By Jim in Idaho
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.
By Steve Herschbach
A quick specification comparison of the two detectors.
White's Goldmaster Goldmaster 24K versus White's GMT
White's GMT Instruction Manual
GMT Information Page
White's Goldmaster 24K Advanced Guide
24K Information Page
Despite similarities these two detectors have a different lineage. The GMT was part of the effort involving engineer Dave Johnson that resulted in both the GMT and MXT. The Goldmaster 24K however I am almost 100% certain is an offshoot of the MX5 project, variants of which also include the MX7 and MX Sport.
Notes on the chart above. The GMT has the ability to directly manipulate the ground balance up and down via the plus and minus buttons on the pod face. The Goldmaster 24K (GMK) relies on either automatic ground tracking or the ground grab, features the GMT also shares. However, the GMK has a ground balance offset feature. Under the section titled "Ground Scan" on page 15 of the White's Goldmaster 24K Advanced Guide:
"In Ground Scan you can also set a ground offset by using the UP and DOWN arrows. This selection will affect the ground offset in normal search mode whether using XGB or locked settings."
Note that the offset, once set, is active in both ground tracking mode and when using the ground grab function. Normally a manual ground balance is used to just tweak the setting derived from tracking or ground grab up or down a small amount. This can be done with the 24K but in a different fashion than the GMT. The fact the offset is active while in ground tracking actually gives the GMK an ability the GMT lacks.
The Goldmaster 24K has a volume control the GMT lacks.
A real biggie in my opinion is that the GMK can completely block the audio from ferrous targets. The best you could get with the GMT is an audio "iron grunt" on ferrous, but no way to shut it up. This is even more an issue when you get into some bad hot rocks that signal as iron. The GMT can get pretty noisy, but the GMK allows those signals to be blocked. It can in fact also block ferrous "wrap around" signals where ferrous reads very high on the scale, almost like a silver target.
Coils compatible? That very important note is to warn you that all past Goldmaster/GMT coils are not compatible with the new Goldmaster 24K. Just another tip that these really are different detectors under the hood.