MINELAB GP EXTREME
By Chris Gholson
From page 41 of the November issue of Lost Treasure magazine.
Copyright © 2001, 2001 Lost Treasure, Inc.
There’s no gold left in those old nugget patches! The surface gold was cleaned out long ago by VLFs in the 1980s, and the deeper ones were plucked out by the SDs in the mid ‘90s. Say that to the new owners of a GP extreme and they’ll just rattle their pokes at you and smile — or perhaps the smarter ones won’t.
Minelab’s newest addition, the GP extreme, comes in its own heavy-duty, plastic carrying case that has an inner skin molded to the shape of the detector’s components. It is supplied with both 11inch and 18 inch extreme coils, metallic blue control box, armrest, shafts, handle assembly, 6 volt/10 AH battery, curly power cable, 110 volt charger, 12 volt vehicle charger, 600 ohm Telex headphones, battery pack and instruction manual. While its overall appearance is ergonomically similar to the SDs, you can rest assured that this is not merely a 2200d wrapped up in a fancy new package.
In fact, it is the first gold detector to utilize Dual Voltage Technology (DVT). This new technology was developed based on the existing Bi-Polar technology used in their military mine detectors. DVT, refers to changes in voltage used to create the electro-magnetic field, transmitted by the coil into the ground. It has nothing to do with the power supply. The magnetic fields, which are transmitted by a metal detector, can ‘magnetically-saturate’ the ground, especially if the coil is held close to the surface. Minelab discovered that by applying two different voltages to the transmit coil they were able to cancel out many of the signals caused by this magnetic saturation. Thereby improving the detector’s sensitivity, depth and its ability to balance out mineralization.
Below is a very brief description of some of the more important features found on the new GP extreme. The Rx setting changes the characteristics of the new ‘extreme’ coils by altering their transmit and receive fields, giving them the ability to change their configuration pattern with the simple flip of a switch. When the Rx switch is set in the Normal position the coil will function as a conventional double D.
If the Rx switch is set in the E (Enhance) position the coil will essentially function as a ‘pseudo’ monoloop. By this I mean, it will exhibit some of the characteristics of a traditional monoloop coil. When operated in this mode the GP’s detection depth is still good, but sensitivity on the right hand side of the coil is virtually non-existent. The Cancel feature changes the electro-magnetic field of the coil so that it is relatively stable in areas of electrical interference. This feature is especially useful when hunting near power lines, electrical fences or under poor atmospheric conditions.
The Boost feature allows the operator to select the type of processing and filtering used while hunting, thereby enhancing the signals produced by different types of targets. Shallow amplifies signals from small, faint targets near the surface. N (Normal) can be used in most any soil conditions. This setting does not boost any signals, regardless of size or depth. Deep may be used when searching for large nuggets in highly mineralized ground at depth.
The Soil feature optimizes the detector for different soil conditions and targets by changing the signal processing. This switch offers three different settings: Normal, Sensitive and Salt. The Normal (N) setting may be used in all types of ground, ranging from lightly to highly mineralized soils. This is my preferred setting for the Soil switch. The Sensitive setting is useful when searching for tiny, shallow gold nuggets. The Salt setting enables the GP to search in areas containing large amounts of conductive salts. Although I have not had an opportunity to test the GP on the salt, I have talked with several professional Australian hunters who are impressed with its capabilities. My advice is this; unless you are hunting the dry salt lakes of the outback avoid using this setting, as it reduces sensitivity towards small nuggets. You will find that the American goldfields are much less mineralized and using this setting is largely unnecessary.
Like its predecessor, the SD 2200d, the GP extreme is also equipped with automatic ground balancing (AGB). The Balance switch, which controls the ground balance function, is located on the front panel. Unlike manual ground balancing detectors, the GP, when placed in the Tracking mode will continually adjust to minimize the effects of ground mineralization. It also has the ability to be dialed or ‘tuned’ in for a particular piece of ground when placed in the Fixed position. Strangely enough, it has come to my attention that the AGB feature often works too well. Tiny or deeply buried gold nuggets are often difficult to hear because of the feeble signal they emit. Usually these signals are in the form of a small dip or rise in the threshold level, and are often so weak they’re nearly impossible to distinguish from the background noise.
Unfortunately the GP, because of its improved canceling ability, may interpret these subtle responses as being nothing more than ground noise and attempt to balance them out. This problem can be remedied by leaving the machine in the Fixed position after it has been properly balanced. Based on my own findings and the comments of others, the general consensus towards the Balance feature is the following. If the ground is quiet to medium mineralized there is a sensitivity advantage if the Fixed position is used for searching. Not to mention, the machine will not accidentally balance out those faint murmurs. If the ground is variably mineralized and noisy, then Tracking is the preferred position.
The GP is outfitted with an Iron Discriminate feature, which allows the user to select between a Disc or an All Metal mode. In the All Metal mode, the detector will respond to all types of metallic targets, including ferrous (iron) items. In the Disc mode, the detector will cause the threshold to be ‘blanked’ or silenced when the coil is passed over a fairly large ferrous target.
Trying to decide where to test the GP was a tough decision. I knew I would have to choose the test site very carefully, as it would be crucial in determining the GP’s performance. After consulting with my father Steve, we finally decided on what we thought was our best ‘hunted out’ spot. Our destination was a nugget patch located in the desert southwest of Quartzsite, Ariz. This was not an area that had been casually hunted in the past by amateur detectorists, oh no! This patch had been tediously gridded, scrapped and pounded to death by some of the most successful hunters in Arizona. That is why we knew it was the ideal place to test the GP.
It was early morning when my father and I finally reached the patch. We decided that I would start off in the immediate patch, while he focused his efforts on the surrounding hillsides. Since the overburden was rather deep in some areas, I decided that the stock 18 inch coil would be the best choice for maximum ground coverage and depth penetration.
I slowly worked my way across the patch without hitting a single target until I reached a promising bit of red stained soil. As I passed the ‘trashcan lid’ sized coil above it I picked up a faint disturbance. It wasn’t exactly a signal, but the variation in the threshold was enough to get my attention. By the time the hole hit ten inches the target was really screaming. Finally it was out of the ground and I began running handfuls of dirt across the coil. When the detector let out a high-pitched squeal I knew it was in my hand. Slowly I peeled back my fingers and there in my palm lay a chunky 4.3 gram nugget!
A few feet away I encountered a hefty boulder partially submerged within the soil. As I walked past I swept the coil across its surface. The rock was rather large and cumbersome, but once out of the way the signal got considerably louder. After digging nearly six inches I finally discovered what was setting off the detector. It was nothing more than a fragment of rusted iron, probably part of an old miner’s pick. Even though it had not been gold, I was utterly amazed that the GP had been able to pick it up so deeply beneath the rock.
Recovering the next target was a difficult task, as it was situated amongst an old-timers drywash tailings pile. The signal was a little stronger than the others, but not by much. After rummaging through the loosely classified material for nearly 15 minutes I finally found what I was looking for. Eureka! Another nugget had been found, this time shaped like a teardrop. I managed to find a few more bits of rubbish in the diggings, but no more gold.
By now it was late afternoon, so I decided to check how my father was getting along with his GP. “How’d you do?” I asked. “Not too bad,” he replied with a smile. He riffled through his pockets and produced a leather pouch, which he immediately dumped out. Three miniature lumps of yellow metal rolled out into my waiting hand. He informed me that all three nuggets were found on the outskirts of the patch with the stock 11 inch coil at an average depth of 5-6 inches.
Much to our surprise the old patch had given up another 5 nuggets, for a total combined weight of 7.2 grams. Truthfully, I didn’t have much hope of finding gold in this particular location, considering my father and I had been over it no less than 20 times — and there’s no telling how many other hunters had been over it. These results lead me to believe that either the GP was indeed outperforming the earlier VLFs and SDs, or we were extremely lucky.
After finding a fair amount of gold in a well-hunted site, the GP extreme has proven itself capable of finding smaller gold than the previous SD 2200d and punching deeper than any other detector on the market. Its new features, ease of operation and uncanny ability to knock out ground mineralization make the GP an extremely tough machine to beat.
While I would highly recommend this machine to anyone, I don’t want this to come across as a sales pitch. All I can offer you is my own honest opinion. The cost for instance, is one drawback that must be taken into consideration. The GP carries a suggested retail price of $3,495 making it the single most expensive gold detector on the market. The increased weight of the coils and general bulkiness of the unit is something a potential buyer should also keep in mind. With that out of the way, let me close this article with one final suggestion.
If you only get the chance to go out detecting a few times a year or are unsure about your interests in prospecting, I suggest you save your money. The GP is a big investment, so there’s no sense shelling out that kind of cash if it is going to sit at home collecting dust. On the other hand, if you are a serious hunter with a passion for detecting or are thinking about becoming heavily involved with prospecting, the GP is probably the perfect machine for you. It is equipped with the very latest in detector technology and will give you that extra edge where it counts most — on the goldfields!
For additional information on the new GP extreme or other Minelab products, contact the factory at Minelab USA Inc., 2700 E. Patrick Lane, Suite 11, Las Vegas, NV 89120; 888-517-2066 / 702-891-8809, or visit their website at minelab.com