GPX 17 Coil Commentary

[Northeast]

6 hours ago, PhaseTech said:

The 14" DD in Normal and Salt is the best combo. 

Very interesting.  Thanks Nenad  👍

[Steve Herschbach]

On 8/18/2021 at 5:06 PM, dig4gold said:

Are you not specifically referring to higher mineralised grounds. What about very mild ground & DD verse Mono. You still think the DD has it over a mono? Cheers 🙂 

 

I prefer the 11” mono over the 14” DD in low mineral ground, but advise doing your own comparisons. Ground varies and I’d never advise taking advice over actual tests you do yourself.  In high magnetite locations, the DD coil will easily detect targets that the 11” mono misses entirely, especially larger items at depth. So there is a point where the 14” DD does pull ahead of the 11” mono, but I do not know where that line occurs. The only way to know for sure is do some test target comparisons in the ground in question. However, for more depth over the 11” mono in mild ground, the 17” mono is probably your best solution.

The 17” mono versus 14” DD in extreme ground is interesting. The DD is easier to handle as far as ground response, and my general preference at this point in extreme ground, but I can get the 17” to work. It benefits from being lifted off the ground a bit, and the tones may reverse compared to the DD. In either case sensitivity may need to go to manual 5 or lower, or Auto. When I say extreme ground, I mean it, like 50% magnetite content or higher. Think decomposed serpentine ground, or beaches. The kind of stuff you drop a magnet, and when you pick it up you have a golf ball of magnetite. Not sure how this translates as far as maghemite in Oz. In the U.S. our culprit is usually magnetite, in Oz it’s more often maghemite causing issues. As usual any commentary I make is more U.S. specific, though may offer clues for the Oz users. The following helps shed light on this basic difference between the U.S. and Australia.

From Bruce Candy at https://www.detectorprospector.com/files/file/52-metal-detector-basics-and-theory/:

"In geologically new soils, the degree of mineralisation is usually weak, except for some volcanic soils. These relatively new soils are commonly found in North America and Europe (from glacier scrapings during the last ice age and mountain erosion etc). In contrast, surface soils which have remained surface soils for a long time often have high mineralisation, because the action of water, over a long period, causes iron compounds to migrate to the surface. For example, Australia has old soils, having had no glaciers recently or significant mountains to be eroded. Some volcanic rocks or sands, known as black sands, may be highly mineralised and are found, for example, in a few USA mainland and Hawaii areas. These black sands (or rocks) are made of mostly magnetite, an iron oxide called ferrite. These typically produce almost entirely X signals, and almost no R. They are heavy, that is they have a high density, and can be identified because they are strongly attracted to a magnet. Small roundish magnetite/maghemite pebbles (a few mm in diameter) are also attracted to a magnet. These, for example, may be found in many Australian goldfields, but do produce significant R signals. Thus, USA goldfields are typically different from Australian goldfields:

• The USA soils are mostly mildly mineralised but in some areas may contain either nearly pure magnetite black sands or rocks, which  are problematic for metal detectors as they have very high X components (strongly attracted to magnets).
• Australian goldfields have highly mineralised soils, but very few black sands or rocks that contain nearly pure X magnetite. The magnetic materials are in the forms of magnetite-rich small pebbles and rock coatings, clays and general “sandy” soils. These all contain magnetic materials that produce high levels of X signals as well as R. The ratio of X and R is random, and the R component arises from extremely small magnetic particles called superparamagnetic materials, which are discussed below."

More details on mineralization:

https://www.detectorprospector.com/forums/topic/1599-gb-numbers-mineralization/?do=findComment&comment=19002

[Jonathan Porter]

Steve as always a very informative post from you and interesting insights into the GPX6000 in your neck of the woods. The 6000 behaviourally is quite different when operated in Normal compared to Difficult so different in fact you could consider it to be almost 2 detectors in one. 

As an example I was working some benign ground recently but had just come from some adjacent variable soils so was still in Difficult mode (using the 17” mono). The overall soils in the area where derivative of granite contacts so I was using the Auto+ mode which really ramps up the sensitivity if the soils will allow (much higher than full manual mode). I was noticing the detector was becoming increasingly jittery the further I moved away from the red stained ground into the paler soils which got me thinking as I was expecting the reverse considering Difficult is so good at ironing out mineralisation, so out of curiosity I switched to Normal, when I did that the whole detector just went silent and smooth. 

The only thing I can put it down to is the inbuilt gain of the difficult timings is much more aggressive than Normal to lift the left over target signals after the ground has been cancelled out, as such combined with the increase in sensitivity in the quieter soils from using the Auto+ the sensitivity of the detector had elevated to the point where the noise floor of the machine was down to the electronics level so Sferics, EMI and some electronics noise was getting into the signal train (all supposition on my part). 

The other thing I have noticed is the channel flipping is much more evident in Normal mode, so you have to be careful on those dipping low toners as they can herald a really nice piece at depth. I have not focused much on chasing deep signals with the 6000 as I have the GPZ7000 for that, but with care and attention there is a huge amount of subtle information with this detector which will improve with time spent in the field.

JP

[Steve Herschbach]

So far in our soils I’ve had a hard time finding much difference between Normal and Difficult. I suspect again it is the differences Bruce talks about that accounts for these observational differences between the U.S. and Australia. Very much like the big ferrite ring debates - our soils here are loaded with ferrite, and I never saw the ring making a difference, though I used it anyway. It was something you really made a point of how important it was, but frankly most people here thought just the opposite.

The same thing happens constantly here with coin hunting in the low mineral areas, versus high magnetite zones. People wonder why their detector gets half the depth of internet reports. They blame the detector, when they should be blaming the soil. Ground condition variations affect everything, and make half the debates on what works best kind of stupid at times. I can only vouch for what works best for me on my ground and my targets, nothing more. It’s why air tests make me crazy for anything more than the most basic information. It’s like racing cars by jacking them up off the ground with the tires off. All that matters is when the rubber meets the road, or the coil meets the soil.

The difference between the DD coil and the 11” mono is night and day in favor of the DD in high magnetite areas, rather shockingly so. The difference between no signal and a good signal. Anyone hunting west coast beaches and California serpentine soils should take note of this. Minelab made the right choice having it as the alternate coil for the western U.S. in particular.

[Jonathan Porter]

14 minutes ago, Steve Herschbach said:

Very much like the big ferrite ring debates - our soils here are loaded with ferrite, and I never saw the ring making a difference, though I used it anyway. It was something you really made a point of how important it was, but frankly most people here thought just the opposite.

The key thing is to NOT have a signal on the Ferrite ring at all, if there’s no signal then all is good, however from the factory more often than not the Ferrite balance is way out so if you try to detect that way then the detector will not be optimal for sure. If you use Semi-Auto and never use Quick-Trak to achieve a calibration then the ferrite balance will be locked to whatever it was set to and can never change. If the ground has heaps of X signal and the salt/conductive signals and saturation signals are minimal then the Auto mode is perfectly fine. 

They KEY is to check and not have any signal on your ferrite ring then go detecting. 😊 Preferably use Semi-Auto to cut down on the risk of some salt signal messing things up, but if you do use Semi-Auto then it is your responsibility to make sure the Ferrite calibration is correct. I barely need to change mine from day to day especially in the warmer months.

Back on topic with the GPX6000, the Normal timings are a combination of Normal and Difficult, the small target sensitivity comes from the Difficult timing, with the 6000 both timings are running at all times this is why you can go from one timing to the other and not need to ground balance (if you perform an Quick-Trak in Difficult then Normal will be balanced as well). If you use Difficult you hear Difficult timings information only and I would say with Auto+ in quiet ground the lack of ground signal highlights all the electronic and Sferic noises (due to the timings having higher gains than Normal) whereas even in very quiet soils Normal always has some level of ground signal which masks the background electronic noises.

Good discussion Steve 😃 

JP

 

[Gold Catcher]

So, I went to one of my favorite spots in Northern NV that I have pounded over and over again over the years with all the detectors I own. I went there not really expecting to get anything, but rather to test the 17 inch and the 14 DD in an area that is very familiar to me. The area is plagued by high salt content and yesterday there was also a strong howling wind that made it almost impossible to detect (not to speak of the dense smoke from the CA wildfires that was lingering in the air and that covered the sun at all times). I could only detect by walking in the direction of the wind, if I would walk sideways or against the wind I could not hear anything, even at full headset volume. I first tried the 17 which I managed to stabilize at 4 clicks/difficult. At times, I was even able to go to Auto/difficult or Auto/normal (always with threshold), but this was only possible in between wind gusts. Let me tell you, this coil is incredible sensitive to shallow targets despite it's large size, almost as sensitive as the 11 inch. I managed to pick up a small flake about 2 inch down that was almost as noticeable as with the 11 inch. Pinpointing is a bit tricky due to the coil size, but totally doable since it is a mono, it just takes a bit practice (highest sensitivity where the ring is). The large coil size may initially suggest that depth is intended, but my first impression is that it rather is an extension of the 11 inch capabilities, just covering a larger surface area. This is great because it allows to sweep open fields with a big coil and covering more ground without loosing sensitivity for shallow fast timing gold. I have only used it once and I don't know about it's capabilities for deeper targets, but I will update once I am more familiar with it. One thing I noticed is that it is is rather bump sensitive. You can use it without bungee for some time, but I opted to use my hipstick/guide arm pretty soon, also for better coil control. I have tried the 14DD only for an hour or so, but my very first impression is that it is an absolute game changer for high salty ground. I ran it in salt cancel mode/4 clicks/normal and probably had the most stable configuration I have ever had in that region. The sensitivity is still remarkably good, with pinpointing possible by using the left side of coil (left D) with good sensitivity around the entire D-edge. For neither coil of the 6000 I noticed  a huge difference between normal and difficult timings, but as Steve mentioned this could have to do with the soil here. But for sure changing from normal to difficult is much more impactful when using the 7000. Overall, I continue to be super impressed with the 6000. All three coil options are extremely useful to have and compliment each other. The 6000 is an amazing machine that I recommend to everyone! As a faithful and loyal 7000 owner I carry my GPZ around wherever I go. But I can't help but notice that I haven't used it much lately....

 

 

 

[WesD]

I  found the 6000 is like all the old Minelabs wrapped in one package.  Basically the ultimate prospecting detector, like swinging a vlf, 2300, old gpx, and gpz, all at the same time.  For new patches of gold this is awesome! For old patches of gold, if you've already gone over them with ALL of the above detectors, the results probably wont be that epic. A few nuggs will be found, but it doesnt seem to be revealing some new dimension of dirt that the combined effort of the old detectors missed. 

[Steve Herschbach]

On 8/22/2021 at 9:31 AM, WesD said:

I  found the 6000 is like all the old Minelabs wrapped in one package.  Basically the ultimate prospecting detector, like swinging a vlf, 2300, old gpx, and gpz, all at the same time.  For new patches of gold this is awesome! For old patches of gold, if you've already gone over them with ALL of the above detectors, the results probably wont be that epic. A few nuggs will be found, but it doesnt seem to be revealing some new dimension of dirt that the combined effort of the old detectors missed. 

That’s about the best summary I’ve seen. 👍🏻 In general the 6000 is all I need now, but a good VLF still has a place in really trashy areas.

[Jonathan Porter]

There is no doubt the 7000 has the extra grunt required to punch in beyond the 6000’s capabilities, a good example is in washes where there are large rocks in the bed of the creek bottoms. In the GP and GPX days I worked many hundreds of kilometres of creek beds in the northern parts of Australia and would often pluck a decent widow nugget in amongst the boulders especially up in the Kimberley. Those nuggets would be randomly distributed along the creek lines and it often left me wondering what else was in there being hidden by the larger chunks of diorite and slates liberally scattered about. 

Unfortunately I have not been able to return to all these locations with the GPZ7000 but the few I did return to were an eye opener with undiscovered mini patches often associated with those original isolated nugget finds. This is just one example of where the ZVT tech provides a definite advantage but its not everywhere, the ground needs to be conducive to the tech and in a lot of places the depth is just not there so the earlier sampling of GeoSense and overall lightness of weight and ease of use of the GPX6000 is far more beneficial. I am actually afraid to use my GPX6000 too much because it is hard to go back to the weight and complexities associated with using the 7000 (harnessing up etc).

But I will say this though, it is nice to listen to a 7000 with its steady happy place audio compaired to the twitchy fast paced behaviour of the 6K 😊. 

JP

[Steve Herschbach]

Condor and I have been playing some more testing 17” mono and 14” DD in extreme magnetite conditions. Testing was on a U.S. nickel to standardize results, simulating a roughly 1/4 ounce nugget, or a men’s gold ring. Ground where no matter what the ground response cannot be entirely eliminated, but is controllable. Depth is hugely impacted, maybe expect about 12” on this type target in ground that is mostly magnetite by weight. It is hard to find ground like this, with west coast beaches being a likely location. This was at a Lake Tahoe beach. Most Tahoe beaches are not all that bad, but I am seeking out the worst of the worst. This stuff kills VLF depth, and even when they work, target id accuracy is a joke past a few inches

Both easily beat the 11” mono, no comparison. In general the 17” mono fares way better than I would expect under these conditions, and tends to be my first choice due to a cleaner signal response. The 14” DD however, under just the right circumstances, does have an edge over the 17” mono in getting a smoother ground balance. The only way I can see to decide which to use, would be to have both, and test in your specific ground. If I had to grab just one without knowing, I’d grab the 17” mono.

This is the first time I’ve seen a significant difference between normal and difficult in taming the ground. I’m also observing tonal flips based on settings, which may be a factor for some people. My biggest take away - DO NOT BE AFRAID TO LOWER THE SENSITIVITY!! The GPX 6000 retains a remarkable amount of depth even at sensitivity setting of 1. Yes, 1. The ground we tested only allowed for manual of 1 to maybe 4 at most, but I would not have any problem hunting at setting of one with the 17” on larger gold, say 2 grams or a pennyweight, or larger. Signal strength reduces, but the target is still there. So larger gold, extreme ground, 17” mono, do not be afraid to reduce sensitivity to get smooth ground action.