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I was out hunting some dredge tailings yesterday and did some testing with the SDC 2300 and the Gold Bug Pro on some specimens. I tested a variety of pieces but the one that is most interesting is in the pic below. I previous tested this with the GPX 5000 with standard 11” mono and it registered only very slightly when touching it to the coil. The GB pro with the 6x9 coil in all metal mode will easily pick this up at 8”-9” in an air test. The SDC in an air test was slightly less at 7”-8”. I then put this at the bottom of an 8” hole without covering it up and retested.  No change on the SDC but the GB was now barely able to pick it up. After filling the hole the SDC still had no problem but I couldn’t pick it up at all with the GB.  Further testing determined that the GB would pick this up at only about 4”-5” when buried. I actually found this specimen about 4” below the bottom of an 8”-10” hole where I dug out a large square nail. Other observations were that on the buried test the GB was only slightly deeper in all metal than in disc. mode but the target response area is far greater in all metal.  In all metal I tested with the machine ground balanced neutral and with ground balance at + 10 and – 10 on the GB screen. Also if I put one of the numerous hot rocks from the tailings over the specimen it almost completely masked it.

 

After this test I carefully covered over a 15’x20’ area with both detectors from 2 directions and marked all targets. I got 7 targets with the GB and 9 with the SDC. The 7 with the GB were all seen by the SDC but the GB could not see the other 2 SDC targets. 6 were square nails and one was a small piece of tin. The 2 the SDC saw that the GB did not were a small (about ½”) tip of a rusty square nail at 4” and the item in pic 2 below at a about 6 1/2 inches. Not certain what this item is. Looks like some kind of melted metal possibly solder. It reads on the GB screen about the same as gold or lead but too hard to be lead. This screamed on the SDC and once out of the ground hits very hard on the GB also. I reburied it at about the same depth and the GB hit it fine. It seems that there are certain situations or rocks that mask targets from the GB. Last observations are that the GB seems much more sensitive to iron targets than the SDC. The deeper nails were stronger signals on the GB but on the specimen in the pic and some heavier gold specimens I tested the SDC clearly had significantly more depth in the ground (at least 25% - 30%).

 

Bottom line the SDC will clearly potentially find more specimens than the GB in tailings if you have the patience to dig every target but with the amount of trash in the area I was hunting it would be difficult to have the discipline to dig all targets. I have gone out many times with the intention of digging everything but after 3-4 hours of digging junk ever couple of feet I usually fall back to using the Disc. to try to determine if its trash. Given the random distribution of specimens in the tailings this is most likely gives the best overall odds but that being said I have found a couple of nice pieces that in ground read and sound just like nails on the GB pro (Target id only in the high 20’s in disc. and 3 or more bars on the iron indicator in all metal. Once out of the ground or reburied they read in the normal 48 to high 50’s range in disc and 0-1 bar on the iron scale in all metal.) I am trying to video as many digs as possible to try to catch one of these to post showing the sounds and readings. It would be great to get some of the groups opinions on the reason for this.

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Welcome to the forum, and fantastic first post! Very much in line with what I would expect. And regarding your last question unfortunately this is a well know problem. Discrimination sucks! http://www.detectorprospector.com/forum/topic/326-metal-detector-discrimination-really-sucks/

The big dilimna is exactly what you outline. What to do in trashy tailing piles? If gold is sure to lurk, dig it all is the only answer it would seem. But that simply is not practical in most situations, usually due to a lack of time or lack of patience, or both.

What I do at this point is use a good VLF detector to try and find which areas in the tailing piles have the best chance of gold. Not all tailings contain gold! If I find any gold, then switch to dig it all mode. I promise you, if you find gold someplace, you will eventually dig everything there. If you do not, somebody else will.

In the meantime discrimination, imperfect as it may be, is our only tool for sorting through horribly trashy locations. That includes using a PI detector and hunting by ear, only digging those sweet pure tones and ignoring those that sound more like junk. Any time you leave a target in the ground you run a risk, so we each simply have to call the odds as best we can, given the particular situation.

Again, great post! It perfectly illustrates why I think a well outfitted prospector needs both a good PI and a good VLF.

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Steve, 

Thanks for the response and insight. I totally agree using discrimination is a crapshoot and I try to avoid it when prospecting. More eye opening to me is the apparent masking of targets by hot rocks or mineralized ground on the GB of what you would think would be easy targets in all metal. I am starting to think this may be fairly common and explain some of the success we are seeing with the SDC in heavily hunted areas.  I also found 3 small nuggets with the SDC in a spot I know has been hunted extensively by others and i'm 90% certain I have covered before. None were very deep and all should have been obvious with any good VLF.

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To quote myself from the article linked above "The only icing on this cake is that there is a huge amount of fantastic stuff in the ground, and not deep at all. It is there, quite shallow, just under or near that thing you discriminated out. If we could see through discriminated items rather than be blocked by them an amazing amount of stuff would come to light."

Discrimination is my best friend, or at least the people that employ it, because it means things remain to be found. The only ground that scares me is ground where no targets can be found at all. As long as trash remains, there is hope.

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