Questions On Garrett ATX - VLF Alternatives For Porous Gold

[Glenn in CO]

12 hours ago, Steve Herschbach said:

Again, I would not expect the alternatives to match a hot VLF in absolute terms. And it is shades of gray, not black and white, since every specimen is unique. The basic question being presented here is what alternative to a hot VLF has the best chance of finding at least some of the types of specimens we are talking about. A redesigned TDI might do it or the QED by all accounts. But sticking with current mainstream devices in my experience the SDC 2300 is about as good as it it gets at the moment. I actually think based on what I know about the technology that the GPZ 7000 is superior, but it needs a smaller coil to really exceed what the SDC 2300 can do. The SDC is a very fact PI but it is still a PI. Pulse induction by definition has a delay between the transmit and receive modes designed to eliminate the responses from bad ground and hot rocks. The type of gold we are talking about falls into that short delay area. It is ironic but it is the ability to react to bad ground and hot rocks that gives a high frequency detector its ability to find porous and wire gold.

The GPZ is not a PI, but a hybrid that employs constant current electronics with time domain processing. The GPZ truly is more a super VLF than a PI detector. That is why it struggles with salt ground and hot rocks the SDC and other PI detectors can ignore. That is also why it is inherently more capable of detecting the type of gold we are talking about. It is why I am anxious to get a small coil for the GPZ.

What is needed is a very fine degree of tuning to ride the fine line between reducing ground and hot rock signals while still retaining as many gold signals as possible. The two overlap. Part of the problem I am seeing is detectors like the SDC and GPZ having a few preset tuning positions. What is needed is more like an infinite potentiometer that would allow the operator to achieve very tiny adjustments in order to get the degree of differentiation needed when dealing with the ferrous/salt/gold overlap area.

In theory the pulse delay on a PI can be shortened to the point where the responses are indistinguishable from a VLF. The delay gets so short that for all practical purposes there is no delay. The ability to make that adjustment is one way to do things. In the GPZ it is done more through post detection processing of the signal. The technology is there, we just need finer control over it. At the end of the day however, just like for every gold jewelry item there is a aluminum item that reads the same, there will be gold that perfectly overlaps with certain ground and salt responses. Eliminating the undesired item eliminates the desired item with it.

"The GPZ truly is more a super VLF than a PI detector." That is a very interesting statement. So would a  GPZ 7000 with a smaller coil have the potential to find sub-grain and possibly porous and wire type gold? How much of a smaller coil size that would be practical and still maintain deep seeking qualities? Is there engineer with Minelab that could develop a coil that would detect porous and wire type gold? If the GPZ 7000 is more like a super VLF type of a detector I would think that this would be possible. I appreciate any thoughts you may have on this.

[Steve Herschbach]

The smallest nugget I have found in the field with the GPZ and 14" coil weighs 0.8 grain.

http://www.detectorprospector.com/forum/topic/2350-the-zed-and-small-gold/?do=findComment&comment=27525

So we have already passed the potential stage with sub grain gold with the existing coil. A smaller coil would simply enhance the ability. Like any small coil you will trade depth however, no free ride.

People already are finding porous and wire gold with GPZ detectors but like I said, it is a gradation of capability and there is no exact definition of what constitutes wire and porous gold. I have found gold with my GPZ that my GPX could not detect at any setting directly touching the coil. The capability exists, the only question is far can Minelab push it. Early days. More GPZ specimen photos here 

[Glenn in CO]

Steve, here is one example I found of the type of wire gold that a PI will not detect. The mass of wires is about the size of a fifty cent coin with only a portion exposed in the picture. The GMT will give a very strong audio response while a PI cannot detect it.

Here are before (when I found it) and after (some cleaning in acid) pictures:

[Steve Herschbach]

Very nice! Yes, classic "invisible gold". That type of stuff has a very short time constant and so falls into the pulse delay zone where items remain invisible to a PI. You really only have much chance with induction balance/constant current machines like what are commonly called VLF detectors. Specifically high frequency models like the GMT or Gold Bug 2. Again, the GPZ has the underlying capability but the emphasis with the machine is on overall depth, not finding stuff like this. Someday if the come out with a small coil for the GPZ I will chase you down and we can test it on some of your samples.

[Glenn in CO]

Thanks! Steve. I have different sizes and types of wire gold specimens that I have found and you are welcome anytime to get together in the future.