Gold detection is the process of finding gold deposits or occurrences by geochemical and geophysical techniques. Many modern gold discoveries have been made by detecting geochemical anomalies in soils and rocks. Geophysical techniques such as ground magnetics, gravity and electrical resistivity can also be used to locate buried gold deposits.
Gold scanners or metal detectors are commonly used by prospectors and treasure hunters to find gold nuggets or flakes in the field. Metal detectors utilize electromagnetic induction to detect metal objects buried below the surface. The question is – can metal detectors also detect pure gold deposits?
How do metal detectors work?
Metal detectors consist of a handheld unit with a sensor coil connected to electronics with an audible signal. The coil generates a magnetic field which penetrates into the ground. When metallic objects like coins, relics or gold are present, they disturb the magnetic field and create a change in coil impedance. This signal change is processed and converted into an audible tone or visual display to indicate metal presence.
There are two main types of metal detectors:
- VLF (Very Low Frequency) detectors – Generate a magnetic field that can penetrate deeper into the ground. Better for finding large objects or ores.
- PI (Pulse Induction) detectors – Emit magnetic pulses to induce currents in metallic objects. More sensitive but limited depth.
In general, factors like the size, shape, depth and orientation of buried metals affect how strongly they respond to metal detectors. Gold nuggets and large ore bodies can be detected at greater depths compared to small flakes and particles.
Can metal detectors find pure natural gold?
Natural or placer gold is usually alloyed with silver and other metals. Raw gold commonly contains 5-40% silver which enhances electrical conductivity and detectability. However, pure crystalline or wire gold has low intrinsic conductivity and is harder to detect with standard metal detectors.
The main considerations when detecting pure gold inclusions are:
- Size – Large nuggets and deposits give a clearer signal.
- Depth – Shallow gold is easier to detect than deep inclusions.
- Detector type – PI detectors have better sensitivity for small or deep gold particles.
- Frequency – Lower frequency coils (VLF) penetrate deeper through ground.
- Ground mineralization – Highly mineralized ground weakens and distorts detector signals.
With optimized detectors and settings, nuggets upwards of a gram can be found up to 10 inches deep. However, very small flakes and pickers are a challenge for standard detectors.
Specialized gold detectors
There are dedicated metal detectors designed specifically for gold prospecting and nugget shooting. They have customized features and circuitry to enhance the detection of natural gold:
- Operating frequencies – Multiple and low frequency (VLF) coils for nugget detection.
- Advanced ground balancing – To cancel out mineralization effects.
- Target identification – Discriminates gold targets from trash items.
- Enhanced audio response – For subtle gold signals.
- Increased transmit power – For deeper penetration.
- Rugged waterproof construction – For use in rivers or streams.
Some advanced detectors also have integrated GPS, data logging and wireless connectivity for detailed surveying. Using such specialty gold detectors greatly improves the odds of finding gold in the field. However, micron sized gold dust and flakes remain difficult to detect consistently.
Scientific gold detection technologies
Industrial and scientific techniques are required for the reliable detection of microscopic or trace gold particles:
X-Ray Fluorescence (XRF)
XRF analyzers direct X-rays at materials to cause atomic excitation and fluorescence. The energy of fluorescent X-rays identifies elements present. Portable XRF guns can detect gold concentrations down to 10-20 parts per million in drill cores, rocks and sediments.
Geochemical testing
Sensitive laboratory techniques like fire assay, AAS, ICP-MS and archimedes measurements can detect and quantify gold at parts per billion (ppb) to parts per trillion (ppt) levels in soil and rock samples. This helps locate target areas through multi-element geochemical signatures.
Cyanide leaching
Small or trace amounts of gold can be extracted from ores using cyanide leaching. The pregnant leach solution is analyzed to measure recovered gold concentrations down to 0.01 ppm. LeachWELL assay uses cyanide pore water extraction to test large drill core intervals.
Magnetic susceptibility
Magnetic susceptibility meters detect gold mineralization through weak magnetic anomalies produced by associated sulfide minerals like pyrite. Airborne, ground and borehole magnetic surveys are valuable for targeting gold exploration drilling.
Hyperspectral imaging
Hyperspectral cameras acquire images across the electromagnetic spectrum to detect characteristic spectral signatures of minerals associated with gold deposits. Advanced spaceborne and airborne sensors are being used for exploration.
Electrical geophysics
Resistivity, IP, EM, SP and other geophysical methods provide subsurface imaging to find geologic features favorable for hosting gold like faults, folds and intrusive contacts. Airborne gravity gradiometry is also being used.
Conclusion
While standard metal detectors can locate larger gold nuggets near the surface, they have limited capabilities for detecting microscale gold particles and deposits buried deeper. Advanced specialty gold detectors improve the detectability somewhat, but tiny gold flakes remain elusive. Industrial scientific instruments using XRF, geochemistry, geophysics and hyperspectral sensors are required for the reliable detection of microscopic and trace gold far below the range of metal detectors.
Integrating multiple complementary geological, geochemical and geophysical techniques provides the best approach to fully evaluate a property and vector in on gold mineralized zones. Once prospective areas are identified, careful follow-up sampling, assaying and drilling are needed to confirm and delineate any gold deposit present.