Facies – Set of all characteristics of a sedimentary rock that indicates its particular environment of deposition and which distinguish it from other facies in the same rock.
Fan Shooting – Seismic refraction technique where the sensors (geophones) are deployed on a segment of a circle centered on the seismic source. Variations in the time of arrival are caused by radial variations in the velocity structure. Could be used, for example, to search for low velocity anomalies caused by buried waste.
Fault – A planar or gently curved fracture in the Earth’s crust across which there has been relative displacement either vertically or horizontally. A fracture, or large crack, in the Earth’s crust where one side moves up/down/sideways relative to the other.
Fault Block – Pieces of crust that have slipped into or alongside a fault.
Fault Plane – Plane that best approximates the fracture surface of a fault.
Fault Zone – Area with multiple faults.
Faunal Succession – Evolutionary sequence of life forms, especially as recorded by the fossil remains in a stratigraphic sequence.
Fayalite – Iron-rich end-member of the olivine solid-solution series (Fe2SiO4).
Fe – Chemical symbol for iron
Feasibility Study – Comprehensive study of a mineral deposit based on scientific, engineering and economic data in which all geological, engineering, legal, operating, economic, social, environmental and other relevant factors are considered in sufficient detail that it could reasonably serve as the basis for a final decision by a financial institution to finance the development of the deposit for mineral production. The common accuracy level of such a study is an accuracy level of +/- 15%.
Felsic – Light-colored igneous rocks with low magnesium and iron content and which are enriched by lighter elements such as silicon, oxygen, aluminum, sodium, and potassium. Felsic rocks have a specific gravity less than 3 and a high content of minerals such as quartz, orthoclase and plagioclase. The most common felsic rock is granite. Rhyolite and granite are felsic rocks. Felsic rock is the opposite of mafic.
Felsite – Light-coloured, fine-grained extrusive or shallow-intrusive igneous rock with or without phenocrysts and composed chiefly of quartz and feldspar.
Feldspar – Constituting 60% of the Earth’s crust, feldspar occurs in all rock types and decomposes to form much of the clay in soil, including kaolinite. The mineral group comprises albite, andesine, anorthite, anorthoclase, banalsite, buddingtonite, bytownite, celsian, hyalophane, labradorite, microcline, oligoclase, orthoclase, paracelsian, plagioclase, reedmergnerite, sanidine, and slawsonite. It is a common form of rock forming minerals composed of silicates of aluminum and one or more of potassium, sodium or calcium.
Ferrimagnetic – Substances having positive and relatively large magnetic susceptibility as well as generally large hysteresis and remanence. This is due to the interaction of atoms and the coupling of magnetic moments aligned in opposition, which result in non-zero net moments. Ferrimagnetic minerals have this property.
Ferromagnesium Minerals – Variety of silicate minerals containing abundant iron and magnesium such as olivine, pyroxene, amphibole and biotite.
Field – Space in which an effect, such as gravity or magnetism, is measurable.
Field Print – Copy of a log obtained at the time of logging that has not been edited or corrected.
Filtering – Passage of fluid through a material, in a geological sense, that retains or filters particles above a certain size. It can also mean the attenuation of a signal’s components based on a measurable property, commonly frequency. Filtering generally involves a numerical operation that enhances only a portion of the signal.
Fiord – Former glacial valley flooded by the sea to form a long, narrow, steep-walled inlet.
First Reading – Depth at which logging began at the bottom of the hole.
Fissure – Extensive crack, break, or fracture in the rocks.
Fissure Vein – Crack in the rock material of the Earth’s crust, filled with mineral matter different from the walls.
Flexural Waves – Occur in bars and refers to the flexing of a bar. They can be created in shafts by impacting the side of a shaft. The velocity of flexural waves depends on their wavelength.
Flood Basalt – Plateau basalt extending many kilometers in flat, layered flows originating in fissure eruptions.
Flood Plain – Level plain of stratified alluvium on either side of a stream; submerged during floods and built up silt and sand carried out of the main channel.
Flood Tide – Part of the tide cycle during which the water is rising or leveling off at high water.
Flotation – Process of concentration in which levitation in water of particles heavier than water is obtained with the use of chemical reagents; typically used in processing of coal or sulphide minerals with the aid of a reagent and the desired product becomes attached to air bubbles in a liquid medium and floats as a froth.
Flotation Cells – Commonly used in conventional copper concentrators and other mineral separation techniques to separate the copper minerals from the waste rock. After being crushed and ground, the copper ore is pumped into flotation cells. Chemical reagents are added and the mixture is aerated and mechanically agitated. The mineral particles are separated from the host rock and float to the surface on air bubbles, forming a froth, which is skimmed off, filtered and dried.
Flow Volcanic – Volcanic rock formed from lava that flowed out onto the earth’s surface.
Flow Cleavage – In metamorphic rock, the parallel arrangement of all planar or linear crystals as a result of rock flowage during metamorphism is referred to as flow-cleavage.
Flowmeter – Device for logging that is designed to measure the rate, and usually the direction, of fluid movement in a well. Majority are designed to measure vertical flow.
Fluid Inclusion – Small body of fluid that is entrapped in a crystal and has the same composition as the fluid from which the crystal formed.
Fluid Sampler – Electronically controlled device that can be operated on a logging cable to take water samples at pre-determined depths in the well.
Flume – Laboratory model of stream flow and sedimentation consisting of a rectangular channel filled with sediment and running water.
Flushed Zone – Zone in the borehole wall behind the mudcake that is considered to have had all mobile native fluids flushed from it.
Flysch – Thick marine sequence of sedimentary rocks recognized by thinly interbedded sandy shale, mudstone, sandstone and conglomerate. Environment is indicative of rapid erosion of a nearby, newly formed mountain belt.
Focus – Initial point within the earth that ruptures in an earthquake, directly below the epicenter.
Focused Log – Resistivity log that employs electrodes designed to focus the current into a sheet that provides greater penetration and vertical resolution.
Fold – Bending, or buckling of rock strata by compressive forces and deformed.
Foliation – Planar set of minerals or banding of mineral concentrations including cleavage, in response to pressure, found in a metamorphic rock.
Footwall – Underlying side of an orebody or stope.
Foraminifera – Class of oceanic protozoa most of which have shells composed of calcite.
Foraminiferal Ooze – Calcareous sediment composed of the shells of dead foraminifera+.
Formation – Distinctive body of rock, identified by lithological characteristics and stratigraphic position, that is named and separated from other rocks on a geological map.
Forset Bed – One of the inclined beds found in crossbedding, and often an inclined bed deposited on the outer front of a delta.
Forsterite – The magnesium rich end-member of the olivine solid solution series (Mg2SiO4). Peridot is the gemstone variety of forsterite.
Formation – The basic unit for the naming of rocks in stratigraphy. A set of rocks that are or once were horizontally continuous, that share some distinctive feature of lithology, and are large enough to be mapped. Used in drill hole-logging to refer to all material penetrated by a drill hole without regard to its lithology or structure.
Formation-Resistivity Factor – Ratio of the electrical resistivity of a rock 100 percent saturated with water (Ro) to the resistivity of the water with which it is saturated (Rw). F = Ro/Rw.
Forward Modelling – Process of developing* models of the earth based upon measured geophysical data. May be as simple as recognizing that an anomaly is likely caused by a buried pipe, or it may involve sophisticated data processing and/or inversion to mathematically build a range of plausible models. Forward modelling is the simulating of data that would occur if a survey were gathered over a known model of the Earth.
Fossil – Impression, cast, outline, or track of any animal or plant that is preserved in rock after the original organic material is transformed or removed.
Fossil Fuel – General term for combustible geologic deposits of carbon in reduced (organic) form and of biological origin, including coal, oil, natural gas, oil shales, peat and tar sands.
Fossil Record – Totality of fossilized artifacts and their placement within the earth’s rock strata. It provides information about the history of life on earth.
Fossiliferous – Rich in fossils.
Free-Air Anomaly – Gravity data that have been corrected for latitude and elevation but not for the density of the rock between the datum and the measurement elevation, also referred to as the Bouguer correction. Sometimes referred to as free-air gravity.
Free Oscillation – Ringing or periodic deformation of the whole Earth at characteristic low frequencies after a major earthquake.
Frequency Domain – Measurements in geophysics analyzed according to their constituent frequencies. The usual alternative is time domain measurements.
Frequency Domain Method – Potential-field analysis in which parameters of interest are estimated from characteristics of amplitude and phase spectra, which involves the variation of apparent resistivity with frequency.
Friction Breccia – AB formed in a fault zone or volcanic pipe by the relative motion of two rock bodies.
Fringing Reef – Coral reef that is directly attached to a landmass not made of coral.
Fumarole – Small vent in the ground from which volcanic gases and heated groundwater emerge, but not lava. Frequently, mineral deposits form around the vent.