Empty holes, vanishing signals and deep-deep targets

[Thumper III]

New to detecting. Have X-terra 50. Used two outings. As I am trying to learn the machine, I tried digging all signals detected in ALL METAL mode. Area is generally high iron content (natural) and ground water is acidic. Unit GB at 11. Sensitivity set 16. All metal mode. Stock 7.5 coil. This is an old (from colonial period up thru 1970's) farm area. Need advice from some experienced users. I found two conditions that I have questions about:

1. Detected a -6, -9 signal at indicated 10 inch depth. Repeatable find. Pinpointed and dug. I had time, was on own property and a shovel. I dug. Each shovel-full was spread and scanned. When I had gone down over a foot with nothing detected in dirt removed, I rechecked down in the hole. Nothing there. No signal. Carefully rescanned all discard. No signal. Tried higher sensitivity. Same negative result. No signal found within the hole or in the discard. (And I hadn't detected my shoes or a tool on earlier signal). Did note that I got a -6 signal whenever the center of the coil passed over the edge of the hole (now 2 feet in diameter). This happened around the entire perimeter of the hole. Any wisdom out there?

2. Detected a solid -6 signal at maximum depth indication. Pinpointed and dug. Rechecked in hole every few inches to make sure signal was still there. It was. At nearly two feet stopped digging. I was now about 6 inches into undisturbed subsurface clay layer so knew it was not anything recent or intentionally buried (due to smooth top contour of clay layer). Hole was over two ft diameter. Scanned bottom of hole. Still registered strong -6, pinpointed over same original location, still with a maximum depth indication. Any opinions?

My thanks to any who can contribute to my knowledge, Thumper III

"Finds" to date: Large draft horse shoe. About 6 3/4 x 7 inches in size with some nails intact, at 8 inch depth --my first find--it should have brought some luck!
Large caliber modern rifle bullet. Lead core and 1/2 of heavy nickel jacket about 6 inches apart, at depth of 6 inches.
Two aluminium dog tags (rabies shot) with steel attachment s hooks, both around 3 inches down
20 ga tinned-copper wire terminal, 4 inches down
Various aluminum foils, can tops and bottle caps
All the above were found at indicated depths with the signal types expected for the materials (read some forum entries with materials/signals information before I started hunting). All pinpointed accurately.
Found misc' styrofoam at 2-8 inches with wildly fluctuating material type readings bouncing anywhere from -9 to +45
Lots of buried barbed wire

 

[nero_design]

If this hole looks remotely familiar to you, then I feel your pain.

I dug the hole above on a Goldfield amongst the old timer diggings from the 1800s. Great, strong signal but right over an undug quartz reef. What self respecting detectorist would pass on such an opportunity? I even made two trips over 800km to try to get to the bottom of this mystery. But the results were much like your own and this is probably why:

The X-Terra machines are VERY good at what they do but the one thing that will confuse them (and even the top-of-the-line Pulse Induction Detectors) is a concentration of fine minerals. If iron ore or rust contaminated water runoff has made its way down the side of a gentle slope, the deposit will become concentrated. Other minerals can do the same. You'll usually get a -6 or even a -8 (depending on your machine) or even a flickering of numbers which indicates a "junk" target like a Horseshoe etc. When the signal stops after digging and it's not found in your extracted dirt, then you can be fairly sure that the concentration of particles has been spread out too far for a signal to be read. I'm going to guess that this is what has happened to you.


Look for wildly jumping numbers and ALWAYS rebalance & noise cancel when possible . The X-70 has Ground Tracking which helps ignore this phenomena although it still trips us up occasionally. From memory, the X-50 doesn't have Tracking so perhaps this was part of the problem which led to you digging a non target.

Sometimes I have been ready to walk away from a target when I found it in the fine dirt and it was quite small... often the same color as the soil itself. If I had not found it, I'd have later complained of a mystery "ghost" signal myself no doubt. Remember that if you dig more than 9 inches, the detector is only going to be picking up a signal from a LARGE object and it may be worth reconsidering anything beyond the 16" depth mark.

.
(LOL.... had to edit my post: Wordfilter seems to be offended with certain common use terms and words)

 

[Jackpine Savage]

Nero "nailed" it (pun intended) about decomposed iron giving a signal in the ground but not when the particles are spread out after digging. The open hole effect is also common in certain soil types since the detector sees the difference between the undisturbed soil and hole as a signal.

One thing to note in iron infested sites, when scanning a dirt pile or overturned plug for the target, sweep the coil very slowly as any iron turned over with the dirt will many times hide the good target. A super slow sweep will many times pick out the good target from the iron and save you having to spread the pile out. Being able to spread the dirt around as you able to do is a good thing.

That deep signal down in the clay layer could have been man made iron, its amazing how stuff can work its way down over time. It also could be some of the host rock, not as yet decomposed, that the clay layer formed from.

HH Tom

 

[Treasure Nut]

Lowering sensitivity will make your X-Terra 50 more stable for the ground you are detecting on. It's one thing I learned in my two years detecting in highly mineralized iron soil.

Hope this may be of some help.

HH

Treasure Nut
X-Terra 50 user

 

[Grant]

After using both VLF's and a minlelab GP3500 I can certainly say this is a ghost ground signal I fought these for years if not a large Tin plate ( which Iv'e dug over 3' to find with my GP3500 ) I found out early that with my GMT and MXT I was just reading very high peices ir iron ore which can be sread or concentrated. Just my two cents from a lot of digging in the heat for nothing! Good luck in the future always watch out for the little dinks though Iv'e had em in my nad one flat with a hole in in my scale could barely read at .01 grams after diging an xtra foot it was stting right beside me! Grant

 

[Thumper III]

My thanks to all those that read my posted questions and especially to those that sent replies. I know that I could probably just lockout the signals with discrimination settings, but I'd rather learn (with your help) what the detector can tell me in open mode.

This area is definately mineralized. I have the remains of a colonial period iron foundry about 12 miles south and there is evidence of old abandoned digs and tailings all over the county. I have a working sand/gravel quarry about 8 miles south, and a working (crushed granite) rock quarry 8 miles east. Also a marble quarry- abandoned about 1940 - about 4 miles west. Seven miles north are several abandoned - probably in the 1950's--quarries dug for chromium. Farmland in the area glitters after plowing. Geologically, this is near the Peachbottom Fold formation at the southern edge of the Piedmont Province in Maryland, USA. Lots of granite upthrusts and quartz rock. (Reported gold (sand and wires) detected sparcely about 12 miles southwest). Susquehanna River cuts through the fold about a mile to the west. I had to add a filter for my well water to trap iron 'sand' brought up by the pump. Plenty of colonial era houses farms around. I'll have to work on getting permission to hunt when I learn the detector a bit better.
Thumper III
X-Terra 50
stock 7.5kHz 9 in coil
DD 18.5kHz 10x5 in coil (not tried yet)

 

[BarnacleBill]

Using the standard coil over a large target free ground with headphones on, and volume set as loud as you can tolerate. Set the sensitivity to 15, listen in All Metal for interference and Noise Cancel if needed. If you still have interference move to an area where there isn't any before proceeding. Oh yeah, leave any wireless devices at home. Push the GB button for GB function, GB to 0(zero), and begin (pumping) raising & lower coil from one inch to 12 inches above ground. Begin pushing (+) till the GB tone becomes a mixed two tone signal. Stay exactly physically where you were to GB proceed to the next step.

Now that you have a proper GB, set sensitivity to 20 and put detector in All Metal mode. Pump the coil up and down exactly like you were GB'ing the detector. The detector will most likely respond to the ground by spitting out various ID's on the screen & issuing low iron tones with occasional higher tones mixed in. The higher the mineral content of the ground the more pronounced this will be. Now begin lowering the sensitivity one step at a time until the random spitting stops. Move the coil in a normal detecting sweep one inch off of the ground in several directions around you(this is why I stated "large target free area"earlier). If the detector doesn't spit any more random ID's then you are good to go, otherwise back it off 1 or 2 more points on the sensitivity setting till it is stable. In areas with hot gravels this can be a little challenging since each piece of gravel is it's own little piece of ground.

If you use the 5x10 coil you should able to run a higher sensitivity and have a quieter detector if mineralization is the issue. Also on these phantom targets(pockets) they usually won't localize well, in other words they pinpoint as a large loosely outlined target, not a sharp point like a coin would.

HH
BarnacleBill

 

[Grant]

Man that Iron! and Bill is right after fighting very mineralized found in AZ with Both my GMT and GP3500 I got the mineralization under control next issue that I forgot about was my shone and various other interferences I had in my own possession! Good luck with your hunts!