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Using The GMT To Find Black Sand Paystreaks


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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 I would have no problem using the DD for this. 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. All of the sand used was smaller than #50.
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

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I figured it was time to do some serious testing on this, Steve. I've seen tidbits here and there, but nothing very definitive. I'd read that you had to pump the coil to make it work. Nobody is going to spend more than few minutes doing that! Talk about arm-weary...LOL. There's a branch of the Snake not far away, that is now dry. River hasn't run there for thousands of years. I thought it might be a good place to look for black sand streaks, and collect some material to pan. I decided I needed to know just what the GMT could do for me in that regard. When I get some time on the dry channel, I'll be sure and post it.

Jim

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The V3i has a black sand tracking feature as well but I haven't tried it either...I just don't live close enough to nugget country to get it out to test.

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On 8/6/2017 at 3:04 PM, johnedoe said:

The V3i has a black sand tracking feature as well but I haven't tried it either...I just don't live close enough to nugget country to get it out to test.

The Prospecting Scan (Alluvial Scan) is, as far as I can tell, a continuous graphic display of the ground phase which is the same thing as the ground balance setting. It is showing you the TYPE of ground mineralization, not the AMOUNT of ground mineral. See here for reference. Low numbers are salt ground and higher numbers ferrous ground. It is therefore not really analogous to the GMT "Follow Black Sand" Fe3o4 reading, which measure the AMOUNT of mineral.

The advantage as Jim has found is tracking ground phase can be done as you sweep normally, whereas making a mineral amount reading requires pumping the coil.

whites-v3i-prospecting-mode-screen-display-small.jpg

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11 hours ago, Steve Herschbach said:

More information here on mineral type (GB numbers) and mineral amount (Fe3O4 readings)

http://www.detectorprospector.com/forum/topic/1599-gb-numbers-mineralization/

 

Thanks, Steve...good read!

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5 hours ago, Steve Herschbach said:

The Prospecting Scan (Alluvial Scan) is, as far as I can tell, a continuous graphic display of the ground phase which is the same thing as the ground balance setting. It is showing you the TYPE of ground mineralization, not the AMOUNT of ground mineral. See here for reference. Low numbers are salt ground and higher numbers ferrous ground. It is therefore not really analogous to the GMT "Follow Black Sand" Fe3o4 reading, which measure the AMOUNT of mineral.

The advantage as Jim has found is tracking ground phase can be done as you sweep normally, whereas making a mineral amount reading requires pumping the coil.

whites-v3i-prospecting-mode-screen-display-small.jpg

yes, and sadly, it's still too slow to change the numbers. Required several pumps over my samples to get the numbers to change....not good. This whole discussion makes me wonder why no mfg. has offered a simple machine to do nothing but track black sand concentrations? Maybe it's more complicated than it appears.

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  • 4 weeks later...

Interesting test Jim, well done, great effort.

I have always used the GND meter to see the changes and where they are at their highest that's when I would use the black sand % meter to measure the actual levels, The GND/Ground Phase is the  quickest way to locate the general bs area, the bobbing of the coil is really like when you ground balance the GMT/MXT's and normally happens within One or Two pumps of the coil so the GND meter responds faster within those one or two pumps of the coil, I only use the black sand meter as a secondary meter having the GND meter do all the major work,

thanks for you efforts.

John.

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Jim in Idaho...

I think they did years ago... It was a BFO machine....:smile:

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