White's Electronics Gmt Goldmaster
By Chris Gholson
From Page 24
March, 2002 issue of Lost Treasure

Whites 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, Whites 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. Whites 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 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 background noise.
As most 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.
Whites 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. Whites 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 Whites 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 1000s 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 machines 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 GMTs 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 machines depth penetration was definitely handicapped, but this was necessary because of the severe ground mineralization.
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 dont 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 wasnt able to locate any more nuggets in the area I was more than pleased with GMTs performance and the days 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 detectors nugget finding abilities. The Whites 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; dont 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 isnt the deepest penetrating detector on the market, but then again it wont 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 its made right here in the good ol USA! For more information I would suggest obtaining a copy of the GMT instructional video or contact the factory at Whites Electronics, 1011 Pleasant Valley Road, Sweet Home, OR 97386; 800-547-6911 / 541-367-6121 or visit their website at

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