Metal detecting for gold nuggets is one of the most difficult detecting tasks, and learning to run a VLF detector in highly mineralized ground will challenge even the best detectorists. There is more to this subject then can be covered in a brief article but I will try and offer some tips to get people started with the Minelab EQUINOX for gold nugget detecting.
The EQUINOX 800 has two modes that are not available on the EQUINOX 600 – Gold Mode 1 and Gold Mode 2. The two Gold Modes are identical except for the default settings. Gold Mode 1 is set up with a default Recovery Speed of 6 and Gold Mode 2 is set up with a default Recovery Speed of 4.
These modes employ a boosted audio that increases both in volume and pitch as a target is detected. This in turn accentuates the signal on tiny gold nuggets. The threshold is also different than the “reference threshold” employed in the other modes and is more responsive to ground changes, providing important audio feedback about changing ground conditions.
The Gold Modes are similar to the threshold based all metal modes available on most VLF nugget detectors with a major difference. A target id number is displayed for strong targets and each target id number can be independently set to accept or reject. In this regard the Gold Modes are a hybrid mode with more discrimination capability than is available in normal threshold based all metal modes.
Normal VLF nugget detecting relies on the operator having their ear very tuned into the threshold sound of the detector. Slight variations in the threshold tone can indicate potential targets. The threshold tone is also very sensitive to changes in the ground mineralization. This includes the so-called “hot rocks” which have mineralization different than the ground they reside in which makes the detector react to them as targets.
The challenge is to get the detector to operate with a relatively smooth threshold as the coil is swept over the ground so that desired targets will stand out. If hot rocks are signaling with every sweep of the coil, then progress will be extremely slow if not impossible. Tuning a VLF detector to hunt nuggets starts with the theoretical most powerful settings, and then reduces those settings until the detector becomes stable. Every setting is a trade off, because making a detector more sensitive to gold also makes the detector more sensitive to mineralized ground and hot rocks. The key settings for the EQUINOX 800 in Gold Mode are:
- Frequency. Multi frequency is the default and the most powerful frequency setting, with 40 kHz and 20 kHz single frequency options. Multi is the most sensitive to gold, but also reacts the most to bad ground and hot rocks. The goal is to get the EQUINOX to run well in Multi but if bad ground or hot rocks make that impossible, going first to 40 kHz and then to 20 kHz will make the EQUINOX progressively less reactive to the ground and the hot rocks.
- Ground Balance. The default is ground tracking on. Tracking attempts to keep up with and smooth out the variations in the ground. In doing so it has a filtering effect and can possibly tune out the slight audio variations that come not just from the ground but from very small or very deep gold. Tracking off is therefore the most sensitive setting, with adjustments made via the Auto (pump) method or manually.
- Sensitivity. The range is 1 – 25 with a default of 20. Increasing sensitivity increases the audio response from all targets, plus the responses from things like electrical interference. Most importantly, too much sensitivity makes the ground itself into one giant target, and so if the detector refuses to ground balance properly then reducing sensitivity until a proper ground balance can be obtained is critical. The default of 20 can easily be too high for the worst ground, and settings in the mid to low teens may be necessary.
- Recovery Speed. The range on the EQUINOX 800 is from 1 – 8. The defaults are 6 for Gold Mode 1 and 4 for Gold Mode 2. Recovery speed as regards nugget detecting can be viewed as a smoothing filter. Higher settings act to smooth out audio responses from the ground and hot rocks. Lower settings enhance audio responses from weak gold signals, but also make hot rocks and bad ground stand out more. False signals from the coil bumping a rock also increase at lower settings. In general the EQUINOX will be easier to handle at higher Recovery Speed settings, with more careful coil control required at lower settings.
- Iron Bias. The range is 0 – 9 with a default of 6 in both Gold Modes. Lower settings reduce the chance of gold being identified as ferrous, while higher settings reduce the chance of ferrous items being misidentified as gold.
- Accept/Reject. The default is -9 through 0 rejected, 1 through 40 accepted. The discrimination range on the EQUINOX runs all the way into the ground signal, with ground signals in highly mineralized ground normally coming in at -9, -8, and possibly -7 though it depends strictly on the ground itself. Hot rocks can read almost anywhere, even in the positive number range in the mid-teens or elsewhere. Electrical interference is also likely to exhibit in the low negative number range. Any offending numbers including trash targets can be blocked directly, but the more numbers that are blocked or rejected come at a cost of slightly less signal strength on desired targets.
- Threshold. The range is 1 – 25 with a default of 12. This is normally set to be just loud enough to hear, but no more. Just a barely discernible tone. However, the threshold can also act as a backend filter. Once all other tuning has been completed, the threshold can be set lower until it is silent, or set higher than normal. Running silent can suppress small variations in the ground signal but also the weakest gold signals. Running the threshold higher than normal can smooth out weak variations, again with a subsequent loss on the faintest gold signals.
My starting point (initial settings) for either Gold Mode are:
Ground Balance: Auto (pump method) with manual tweaking
Recovery Speed: 6
Iron Bias: 0
Accept/Reject: -9 through 40 accepted (either through the settings or by hitting the “Horseshoe button”)
The main thing I am going to try and do is operate the EQUINOX in Gold Mode without blocking out or rejecting any target id numbers. The goal is to find settings that reduce and smooth out ground responses while reducing the signal from gold as little as possible. These two things fight each other and there are no perfect settings, but simply the best compromise possible. For some people that will mean making the machine very stable, while others may prefer hotter settings that require more audio interpretation from the operator.
The first step is to find an area clear of trash, and walk a bit waving the coil over the ground. Chances are you will get lots of ground noise. Go into the settings and adjust the ground balance. This normally means pumping the coil over the ground while holding the accept/reject button (see the manual) until the ground response evens out. If the ground is highly variable with mixed hot rocks, waving the coil from side to side may work better than pumping the coil.
With any luck the machine will settle right down. However, in bad ground it will not, and the solution normally will be to lower the sensitivity setting. Basically this just takes some experimentation, lowering the sensitivity and adjusting the ground balance until the detector reacts very little or not at all to being waved over the ground. If you can get the EQUINOX set to where no target id numbers are popping up at all as the coil passes over the ground but where you can still hear faint variations in the ground, you are there.
Then it is simply a matter of going detecting, and digging every target that stands out above the faint ground variations present in the threshold tone. Gold can read anywhere from negative numbers all the way up into the 30’s so typical nugget detecting involves digging everything. However, most nuggets weighing under 1/10th gram will give a target id number of 1 or 2, nuggets under a gram in the single digits, and several gram nuggets reading in the teens and higher. The smallest or the deepest large nuggets will produce no target id number at all, just a variation in the threshold.
In real bad ground you may have to not only reduce the sensitivity setting, but possibly even increase the recovery speed setting to 7 or 8. In ground that refuses to behave, switching to first 40 kHz and then 20 kHz will progressively detune the EQUINOX , making it easier to get a stable ground balance. Engaging ground tracking may also help smooth out the worst ground – you have to experiment.
In severe ground all this may not work, with ground signals still coming in around the low negative numbers and possibly higher. Some hot rocks may read as positive numbers. This is where the EQUINOX can go to the next level. Go into the settings and reject or “notch out” the worst offending target id numbers. This will usually be -9, -8, and -7 but may include even higher numbers, including positive numbers.
Block as few numbers as you can. Simply rejecting the bottom three negative numbers will usually settle the machine down a lot, especially if there is any residual electrical interference being encountered. Rejecting target id numbers does come at a cost in reduced signal strength on desired targets, but you may find now that the sensitivity level can be increased from one to several points, reclaiming that lost sensitivity.
In theory if you can get the EQUINOX running stable with no target id numbers rejected you have the ideal situation. However, EQUINOX allowing some offending signals to be rejected with an attendant increase in the sensitivity setting may be the better way to go. It just depends on the situation.
So far we have been trying to deal with bad ground by using various detuning methods. In low mineral ground you can go the other direction. If the detector ground balances immediately with a sensitivity setting of 20, then try higher settings. You can also try reducing the recovery speed setting from 6 to 5 or 4 or even lower. Each reduction of the recovery speed setting is fairly dramatic and you will find it suddenly very hard to get and hold a decent ground balance if you go too low with the setting. In mild ground however it can add substantially to the signal strength of the weakest targets.
Finally, for the worst ground and for EQUINOX 600 owners we have other alternatives. There is no reason at all why the other modes cannot be used to nugget hunt. Park 2 and Field 2 are both very hot on small targets and offer the ability to use tones while nugget hunting. Prospectors who encounter salt lakes/salt flat situations would do well to remember the Beach modes as possible last ditch settings.
Either Park 2 or Field 2 can make for very good nugget hunting modes. I prefer to use Park 2 as a base because by default Field 2 blocks out or rejects the key target id numbers 1 and 2. Small gold nuggets read there, so using Park 2 makes sure somebody will not accidently reject nuggets in that range. You can use Field 2, but beware those blocked numbers and adjust accordingly.
For Park Mode 2:
Ground Balance: Auto (Ground pump method with manual tweaking)
Sensitivity: 16 – 25
Recovery Speed: 4 - 6 (default is 6)
Iron Bias: 0
Accept/Reject: Everything accepted, rely on tones (alternative reject -9, -8, and -7 if too much ground feedback)
I have suggested accepting everything, and then using the two tone mode to hunt by ear. If trash is minimal then set the tone break lower than normal, so that 0 and several negative numbers read as non-ferrous. This way you can have ground signals reading as low tones (and possibly at a lower volume) and signals from gold as higher tones. Again, this works well with both EQUINOX models.
To sum up, I suggest trying to use the EQUINOX 800 in the Gold Modes with no target id numbers rejected. Tune up just like any normal nugget hunting detector, and dig all decent audio signals. Some nuggets may deliver a negative number response or no number at all. A secondary method for more difficult ground is to reject or block out offending ground and hot rock signals. And a third method for both EQUINOX 800 and 600 owners involves using the Park 2 mode as a nugget hunting mode.
That should give people plenty to experiment with. Nugget detecting can be very challenging, but learning to do so means you will learn how to wring every bit of performance possible out of your EQUINOX , and that can benefit you in other areas of detecting as well. Good luck!
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