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Gold Placer Probe
By Reginald Sniff
From page 6 of the February, 1991 issue of Lost Treasure
Copyright © 1991 Lost Treasure, Inc. all rights reserved
From page 6 of the February, 1991 issue of Lost Treasure
Copyright © 1991 Lost Treasure, Inc. all rights reserved
The MD 8 Gold Placer Probe, manufactured by Falcon Prospecting and distributed by Down Under Treasures, is unlike most other metal detectors. The MD 8 Gold Placer Probe is designed for one primary purpose-searching for gold nuggets. One of the features that makes this detector unique is the standard sized searchcoil, about one inch in diameter. Because of the coil size, this instrument lends itself well to searching in very tight places such as in crevices and between boulders, typical hiding places of gold nuggets.
The depth capabilities of the NID 8 are quite limited (somewhere around three inches maximum) due to the small coil size. Although it's limited in depth, the MD 8 is very sensitive to extremely small-sized pieces of gold.
The MD 8 Gold Placer Probe consists of lightweight, compact control housing, the small search probe equipped with a five-foot cable, and a two-part extension handle. When disassembled, the complete system is very compact. Overall, the unit is extremely lightweight and easy to assemble. The two nine-volt transistor batteries required for operation make up a fair portion of the unit's weight.
The sensing of targets is done two ways. The first is by a visual target alert (lighting of a red LED), and the second is audibly with a small piezoelectric buzzer. A selector switch is provided that allows the operator the option of turning off the audio response. The audio signal is a high pitch squeal that is either fully on or off in most cases.
Not following my own recommendations, I began by testing the detector's ability to sense various sizes of gold without reading the owner's manual. As a result, I quickly found out that I didn't know the functions of the three primary controls. Although these controls have similar names as those found on a typical VLF, they are not quite the same.
My next step should have been my first-read the manual. The first couple of pages are a good introduction of the purpose of this instrument and a brief, but very good, explanation of metals and minerals and a detector's ability to detect them. Summarizing their explanation, the reference to minerals refers to the iron oxides found in the soil. Any reference to metals includes any man-made metal as well as natural gold and silver nuggets.
MD 8 CONTROLS
The MD 8 has three main controls and a toggle switch that determine the detector's operations. A brief explanation of the controls and their functions are listed below:
Sensitivity Control - This control has two functions. It turns the detector on and sets the sensitivity in the static or no-motion mode. In the motion mode this control is normally set at or near minimum.
Automatic Ground Balance Control - This control is really the motion mode selection and sensitivity control for that mode. If the motion mode is to be the primary mode of operations, the above mentioned sensitivity control is set at minimum, and the Auto Ground Balance Control is advanced to the audio threshold point.
Threshold Control - This control can be used with either mode of operation to finely tune the sensitivity of the detector. When properly set, the audio signal is silent but right at the threshold of turning on.
Audio/Silent Switch - This switch either enables or disables the audio. When disabled, the operator can use the red LED to signal a target.
The initial setup and use of the controls seemed confusing at first, but with practice they became quite logical.
MODES OF OPERATION
The MD 8 Gold Placer Probe has two modes of operation - a static or non-motion mode, and a motion mode. In the static mode, the detector is not ground canceling and, therefore, any mineralization content of the soil can affect the detector's depth capabilities as well as cause false signals.
In this mode, the detector will react to the ground minerals similar to the old TR detectors. If the detector is adjusted to the threshold point with the searchcoil on the ground, raising the coil quite possibly will cause the detector to emit a false response.
In the static mode, the detector will only respond to metallic objects including gold nuggets (some iron oxides can indicate as metallic objects). This mode of operations is primarily used in low-mineralized areas. Heavy concentrations of black sand greatly diminish the effectiveness of this mode.
The motion mode is designed to be used in highly mineralized areas. In the motion mode, the detector will respond to both metallic objects and any significant changes in mineralization including hot rocks and pockets of black sand. Fortunately, it is easy to distinguish between most metallic and mineral targets. Sweeping an unknown target will yield a target response in the same physical location if the target is metallic, while a small hot rock or a pocket of black sand will give a response on either side of the target and null at the location of the target.
INITIAL SETUP AND USE
All three main controls should be counterclockwise at initial setup. Next, the operator needs to determine which mode of operations he or she prefers. If the no-motion of operations is selected, the sensitivity control is advanced until the LED lights and the audio responds, then the control is reduced to the point where they go off. Both the automatic ground-balance control and the threshold control should be at minimum at this time.
If the motion mode is selected, the detector is turned on with the sensitivity control but the control is left at minimum. The automatic ground-balance control is advanced until the LED lights and an audio response is heard. The control is then reduced until both the light and the audio go off. Remember, all controls - especially the sensitivity and the auto ground-balance control - should be at minimum at the start of the initial setup.
Once the detector is tuned, the threshold control can be adjusted to fine tune the instrument to the threshold point.
Initial testing was an air test using gold nuggets as targets. The initial setup of the MD 8 was as follows: the auto-ground balance at minimum; the sensitivity control advanced to the level where an audio output was heard and then backed off until the audio was quiet; then the threshold was advanced until a slight audio signal was heard. This setup is commonly called the static mode of operations.
With the above settings, the MD 8 detector would easily detect my smallest nugget, a 1.6-grain piece of gold to a distance of about a half inch. Testing with larger nuggets indicated that the maximum depth of detection was about three inches.
With the above settings, I also found out that the unit would also respond to my hand. Due to the detector's high sensitivity and small coil size, the response to the salts in my hand, plus something called a capacitive effect, was the reason the detector sensed my hand.
When using this detector to analyze targets, one should make sure that the detector isn't responding to the background (my hand in this case), as well as the primary target.
I reduced the threshold control until the detector didn't respond to any part of my hand and repeated the test. Surprisingly, little overall depth loss was noticed.
Additional air testing indicated the Falcon MD 8 could be used to test rocks that have the appearance of gold. Iron pyrite crystals (fools gold) and other minerals, such as mica (commonly suspected as gold by novice gold seekers) gave no signal at all, making the instrument a quick and easy ore-testing device.
Generally, mineralized rocks will cause the MD 8 to go quiet instead of give an audio signal in the static mode. By adjusting the detector for a slight audio output and moving the suspected specimen towards the search head, I verified this response.
The Falcon MD 8 did respond positively to certain rocks containing iron oxides, a condition common to VLF and other detectors. Some poorly formed iron pyrite and other iron oxides can indicate positive or metallic.
Field testing in several of the better-known gold locations in the Colorado Mountains didn't produce any gold. This wasn't a fault of the detector, but rather a combination of problems including the weather and something called luck.
I was able to find plenty of pieces of iron trash, including the ever-present shoe tacks that plague the serious nugget hunter. Pieces of lead were also common finds.
In creek beds where the rocks were fairly large, the little coil of the MD 8 made searching the creek bottom much easier. The searchcoil could easily be maneuvered in locations where a conventional detector couldn't reach. In the case of creek beds containing medium-sized rocks, the little coil would easily slide between most of them, making it possible to search much closer to the creek bottom.
If a small nugget had been trapped between these rocks, it would have been out of typical range of even the most sensitive VLF gold-hunting detector, even equipped with a three-inch coil. The rocks inhibited any close inspection of the creek bottom.
To substantiate this fact, I used small pieces of lead to simulate a gold nugget. By dropping the pieces of lead between rocks and searching with both a typical gold-hunting VLF detector and the MD 8, 1 found that small pieces of lead would easily be missed using the VLF gold-hunting detector, but were detected by the MD 8.
The rocks inhibited the searchcoil of the VLF gold detector from getting close enough to the lead targets for detection. The MD 8 with its little coil could manipulate between the rocks allowing the detection of most of the lead targets. Because the Falcon MD 8 was ground sensitive, it took some time to fine tune the instrument to minimize false ground signals and still have respectable sensitivity.
Although the owner's manual recommends the use of the motion mode in extremely mineralized conditions, I found this mode very difficult to use in the locations I was hunting, because of the high incidence and different types of hot rocks. In the motion mode, the MD 8 would respond too many of the rocks. In the case of the small rocks, this response would normally be on either side of the rock as outlined *in the owner's manual. On large hot rocks the detector would respond even before the rock was passed, leaving the impression that the rock may contain some positive signal causing metal.
One weakness I found when using the Gold Placer Probe in the field was the audio level. The out put of the audio transducer is a high-pitch squeal that is sufficient under quiet conditions. But if the wind was blowing and the transducer was not pointing towards me, I found it difficult to hear. Unfortunately, there is no provision for earphones.
The Falcon MD 8 Placer Gold Probe has the capabilities of being a positive asset to the serious gold hunter. The small coil allows this detector to search those tight, hard-to-reach areas which cannot be searched with typical VLF detectors.
In severely mineralized areas, some sensitivity will be lost but, with practice, many of the problems caused by the black sand and the high number of hot rocks can be minimized.
This instrument responds differently than most typical VLF metal detectors. Therefore, regardless of the soil conditions, practice will be required to fully master the capabilities of this instrument, even for the experienced operator.
Because of its reasonably low price of $159, this detector could easily pay for itself by sensing one respectable gold nugget.
For more information, write the factory at Falcon Prospecting, P.O. Box 1672, Montrose, CO 81402, and tell them that you read about it in Lost Treasure.