological evidence and limited sampling and reasonably assumed, but not verified, geological and grade continuity. The estimate is based on limited information and sampling gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes.
Inferred Resource – That part of a resource for which tonnage, grade and content can be estimated with a low level of confidence. It is inferred from geological evidence and assumed but not verified geological and/or grade continuity. It is based on information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes which may be limited or of uncertain quality and reliability.
Inferred Resources – Mineralization which does not have demonstrated economic viability.
Infill Drilling – Method of drilling intervals between existing holes, used to provide greater geological detail and to help establish reserve estimates.
Infiltration – Movement of groundwater or hydrothermal water into rock or soil through joints and pores.
Inosilicate – Mineral with interlocking single or double chains of silicate tetrahedra groups. Asbestos is a good example of the fibrous structure of inosilicates whereas pyroxenes are noted single-chain inosilicates, and amphiboles noted double chain inosilicates.
In-Phase – Specific part of a periodic signal that has zero phase shift with a reference signal.
Interbedded – Beds or layers of rock situated between or alternating with beds of a different kind of rock.
Interfacial Angle – Angle between two crystal faces of a crystal which could be described as characteristic of a mineral’s symmetry.
Interior Drainage – System of streams that converge in a closed basin and evaporate without reaching the sea.
Intermontane Basin – Basin between mountain-ranges and quite often formed over a graben.
International Geomagnetic Reference Field – IGRF is a long wavelength regional magnetic-field model determined and adjusted by an international committee about every five years or so. To determine the local field data the IGRF is deducted from the observed data.
Interpolation – Method of determining intermediate values from surrounding known values.
Interpretation – For geophysicists it is the science of transforming geophysical measurements into subsurface structure. Interpretation of geophysical data requires a couple of steps. 1) The data has to be interpreted in terms of a causative distribution of the relevant physical property. This interpretative ‘model’ can then be interpreted in terms of geological structures, minerals, rock type alteration, and so on. 2) Geophysical interpretation may then be carried out in many ways, ranging from simple data inspection to sophisticated inversion and modelling.
Interval Transit Time – Time required for a compressional acoustic wave to travel a unit-distance. Transit time is generally measured by acoustic or sonic logs in microseconds per foot. It is the reciprocal of velocity.
Intrusion – Mass of igneous rock that while it was liquid intruded, by forcing its way into older rock, then solidified.
Intrusion Breccia – Rock comprised of angular pieces of country rock in a matrix of intrusive igneous rock.
Intrusions – Body of igneous rock formed below the surface and formed by the consolidation of magma intruded into other rocks. This is in contrast to lavas which are extruded upon the surface from the volcanic eruption. It is through the intrusion of magma bodies that porphyry deposits are formed. These are the opposite of an extrusive.
Invaded Zone – Annular interval of material around a drill hole where drilling fluid has replaced all or part of the native interstitial fluids.
Inversion – Process of mathematically estimating one or more models of subsurface physical property distributions that could explain a dataset which has been collected in the field. Commonly refers to a more specific methodology than interpretation.
Ion – Atom or group of atoms that has gained or lost electrons and so has a net electric charge.
Ionic Bond – Bond formed between atoms by electrostatic attraction between oppositely charged ions.
Iron Formation – Sedimentary rock containing considerable iron generally exceeding 15 percent as sulfide, oxide, hydroxide, or carbonate.
IRR – Internal rate of return.
Island Arc – Curved chain of islands that rise from the sea floor, usually in close proximity to a continent. The convex side generally faces the open ocean, while the concave side usually faces the continent. An excellent example would be the Alaska’s Aleutian Islands.
Isograd – Line or curved surface connecting rocks that have undergone an equivalent degree of metamorphism.
Isostasy – Mechanism whereby areas of the crust rise or subside until the mass of their topography is buoyantly supported or compensated by the thickness of crust below, which “floats” on the denser mantle. This is the theory behind the belief that continents and mountains are supported by low-density crustal roots.
Isotope – One of several forms of one element all having the same number of protons in the nucleus, but differing in their number of neutrons and thus atomic weight.
Isotope Geology – Study of the relative abundances of isotopes in rocks to determine their ages or conditions of formation.
Isotopes – Atoms of the same element that have the same atomic number but a different mass number. Unstable isotopes are radioactive and decay to become stable isotopes.
Isotropic Substance – One in which the magnitude of a physical property such as transmission of light is independent of crystallographic direction.