Minerals and the subsurface

Chapter B · Spectral imaging, magnetics, gravity, GPR, resistivity and IP, electromagnetics

No instrument sees ore. Each method measures one physical property — reflected light, magnetisation, density, electrical conductivity, chargeability — and a mineralised body is only detectable when it changes that property enough, close enough to the instrument, against a quiet enough background. Where the instrument sits matters as much as what it measures: a satellite, an aircraft or drone, a ship and a ground crew see very different things. This chapter sets out what each method measures, from where, to what depth, and what it cannot claim.

Status labels. OPERATIONAL — the method is in routine professional use; that is a statement about the method, never a promise about any particular site. EXPERIMENTAL — demonstrated in research or in emerging products, not routine for this purpose. GEASPIRIT PROPOSAL — an idea for GeaSpirit that has not been built.

Platform labels show where the instrument physically is. The platform decides what is possible: an instrument in orbit cannot see what a ground crew sees, and a ground crew cannot cover a continent.

Platform: where the instrument is

The same physical property looks completely different from 500 km, from 100 m and from the ground. Distance blurs: a magnetic or gravity source is smeared over a width comparable to its distance from the sensor, so an instrument in orbit only sees features tens to hundreds of kilometres across. Satellites give global, consistent coverage — of fields at coarse resolution or, for optical imaging, of the surface only. Aircraft and drones bring the sensor to tens or hundreds of metres from the ground; ground surveys put it on or in the ground, with the best resolution and the smallest coverage.

SCHEMATIC — NOT TO SCALE

Satellite: surface spectra; very long-wavelength gravity and magnetic fields.
Aircraft / drone: magnetics, radiometrics, EM, gravity, imaging spectroscopy.
Ship / AUV: sonar, magnetics, gravity, seismic.
Ground: GPR, resistivity, IP, EM, gravity, magnetics — and drilling.

Figure B1. Platforms compared. Coverage grows towards orbit; resolution and depth detail grow towards the ground. Altitudes are indicative.

Multispectral and hyperspectral imaging

ASTER, Sentinel-2, Landsat; EMIT, EnMAP, PRISMA; airborne and field spectrometers

SATELLITEAIRCRAFT / DRONEGROUNDOPERATIONAL

Identifies certain minerals at the exposed surface by their absorption features. It sees the top micrometres to millimetres of rock and soil — nothing beneath.

SCHEMATIC — NOT TO SCALE

Figure B2. Schematic reflectance spectra (offset for clarity). Absorption positions follow the USGS spectral library and the literature cited; curve shapes are simplified.

Technical sheet — principle, instrument, reach, resolution, limits

Physical principle: Minerals absorb sunlight at characteristic wavelengths. Electronic transitions in iron give broad features in the visible and near-infrared (hematite near 0.86 µm, goethite near 0.91 µm); vibrations of Al–OH, Mg–OH and carbonate bonds give narrow features in the shortwave infrared (the kaolinite doublet near 2.165 and 2.205 µm, alunite's main feature near 2.17 µm, calcite near 2.34 µm). Multispectral sensors sample a few broad bands and can separate mineral groups; hyperspectral sensors (imaging spectroscopy) sample hundreds of narrow, contiguous bands and can separate individual minerals.
Instrument and platform: Multispectral: ASTER on Terra — its shortwave-infrared detectors stopped producing usable data in 2008 after overheating, but the earlier archive remains valuable — Sentinel-2 MSI and Landsat 8 and 9 OLI. Hyperspectral from orbit: NASA's EMIT on the International Space Station (60 m pixels, about 380–2500 nm), Germany's EnMAP (30 m, about 420–2450 nm, 224 bands) and Italy's PRISMA (30 m, 400–2500 nm). Airborne imaging spectrometers and handheld field spectrometers give finer detail.
What it measures directly: Reflected sunlight as a function of wavelength — a spectrum — for each pixel, after atmospheric correction.
What it allows us to infer: Surface mineralogy — clays (kaolinite, illite/sericite), sulphates (alunite, jarosite), carbonates, iron oxides — and from their patterns, hydrothermal alteration zones that surround some ore systems.
Reach and depth (conditional): Surface only: the uppermost micrometres to millimetres. Vegetation, soil, lichen, desert varnish, water and cloud hide or dilute the signal. Works best in arid, sparsely vegetated terrain.
Resolution and error sources: Pixels from 10–30 m (Sentinel-2, Landsat, EnMAP, PRISMA, ASTER) to 60 m (EMIT); a mineral covering part of a pixel is mixed with everything else in it. Errors from atmospheric correction, illumination and topography, mixtures and look-alike minerals.
Real mining application: A standard first step in arid regions: mapping alteration around porphyry copper and epithermal gold systems, iron oxides over gossans and iron-rich rocks, carbonates for limestone and dolomite, and clays for industrial minerals; also used on mine waste and tailings to map iron oxides and secondary minerals.
Limitations: It does not see metals: copper, gold or lithium have no usable signature from orbit; it maps minerals that may accompany them. Alteration is not ore — many altered areas are barren — and a few centimetres of soil hide everything.
Status: OPERATIONAL. An established mapping tool; its detections are surface indications, never a grade.
References: [1] [2] [3] [4] [5] [6] [7] [8] [9]

Magnetometry

Satellite (Swarm), aircraft and drone, marine and ground surveys

SATELLITEAIRCRAFT / DRONESHIP / AUVGROUNDOPERATIONAL

Maps variations in the magnetisation of rocks, mostly due to magnetite. Excellent for structure and rock type; it does not detect gold or copper themselves.

SCHEMATIC — NOT TO SCALE

Figure B3. Magnetometry. A shallow magnetite-rich body gives a sharp anomaly; a deeper one, a broader and weaker anomaly.

Technical sheet — principle, instrument, reach, resolution, limits

Physical principle: Rocks containing magnetic minerals — above all magnetite, and pyrrhotite — are magnetised by Earth's field (induced magnetisation, proportional to magnetic susceptibility) and may also carry a remanent magnetisation. They add small anomalies, measured in nanotesla, to the main field. Processing (reduction to the pole, derivatives, upward continuation, inversion) turns them into maps and models of magnetic bodies, contacts, faults and dykes.
Instrument and platform: Ground and drone magnetometers; airborne surveys flown on closely spaced lines at low altitude; marine and near-bottom AUV magnetometers; ESA's Swarm constellation (launched 22 November 2013, satellites at roughly 450–530 km altitude) for the global field.
What it measures directly: Total magnetic intensity — or its components and gradients — at the sensor.
What it allows us to infer: The distribution of magnetic minerals below ground: intrusions, mafic and ultramafic rocks, banded iron formations, faults and shear zones, and — where hydrothermal fluids destroyed magnetite — demagnetised alteration zones.
Reach and depth (conditional): Sources from the surface to several kilometres, but resolution falls with depth: a body is blurred over a width comparable to its distance from the sensor. From satellite altitude only very long wavelengths remain; lithospheric field models from satellite data resolve features of the order of a few hundred kilometres.
Resolution and error sources: Airborne: set by line spacing and flying height, tens to hundreds of metres. Satellite: hundreds of kilometres. Errors from daily variations of the field, cultural noise (fences, pipes, power lines), remanence pointing the “wrong” way and non-uniqueness — many source geometries fit the same anomaly.
Real mining application: Direct targeting of magnetite-rich iron ore; mapping intrusions and structures that control porphyry copper, iron-oxide-copper-gold and orogenic gold systems; locating kimberlites; outlining demagnetised alteration halos.
Limitations: Gold, most copper sulphides, lithium minerals and most rare-earth minerals are not magnetic enough to be seen directly. Satellite magnetics is a continental-scale tool, not an exploration-scale one.
Status: OPERATIONAL. A routine exploration method from aircraft, drone and ground; satellite data serve regional geology.
References: [11] [14] [21]

Gravimetry

GRACE / GRACE-FO and GOCE from orbit; airborne, marine and ground gravity

SATELLITEAIRCRAFT / DRONESHIP / AUVGROUNDOPERATIONAL

Measures tiny changes in gravity caused by density contrasts. From orbit it sees continents and basins; to see a single orebody, the gravimeter must be on or near the ground.

SCHEMATIC — NOT TO SCALE

Figure B4. Gravimetry. A dense body produces a positive Bouguer anomaly; a sedimentary basin, a negative one. From orbit, both are blurred into features tens to hundreds of kilometres wide.

Technical sheet — principle, instrument, reach, resolution, limits

Physical principle: Denser rock adds mass and slightly increases the local acceleration of gravity; lighter material (sediment, some granites, altered rock, cavities) lowers it. After corrections for latitude, elevation, terrain and tides, the remaining Bouguer anomaly reflects density variations below the instrument. Values are in milligals (1 mGal = 10⁻⁵ m/s²).
Instrument and platform: Relative gravimeters on precisely surveyed ground stations; airborne gravimeters and gravity gradiometers; marine gravimeters. From orbit: GRACE (2002–2017) and GRACE-FO (since 2018) measure month-to-month mass changes from the varying distance between twin satellites; GOCE (2009–2013) mapped the static field with a gradiometer.
What it measures directly: The acceleration of gravity, or its gradients, at the sensor; from orbit, the satellites' motion in the gravity field.
What it allows us to infer: Density structure: sedimentary basins, dense mafic intrusions, massive sulphide or iron-ore bodies when large and shallow enough, faults, low-density granites and karst.
Reach and depth (conditional): Sensitive to sources at all depths, with the same blurring as magnetics: the deeper the source, the broader and weaker the anomaly. GOCE models resolve about 80–100 km (half-wavelength) and GRACE monthly fields roughly 300 km. Closely spaced ground stations can resolve bodies of tens to hundreds of metres if the density contrast is large.
Resolution and error sources: Ground instruments reach microgal-level precision; accuracy is limited by elevation and terrain corrections. Satellite resolution is far too coarse for deposits. Non-uniqueness: a small, very dense body and a large, slightly dense one can produce the same anomaly.
Real mining application: Delineating dense massive sulphide and iron-ore bodies, chromite in ultramafic rocks, basins and structures, and depth to basement. Regional gravity is discussed in detail in the Gravity Intelligence module of Experimental Intelligence.
Limitations: Satellite gravity cannot detect individual deposits. Gold and lithium cannot be found by density. Interpretation needs independent constraints: geology, drilling, other geophysics.
Status: OPERATIONAL on the ground and from aircraft; satellite gravity is OPERATIONAL for geodesy and regional geology, not for deposits.
References: [12] [13] [14] [22]

Ground-penetrating radar (GPR)

Antennas on or just above the ground — not a satellite method

GROUNDAIRCRAFT / DRONEOPERATIONALEXPERIMENTAL

Images the shallowest metres of the ground with radar pulses. Clay, saline water and conductive ground absorb it, often within a metre.

Technical sheet — principle, instrument, reach, resolution, limits

Physical principle: An antenna emits short electromagnetic pulses, typically from tens of MHz to a few GHz. Where the electrical permittivity changes — at layers, fractures, the water table, voids or buried objects — part of the energy reflects. Travel time and wave velocity give depth. Lower frequencies penetrate deeper with less detail; higher frequencies give more detail at shallower depth.
Instrument and platform: Antennas dragged on the ground or mounted on carts and vehicles; experimental drone-mounted systems flown very close to the surface. Satellite imaging radar (SAR) is a different technique and does not replace GPR.
What it measures directly: Two-way travel time and amplitude of reflected radar pulses.
What it allows us to infer: Shallow layering, overburden thickness, fractures, water table, voids and ice; in mining, the shallow geometry of placers, weathering profiles and tailings structures.
Reach and depth (conditional): Strongly conditional on ground conductivity. The US EPA notes that penetration seldom exceeds about 10 m in earth materials and that clays strongly reduce it; in wet clay or saline ground less than a metre is common, while dry sand, ice or resistive rock can allow tens of metres.
Resolution and error sources: Centimetres to decimetres at high frequency, coarsening with depth. Errors from velocity assumptions, clutter, ground coupling and conductive layers.
Real mining application: Overburden and placer-gravel thickness, ice and permafrost, shallow karst, fractures and veins in resistive quarry rock such as dimension stone, and investigations of tailings dams and leach pads.
Limitations: Not a deep-exploration tool; it cannot see through clay or saline water and does not identify minerals.
Status: OPERATIONAL on the ground for shallow targets. Drone-borne GPR is EXPERIMENTAL.
References: [14] [15]

Electrical resistivity and induced polarisation (IP)

Ground and borehole surveys with current and potential electrodes

GROUNDOPERATIONAL

Drives current into the ground. Resistivity maps conductive and resistive zones; IP measures chargeability, the method most sensitive to disseminated sulphides.

SCHEMATIC — NOT TO SCALE

Figure B5. Resistivity and IP. Current is driven between C1 and C2 and the voltage read between P1 and P2; after switch-off, a slow voltage decay (chargeability) points to disseminated metallic grains.

Technical sheet — principle, instrument, reach, resolution, limits

Physical principle: Current is driven between two electrodes and the voltage measured between two others; their ratio gives apparent resistivity. When the current is switched off, the voltage does not vanish at once: metallic grains (sulphides, graphite) and some clays store charge at their surfaces and release it slowly. That decay — chargeability, in milliseconds or mV/V — is the IP effect. Measurements at many electrode spacings are inverted into 2D or 3D models.
Instrument and platform: Ground arrays (dipole–dipole, pole–dipole, gradient) with transmitters and receivers; borehole IP; distributed multichannel systems.
What it measures directly: The injected current and the resulting voltage, and the voltage decay after switch-off (or the phase shift in frequency-domain IP).
What it allows us to infer: Resistivity: clay alteration, groundwater, faults, silicified zones. Chargeability: disseminated sulphides (pyrite, chalcopyrite), graphite, some clays.
Reach and depth (conditional): Typically tens of metres to a few hundred metres, depending on array length, current and noise; deeper with long arrays and distributed systems.
Resolution and error sources: Decreases with depth; near the surface roughly comparable to the electrode spacing. Errors from electrode contact, electromagnetic coupling, cultural noise and 3D effects interpreted in 2D.
Real mining application: The classic geophysical method for porphyry copper systems, whose pyrite-rich halos give strong chargeability; also used for disseminated gold-bearing sulphides and graphite, and for mapping clay alteration and groundwater in mine planning.
Limitations: Chargeability does not separate copper sulphides from barren pyrite or graphite: a strong IP anomaly can be a pyrite halo with no copper. Slow, labour-intensive ground work.
Status: OPERATIONAL. A routine ground method in mineral exploration.
References: [14] [16]

Electromagnetic methods (EM)

Ground and airborne (helicopter, fixed-wing, drone) systems in the time and frequency domains

GROUNDAIRCRAFT / DRONEOPERATIONAL

Induces electric currents in conductive bodies without touching the ground. Strongest response from connected massive sulphides and graphite — and also from conductive cover and saline water.

Technical sheet — principle, instrument, reach, resolution, limits

Physical principle: A transmitter loop carries a changing current that creates a primary magnetic field. In conductive ground it induces eddy currents, which generate a secondary field measured by a receiver coil. In time-domain EM the secondary field is recorded after the transmitter switches off; late-time signal comes from deeper or better conductors. Frequency-domain systems use several frequencies, the lower ones sensing deeper.
Instrument and platform: Ground loops (fixed-loop, moving-loop) and borehole EM; airborne time-domain systems (helicopter-towed loops such as VTEM, and fixed-wing systems); frequency-domain helicopter systems; natural-field methods (magnetotellurics, airborne ZTEM) for greater depth.
What it measures directly: The secondary magnetic field, or its rate of change, induced in the ground.
What it allows us to infer: Conductivity distribution: massive sulphides, graphite, saline groundwater, clay-rich cover, faults; layered conductivity–depth sections.
Reach and depth (conditional): Airborne time-domain systems are typically used for conductors in the upper few hundred metres; ground and borehole EM and natural-field methods reach deeper. Conductive overburden can mask everything below it.
Resolution and error sources: Airborne: set by line spacing and footprint, tens to hundreds of metres; ground surveys are finer. Errors from conductive cover, superparamagnetic soils, cultural conductors (power lines, fences) and model assumptions.
Real mining application: Massive sulphide exploration (volcanogenic massive sulphides, magmatic nickel–copper sulphides), graphite, groundwater and brine mapping, cover thickness and palaeochannels.
Limitations: Disseminated sulphides that are not electrically connected give weak EM responses — IP is preferred there; graphite and saline water produce false positives.
Status: OPERATIONAL from aircraft and on the ground.
References: [14]

Comparison table

Indicative values. Reach and resolution depend on the survey design and on the ground itself; the method cards above give the conditions.

Method	Platforms	Physical property measured	Reach	Typical resolution	Typical applications	Main limits
Multispectral and hyperspectral imaging	Satellite, aircraft/drone, ground	Spectral reflectance (absorption features)	Surface only (µm–mm)	10–60 m from satellite; cm–m airborne or in the field	Alteration, iron oxides, carbonates, clays	Vegetation and cover; no metals; alteration is not ore
Magnetometry	Satellite, aircraft/drone, ship, ground	Magnetic susceptibility and remanence	Surface to km; detail falls with depth	Hundreds of km (satellite); tens–hundreds of m (airborne)	Structure, intrusions, iron ore, kimberlites	Non-unique; gold and copper not magnetic
Gravimetry	Satellite, aircraft, ship, ground	Density	Surface to km; detail falls with depth	80–300 km (satellite); tens–hundreds of m (ground)	Basins, dense bodies, structure	Non-unique; needs a large density contrast
Ground-penetrating radar	Ground (drone: experimental)	Electrical permittivity	< 1 m (clay, saline) to tens of m (dry, resistive)	cm–dm	Overburden, placers, dimension stone, tailings	Fails in conductive ground
Resistivity and induced polarisation	Ground, borehole	Resistivity and chargeability	Tens to hundreds of m	≈ electrode spacing near surface	Disseminated sulphides, porphyry halos, clays, water	Pyrite and graphite mimic ore; slow
Electromagnetic methods	Ground, borehole, aircraft/drone	Electrical conductivity	Upper few hundred m airborne; deeper on the ground	Tens–hundreds of m airborne	Massive sulphides, graphite, water, cover	Conductive cover; weak on disseminated ores

Illustrative example: a copper body at 150 m

ILLUSTRATIVE — HYPOTHETICAL, NOT REAL DATA

A hypothetical porphyry-style copper body whose top lies 150 m below the surface, beneath a leached cap and inside an alteration halo. No real site, data or grade is represented. The steps show how evidence accumulates — each step narrows uncertainty without removing it.

ILLUSTRATIVE — HYPOTHETICAL, NOT REAL DATA

Figure B6. Illustrative geological section. A hypothetical mineralised body at 150 m, with the surface expression that remote sensing can see and the volume that only drilling reaches.

Satellite. Imaging spectroscopy, or archived ASTER imagery, maps sericite and clay alteration and iron oxides over a few square kilometres. Inference: a hydrothermal system may be present. Not evidence of copper.
Geology. Field mapping and rock sampling check the alteration, the intrusion, the structures and the leached cap. Inference: the setting is compatible with a porphyry system.
Geophysics. Airborne magnetics outlines the intrusion and a demagnetised core; ground IP finds a chargeability high at depth; resistivity separates clay-altered zones. Inference: sulphides are probably present below about 100–200 m — pyrite or copper, the data cannot tell.
3D model. Geology and inverted geophysics are combined into a model with explicit uncertainty. Result: a drill target with stated assumptions — a hypothesis, not a resource.
Drilling. Diamond or reverse-circulation holes test the model. Only now is the rock itself recovered.
Laboratory. Certified assays with quality control (blanks, standards, duplicates) measure the copper grade. Only drilling and assays confirm mineralisation; only systematic drilling, estimation by a Competent or Qualified Person and the Modifying Factors can lead to a resource or a reserve.

Figure B7. From observation to confirmation. Every step before drilling produces a hypothesis; a step that fails sends the work back, not forward.

[16] [17]

Applications by commodity

Gold

Not detectable by any remote method: gold occurs at grams per tonne and has no usable spectral, magnetic or density signature. The methods map what controls it — structures and shear zones (magnetics), alteration (spectral imaging; IP where gold travels with disseminated sulphides), intrusions, and placer gravels (GPR; LiDAR over land). Confirmation is by drilling and assay, and coarse gold is notoriously hard to sample (the nugget effect).

Copper

Porphyry systems: alteration zoning (spectral imaging), intrusions and demagnetised cores (magnetics), pyrite–chalcopyrite halos (IP), clay and leached zones (resistivity). Volcanogenic massive sulphides: EM and gravity. The copper grade itself is known only from assays.

Iron

One of the few commodities with direct geophysical expression: magnetite ores give strong magnetic anomalies, dense iron formations give gravity highs, and hematite and goethite have visible–near-infrared absorption features. Even so, grade, impurities (phosphorus, sulphur, silica, alumina) and tonnage require drilling.

Lithium

Brines in salars: optical satellites map evaporite crusts and surface water, while EM and resistivity map conductive brine at depth; lithium concentration needs sampling and pumping tests. Pegmatites: lithium itself has no remote signature; research studies test spectral detection of lithium-bearing minerals and their host pegmatites, with frequent false positives. Magnetics and radiometrics help map host granites and structures. Neither type is confirmed remotely.

Rare earth elements

Carbonatites and alkaline complexes: magnetics and radiometrics (thorium) outline the complexes; neodymium has narrow absorption features that imaging spectroscopy can detect on clean, exposed outcrop (Boesche et al., 2015), but not under cover, vegetation or iron-oxide staining. Ion-adsorption clay deposits have no remote signature. Grade requires assays.

Ornamental limestone and dimension stone

Carbonates absorb in the shortwave infrared (calcite near 2.34 µm), so multispectral and hyperspectral imaging map them at the surface. But the value of a dimension-stone deposit lies in what remote sensing cannot see: colour uniformity, fracturing, block size and soundness — assessed with quarry-face mapping, GPR and resistivity for fractures and karst, and core drilling.

[1] [10] [14] [16]

Occurrence, anomaly, target, resource, reserve

These words are often used loosely. In public reporting they are not interchangeable. The last two have strict meanings under the CRIRSCO family of codes — JORC (Australasia), PERC (Europe), the CIM Definition Standards incorporated in NI 43-101 (Canada) and others — and may only be reported by a Competent or Qualified Person. What follows is a conceptual summary, not legal or reporting advice.

Occurrence (showing)Mineralisation observed at a point — an outcrop, an old working, a sample. A fact about one place; it says nothing about size or continuity. Not a code category.
AnomalyA measured value that departs from background — magnetic, gravity, chargeability, geochemical or spectral. It may or may not be caused by mineralisation. Not a code category.
Exploration targetA hypothesis about where mineralisation may occur. Under JORC, an Exploration Target may be reported only as ranges of tonnage and grade, with a statement that it is conceptual and that it is uncertain whether further exploration will define a Mineral Resource. It is not a resource.
Mineral Resource — Inferred, Indicated, MeasuredA concentration of material with reasonable prospects for eventual economic extraction, whose location, quantity, grade, continuity and geological characteristics are known, estimated or interpreted from specific geological evidence, including sampling. Confidence increases from Inferred to Indicated to Measured.
Mineral (Ore) Reserve — Probable, ProvedThe economically mineable part of an Indicated or Measured Resource, after applying the Modifying Factors — mining, processing, metallurgical, infrastructure, economic, marketing, legal, environmental, social and governmental — demonstrated by at least a pre-feasibility study.

No remote-sensing or geophysical method — and nothing on GeaSpirit — produces a Mineral Resource or a Mineral Reserve. GeaSpirit works at the first three levels: it organises occurrences, anomalies and evidence; it does not report resources.

[17] [18] [19] [20]

Future: Mineral Prospectivity in the Asset Map

GEASPIRIT PROPOSAL

A GeaSpirit proposal, not developed: a multi-commodity Mineral Prospectivity view for the Asset Map. It would be separate from the existing REE Prospectivity regional screening model, which is its own experimental layer.

Explainable scores. Every value broken down into the evidence layers that produced it and their weights, readable by a geologist — no black box.
Sources. Each input layer — geology, geophysics, spectral, geochemistry, known occurrences — named with its provider, licence, scale and date.
Uncertainty. Shown next to every score, including where data are missing; absence of data never displayed as low prospectivity.
Validation against known deposits. Tested on deposits withheld from the model, with results published whether good or bad, and deposit-type-specific models rather than one universal score.
Language limits. A score would mean “resembles settings where deposits of this type have been found”, never “a deposit is here”.

Status: GEASPIRIT PROPOSAL. Not built and not scheduled; subject to the same validation rules as every other GeaSpirit research line.

References

Sources consulted in October 2026. Figures quoted on this page come from these sources; where a figure varies between sources, the text says so.

Kokaly, R. F. et al. (2017). USGS Spectral Library Version 7. U.S. Geological Survey Data Series 1035. doi.org/10.3133/ds1035
Hunt, G. R. (1977). Spectral signatures of particulate minerals in the visible and near infrared. Geophysics 42(3), 501–513. doi.org/10.1190/1.1440721
Morris, R. V. et al. (1985). Spectral and other physicochemical properties of submicron powders of hematite, maghemite, magnetite, goethite and lepidocrocite. Journal of Geophysical Research 90(B4), 3126–3144. doi.org/10.1029/JB090iB04p03126
NASA Earthdata. ASTER SWIR anomaly (detectors not usable since April 2008). earthdata.nasa.gov/data/alerts-outages/aster-swir-anomaly
NASA JPL. EMIT — Earth Surface Mineral Dust Source Investigation. earth.jpl.nasa.gov/emit/
Storch, T. et al. (2023). The EnMAP imaging spectroscopy mission towards operations. Remote Sensing of Environment 294, 113632. doi.org/10.1016/j.rse.2023.113632
Agenzia Spaziale Italiana. PRISMA. asi.it/en/earth-science/prisma/
Copernicus. Sentinel-2 mission (MultiSpectral Instrument). sentiwiki.copernicus.eu/web/s2-mission
USGS. Landsat 9. usgs.gov/landsat-missions/landsat-9
Boesche, N. K. et al. (2015). Hyperspectral REE (rare earth element) mapping of outcrops — applications for neodymium detection. Remote Sensing 7(5), 5160–5186. doi.org/10.3390/rs70505160
ESA. Swarm. esa.int/Applications/Observing_the_Earth/FutureEO/Swarm
ESA. GOCE. esa.int/Applications/Observing_the_Earth/FutureEO/GOCE
NASA JPL. GRACE Follow-On. gracefo.jpl.nasa.gov/
Dentith, M. and Mudge, S. T. (2014). Geophysics for the Mineral Exploration Geoscientist. Cambridge University Press. doi.org/10.1017/CBO9781139024358
US EPA (archive). Ground-penetrating radar. archive.epa.gov/esd/archive-geophysics/web/html/ground-penetr…
John, D. A., ed. (2010). Porphyry copper deposit model. USGS Scientific Investigations Report 2010-5070-B. pubs.usgs.gov/sir/2010/5070/b/
JORC (2012). Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves. jorc.org/docs/jorc_code2012.pdf
PERC (2021). Pan-European Standard for Reporting of Exploration Results, Mineral Resources and Mineral Reserves. percstandard.org/perc-standard/
CIM. Definition Standards for Mineral Resources and Mineral Reserves (incorporated by reference in NI 43-101). mrmr.cim.org/
CRIRSCO. Committee for Mineral Reserves International Reporting Standards. crirsco.com/
Thébault, E. et al. (2013). Swarm SCARF dedicated lithospheric field inversion chain. Earth, Planets and Space 65, 1257–1270. doi.org/10.5047/eps.2013.07.008
Pail, R. et al. (2011). First GOCE gravity field models derived by three different approaches. Journal of Geodesy 85, 819–843. doi.org/10.1007/s00190-011-0467-x

This chapter describes measurement methods. It is not an exploration service, not investment advice, and contains no detection, resource, reserve or grade claim by GeaSpirit. Third-party figures are quoted with their sources; schematic figures are drawn by GeaSpirit and are not to scale.