Mineral exploration
Encyclopedia
Mineral exploration is the process of finding ore
(commercially viable concentrations of minerals) to mine
. Mineral exploration is a much more intensive, organized and professional form of mineral prospecting
and, though it frequently uses the services of prospecting, the process of mineral exploration on the whole is much more involved.
Area selection is based on applying the theories behind ore genesis
, the knowledge of known ore occurrences and the method of their formation, to known geological regions via the study of geological maps, to determine potential areas where the particular class of ore deposit being sought may exist. Oftentimes new styles of deposits may be found which reveal opportunities to find look-alike deposit styles in rocks and terrains previously thought barren, which may result in a process of pegging of leases in similar geological settings based on this new model or methodology. This behaviour is particularly well exemplified by exploration for Olympic Dam style deposits, particularly in South Australia
and worldwide based on models of IOCG
formation, which results in all coincident gravity and magnetic anomalies in appropriate settings being pegged for exploration.
This process applies the disciplines of basin modeling, structural geology, geochronology, petrology and a host of geophysical and geochemical disciplines to make predictions and draw parallels between the known ore deposits and their physical form and the unknown potential of finding a 'lookalike' within the area selected.
Area selection is also influenced by the commodity being sought; exploring for gold occurs in a different manner and within different rocks and areas to exploration for oil or natural gas or iron ore. Areas which are prospective for gold may not be prospective for other metals and commodities.
Similarly, companies of different sizes (in terms of market capitalisation and financial strength) may look for different sized deposits, or deposits of a minimum size, depending on their will and ability to finance construction. Often the major mining houses will not look for deposits of less than a certain size class because small deposits will not meet their criteria for an internal rate of return. This practise may result in larger mining companies relinquishing control of smaller ore bodies they find, or may preclude them from entering a terrane which is characterised by deposits of a particular type or style. For example, a mining major would not look for a relatively small, high-cost Kambalda style
nickel deposit and would direct their efforts toward discovering a Mt Keith style deposit.
Often a company or consortium wishing to enter mineral exploration may conduct market research
to determine, if a resource in a particular commodity is found, whether or not the resource will be worth mining based on projected commodity prices and demand growth. This process may also inform upon the Area Selection process as noted above, where areas with small-sized deposit styles will be ruled out based on likely economic returns should a deposit be found. This occurs because often smaller deposits are more expensive to run, and hence, carry greater risks of closure if commodity prices fall significantly.
Area selection may also be influenced by previous finds, a practice affectionately named subsurface control or nearology, and may also be determined in part by financial and taxation incentives and tariff systems of individual nations. The role of infrastructure may also be crucial in area selection, because the ore must be brought to market and infrastructure costs may render isolated ore uneconomic.
The ultimate result of an area selection process is the pegging or notification of exploration licenses, known as tenements.
In some cases, for instance in areas covered by soil, alluvium and platform cover
, drilling may be performed directly as a mechanism for generating targets.
, electromagnetism (resistivity
of rocks) and a number of different other variables in a certain area. The most effective and widespread method of gathering geophysical data is via flying airborne geophysics.
Geiger counter
s and scintillometer
s are used to determine the amount of radioactivity. This is particularly applicable to searching for uranium ore deposits but can also be of use in detecting radiometric anomalies associated with metasomatism
.
Airborne magnetometer
s are used to search for magnetic anomalies in the Earth's magnetic field
. The anomalies are an indication of concentrations of magnetic minerals such as magnetite
, pyrrhotite
and ilmenite
in the Earth's crust. It is often the case that such magnetic anomalies are caused by mineralization events
and associated metals.
Ground-based geophysical prospecting in the target selection stage is more limited, due to the time and cost. The most widespread use of ground-based geophysics is electromagnetic geophysics
which detects conductive minerals such as sulfide minerals within more resistive host rocks.
Ultraviolet lamps may cause certain minerals to fluoresce
, and is a key tool in prospecting for tungsten
mineralisation.
systematics and vegetation cover across a region. Aerial photography
was first used post World War II
and was heavily adopted in the 1960s onwards.
Since the advent of cheap and declassified Landsat images in the late 1970s and early 1980s, mineral exploration has begun to use satellite imagery to map not only the visual light spectrum over mineral exploration tenements, but spectra which are beyond the visible.
Satellite
based spectroscopes allow the modern mineral explorationist, in regions devoid of cover and vegetation, to map minerals and alteration
directly. Improvements in the resolution of modern commercially based satellites has also improved the utility of satellite imagery; for instance GeoEye satellite images can be generated with a 40 cm pixel size.
, here used to describe assay
ing or geological media, in mineral exploration is to find an area anomalous in the commodity sought, or in elements known to be associated with the type of mineralisation sought.
Regional geochemical exploration has traditionally involved use of stream sediments to target potentially mineralised catchments. Regional surveys may use low sampling densities such as one sample per 100 square kilometres. Follow-up geochemical surveys commonly use soil
s as the sampling media, possibly via the collection of a grid of samples over the tenement or areas which are amenable to soil geochemistry. Areas which are covered by transported soils, alluvium, colluvium or are disturbed too much by human activity (roads, rail, farmland), may need to be drilled to a shallow depth in order to sample undisturbed or unpolluted bedrock.
Once the geochemical analyses are returned, the data is investigated for anomalies (single or multiple elements) that may be related to the presence of mineralisation. The geochemical anomaly is often field checked against the outcrop
ping geology and, in modern geochemistry, normalised against the regolith
type and landform, to reduce the effects of weathering
, transported materials and landforms.
Geochemical anomalies may be spurious or related to low-grade or sub-grade mineralisation. In order to determine if this is the case, geochemical anomalies must be drilled
in order to test them for the existence of economic concentrations of mineralisation, or even to determine why they exist in the place they exist.
The presence of some chemical elements may indicate the presence of a certain mineral. Chemical analysis of rocks and plants may indicate the presence of an underground deposit. For instance elements like arsenic and antimony are associated with gold deposits and hence, are example pathfinder elements. Tree buds can be sampled for pathfinder elements in order to help locate deposits.
to sample the prospective horizon, lode
or strata
where the minerals of interest occur.
The ultimate aim is to generate a density of drilling sufficient to satisfy the economic and statutory standards of an ore resource
. Depending on the financial situation and size of the deposit and the structure of the company, the level of detail required to generate this resource and stage at which extraction can commence varies; for small partnerships and private non-corporate enterprises a very low level of detail is required whereas for corporations which require debt
equity
(loans) to build capital
intensive extraction infrastructure
, the rigor necessary in resource estimation is far greater. For large cash rich companies working on small ore bodies, they may work only to a level necessary to satisfy their internal risk assessment
s before extraction commences.
Resource estimation may require pattern drilling on a set grid, and in the case of sulfide minerals, will usually require some form of geophysics
such as down-hole probing of drillholes, to geophysically delineate ore body continuity within the ground.
The aim of resource evaluation is to expand the known size of the deposit and mineralisation. A scoping study is often carried out on the ore deposit during this stage to determine if there may be enough ore at a sufficient grade to warrant extraction; if there is not further resource evaluation drilling may be necessary. In other cases, several smaller individually uneconomic deposits may be socialised into a 'mining camp' and extracted in tandem. Further exploration and testing of anomalies may be required to find or define these other satellite deposits.
. The process is similar to resource evaluation, except more intensive and technical, aimed at statistically quantifying the grade continuity and mass of ore.
Reserve definition also takes into account the milling and extractability characteristics of the ore, and generates bulk samples for metallurgical testwork
, involving crushability, floatability
and other ore recovery
parameters.
Reserve definition includes geotechnical assessment and engineering
studies of the rocks within and surrounding the deposit to determine the potential instabilities of proposed open pit or underground mining methods. This process may involve drilling diamond core samples to derive structural
information on weaknesses within the rock mass such as faults, foliations
, joints and shearing.
At the end of this process, a feasibility study
is published, and the ore deposit may be either deemed uneconomic or economic.
Extraction methods may vary considerably and it is the discipline of engineers trained in mining engineering
to determine the most safe, cost effective and efficient method of mining
the ore body.
Mineral exploration and development does not cease upon a decision to mine. Exploration of a brownfields nature is conducted to find near-mine repetitions, extensions and continuity of the existing ore body. In-mine exploration and grade control drilling is a major concern of operating mines and can be an effective tool in adding value to existing mineral operations.
Often the lessons learned from studying an exposed ore body, both empirically and scientifically, are invaluable to the exploration geologist and geophysicist, for they get to see the proof of their concepts and the errors of the assumptions they used in the search for the ore body. It is always the case that the exact nature of the ore body does not exactly match the models used to find it.
Greenfields exploration is highly conceptual, relying on the predictive power of ore genesis
models to search for mineralisation in unexplored virgin ground. This may be territory which has been drilled for other commodities, but with a new exploration concept is considered prospective for commodities not sought there before.
The success rate of exploration and the return on investment is low because exploration is an inherently risky business. Figures for success rates depend on the commodity in question but a good strike rate can be measured in the oil industry; the supergiant Prudhoe Bay oilfield was found on the 12th well drilled into the area. Within gold deposits a discovery hole may be one in one thousand and within some base metals commodities strike rates range from one in fifty to one in one hundred.
Greenfields exploration has a lower strike rate, because the geology is poorly understood at the conception of an exploration program but the rewards are greater because it is easier to find the biggest deposit in an area earlier, and it is only with more effort that the smaller satellite deposits are found. Brownfields exploration is less risky, as the geology is better understood and exploration methodology is well known, but since most large deposits are already found the rewards are incrementally less.
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....
(commercially viable concentrations of minerals) to mine
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
. Mineral exploration is a much more intensive, organized and professional form of mineral prospecting
Prospecting
Prospecting is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking.Prospecting is a small-scale form of mineral exploration which is an organised, large scale effort undertaken by mineral resource companies to find commercially viable ore...
and, though it frequently uses the services of prospecting, the process of mineral exploration on the whole is much more involved.
Stages of mineral exploration
Mineral exploration methods vary at different stages of the process depending on size of the area being explored, as well as the density and type of information sought. Aside from extraplanetary exploration, at the largest scale is a geological mineral Province (such as the Eastern Goldfields Province of Western Australia), which may be sub-divided into Regions. At the smaller scale are mineral Prospects, which may contain several mineral Deposits.Province scale - area selection
Area selection is a crucial step in professional mineral exploration. Selection of the best, most prospective, area in a mineral field, geological region or terrain will assist in making it not only possible to find ore deposits, but to find them easily, cheaply and quickly.Area selection is based on applying the theories behind ore genesis
Ore genesis
The various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
, the knowledge of known ore occurrences and the method of their formation, to known geological regions via the study of geological maps, to determine potential areas where the particular class of ore deposit being sought may exist. Oftentimes new styles of deposits may be found which reveal opportunities to find look-alike deposit styles in rocks and terrains previously thought barren, which may result in a process of pegging of leases in similar geological settings based on this new model or methodology. This behaviour is particularly well exemplified by exploration for Olympic Dam style deposits, particularly in South Australia
South Australia
South Australia is a state of Australia in the southern central part of the country. It covers some of the most arid parts of the continent; with a total land area of , it is the fourth largest of Australia's six states and two territories.South Australia shares borders with all of the mainland...
and worldwide based on models of IOCG
Iron oxide copper gold ore deposits
Iron oxide copper gold ore deposits are important and highly valuable concentrations of copper, gold and uranium ores hosted within iron oxide dominant gangue assemblages which share a common genetic origin....
formation, which results in all coincident gravity and magnetic anomalies in appropriate settings being pegged for exploration.
This process applies the disciplines of basin modeling, structural geology, geochronology, petrology and a host of geophysical and geochemical disciplines to make predictions and draw parallels between the known ore deposits and their physical form and the unknown potential of finding a 'lookalike' within the area selected.
Area selection is also influenced by the commodity being sought; exploring for gold occurs in a different manner and within different rocks and areas to exploration for oil or natural gas or iron ore. Areas which are prospective for gold may not be prospective for other metals and commodities.
Similarly, companies of different sizes (in terms of market capitalisation and financial strength) may look for different sized deposits, or deposits of a minimum size, depending on their will and ability to finance construction. Often the major mining houses will not look for deposits of less than a certain size class because small deposits will not meet their criteria for an internal rate of return. This practise may result in larger mining companies relinquishing control of smaller ore bodies they find, or may preclude them from entering a terrane which is characterised by deposits of a particular type or style. For example, a mining major would not look for a relatively small, high-cost Kambalda style
Kambalda type komatiitic nickel ore deposits
Kambalda type nickel ore deposits are a class of magmatic nickel-copper ore deposit in which the physical processes of komatiite volcanology serve to enrich, concentrate and deposit nickel-bearing sulfide within the lava flow environment of an erupting komatiite volcano.-Classification:The...
nickel deposit and would direct their efforts toward discovering a Mt Keith style deposit.
Often a company or consortium wishing to enter mineral exploration may conduct market research
Market research
Market research is any organized effort to gather information about markets or customers. It is a very important component of business strategy...
to determine, if a resource in a particular commodity is found, whether or not the resource will be worth mining based on projected commodity prices and demand growth. This process may also inform upon the Area Selection process as noted above, where areas with small-sized deposit styles will be ruled out based on likely economic returns should a deposit be found. This occurs because often smaller deposits are more expensive to run, and hence, carry greater risks of closure if commodity prices fall significantly.
Area selection may also be influenced by previous finds, a practice affectionately named subsurface control or nearology, and may also be determined in part by financial and taxation incentives and tariff systems of individual nations. The role of infrastructure may also be crucial in area selection, because the ore must be brought to market and infrastructure costs may render isolated ore uneconomic.
The ultimate result of an area selection process is the pegging or notification of exploration licenses, known as tenements.
Target generation - Regional Scale
The target generation phase involves investigations of the geology via mapping, geophysics and conducting geochemical or intensive geophysical testing of the surface and subsurface geology.In some cases, for instance in areas covered by soil, alluvium and platform cover
Platform cover
In geology, a platform cover is the sedimentary and volcanic deposits that lie on top of a craton....
, drilling may be performed directly as a mechanism for generating targets.
Geophysical methods
Geophysical instruments play a large role in gathering geological data which is used in mineral exploration. Instruments are used in geophysical surveys to check for variations in gravity, magnetismMagnetism
Magnetism is a property of materials that respond at an atomic or subatomic level to an applied magnetic field. Ferromagnetism is the strongest and most familiar type of magnetism. It is responsible for the behavior of permanent magnets, which produce their own persistent magnetic fields, as well...
, electromagnetism (resistivity
Resistivity
Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...
of rocks) and a number of different other variables in a certain area. The most effective and widespread method of gathering geophysical data is via flying airborne geophysics.
Geiger counter
Geiger counter
A Geiger counter, also called a Geiger–Müller counter, is a type of particle detector that measures ionizing radiation. They detect the emission of nuclear radiation: alpha particles, beta particles or gamma rays. A Geiger counter detects radiation by ionization produced in a low-pressure gas in a...
s and scintillometer
Scintillometer
A scintillometer is a scientific device used to measure small fluctuations of the refractive index of air caused by variations in temperature, humidity, and pressure. It consists of an optical or radio wave transmitter and a receiver at both ends of an atmospheric propagation path...
s are used to determine the amount of radioactivity. This is particularly applicable to searching for uranium ore deposits but can also be of use in detecting radiometric anomalies associated with metasomatism
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
.
Airborne magnetometer
Magnetometer
A magnetometer is a measuring instrument used to measure the strength or direction of a magnetic field either produced in the laboratory or existing in nature...
s are used to search for magnetic anomalies in the Earth's magnetic field
Earth's magnetic field
Earth's magnetic field is the magnetic field that extends from the Earth's inner core to where it meets the solar wind, a stream of energetic particles emanating from the Sun...
. The anomalies are an indication of concentrations of magnetic minerals such as magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...
, pyrrhotite
Pyrrhotite
Pyrrhotite is an unusual iron sulfide mineral with a variable iron content: FeS . The FeS endmember is known as troilite. Pyrrhotite is also called magnetic pyrite because the color is similar to pyrite and it is weakly magnetic...
and ilmenite
Ilmenite
Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....
in the Earth's crust. It is often the case that such magnetic anomalies are caused by mineralization events
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
and associated metals.
Ground-based geophysical prospecting in the target selection stage is more limited, due to the time and cost. The most widespread use of ground-based geophysics is electromagnetic geophysics
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
which detects conductive minerals such as sulfide minerals within more resistive host rocks.
Ultraviolet lamps may cause certain minerals to fluoresce
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
, and is a key tool in prospecting for tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
mineralisation.
Remote sensing
Aerial photography is an important tool in assessing mineral exploration tenements, as it gives the explorer orientation information - location of tracks, roads, fences, habitation, as well as ability to at least qualitatively map outcrops and regolithRegolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
systematics and vegetation cover across a region. Aerial photography
Aerial photography
Aerial photography is the taking of photographs of the ground from an elevated position. The term usually refers to images in which the camera is not supported by a ground-based structure. Cameras may be hand held or mounted, and photographs may be taken by a photographer, triggered remotely or...
was first used post World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
and was heavily adopted in the 1960s onwards.
Since the advent of cheap and declassified Landsat images in the late 1970s and early 1980s, mineral exploration has begun to use satellite imagery to map not only the visual light spectrum over mineral exploration tenements, but spectra which are beyond the visible.
Satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
based spectroscopes allow the modern mineral explorationist, in regions devoid of cover and vegetation, to map minerals and alteration
Metasomatism
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids.Metasomatism can occur via the action of hydrothermal fluids from an igneous or metamorphic source. In the igneous environment, metasomatism creates skarns, greisen, and may affect hornfels in the contact...
directly. Improvements in the resolution of modern commercially based satellites has also improved the utility of satellite imagery; for instance GeoEye satellite images can be generated with a 40 cm pixel size.
Geochemical methods
The primary role of geochemistryGeochemistry
The field of geochemistry involves study of the chemical composition of the Earth and other planets, chemical processes and reactions that govern the composition of rocks, water, and soils, and the cycles of matter and energy that transport the Earth's chemical components in time and space, and...
, here used to describe assay
Assay
An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
ing or geological media, in mineral exploration is to find an area anomalous in the commodity sought, or in elements known to be associated with the type of mineralisation sought.
Regional geochemical exploration has traditionally involved use of stream sediments to target potentially mineralised catchments. Regional surveys may use low sampling densities such as one sample per 100 square kilometres. Follow-up geochemical surveys commonly use soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s as the sampling media, possibly via the collection of a grid of samples over the tenement or areas which are amenable to soil geochemistry. Areas which are covered by transported soils, alluvium, colluvium or are disturbed too much by human activity (roads, rail, farmland), may need to be drilled to a shallow depth in order to sample undisturbed or unpolluted bedrock.
Once the geochemical analyses are returned, the data is investigated for anomalies (single or multiple elements) that may be related to the presence of mineralisation. The geochemical anomaly is often field checked against the outcrop
Outcrop
An outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. -Features:Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be...
ping geology and, in modern geochemistry, normalised against the regolith
Regolith
Regolith is a layer of loose, heterogeneous material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, some asteroids, and other terrestrial planets and moons.-Etymology:...
type and landform, to reduce the effects of weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
, transported materials and landforms.
Geochemical anomalies may be spurious or related to low-grade or sub-grade mineralisation. In order to determine if this is the case, geochemical anomalies must be drilled
Drilling rig
A drilling rig is a machine which creates holes or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person...
in order to test them for the existence of economic concentrations of mineralisation, or even to determine why they exist in the place they exist.
The presence of some chemical elements may indicate the presence of a certain mineral. Chemical analysis of rocks and plants may indicate the presence of an underground deposit. For instance elements like arsenic and antimony are associated with gold deposits and hence, are example pathfinder elements. Tree buds can be sampled for pathfinder elements in order to help locate deposits.
Resource evaluation
Resource evaluation is undertaken to quantify the grade and tonnage of a mineral occurrence. This is achieved primarily by drillingDrilling rig
A drilling rig is a machine which creates holes or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person...
to sample the prospective horizon, lode
Lode
In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure in a rock formation or a vein of ore that is deposited or embedded between layers of rock....
or strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
where the minerals of interest occur.
The ultimate aim is to generate a density of drilling sufficient to satisfy the economic and statutory standards of an ore resource
Mineral resource classification
Mineral resource classification is the classification of mineral deposits based on their geologic certainty and economic value.Mineral deposits can be classified as:...
. Depending on the financial situation and size of the deposit and the structure of the company, the level of detail required to generate this resource and stage at which extraction can commence varies; for small partnerships and private non-corporate enterprises a very low level of detail is required whereas for corporations which require debt
Debt
A debt is an obligation owed by one party to a second party, the creditor; usually this refers to assets granted by the creditor to the debtor, but the term can also be used metaphorically to cover moral obligations and other interactions not based on economic value.A debt is created when a...
equity
Ownership equity
In accounting and finance, equity is the residual claim or interest of the most junior class of investors in assets, after all liabilities are paid. If liability exceeds assets, negative equity exists...
(loans) to build capital
Capital (economics)
In economics, capital, capital goods, or real capital refers to already-produced durable goods used in production of goods or services. The capital goods are not significantly consumed, though they may depreciate in the production process...
intensive extraction infrastructure
Infrastructure
Infrastructure is basic physical and organizational structures needed for the operation of a society or enterprise, or the services and facilities necessary for an economy to function...
, the rigor necessary in resource estimation is far greater. For large cash rich companies working on small ore bodies, they may work only to a level necessary to satisfy their internal risk assessment
Risk assessment
Risk assessment is a step in a risk management procedure. Risk assessment is the determination of quantitative or qualitative value of risk related to a concrete situation and a recognized threat...
s before extraction commences.
Resource estimation may require pattern drilling on a set grid, and in the case of sulfide minerals, will usually require some form of geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
such as down-hole probing of drillholes, to geophysically delineate ore body continuity within the ground.
The aim of resource evaluation is to expand the known size of the deposit and mineralisation. A scoping study is often carried out on the ore deposit during this stage to determine if there may be enough ore at a sufficient grade to warrant extraction; if there is not further resource evaluation drilling may be necessary. In other cases, several smaller individually uneconomic deposits may be socialised into a 'mining camp' and extracted in tandem. Further exploration and testing of anomalies may be required to find or define these other satellite deposits.
Reserve definition
Reserve definition is undertaken to convert a mineral resource into an ore reserve, which is an economic assetAsset
In financial accounting, assets are economic resources. Anything tangible or intangible that is capable of being owned or controlled to produce value and that is held to have positive economic value is considered an asset...
. The process is similar to resource evaluation, except more intensive and technical, aimed at statistically quantifying the grade continuity and mass of ore.
Reserve definition also takes into account the milling and extractability characteristics of the ore, and generates bulk samples for metallurgical testwork
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
, involving crushability, floatability
Froth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in several processing industries...
and other ore recovery
Beneficiation
In mining, beneficiation is a variety of processes whereby extracted ore from mining is separated into mineral and gangue, the former suitable for further processing or direct use....
parameters.
Reserve definition includes geotechnical assessment and engineering
Rock mechanics
Rock mechanics is the theoretical and applied science of the mechanical behaviour of rock and rock masses;also compared to the geology, it is that branch of mechanics concerned with the response of rock and rock masses to the force fields of their physical environment.Rock mechanics itself forms...
studies of the rocks within and surrounding the deposit to determine the potential instabilities of proposed open pit or underground mining methods. This process may involve drilling diamond core samples to derive structural
Structural geology
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, and...
information on weaknesses within the rock mass such as faults, foliations
Foliation (geology)
Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic belts. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and...
, joints and shearing.
At the end of this process, a feasibility study
Feasibility study
Feasibility studies aim to objectively and rationally uncover the strengths and weaknesses of the existing business or proposed venture, opportunities and threats as presented by the environment, the resources required to carry through, and ultimately the prospects for success. In its simplest...
is published, and the ore deposit may be either deemed uneconomic or economic.
Extraction
The ultimate goal of mineral exploration is the extraction, beneficiation and profitable and beneficial sale of mineral commodities.Extraction methods may vary considerably and it is the discipline of engineers trained in mining engineering
Mining engineering
Mining engineering is an engineering discipline that involves the practice, the theory, the science, the technology, and application of extracting and processing minerals from a naturally occurring environment. Mining engineering also includes processing minerals for additional value.Mineral...
to determine the most safe, cost effective and efficient method of mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
the ore body.
Mineral exploration and development does not cease upon a decision to mine. Exploration of a brownfields nature is conducted to find near-mine repetitions, extensions and continuity of the existing ore body. In-mine exploration and grade control drilling is a major concern of operating mines and can be an effective tool in adding value to existing mineral operations.
Often the lessons learned from studying an exposed ore body, both empirically and scientifically, are invaluable to the exploration geologist and geophysicist, for they get to see the proof of their concepts and the errors of the assumptions they used in the search for the ore body. It is always the case that the exact nature of the ore body does not exactly match the models used to find it.
Greenfields vs brownfields
Exploration is termed either Greenfields or Brownfields depending on the extent to which previous exploration has been conducted on the tenements in question. Greenfields alludes to unspoilt grass, and brownfields to that which has been trodden on repeatedly. While loosely defined, the general meaning of brownfields exploration is that which is conducted within geological terrain within close proximity to known ore deposits. Greenfields are the remainder.Greenfields exploration is highly conceptual, relying on the predictive power of ore genesis
Ore genesis
The various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
models to search for mineralisation in unexplored virgin ground. This may be territory which has been drilled for other commodities, but with a new exploration concept is considered prospective for commodities not sought there before.
The success rate of exploration and the return on investment is low because exploration is an inherently risky business. Figures for success rates depend on the commodity in question but a good strike rate can be measured in the oil industry; the supergiant Prudhoe Bay oilfield was found on the 12th well drilled into the area. Within gold deposits a discovery hole may be one in one thousand and within some base metals commodities strike rates range from one in fifty to one in one hundred.
Greenfields exploration has a lower strike rate, because the geology is poorly understood at the conception of an exploration program but the rewards are greater because it is easier to find the biggest deposit in an area earlier, and it is only with more effort that the smaller satellite deposits are found. Brownfields exploration is less risky, as the geology is better understood and exploration methodology is well known, but since most large deposits are already found the rewards are incrementally less.
See also
- Mineral resource classificationMineral resource classificationMineral resource classification is the classification of mineral deposits based on their geologic certainty and economic value.Mineral deposits can be classified as:...
- Mineral industryMineral industryThe mineral industry is the branch of industry responsible for the exploitation of minerals from soil deposits. This is achieved by mining , but also by processing plants. Products of mineral industry include various building materials, such as rocks The mineral industry is the branch of industry...
- Ore genesisOre genesisThe various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
- Exploration loggingExploration LoggingExploration logging is a term used to describe the process of wireline logging, geophysical logging, geotechnical logging or geological logging of a drill hole, its core, or its rock cuttings for petrophysics or petrology....
- Drilling rigDrilling rigA drilling rig is a machine which creates holes or shafts in the ground. Drilling rigs can be massive structures housing equipment used to drill water wells, oil wells, or natural gas extraction wells, or they can be small enough to be moved manually by one person...
- ProspectingProspectingProspecting is the physical search for minerals, fossils, precious metals or mineral specimens, and is also known as fossicking.Prospecting is a small-scale form of mineral exploration which is an organised, large scale effort undertaken by mineral resource companies to find commercially viable ore...
- Prospectivity MappingProspectivity MappingProspectivity mapping, also known as mineral prospectivity mapping or mineral potential mapping, defines a process used to make better use of mineral exploration data...