PI vs VLF Gold Detectors: Pulse Induction or VLF for Prospecting

Both kinds of detector send a magnetic field into the ground and listen for the response from metal. They differ in how they do it, and that decides how they cope with mineralised soil.

• VLF (very low frequency) detectors transmit a continuous signal, typically 18–71 kHz on gold machines, and measure the phase shift of the return. Higher frequencies are more sensitive to small gold. VLF can discriminate, telling gold from iron trash, but iron-rich soil also produces a strong signal, so depth and stability fall in laterite.
• PI (pulse induction) detectors send short, powerful pulses and listen to the decaying echo after each one. Mineralised ground's signal fades quickly while metal's lingers, so a PI largely ignores the ground. The trade-off is weak discrimination: a PI finds every nail and bullet, and is heavier and more expensive.
• Multi-frequency VLF detectors transmit several frequencies at once, recovering some of the ground tolerance of PI while keeping discrimination. They are a practical all-rounder on moderately mineralised ground.

A detector recovers coarse, free gold only. Fine gold in gravel or crushed ore needs gravity equipment such as a shaking table or centrifugal concentrator.

Choosing a coil

• Double-D (DD) coils handle mineralised ground better and give a narrow, predictable detection pattern. They are the default on most Tanzanian ground.
• Mono coils on a PI give maximum depth and sensitivity, but are noisier in heavy mineralisation.
• Coil size trades depth for small-gold sensitivity: 15–25 cm coils for small gold and trashy ground, 35–45 cm for depth on larger nuggets and open ground.

Ground balance and hot rocks

Ground balance tells the detector what the soil sounds like so it can ignore it. Balance at the start of every new patch of ground, and re-balance when the soil colour changes. Ironstone and magnetite pebbles ("hot rocks") still give signals. Learn their sound by passing the coil over a known hot rock before hunting.

Technique that finds more gold

1. Sweep slowly and overlap each pass by about half a coil width, keeping the coil flat and close to the ground.
2. Dig every repeatable signal on a PI. Small and deep gold often gives the faintest response.
3. Check the hole and the spoil separately to confirm where the target is before digging further.
4. Log every nugget with GPS and depth. Clusters and lines of finds point to where the gold came from.
5. Work upslope from clusters. Eluvial gold sheds downhill from its source, so the trail narrows towards the reef, which then needs proper exploration such as trenching or RC drilling.

• Match the machine to your ground. Test on your own soil with a known small gold target, or ask the supplier to demonstrate on similar laterite, before paying.
• Buy genuine. Copies of well-known detectors circulate in the region. Check the serial number with the manufacturer and insist on a written warranty.
• Warranty and repairs. Ask where the unit is serviced and how long a repair takes. A detector away for months is a lost season.
• Spare coil and cover. Coils crack on rocky ground. A spare coil cover is cheap; a spare coil keeps you working.
• Power off grid. Plan batteries and charging: spare battery packs and a solar or vehicle charger for multi-day trips.
• Headphones and pinpointer. Good headphones reveal faint deep signals; a handheld pinpointer halves digging time.
• Training. Ground balancing and signal reading take practice. Budget time for it before judging a detector.

Prices vary widely by type, coil and whether the unit is genuine. Tell us your ground, the gold you are chasing and your budget on WhatsApp, and we will recommend a detector type and quote.