White’s Electronics, a name known throughout the gold prospecting community, has
been manufacturing metal detectors for nearly 55 years. The success of their
4900, Eagle, and Goldmaster series machines has earned them a solid reputation
among nugget hunting enthusiasts. Although many of these detectors have been
discontinued, White’s commitment to product excellence has not. Their newest
addition is the GMT E-Series. Unlike the previous GM/4, GMT users now have the
flexibility of choosing between automatic or manual-type ground balance. White’s
has also given the GMT a more friendly appearance by reducing the number of
knobs, dials, and gadgets on the control box. The detector is powered by eight
“AA” batteries, which should supply enough juice for about 40 hours of
operation. The GMT is outfitted with a 10 ½” elliptical Twin-D search coil,
however it is compatible with earlier Goldmaster coils. It operates at a fixed
48 kHz and is available exclusively as a polemount. While you can undoubtedly
find coins, relics and buried treasure with the GMT, it was really designed with
one thing in mind – finding gold!
Besides turning the unit on and off, the primary function of the GAIN control is
to adjust the signal strength coming from the ground. The various levels of
signal strength are indicated by the numbers 1-10, which appear around the knob.
Turning the Gain in the clockwise position will increase depth penetration,
turning it counter clockwise has the opposite effect. The gain should be set in
the highest setting whenever possible, as this will allow maximum penetration.
However, when working noisy or “hot” ground you may be forced to reduce Gain, as
the mineralization may actually bounce back the signal making it virtually
impossible to hear targets over the ground “chatter”.
The Variable SAT
Speed (or V-SAT) control, adjusts the speed that the GMT recovers its threshold
“hum” when the search-coil passes over changes in ground mineralization. These
mineralization changes affect the consistency of the threshold “hum” and can
potentially mask a buried target. Unlike the Gain knob, turning the V-SAT in the
clockwise position will decrease detection depth, and vice-versa. Remember,
overall depth will be diminished with a faster V-SAT speed, but if the ground is
too noisy to separate a good target from a false signal, it is better to operate
with a little more V-SAT speed than to lose a target altogether.
The Audio Signal
Boost switch acts as both a battery tester and an audio amplifier. This feature
is especially useful when seeking out extremely tiny nuggets or for
“boosting-up” those faint, deeply buried targets. The boost feature should
probably only be used on an as-needed basis since it also amplifies the
experienced prospectors already know, gold is usually found in mineralized soil.
In order to find this gold a metal detector must be able to cancel out or adjust
to this mineralization – this is where ground balancing comes in. The GMT can be
ground balanced using either the new Fast AutoTrac system or the more
traditional “Manual” balance method. When placed in the Fast AutoTrac position
the GMT automatically compensates for changing ground mineralization. Or if you
prefer to do it yourself, just flip the switch into the Manual Balance position
and have at it! The Ground Balance Touch Pad buttons and new digital
microprocessor control with a 4000:1 resolution make manually ground balancing
this detector quick and easy. Adjustments are as simple as tapping either the
plus (+) or minus (-) pads on the display while pumping the coil.
White’s has also incorporated a state-of-the-art, iron identification system.
This unique development applies digital analyzing to predict the probability of
a target being iron. The Iron I.D. System is presented to the user both visually
on the display and audibly when desired. When the Iron I.D. trigger is in the
center position the GMT responds to all metallic targets. Although this is the
All Metal mode the “ferrous” probability of all targets will still be shown,
however it is not as accurate as the Target Analyzer. If the trigger is locked
in the forward position, sound is added to the Iron I.D. System. When the coil
passes over a target registering at least 85% iron, a “GRUNT” sound is added to
the tail end of the signal. While the trigger is squeezed, the GMT stops
tracking and analyzes the suspected target. With each successive pass of the
coil more information is added to its memory bank and the % probability of it
being ferrous is shown on the display. White’s claim that their Iron I.D. System
does not alter detection depth.
At last the day had finally come! The appearance of a brown UPS truck and a
knock at the front door signaled the arrival of my new White’s GMT. I quickly
snatched up the package and plopped down on the living room floor – it was as if
Christmas had come early! I had been hearing for weeks about the remarkable
finds some of my friends were making with it in the deserts of Arizona and
California, needless to say I was excited to get it out of the box and into the
field. Luckily I was already planning a prospecting expedition to northwestern
Arizona and knew this was the ideal opportunity to test out the new Whites.
This area, located not far from the town of Kingman has yielded 1000’s of placer
nuggets, some in excess of 15 ounces! Evidence of past mining activities since
its’ discovery at the turn of the century can be found throughout the district,
most notably along the banks of the gullies and washes. Because running water is
virtually non-existent, the drywasher was the old-timers most popular method for
recovering gold in this region. Drywashers are not nearly as efficient as wet
washing methods; therefore the tailings mounds should always be thoroughly
investigated. The coarse piles may be especially lucrative, as they could
contain nuggets that were too large to pass through the grizzly.
Despite my urge to jump down into the gullies I held back, deciding it was
better to begin on the hilltops until I became more familiar with the machine’s
operation. With the machine set in the AutoTrac position, the Gain at 7, V-SAT
at 3.5x, All Metal mode, and the audio boost turned off, I began scanning one of
the ridge tops. The first target let off a solid “zip-zip”. The meter showed an
iron probability of 50-60%, however when I squeezed Iron I.D. trigger it quickly
jumped up to 75%, a few more passes and it was up to 85%. The GMT’s analysis had
been correct the target was a rusty nail. A careful search of the area produced
a handful of worthless objects such as nails, decomposed cans, and boot tacks.
For the most part, I found the Target Analysis System very reliable. Nearly
all-ferrous trash registered 75% or higher, while objects like gold and lead
registered well below the 25% mark. While this feature works well, it can and
will make mistakes from time to time. For instance, flat pieces of iron with a
hole in them, like washers will usually not be recognized as being ferrous.
Errors will also be made if there are many metallic targets within the vicinity
of the object you are trying to I.D.
Now that I had a better feel for the machine I decided to try my luck in one of
the drywashed gullies. I quickly realized that my current settings would not do.
Streaks of heavy black sands, clusters of darkly colored stones, and the erratic
behavior of the detector alerted me that the mineralization had changed
considerably. The instruction manual states that a setting between 7-8 on the
Gain and a setting of 3-4x on the V-SAT are suitable for most detecting. While
it would be nice to maintain these settings, it is virtually impossible in
mineralized ground. In order to keep the machine stable, the Gain was reduced to
4 and the V-SAT was speeded up around 7-8x. The machine’s depth penetration was
definitely handicapped, but this was necessary because of the severe ground
If you experience false signals while out hunting or the words “BAD GROUND”
appears in the display you should turn the Gain down a bit. As mentioned before,
lowering the Gain will reduce overall depth penetration, but it will allow you
to find nuggets in noisy ground. Also, if you experience a slight fluctuation in
the threshold while in the AutoTrac mode don’t panic; this is just the GMT
tracking out ground mineralization. False signals will also come from rocks
whose mineralization content differs from the surrounding soil matrix. Some give
off a “boing” sound while others ring out like a piece of metal. Although “hot
rocks” make our lives difficult, it is still possible to pluck gold out from
amongst them. Occasionally those of the “negative” variety like magnetite can be
ground balanced out or eliminated using the Iron Analyze mode. The “positive”
type like maghemite is another story. Many sound just like a nugget and are
nearly impossible to tune out. The only way to cope with these pests is to
reduce Gain and remember what they look like.
With the machine properly tuned I began scanning the remains of several coarse
piles. After digging a variety of surface rubbish I finally hit upon my first
promising target. It sounded sweet and it registered below 50% - this was
definitely a positive sign. Rummaging through the loose material I eventually
isolated the target. It was covered in caliche, but sounded off nicely on the
detector. YES! A quick wash revealed a lovely 1.2-gram nugget. My blood was
really pumping now. Five feet away I unearthed yet another nugget, a little
smaller but gold nonetheless.
Excited by the discovery of the two nuggets I pushed further up the gully. Near
its headwaters I spotted an unusually bit of red stained earth. Upon closer
inspection I found the remains of several detector dig holes. Fifteen minutes
had passed before I picked up what sounded like a faint target. I decided to
activate the Audio Signal Boost. What a difference this made, the target was now
clearly audible and distinct. Two inches later I was rewarded with a tiny
0.4-gram nugget. Although I wasn’t able to locate any more nuggets in the area I
was more than pleased with GMT’s performance and the day’s outcome.
A total of three
nuggets were found during the course of the field test. The two largest nuggets
were recovered from coarse drywash piles found along the banks of a gully. The
third, and much smaller nugget, was found embedded within a section of reddish
stained soil at the headwaters of the gully. Although my finds were not
tremendous, it still said a lot about this detector’s nugget finding abilities.
The White’s GMT proved itself capable of finding sub-gram and larger sized
nuggets in areas of heavy mineralization containing abundant hot rocks. Even
more amazing was the fact that one of the pieces was discovered in an area that
had obviously been worked by other detectorists.
The GMT is one of the finest gold machines I have ever used, however this
detector is probably not for everyone. It is a complex, high performance gold
machine that takes practice and dedication. If you purchase the unit be
realistic; don’t expect to master it your first trip out. It will find nuggets,
but only if you are willing to take the time to learn how to operate it
properly. With a suggested retail price of $799.95 and a transferable 2-year
parts and labor warranty, the GMT is by far one of the most affordable, high
quality detectors around. It isn’t the deepest penetrating detector on the
market, but then again it won’t drain your pocket book either. Its extreme
lightweight, automatic ground tracking capabilities, refined iron
discrimination, and reasonable price tag make the GMT worthy of serious
consideration when shopping for a new gold machine - not to mention it’s made
right here in the good ol’ USA!