Fisher Gemini 3 Deep Seeking 2 Box Cache, Relic and Treasure Metal Detector

The Fisher Gemini-3 is a two-box deep seeking metal detector: a transmitter and a receiver on one handle, running a crystal-controlled 81.92 kHz frequency to locate large, deeply buried objects. First Texas says it detects large targets like 55-gallon drums at depths up to 10 feet, and even deeper for larger objects, and it also traces pipes, cables and ore veins. It weighs 7.5 lb (3.4 kg) for the complete system and carries a 2-year Fisher warranty.

What is in the box with the Fisher Gemini-3

Fisher's standard contents for the Gemini-3

• Gemini-3 transmitter box
• Gemini-3 receiver box
• Three-piece handle
• Extra-long handle section
• Carrying strap

Who the Fisher Gemini-3 is for

The Gemini-3 suits cache hunters looking for buried containers on old homesteads, farms and outbuildings, anyone locating underground tanks, pipes and cables, and prospectors and geologists following ore veins. First Texas designed it for utility work, geology and treasure hunting. It is not a coin or jewelry detector.

How a two-box detector differs from a standard detector

A standard single-coil detector finds small targets near the surface and tells them apart with discrimination and target ID. The Gemini-3 does the opposite job: it looks for large objects buried deep and gives no information about the target beyond its signal strength. There is no discrimination, no target ID and no searchcoil, by design. We would pair it with a standard detector, the Gemini-3 to find the deep, large target and the standard detector to work the site around it.

Search and trace modes

First Texas lists four operating modes: narrow-scan inductive, wide-scan inductive, inductive trace and conductive trace. Narrow scan is the one-person search with both boxes on the handle, and we would use it for caches and other compact targets; Fisher's starting sensitivity for narrow scan is 7. Wide scan separates the boxes for two operators, who line up at least 20 feet apart, and follows long targets such as pipes, cables and ore veins 40 feet or longer. Audio is VCO, so pitch and volume rise as the signal gets stronger, and an analog meter shows signal strength for pinpointing. The trace modes follow something long, such as a pipe, cable or vein. Inductive trace starts from two points on the line at least 30 feet apart, and conductive trace connects the transmitter to an exposed section of the line through the optional ground plate assembly, with the receiver at least 30 feet away. A nonconductive gasket in a pipe ends the signal. Balance the Gemini-3 with the knob on the handle before each search, well away from any metal, since Fisher warns against tuning near metal objects.

How deep the Fisher Gemini-3 detects

Depth on the Gemini-3 depends on the size of the object and the ground it sits in. Fisher's manual says it will not detect small coin-sized objects, and gives these examples:

• A quart jar full of coins: about 1 to 3 feet.
• A 55-gallon drum: as deep as 10 feet.
• A very large object, such as a car: 20 feet or more.

Ground mineralization cuts those numbers sharply. Fisher's example is an object detected at 15 feet in neutral ground that may show no deeper than 5 feet in highly mineralized ground, and magnetite in particular reduces penetration. For extra depth, Fisher suggests hooking the fully lengthened carrying strap to the eyelets at the ends of the handle; over highly mineralized ground and some asphalt the unit may be hard to tune that low, so shorten the strap there. Our guide on how deep metal detectors go explains why target size changes depth so much.

Where the Gemini-3 works best and its limits

The Gemini-3 works best on open, fairly level ground where large objects may be buried deep: old homesteads, farm sites, relic sites with large iron, utility routes and mineralized ground with veins. Every large mass of metal sounds the same, it is the wrong tool for coins and jewelry, and it is not fully waterproof. For coins, rings and small relics, see our relic and treasure metal detectors, and for other deep-target tools our deep seeking metal detectors.

• Salt water and salty ground: Fisher warns that saline water or water-saturated soil high in salt may hinder the Gemini-3, so it is not a beach machine.
• Rough terrain: the handle has to stay level and steady. In very rough terrain that is hard to do, and Fisher says an unsteady handle causes false signals and a loss of sensitivity.
• Fault zones: highly fractured fault zones often give positive readings.
• Surface junk: scrap iron, tin cans and other conductive debris near the surface can give unexpectedly high readings, so an old dump will light up.

Before the first real search, we would bury a known target, such as a coffee can, at a known depth and learn how it sounds and reads on the meter. Fisher's manual calls practice over buried targets of known size and depth essential, and it makes the first real signal much easier to trust. Our guide to relic hunting detectors covers the single-coil machines that pair well with a Gemini-3 on old sites.

Is the Fisher Gemini-3 a gold detector?

Not for nuggets. Fisher's manual says the Gemini-3 will not detect small coin-sized objects, and that placer gold deposits generally cannot be found with a traditional hand-held detector. What the Gemini-3 can detect is the black sand and iron sulfide often associated with placer gold, both of which are conductive, so prospectors use it to point to likely ground. For detectors and gear that find the gold itself, see our gold prospecting equipment.

Batteries and headphones

Each box takes eight AA batteries. Fisher gives about 30 hours for the receiver and 25 for the transmitter on high-quality alkaline batteries, so the transmitter needs fresh batteries first. Change all eight in a box together and do not mix old and new. The Gemini-3 has a 1/4 inch headphone jack for wired headphones with a stereo or mono plug; plugging them in silences the speaker, and Fisher says headphones significantly increase battery life. They also help in wind or near traffic. See our metal detector headphones.

Fisher Gemini-3 specifications

The free Gemini-3 digital manual, in English and Spanish, is in our Fisher Gemini-3 collection; read the trace procedures before you head out. Our Fisher buying guide covers the rest of the range.

Authorized Fisher dealer with a showroom in Ypsilanti, Michigan. Full manufacturer warranty and help from our staff by phone or email.