Geophysics in Mineral Exploration

Geophysics measures contrasts in the physical properties of rocks — magnetism, electrical conductivity, density, and chargeability — to infer what lies beneath the surface without drilling. It bridges the gap between surface geochemistry, which samples only the near-surface, and drilling, which is expensive and tests only one location at a time.

Surveys can be flown from aircraft to cover large areas quickly, or collected on the ground for higher resolution over priority targets. Results are modelled and integrated with geology to refine where mineralization is most likely to occur.

Magnetic surveys map variations in rock magnetism, helping outline intrusions, structures, and alteration. They are inexpensive, commonly flown over wide areas, and provide a regional geological framework.

Electromagnetic (EM) surveys detect conductive bodies and are especially effective for finding sulphide accumulations such as massive sulphides. Airborne magnetic and EM surveys are frequently combined to map both structure and conductors in a single campaign. Regional airborne data can be revealing on their own — the ultramafic complex at the Iron Lake property, for example, corresponds to both very strong regional magnetic and regional airborne gravity highs.

Induced polarization (IP) measures chargeability, the ability of rock to store electrical charge. Disseminated sulphides such as those in porphyry systems produce strong IP responses, making the method a workhorse for porphyry copper exploration even where sulphides are not massive enough to be conductive.

IP and resistivity are often surveyed together to distinguish sulphide zones from barren but conductive features such as graphite or clay. Anomalies are ranked alongside geochemistry and geology to prioritise drill targets.

Geophysics is powerful but indirect: it detects physical contrasts, not metal directly, so anomalies always require geological interpretation and, ultimately, drilling to confirm. The best programs treat geophysical data as one of several converging lines of evidence rather than proof of a deposit.

This article provides general educational information about mineral exploration. For information concerning Eastfield's mineral projects, readers should refer to the Company's project disclosures, news releases and continuous-disclosure filings on SEDAR+.