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GMT and "follow the black sand" function...
Posted by: Jim in Idaho
Date: August 06, 2017 02:41PM
I've been planning on some testing of the GMT's ability to find paystreaks of black sand. Finally went down near the Utah border and collected some sand to use. I was disappointed in how slow the GMT's indicator changed over the sand I used. Much too slow, unless you want to die of boredom before finding any. That's probably why so little is written about it. It only works in "autotrack", too. I tried various levels of V-Sat, Gain, etc., but nothing worked in a way I'd spend much effort doing. But, I DID find something that works.` I put the GB in Manual, and cranked the GB as POSITIVE as it goes (99). That way, it only responds to REALLY strong positive signals, and most negative signals. I turned the THRESHOLD all the way down. At those setting you hear very little ground noise, but still get a good response on the black sand. The gain can be adjusted to ignore the general levels of blacksand on a bar, but still respond to a higher concentration of it. The response is fast, so you can run the detector as if looking for gold. Of course, you won't hear any non-ferrous targets at these settings...they're strictly for finding concentrations of bs. The concentric coils had a definite advantage over the DD, but the DD worked plenty well enough. I was using blends of pure magnetite,or at least ALL of the black sand I used could be picked up with a magnet, mixed with sand that had no magnetic iron in it. I used both a 1:5 ratio of bs to white sand, and a 1: 10 ratio. Both were detected at nearly 4". I didn't try any ratios below 1:10, but I'm sure a ratio of 1: 20 would be detected, but might be only at shallower depth, depending on where the gain was set, and that would depend on the level of bs in the general run of the bar being detected. Another thing on the mixes used....I used a teaspoon of magnetite in each mix. Put them in sandwich bags, and spread it into a thin layer. But, to be fair, the coils could always see the entire teaspoon of magnetite, as the test blend, even spread out, was smaller than the area of the coil.
I tried using the "learn accept" function on the DFX, but could make nothing work on that for finding black sand. Tried several different programs and settings, with complete lack of success.
Jim



Edited 1 time(s). Last edit at 08/06/2017 03:03PM by Jim in Idaho.

Re: GMT and "follow the black sand" function...
Posted by: calibil
Date: August 26, 2017 12:37PM
What size coil was used?

Re: GMT and "follow the black sand" function...
Posted by: MI-AuAg
Date: August 26, 2017 02:30PM
IMO, that feature isn't mentioned a great deal because most probably consider it just a general indicator. Not something that's considered essential to their search. While the presence of magnetite can be a POSSIBLE indicator, it's not a surefire thing that gold is present. It's just one of many possible indicators, or clues.

In my limited visits to gold country with my GMT, the majority of my searching has been done on old tailing piles on private land. Magnetite wasn't a concern, as I was in a past gold producing area looking for missed pickers, or that rare nugget.

I wonder, in terms of the percentage of locations with magnetite deposits, how many actually give up some gold? I'm thinking it's not a high percentage. Lots of magnetite out there, not so much gold!

I'd be interested to hear from some experienced folks from gold country who use(d) the GMT with their thoughts. Steve, you out there?

Re: GMT and "follow the black sand" function...
Posted by: Architex
Date: August 26, 2017 04:23PM
That feature is intended to indicate plentiful heavy material like magnetite. Might help to locate not-so plentiful heavy material like gold.



One Man's Trash...........is what I usually find.

XP Deus / CTX 3030

Where are the diamond rings?.............They said there'd be diamond rings !.

Re: GMT and "follow the black sand" function...
Posted by: Jim in Idaho
Date: August 26, 2017 05:53PM
Quote
calibil
What size coil was used?
6 x 10 in both DD and Concentric.
jim

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