M Electrode – Potential electrode nearest to the A electrode in a resistivity device.

m – Metre.

Maar Volcano – Volcanic crater without a cone that is believed to have been formed by an explosive eruption of trapped gases.

Mafic – Igneous rocks composed mostly of dark, dense, iron amphibole, or olivine and magnesium-rich minerals. Mafic rocks have gravities greater than 3. Mafic minerals and rocks are the opposite of felsic.

MAG3D – Program library developed by the University of British Columbia Geophysical Inversion Facility (UBC-GIF) for carrying out forward modelling and inversion of surface, airborne, and/or borehole magnetic data in the presence of a three dimensional earth.

Magma – Molten rock generated within the earth in the form of molten lava that forms igneous rocks upon cooling. The rocks are called intrusive if the magma solidifies below the surface. Magma that reaches the surface is called lava, and the rocks that form when lava solidifies above the surface are classified as extrusive.

Magma Chamber – Cavity within the lithosphere filled with molten rock called magma.

Magmatic Water – Water that is dissolved in a magma or that is derived from magma.

Magnesite – White mineral composed of magnesium carbonate that is an important source of magnesium.

Magnetic Anomaly – Value of the local magnetic field remaining after the subtraction of the dipole portion of the earth’s field.

Magnetic Coupling – Transfer of momentum between celestial bodies, especially dust and gas clouds through magnetic forces.

Magnetics – Geophysical methodology for studying anomalies in the geomagnetic field through the use of magnetometers due to non-uniform magnetization of the subsurface.

Magnetic North Pole – Point where the earth’s surface intersects the axis of the dipole that best approximates the earth’s field, and the point where the earth’s magnetic field dips vertically downward.

Magnetic Permeability – Acteristic of a material. It is proportional to the magnetism induced in that material divided by strength of the magnetic field used.

Magnetic Stratigraphy – Study and correlation of polarity epochs and events in the history of the earth’s magnetic field as contained in magnetic rocks.

Magnetic Survey – Geophysical survey conducted on the earth’s surface that measures variations in the earth’s magnetic field caused by variations in rock type or geological structures.

Magnetic Susceptibility – Measure of the degree to which a substance may be magnetized and it represents the ratio of magnetization to magnetic field strength.

Magnetite – Black, magnetic, iron oxide mineral which is an important source of iron.

Magnetization – Local magnetic anomalies in the data are due to the magnetic field produced by magnetically susceptible material beneath the surface that has been magnetized by the earth’s ambient magnetic field. The majority of the response comes from shallow material due to the fast fall-off nature of the magnetic field.

Magnetometer – Instrument for measuring the intensity of the earth’s magnetic field. Variations in the field strength may indicate changes in magnetic properties of soil and rock or presence of ferrous metals.

Magnitude – Measure of earthquake size, determined by taking the common logarithm (base 10) of the largest ground motion observed in a seismic surface wave and normalized to be the same as one at a distance of 100 km from the epicenter.

Malachite – Greenish crystalized mineral CuCO3 (OH)2.

Manganese Nodule – Small, rounded concretion found on the deep ocean floor that may contain as much as 20 percent manganese and smaller amounts of iron, copper, and nickel oxides and hydroxides.

Mantle – Portion of the interior of the earth that lies between the crust and the core composed mainly of ultramafic rocks..

Mapping – Recording and locating geological observations and geological, chemical or geophysical information in location on a map, as opposed to time which is monitoring.

Marble – Metamorphic rock type formed by metamorphosism of limestone or dolostone.

Marcasite – Iron sulphide mineral with symbol FeS2, found in low-temperature, near-surface deposits in sedimentary rocks.

Marine Terrace – Platform of marine deposits, usually of sand, silt, and/or gravel that is sloping gently seaward. Such a platform may be exposed along the coast, forming cliffs, due to uplift and/or the lowering of sea level. An excellent example would be the coastal marine terraces along southern California.

Marl – Loose, crumbly deposit consisting of clay and calcium carbonate and formed in marine or freshwater conditions.

Mass Density – Known physical matter, including rocks, that has mass. It is the term given to the mass per unit volume usually reported in units of g/cm3 of a given material. In geophysics, the mass density of rock units is fundamentally important as it is linked to the gravitational field. For example, the higher mass density the faster sound travels through it.

Mass Movement – Downhill movement of soil or fractured rock under the force of gravity.

Mass Spectrometer – Instrument for separating ions of different mass but equal charge; comprising mainly isotopes in geology. Used to measure their relative quantities.

Massive Rock – Rock that is little or not at all broken by joints, cracks, foliation, or bedding.

Matrix – The finer grained rock material filling the spaces between larger particles or crystals in a rock.

Matsitama Belt – Assemblage of metasedimentary rocks that lies on the western margin of the Zimbabwean Craton within the Matsitama Belt.

Maturity – Stage in the geomorphic cycle in which maximum relief and well-developed drainage are both present.

McArthur River – World’s largest high-grade uranium mine with proven and probable reserves of some 335.5 million pounds U3O8. Owned by Cameco Corporation (70%) and AREVA Resources Canada Inc. (30%).

Meander – Broad, looping bend in a river or curves in a stream that develop as the stream erodes the outer bank of a curve and deposits sediment against the inner bank .

Measured Mineral Resource – Part of a mineral resource for which quantity, grade or quality, densities, shape, and physical characteristics are so well established that they can be estimated with confidence sufficient to allow the appropriate application of technical and economic parameters, to support production planning and evaluation of the economic viability of the deposit. The estimate is based on detailed and reliable exploration, sampling and testing information gathered through appropriate techniques from locations such as outcrops, trenches, pits, workings and drill holes that are spaced closely enough to confirm both geological and grade continuity.

Mechanical Weathering – Set of all physical processes by which an outcrop is broken up into small particles.

Medial Moraine – Long stripe of rock debris carried on or within a glacier resulting from the convergence of lateral moraines where two glaciers join.

Medical Geology – Application of geologic science to problems of health such as those relating to mineral sources of toxic or nutritious elements and natural dispersal of toxic pollutants.

Mélange – Body of rocks consisting of large blocks of a map-able size of different rocks jumbled together with little continuity of contacts.

Mercalli Scale – Subjective scale for measuring the intensity of an earthquake based on how the earthquake is perceived by people and on the amount of destruction caused by the tremors.

Mesa – Land formation, less extensive than a plateau, having steep walls and a relatively flat top.

Mesh – 1D, 2D or 3D grid used to approximate a continuous or semi-continuous surface or volume for computer modelling.

Mesophere – Lower mantle.

Mesoproterozoic – Era some 1600 to 1000 mya with three periods; 1) Calymmian, 2) Ectasian, and 3) Stenian periods.

Mesozoic – Era of time during the Phanerozoic eon lasting from 251 million years ago to 65.5 million ago.

Metallurgical – Physical properties of metals as to composition, mechanical working and heat-treatment. Also referred to in the process of extracting metals from their ores and the refining of metals.

Metamorphic Rock – Any rock derived from other pre-existing rocks in the earth’s crust by chemical, mineralogical and structural changes resulting from pressure, temperature or shearing stress.

Metamorphism – A process whereby the composition of rock is altered by heat and pressure in the earth’s interior.

Metasediment – Metamorphosed sedimentary rock.

Meteoric Water – Rainwater derived from snow, hail, and sleet as opposed to ground water.

Meteorite – Stony or metallic object from inter-planetary space.

Mho – Unit of electrical conductance that is the reciprocal of ohm.

Mica – Group of silicate minerals that cleave perfectly into thin sheets.

Microfossil – Very small fossil usually studied with the aid of a microscope such as foraminifera, radiolarians, and small vertebrate fossils.

Micro-Gravity Survey – Surface geophysical survey undertaken on a very small scale such as that of a few meters and requiring a high meter sensitivity. Used to ensure the earth’s gravitational field at different points over an area of interest.

Micrometeorite – Meteorite less than 1 millimeter in diameter.

Microresistivity Log – Group of short-spaced resistivity logs that are used to make measurements of the mud cake and invaded zone.

Microseism – Weak vibration of the ground that can be detected by seismographs and which is caused by waves, wind, or human activity; but not by an earthquake.

Mid-Oceanic Ridges – Elongated rises on the ocean floor where basalt periodically erupts forming new oceanic crust.  Similar to continental rift zones.

Migmatite – Mixture of igneous and metamorphic rocks in which thin dykes and stringers of granitic material interfinger with metamorphic rocks. Rock of both igneous and metamorphic characteristics that displays large crystals and laminar flow structures. Likely formed metamorphically in the presence of water and without melting.

Migration – Movement of chemicals, bacteria, gases, and so on, in flowing water or vapor in the subsurface. A very typical result of migration is the removal of hyperbolic events on the record resulting from diffractions from faults and other discontinuities.

Mill – Plant where ore is crushed and ground fine and further undergoes physical or chemical treatment to extract the valuable metals.

Milling – Process in which the ore is crushed and ground and subjected to physical or chemical treatment to extract the value metals to a concentrate or finished product.

Mine – Underground excavation in the earth for the purpose of extracting minerals.

Mineral – Naturally occurring, inorganic solid chemical substance that has a fixed chemical composition and a characteristic crystal form found in the earth’s crust.

Mineral Deposit – Identified in-situ mineral occurrence from which valuable or useful minerals may be recovered; mineral deposit estimates are not precise calculations, being dependent on the interpretation of limited information on the location, shape and continuity of the occurrence of mineralization and on the available sampling results.

Mineral Reserve – A mineral reserve is the economically mineable part of a measured or indicated mineral resource demonstrated by at least a preliminary feasibility study. The study must include adequate information on mining, processing, metallurgical, economic, and other relevant factors that demonstrate, at the time of reporting, that economic extraction can be justified. A mineral reserve includes diluting materials and allowances for losses that may occur when the material is mined. Mineral reserves are sub-divided in order of increasing confidence into probable mineral reserves and proven mineral reserves, which are defined as follows: probable: the economically mineable part of an indicated, and in some circumstances, a measured mineral resource demonstrated by at least a preliminary feasibility study. The study must include adequate information on mining, processing, metallurgical, economic, and other relevant factors that demonstrate, at the time of reporting, that economic extraction can be justified. Proven: the economically mineable part of a measured mineral resource demonstrated by at least a preliminary feasibility study. The study must include adequate information on mining, processing, metallurgical, economic, and other relevant factors that demonstrate, at the time of reporting, that economic extraction is justified.

Mineralization – Concentration of elements and minerals of value within a body of rock.

Mineralogical Zonation – Segregation of rock composition based on contained minerals.

Mineralogy – Study of chemistry, crystal structure, and physical properties of minerals.

Miocene Epoch – Epoch from 23.03 to 5.3 million years ago with six Ages: the 1) Aquitanian, 2) Burgidalian, 3) Langhian, 4) Serravalian, 5) Tortonian, and 6) Messinaian ages.

Miogeosyncline – Geosyncline that is situated near a craton and receives chemical and well-sorted elastic sediments from the continent.

Mohorovicic Discontinuity – Boundary between crust and mantle at between 5 and 45 kms of depth marked by a rapid increase in seismic wave velocity to more than 8 kilometers per second. The measurements are abbreviated as Moho or M-discontinuity.

Mohs Scale of Hardness – Empirical, ascending scale of mineral hardness with talc as 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, and diamond 10.

Molds – Fossils formed when the sediment surrounding a buried organism hardens. When the organism decays, its impression is left in the rock and can be seen if the rock is broken open.

Molybdenum – Element, abbreviated as Mo often found in copper porphyry deposits. It is used extensively in steel manufacturing as a filament material. It is often referred to as simply Moly.

Monadnock – Isolated hill or mountain rising above a peneplain.

Monitoring – Observing the change in a geophysical, hydrogeological or geochemical measurement with time.

Monocline – Set of rock layers that all slope downward from the horizontal in the same direction.

Moraine – Glacial deposit of sediment or debris of rock, gravel, sand or clay left at the margin of an ice sheet. A lateral moraine is one deposited to the side of a glacier. A terminal moraine is one deposited to the front of a glacier. A ground moraine is one deposited on the land surface.

Mosetse Complex – Interrelated series of granites and metasediments which contains the Matsitama Belt on the western margin of the Zimbabwean Craton, which host southern Africa native copper.

Mountain – Steep-sided topographic elevation larger than a hill.

Mud Crack – Polygonal shaped cracks that form in a layer of mud or silt resulting from the contraction that accompanies drying.

Muscovite – Light-coloured variety of the mica group of minerals containing potassium and aluminum which splits easily into thin transparent sheets.

Mylonite – Fine-grained metamorphic rock formed by extreme crushing and pulverizing along a fault zone.

Mud Cake – Layer of mud particles that builds up on the wall of a rotary-drilled hole as mud filtrate is lost to the formation.

Mud Filtrate – Liquid effluent of drilling mud that penetrates the wall of the hole.

Mudflow – Mass movement of material finer than sand which is most often lubricated with large amounts of water.

Mudstone – Fine grained sedimentary rock similar to shale but more massive.

Muting – Change in the amplitude of all or part of a trace before additional processing. Noisy or clearly erroneous traces are given zero amplitude. Data before the first break and the known refraction arrivals are also often reduced to zero amplitude.

my – million years.

mya – million years ago.

Mylonite – Very fine lithified fault breccia commonly found in major thrust faults and produced by shearing and rolling during fault movement.