Mineral exploration is the process undertaken by companies, partnerships or corporations in the endeavour of finding ore (commercially viable concentrations of minerals) to mine. Mineral exploration is a much more intensive, organised 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.
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, drilling may be performed directly as a mechanism for generating targets.
[edit] Geophysical methods
Main article: Exploration geophysics
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, magnetism, electromagnetism (conductivity and 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 counters and scintillometers 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 magnetometers 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.
[edit] 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 regolith systematics and vegetation cover across a region. Aerial photography was first used post World War II and was heavily adopted in the 1960's onwards.
Since the advent of cheap and declassified Landsat images in the late 1970's an early 1980's, 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 IKONIS satellite images can be generated with a 30cm pixel size.
[edit] Geochemical methods
Main article: Geochemistry
The primary role of geochemistry, here used to describe assaying 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 soils 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 outcropping 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.
These are jsut a few ways to explore for minerals. There are also many "secret" techniques explorers use for finding economic deposits of minerals, including oil and gas.
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, drilling may be performed directly as a mechanism for generating targets.
[edit] Geophysical methods
Main article: Exploration geophysics
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, magnetism, electromagnetism (conductivity and 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 counters and scintillometers 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 magnetometers 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.
[edit] 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 regolith systematics and vegetation cover across a region. Aerial photography was first used post World War II and was heavily adopted in the 1960's onwards.
Since the advent of cheap and declassified Landsat images in the late 1970's an early 1980's, 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 IKONIS satellite images can be generated with a 30cm pixel size.
[edit] Geochemical methods
Main article: Geochemistry
The primary role of geochemistry, here used to describe assaying 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 soils 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 outcropping 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.
These are jsut a few ways to explore for minerals. There are also many "secret" techniques explorers use for finding economic deposits of minerals, including oil and gas.