What geophysical method would be most effective in delineating the lateral extent of a 2000 ft deep metallic sulfide deposit containing Pb, Zn, and Ag?

• A. Induced polarization
• B. Magnetic survey
• C. Seismic reflection
• D. Ground-penetrating radar

Answer: (A)

Induced polarization works best here because it detects the chargeability of sulfide minerals. Metallic sulfides, such as those containing Pb, Zn, and Ag, store and release electric charge when a current is applied, producing a delayed voltage that stands out where sulfide minerals are present. This delayed, recoverable signal maps out the lateral extent of a sulfide body because the chargeability anomaly follows the ore zone more reliably than other properties, even when the rocks surrounding it have similar resistivity or density. For a deep target like a 2000 ft (roughly 600 m) deposit, properly designed IP surveys can still image the sulfide body in plan view with appropriate electrode spacing, whereas the other methods have limitations: magnetic surveys depend on magnetic contrasts that may be weak or inconsistent for sulfides; seismic reflection tracks contrasts in acoustic impedance and is more about structure than mineral content, making it less direct for delineating sulfide ore bodies; and ground-penetrating radar penetrates only near-surface and is severely limited by conductive ground, making it impractical for deep targets.