MobileMT geophysical surveys

MobileMT geophysical surveys are a new generation of airborne electromagnetic (EM) technology that allow explorers to “see” resistivity structures in the subsurface from near surface to well over a kilometre deep, quickly and cost-effectively.

What is MobileMT?

MobileMT is an airborne EM system developed by Expert Geophysics. It belongs to the AFMAG (audio-frequency magnetics) family of methods and uses natural electromagnetic fields (from global lightning activity and ionospheric currents) instead of an artificial transmitter. The system measures:

Three-component magnetic field in a helicopter-towed “bird”
Two-component electric field at a ground base station

By combining these measurements over a broad frequency range (typically ~25 Hz to 20 kHz), MobileMT derives high-resolution resistivity models of the subsurface.

Unlike traditional time-domain EM (TDEM) systems that rely on controlled pulses, MobileMT continuously records natural fields and processes them into multiple frequency “windows,” giving sensitivity to both shallow and deep structures in a single survey.

How does a MobileMT survey work?

A typical survey layout includes:

Helicopter and bird – a lightweight, aerodynamic EM receiver towed beneath the helicopter measures the magnetic field as it flies along survey lines.
Base station – grounded electrodes on the surface measure orthogonal electric fields as a reference.
Broadband acquisition – the system records natural EM variations across several orders of magnitude in frequency, which are then split into 20–30 adjustable frequency channels.
Inversion & imaging – specialized processing transforms the EM responses into 1D, 2D or 3D resistivity models, sections and depth slices that geologists and geophysicists can interpret.

Because it’s airborne, a survey can cover thousands of line-kilometres in a matter of days, even in remote or rugged terrain.

Key technical advantages

Compared with conventional airborne EM methods, MobileMT offers several important benefits:

Exceptional depth of investigation
- MobileMT typically images to 1–1.5 km depth, and in favourable resistive conditions can exceed this, significantly deeper than many time-domain airborne systems.
Sensitivity across a wide resistivity range
- It is sensitive to both very conductive and very resistive rocks, detecting contrasts associated with sulphides, alteration zones, faults, structures and lithological contacts in virtually any direction.
High spatial and resistivity resolution
- The broad frequency range and three-component measurements give good lateral resolution along survey lines and in depth, making it possible to distinguish multiple stacked units or discrete conductors.
Effective in challenging environments
- MobileMT has shown strong performance in both highly conductive and highly resistive terrains, and can often recover reliable data even near industrial noise sources, where other EM systems struggle.
Passive source, efficient logistics
- Because it uses natural fields, there is no heavy transmitter loop or high-power generator to move and maintain. This reduces survey complexity and makes operations easier in remote areas.

Applications in mineral exploration

MobileMT is particularly attractive for:

Base and precious metal systems
Mapping sulphide-rich structures, alteration halos and feeder zones at depth, supporting target generation for copper, nickel, zinc, gold and polymetallic deposits.
Critical minerals (Ni, Cu, Co, rare metals, uranium, etc.)
Deep fault zones, basin structures and conductive horizons important for critical mineral deposits can be imaged to depths suitable for modern exploration drilling. Recent MobileMT programs have been deployed on uranium and copper projects to refine drill targeting.
Extension of active and historic mines
MobileMT can map structures beneath or around existing operations, identifying new ore lenses or extensions below previous drilling and old mine workings.
Regional reconnaissance and greenfields exploration
For under-explored terrains, the method quickly establishes a resistivity framework that highlights major faults, basin architecture and prospective conductive corridors, guiding follow-up ground EM and drilling.

Beyond mineral exploration, the method is also being researched for geothermal, groundwater and broader structural geology mapping where deep resistivity information is valuable.

From data to drill targets

A MobileMT project typically fits into an exploration workflow as follows:

Survey design – defining line spacing, orientation and base station positions to capture key structural trends.
Acquisition & QA/QC – airborne data collection with continuous monitoring of system performance, noise and natural field strength.
Processing & inversion – rigorous noise suppression, calibration and 1D/2D/3D inversion to produce resistivity sections and depth slices.
Integrated interpretation – combining MobileMT resistivity models with geology, magnetics, gravity and existing drilling to delineate targets.
Target ranking & drilling – converting the best resistivity anomalies and structures into prioritized drill targets, often with follow-up ground EM for refinement.

Because MobileMT images both near-surface and deep responses in a single dataset, it helps reduce ambiguity between shallow conductive cover and genuine bedrock targets, improving confidence before committing to expensive drilling.

Why MobileMT matters

As exploration moves deeper and into more complex terrains, technologies that can provide reliable, deep-penetrating geophysical images are becoming indispensable. MobileMT stands out because it:

Combines MT/MV principles with modern electronics and processing
Delivers both reconnaissance-scale coverage and drill-scale targeting in one pass
Works effectively in a wide range of geological and logistical settings

For explorers, MobileMT geophysical surveys offer a powerful way to de-risk projects, discover hidden mineral systems and extend the life of existing operations by revealing what lies beyond the reach of traditional airborne EM.