Geophysical survey selection tool

This tool allows you to browse through deposit types to help you understand which geophysical methods could be used to discover resources. This tool will also help you understand the geophysical terms better.

Ag - Silver

Silver is usually found in its native form and is associated with disseminated sulphides. It is often a by-product of other mineral deposits.

Native silver has high electrical and thermal conductivity. However, it does not occur in large concentrations and these properties cannot, therefore, be used to explore silver. Typically, geophysics is used to detect the associated sulphide minerals.

Recommendations for SILVER Exploration

IP/resistivity: When silver is associated with disseminated sulphides.
TDEM, FDEM and Gravity: When silver and gold represent a by-product of massive sulphide deposits
Magnetics and Spectrometry: On a regional scale to map geological lithology and structure, and locally to map alteration, enrichment and/or zonation within deposits.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how the correct geophysical tool has helped others find mines.

Alkaline Intrusive (Au)

Alkaline intrusive is known for its low-grade gold content associated with disseminated sulphides. Mineralization is usually concentrated in stockwork within the plutonic intrusive system or the surrounding rocks.

Reconnaissance Scale

Regional reconnaissance surveys are required to locate the intrusive plutonic core, which may be mineralized.

Gravimetry: Intrusive plutonic rocks are usually not as dense as the surrounding rocks. As a result, the intrusive usually corresponds to a discrete negative gravimetric anomaly within a larger regional scale positive anomaly.
Magnetics: Magnetite and pyrrhotite crystallize along the metamorphic contact of the intrusive. As a result, the intrusive usually corresponds to a positive cylindrical aeromagnetic anomaly.

Local Scale

Magnetics: Intrusive rock fracture patterns are usually different from the surrounding rocks. As a result the intrusive contact, the homogeneity and the structure of the intrusive rock can be mapped in detail
IP/Resistivity: Disseminated sulphides are associated with the ore bearing zone. IP will, therefore, detect sulphides. In addition, the resistivity component is useful for mapping structures such as contacts and faults.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical

Anorthosite (Fe-Ti)

Fe-Ti oxide deposits are known for their association with mafic intrusives such as anorthosite.

Reconnaissance Scale

Gravimetrics: Fe-Ti-rich layers provide a density contrast between surrounding granitic and gneissic rock. As a result, the layers provide a positive gravity anomaly.
Magnetics: Fe-Ti is occasionally associated with layers of titaniferous magnetite such as the Lac Lablache deposit. The layers are associated with magnetic anomalies as a result.

Local Scale

Magnetics: Fe-Ti is associated with semi-massive to massive titanium-rich ilmenite or magnetite lenses. As a result, massive lenses are associated with local magnetic anomalies.
Gravity: Some deposits are semi-massive to massive oxide lenses with a density that can exceed 4,5. As a result, a detailed gravity survey provides a strong response over the deposit. It can also provide a tonnage estimate of the ore lenses.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Au - Gold

Gold is commonly found in its native form, usually associated with other disseminated sulphide minerals. It is often produced as a by-product of other mineral deposits.

Native gold is very conductive; however, like other precious metals, it occurs in extremely small concentrations. Conductivity cannot, therefore, be used to directly detect the occurrence of gold. Typically, geophysics is used to detect the associated sulphide minerals.

Abitibi Geophysics: Recommendations for GOLD Exploration

IP/resistivity: When gold is associated with disseminated sulphides.
TDEM, FDEM and Gravity: When gold occurs as a by-product of massive sulphide deposits.
Magnetics and Spectrometry: On a regional scale to map geological lithology and structure and locally to map alteration, enrichment and/or zonation within deposits.

Banded Iron Formation (Fe)

Iron formation deposits are known for their high iron metal content. Depending on their deposition setting they could be at the sulphide, oxide or carbonate facies. Worldwide, they could be grouped within two different classes:

Superior type oxide iron formation;
Algoma type sulphide-carbonate type iron formation.

Reconnaissance Scale

Magnetics: For the Superior type oxide facies, magnetite and to a lesser extent pyrrhotite, could produce huge magnetic contrasts. As a result, aeromagnetics is a cost-effective tool for mapping banded iron formations
Electromagnetics: For the Algoma type carbonate iron formation, graphite is occasionally associated with the sulphide facies, which provides an EM anomaly.
Gravity: Banded Iron formations provide a strong density contrast with the surrounding rocks. As a result, a regional scale survey would indicate a positive gravimetric anomaly.

Local Scale

Borehole Logging: Magnetic susceptibility measurements can be used to delineate iron enrichment.
Gravity: Banded Iron Formations provide strong density contrasts with the surrounding rocks. As a result, a regional scale survey provides a stronger positive gravimetric anomaly in an iron enrichment zone. It can also provide a tonnage estimate of the ore lenses.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Brines and Salt Lakes (Li)

The majority of the world’s lithium production comes from brines and salt lakes, known as salars.

Reconnaissance Scale

Gravity: Gravity surveys can assist in determining depth of bedrock, the potential size of the aquifer, and estimating the basin volume and porosity.
IP/Resistivity: May help to focus on the brine bearing horizon.
Seismic: Brine deposits are usually trapped in high-angle fault scarps. Seismic is a useful tool when identifying and helping to understand the stratigraphy of sediment bedrock. It is also useful in identifying trap locations.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

C - Carbon

Carbon in its native form may be found in the form of graphite, coal or diamonds (see Geophysics and Exploration for Diamonds, which is discussed separately).

Stratigraphic graphitic sediments can be closely associated with Cu-Zn or Ni massive sulphide deposits, or along an unconformity associated with uranium deposits. Graphite can also be closely associated with fractures in lode gold deposits. Often graphitic horizons are mapped and used to provide a stratigraphic marker for other minerals. Graphite is both polarizable and conductive, has a low density and low magnetic susceptibility compared to metamorphic or igneous rocks.

In higher metamorphic grades, it can form thick layers of coal.

Recommendations for GRAPHITE Exploration

TDEM and FDEM: To map stratigraphic units or fracture patterns filled with graphite. Advanced TDEM and FDEM can, in some cases, differentiate between graphitic and sulphide conductors.
IP/Resistivity: To map graphitic zones that are important geological markers.
Magnetics in addition to the TDEM: To differentiate graphitic horizons that have a low magnetic susceptibility from sulphide conductors that may contain magnetite.
Gravimetry in addition to TDEM: To differentiate graphitic horizons characterized by a lack of excess mass compared to a sulphide conductor.

Recommendations for COAL Exploration

TDEM and FDEM: To map coal beds below overburden and to identify intrusions within the coal (e.g., dykes)
IP/Resistivity: To map depth of overburden, thickness of coal bed, delineate boundaries of coal deposit and intrusions.
Magnetics: To map basin structure and intrusions in the coal deposit, that may contain magnetite.
Gravimetry: To map basin structure.

Carbonatite (REE)

Carbonatites are intrusive carbonate-mineral-rich igneous rocks known for their association with economic concentrations of exotic minerals such as rare earth elements and niobium.

Reconnaissance Scale

Magnetics: Some carbonatites contain magnetic mineral concentrations such as pyrrhotite or magnetite. In addition, many carbonatite complexes are surrounded by mafic alkaline rocks. As a result, the carbonatite is usually associated with positive mag anomalies.
Gravimetrics: Carbonatite pipes and layers provide a density contrast to the surrounding rock. As a result, the layers provide a negative gravity anomaly that is coincident with the magnetics.
Spectrometry: Some REE carbonatite complexes may be associated with thorium or uranium. As a result, the carbonatite may be mapped with gamma-ray spectrometry.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Co - Cobalt

Cobalt rarely occurs in its native form. It is usually produced as a by-product of copper and nickel sulphide or oxide deposits.

Native cobalt is radioactive, dense and conductive. However, cobalt exploration is usually focused on the host base metal sulphides or oxides, which occur in larger concentrations and may also be conductive and/or polarizable, dense and magnetic.

Recommendations for COBALT Exploration

IP/resistivity: When cobalt is associated with polarizable disseminated sulphides.
TDEM and FDEM: When cobalt is associated with conductive massive sulphide deposits.
Gravity: When cobalt is associated with dense massive sulphide deposits.
Spectrometry: To map enrichment and/or zonation within deposits.

Cr - Chromium

Chromium usually occurs as an oxide mineral, most often chromite.

There are two main types of chromite deposits:

Stratiform deposits, consisting of laterally persistent chromite-rich layers.
Podform chromite deposits, consisting of pod to pencil-like, irregularly shaped massive chromite bodies.

Chromite is commonly associated with magnetic minerals (magnetite, pyrrhotite, pentlandite).

Recommendations CHROMIUM Exploration

Magnetics: For mapping geological lithology.
IP/resistivity: To search for associated minerals such as magnetite, this may, under certain conditions, be polarizable.

Cu - Copper

Copper can occur in its native state; however, most commercial deposits are disseminated or massive sulphides (chalcopyrite, etc.) and to a lesser extent, oxide minerals (bornite, etc.).

Native copper and copper sulphide minerals are highly conductive. Oxide copper minerals are associated with magnetic oxide minerals such as magnetite or pyrrhotite.

Recommendations for COPPER Exploration

TDEM or FDEM: For massive sulphide copper-rich ore bodies.
IP/resistivity: For disseminated sulphide deposits.
Gravity: To detect excess mass that may be attributed to a sulphide conductor.
Aeromagnetics: To delineate stratigraphic or structural trends associated with iron oxide copper ore bodies.

Diamond

Diamonds occur in native form usually in kimberlite pipes or as secondary, alluvial deposits from eroded pipes. A diamond is formed from carbon at high temperature and pressure at depths greater than 100 km below surface. It is the hardest known rock and is associated with dense minerals, usually within a kimberlite pipe. Exploration for diamonds is focused on locating a kimberlite pipe. The geophysical signature of a kimberlite may vary considerably relative to its environment. For example, the weathered kimberlite cap may be conductive in an igneous host, or if the weathered cap has been glaciated, the kimberlite may appear resistive in a sedimentary host.

Recommendations for DIAMOND Exploration

Magnetics: To locate circular anomalies that could represent a kimberlite.
Airborne Electromagnetics: Airborne EM is used in a reconnaissance to identify isolated conductive features which may represent pipes.
Ground Electromagnetics: Both TDEM and FDEM are used to delineate the conductive weathered layer over the pipe.
Gravimetrics: To delineate the kimberlite pipes that typically appear as circular anomalies, which may be positive or negative with respect to the host environment.
IP/Resistivity: To delineate the pipe boundaries.
Spectrometry: To detect associated radioactive minerals.

Fe - Iron

Bedded Iron formation is a chemical sedimentary rock that can be divided on the basis of the dominant original iron mineral into four principal facies. The classic facies zonation from shallow to deep water deposition is oxide to silicate to carbonate to sulphide. Graphite is often associated with the sulphide facies.

Most of the economic deposits are associated with the Iron oxide facies known as Superior type. Other deposits are associated with Iron Oxide-Silicate-Sulphide facies known as Algoma type.

Recommendations for SUPERIOR type:

Iron oxide minerals such as the one in the Labrador Trough are magnetic. In this case, Abitibi Geophysics recommends:

Magnetics: To delineate stratigraphic magnetic trends.
Borehole Logging: To delineate iron enrichment.

Recommendation for ALGOMA type:

Iron Oxide-Silicate-Sulphide minerals are more conductive.

Magnetics: Since pyrite is not a magnetic mineral, the survey helps to delineate low mag responses along stratigraphic magnetic trends.
TDEM and FDEM: To delineate sulphide enrichment with associated graphite.

Iron Oxide Deposits (Fe-Cu-Au-Co-U-REE)

Iron oxide deposits are known for their high iron and associated metal content. Worldwide, they are grouped within three different classes:

Iron-copper-gold-cobalt - associated with oxides;
Iron-copper-gold-cobalt - associated with sulphides and oxides;
Iron-copper-gold-uranium-rare earth - associated with oxides.

Reconnaissance Scale

Gravimetry: Hematite and magnetite-rich layers contrast in density with the surrounding rock. As a result, the layers show a positive gravity anomaly.
Magnetics: Hematite magnetite-rich layers show a magnetic susceptibility contrast with surrounding rock. As a result, the layers show a positive magnetic anomaly.
Most of the deposits have a positive superimposed magnetic and gravity anomaly.

Local Scale

Spectrometry: Potassic alteration is commonly associated with the surroundings of the deposit. As a result, spectrometry for K, U and Th provide a contrast with surrounding rock. The alteration halo also provides a positive gamma-ray spectrometric anomaly.
Gravimetry: The hematite magnetite-rich layers provide a density contrast with surrounding rock.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Kimberlite (Diamond)

Kimberlites are known as the host for diamonds.

Reconnaissance Scale

Magnetics: Kimberlite pipes usually provide a contrast in magnetic susceptibility with surrounding rocks. As a result, they provide a circular shape anomaly, usually positive but it could be negative or in a few cases have no magnetic signature.
Electromagnetics: In non-glaciated terrain, the kimberlite pipe tends to weather producing a conductive cap of clay minerals. As a result, in a resistive environment it would generate a near-surface electromagnetic anomaly. This may be coincident with a magnetic anomaly.

Local Scale

Spectral IP: Kimberlite pipes contain exotic minerals that may or may not be associated with the surrounding rock. Spectral IP is a diagnostic tool for distinguishing fertile from barren kimberlites. Spectral IP is sensitive to both magnetite and argilitic minerals, both of which are found in kimberlites Spectral IP will distinguish between the IP signature of magnetite (lower time constant) and argilitic Piargilitic minerals (longer time constant)
Spectrometry: Kimberlite pipes contain exotic minerals that may be radioactive. Spectrometry is an effective tool in this instance. Kimberlite pipes in igneous environments may be much less radioactive than the host environment.
Gravity: Kimberlite pipes in igneous environments result in negative gravity anomalies because the kimberlite is less dense than typical igneous rocks.
Resistivity: The boundaries and depth of the weathered cap of a kimberlite pipe can be mapped with resistivity in a resistive host environment.
Magnetics: May be used to map the boundaries of magnetic kimberlite pipes of kimberlite flows (e.g., sill or dyke off shoots from kimberlite pipes).
FDEM: May be used for rapid mapping of the weathered cap of kimberlite pipes in a resistive host environment and to map the depth of weathering.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Komatiite (Ni, Cu, PGE)

Komatiites are known for their association with massive sulphide lenses located at the lower flow contact.

Reconnaissance Scale

Magnetics: Komatiic layers have a distinct magnetic signature. As a result, magnetics is an effective tool to map strong, positive linear shape structures.
Electromagnetics: Airborne EM systems may be used to detect the highly conductive massive sulphide bodies.

Local Scale

Electromagnetics: Massive sulphide lenses are highly conductive. EM systems that can measure the B-field during the on-time and off-time are an effective tool for detecting the bottom flow enrichment contacts
Gravimetry: Massive sulphide lenses usually provide a strong contrast of density with surrounding rocks. Since the host rock is komatiite, a weaker contrast of density is expected. In addition, it can also provide a tonnage estimate of the ore lenses.
IP/Resistivity: Disseminated sulphides are commonly located above the massive sulphide lenses. As a result, IP may be more effective in mapping a larger halo of disseminated sulphides than the massive lens itself.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Lateritic Soil (Ni)

Lateritic nickel deposits are generally flat-lying, tabular shaped, very large tonnage, low-grade deposits located close to the surface. They represent 73% of the world’s nickel resources and will in the future be the dominant source for nickel. They are weathered rinds formed on ultramafic rocks.

There are two kinds of lateritic nickel ore:

Limonite oxide type - highly enriched in iron oxide due to very strong leaching of magnesium and silica. They contain 1-2% nickel in a goethite host.
Silica saprolite - formed beneath the limonite oxide zone. All the nickel is leached downwards from the over-lying limonite oxide zone.

Reconnaissance Scale

Magnetics: The ultramafic units located beneath the oxide cap are usually buried. They usually have a stronger magnetic susceptibility than the surrounding rocks. As a result, an airborne survey could help in mapping the ultramafic rocks obscured by the regolith.
Spectrometry: Areas with considerable development of lateritic crust (rich in Fe-Ni-Co) register high eU and eTh content. An airborne survey may detect a laterite crust in a positive large regional scale anomaly.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Li - Lithium

Lithium never occurs as a free element in nature. The majority of the world’s lithium production comes from:

Salars, or salt lakes, where prospective lithium mineralization is generally found in brine horizons.
Pegmatite minerals associated with plutonic rocks. Granitic pegmatite provides the greatest concentration of lithium-containing minerals, with spodumene being the most commercially viable source.

Recommendations for LITHIUM Exploration in BRINES

Since brine deposits form in evaporate depositional environments where brines have generally obtained lithium from geothermal waters, Abitibi Geophysics recommends:

IP/resisitivity: to calculate the brine bearing horizon within the northern portion of the salar using a resisitivity cut-off.

Recommendations for LITHIUM Exploration in PEGMATITES

Since pegmatite is usually associated with intrusive rock, Abitibi Geophysics recommends:

IP/Resistivity: To delineate major pegmatitic dykes, which are usually more resistive than the surrounding rocks.
Magnetics: To delineate major plutonic masses and fracture trends where dykes may have occurred.

Lode Deposits (Au-Ag-Cu)

Lode deposits often occur along major regional shear zones, faults and subsidiary faults. They can be closely associated with brittle regional scale fracture networks.

Reconnaissance Scale

Magnetics: Lode deposits are associated with faults and fractures that cause discontinuities in the stratigraphic sequence and intrusive contact. Regional airborne magnetics can aid in mapping those discontinuities.

Local Scale

FDEM: Erosion increases along major fracture networks and shear zones resulting in discontinuities in overburden thickness. EM systems, which are sensitive to these overburden variations, are used frequently in this situation.
IP/Resistivity: Disseminated sulphide halos, frequently associated with the veins, present a good polarizable source that makes IP an effective tool. Localized concentrations of quartz veins may be identified as higher resistivity features.
Magnetics: Detailed GPS Magnetics may provide additional information to locate faults and fractures in the stratigraphic sequence and map the intrusive contact.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Mississippi Valley Type (MVT) (Zn)

Mississippi Valley-Type deposits are known for replacement within layered horizons and associated fractures related to the same stratigraphic level, usually in limestone.

Local Scale

Gravimetrics: Gravimetry would be an efficient tool to map the density contrast between flat-lying sulphide lenses and the surrounding rocks.
IP: Both galena and sphalerite are polarizable; IP is, therefore, effective in detecting weak conductors such as lead-zinc deposits.
TDEM: A TDEM system sensitive to rapid decay of weak conductors may be used to map massive occurrences of lead-zinc deposits.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Mo - Molybdenum

Molybdenum never occurs free in nature, but rather as oxidized mineral such as molybdenite and wulfenite. Molybdenum is mined as a principal ore and is also recovered as a by-product of some copper and tungsten deposits. Exploration focuses on the plutonic intrusive body setup, rather than the search for the mineral itself.

Recommendations for MOLYBDENUM Exploration

Aeromagnetics: To delineate plutonic rocks.
IP/resistivity: To delineate the associated disseminated sulphide minerals.
Spectrometry: To delineate potassic alteration associated with these deposits.

Ni - Nickel

Nickel does not occur free in nature. It is commonly found as disseminated or massive sulphide minerals (pentlandite, etc.) in magmatic environments or as oxide minerals in laterites. Nickel sulphide minerals are highly conductive to superconductive and are often associated with pyrrhotite, which is highly conductive.

Recommendations for NICKEL Exploration

TDEM and FDEM: To delineate massive sulphide-rich ore bodies.
Magnetics: To delineate magnetic ultramafic horizons and associated magnetite minerals.
IP/resistivity: For disseminated sulphide ore bodies.

Pegmatite (Li)

Granitic pegmatites provide the greatest concentration of minerals containing lithium, with spodumene being the most commercially viable source.

Spodumene minerals are relatively rare. They can develop in very large mineral deposits, sometimes within the pegmatites. As a result, exploration focuses on the granitic pegmatites associated with dyke swarms, rather than on the search for the mineral itself. Dyke swarms occur in corridors up to five kilometres, each consisting of several dykes, ranging in width from two to more than 30 metres.

Reconnaissance Scale

Aeromagnetics: To delineate the plutonic rocks and areas with dykes.
Gravity: To delineate the plutonic rocks and areas with dykes.

Local Scale

Ground MAG: Detailed surveys can delineate spodumene-bearing intrusive dyke swarms.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

PGE - Platinum

The platinum group elements (PGE) include platinum, palladium, iridium, ruthenium, osmium and rhodium. PGE can be native, although it is generally associated with sulphide minerals in Ni-Cu and chromite ore bodies. PGE associated with sulphide are highly conductive

Abitibi Geophysics: Recommendations for PGE Exploration

Magnetics: To delineate magnetic ultramafic horizons and associated magnetite minerals.
TDEM and FDEM: For massive sulphide-rich ore bodies.
IP/resistivity: For disseminated sulphide ore bodies.

Porphyry Copper (Cu-Mo, Cu-Au)

Porphyry copper is known for its low-grade metal content associated with disseminated sulphides occurring in a diorite to quartz monzonite composition with porphyritic textures. Mineralization is usually concentrated in a stockwork within the plutonic intrusive system or the surrounding rock.

Reconnaissance Scale

Regional reconnaissance surveys are required to locate the intrusive plutonic core, which may be mineralized.

Gravimetrics: Intrusive plutonic rocks are usually not as dense as the surrounding rocks. As a result, the intrusive corresponds commonly to a discrete negative gravimetric anomaly within a larger regional scale positive anomaly.
Magnetics: Magnetite and pyrrhotite crystallize along the metamorphic contact of the intrusive. As a result, the intrusive corresponds commonly to a positive cylindrical aeromagnetic anomaly.

Local Scale

IP: Large scale porphyry mineralization occurs as disseminated sulphides, which are polarizable and may be mapped with IP.
Spectrometrics: Large scale alteration patterns are associated with porphyry deposits. Mineral types vary from the core of the ore body to the edge. As a result, spectrometry is a useful tool to discriminate between minerals.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

REE - Rare Earth

Rare earth elements (REE) consist of 17 elements generally found in, or associated with, alkaline igneous rocks and carbonatites.

Despite the name, rare earth elements (cerium, yttrium, etc.) are relatively plentiful in the earth's crust, with cerium being the 25th most abundant element. However, because of their geochemical properties, rare earth elements are typically dispersed and not often found in concentrated and economically exploitable forms.

Recommendations for REE Exploration

The first step is to identify environments where these complexes occur.

Airborne Magnetic and Gravity: To delineate host rocks. Because many carbonatite complexes are surrounded by mafic alkaline rocks, they often show up as a magnetic bull’s eye combined with a gravity low ringed by a gravity high.
Radiometrics: Useful in mapping the lithology, which often has traces of K, Th and U.

Sandstone - Roll-Front (U)

Sandstone or roll-front type uranium deposits are known for their association with the oxide-reduction contact between the oxide and sulphide limits.

Reconnaissance Scale

Magnetics: Oxidation should provide more magnetic oxide mineral than the sulphide facies. As a result, a regional aeromagnetics survey can be an efficient tool for mapping the oxide reduction limit.
Spectrometry: Uranium is radioactive. As a result, gamma-ray spectrometry can identify a positive anomaly.
Electromagnetics: Graphitic layers could be located along discondances. As a result, TDEM survey provides positive anomaly.
IP/resistivity: Used to map the lower resistivity alteration associated with this type of deposit.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Skarn Deposits (Cu-Zn-Au-Fe-Mo)

Skarns can form during regional or contact metamorphism and from a variety of metasomatic processes involving fluids of magmatic, metamorphic, meteoric, and/or marine origin.

Reconnaissance Scale

Gravimetrics: Almost all skarns are significantly denser than the surrounding rock and may, therefore, form a gravitational anomaly. This is particularly evident in some of the large iron skarns. As a result, they provide a positive gravimetric anomaly.
Seismic: The skarn environment provides a seismic discontinuity.
Magnetics: Some large iron skarns contain magnetite or high-temperature pyrrhotite. As a result, they provide a positive magnetic anomaly.
IP: Polarizable material in a skarn may be disseminated sulphides or metasomatism of carbonate rock, which necessarily involves redistribution of carbon. As a result, IP needs to be interpreted carefully to determine the source.
Spectrometry: Some skarns contain uranium and thorium and as a result, may be detectable by airborne or ground radiometric surveys.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Strata-bound Sedimentary (SEDEX) (Pb-Zn)

SEDEX deposits are known for tabular shape sulphide mineralization concentrations along marble layers. Targets are usually located along the basement contact.

Reconnaissance Scale

Gravimetrics: The marble sulphide-rich horizon usually has a higher density than the surrounding rocks. As a result, gravity is a useful tool for mapping the mineralization.
Electromagnetics: Zinc sulphides are poor conductors; however, EM systems capable of measuring fast decay times are suitable for mapping these types of deposits.
Magnetics: Magnetic contrast between sediment and basement is commonly shown on regional scale survey data. The survey is also used to locate faults and structurally-controlled lithologies.
IP: Low response associated with the deposit.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

U - Uranium

Uranium could be native or associated with oxide minerals. Uranium occurs in a number of different igneous, hydrothermal and sedimentary geological environments. Uranium deposits worldwide can be grouped into 14 major deposit-type categories, based on the geological setting of the deposits, the major being:

Unconformity-related deposits, which constitute approximately 33% of world deposits;
Iron oxide such as Olympic Dam deposits;
Sandstone (roll-front) deposits.

Uranium is radioactive and commonly associated with other radioactive minerals.

Recommendations for URANIUM Exploration

Radiometrics: For detection of the deposit and to trace the stratigraphic layers of an anomaly.
Gravimetry: As the unconformity occur between basement and sediment, that can also represent a contrast of density between both units.
Seismic: To map the unconformity between homogeneous basement and layered sediments.
Magnetics: To map the magnetic basement and determine the basin depth and underlying basement structure.

To map magnetic horizons when the uranium is associated with the magnetic minerals of iron oxide deposits

IP/Resistivity: To map the alteration zone above the deposit and to determine basin depth
Electromagnetics: To trace conductive graphitic/stratigraphic layers commonly associated with the unconformity.

Ultramafic Layered Intrusions (Cr-Co-Ni-Cu-PGE)

Large ultramafic layered intrusions usually contain elevated amounts of chromium and nickel.

Reconnaissance Scale

Gravimetrics: These deposits are generally associated with ultramafic intrusive, which usually provide a strong density contrast with surrounding rocks. As a result, the intrusive generally corresponds to a large regional scale positive anomaly.
Magnetics: These deposits are generally associated with ultramafic intrusive, which usually provides a strong contrast of magnetic susceptibility with surrounding rocks. As a result, the survey produces strong magnetic anomalies, useful for targeting prospective geology within regional magnetic surveys.

Local Scale

Gravimetrics: It can also provide a tonnage estimate of the ore lenses.
Electromagnetics: Layered intrusions containing up to 50% chromium oxide may impact negatively on conductivity, more specifically if there is silica between minerals. As a result, EM might provide a weaker response. Layered intrusions containing sulphides are conductive. EM may therefore, provide a strong response
Magnetics: These deposits are occasionally associated with magnetic minerals such as pyrrhotite. As a result, the survey produces local magnetic anomalies, useful for targeting prospective geology along the favourable trends.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Volcanic Massive Sulfide (VMS) (Cu-Zn-Au-Ag)

Volcanic massive sulphide deposits (VMS) are known for their location at the contact between a volcanic sequence and a cherty or graphitic sedimentary horizon.

Reconnaissance Scale

Gravimetrics: These deposits consist of massive sulphide lenses which may provide a strong density contrast with surrounding rocks. As a result, the ore body might correspond to an isolated regional scale positive anomaly.
Magnetics: These deposits might contain magnetite and/or pyrrhotite, which usually are very magnetic. As a result, the ore body might correspond to an isolated regional anomaly.
Electromagnetics: The conductivity of VMS deposits varies from weak (Zn-rich deposits) to high (Curich deposits). Electromagnetics is widely used to explore for VMS deposits.

Local Scale

Electromagnetics: EM systems capable of detecting a wide range of conductivities should be selected for VMS conductivity expected.
Gravity: The deposit is sometimes capped by regional scale graphitic sediments that provide long, conductive targets. The massive sulphide ore body provides a strong density contrast with surrounding rocks. As a result, the ore body might correspond to an isolated localized gravimetric anomaly along a formational graphitic conductor. In addition, it can also provide a tonnage estimate of the ore lenses.
IP Ore bodies are commonly associated with a stringer zone located beneath the mineralized zone. As a result, IP survey should identify easily the polarisable source.

The above information is a guideline only. Each exploration project requires an in-depth assessment in order to select the best possible geophysical application from the tools available. See our Case Study Tool for examples of how we’ve helped others find mines using the correct geophysical tool.

Zn - Zinc

Zinc occurs as a sulphide (sphalerite, etc.) in disseminated or massive deposits commonly associated with copper minerals in volcanic settings and with lead minerals in sedimentary settings. Zinc and sphalerite are poor conductors, unlike copper and nickel sulphides.

Recommendations for ZINC Exploration

TDEM and FDEM: For zinc-rich massive sulphide deposits, especially when the zinc is found in association with Cu sulphides, which increase the conductivity of the deposit.
IP/resistivity: For disseminated sulphide ore bodies.
Gravity: To determine the excess mass of the mineral deposit.
Magnetics: To map the lithology and structure of the geological environment.

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