DD vs. Mono revisted

[sdf527]

My experience at Moore Creek has got me thinking about the great Mono vs. DD debate. The concensus suggests that Mono gives greater depth and sensitivity. I certainly experienced one of those Mono moments at Moore Creek when I was detecting the push. I was concentrating on low and slow and putting that coil right on the ground. As a result I was generally ignoring the "wind rows" of the dozer push, trying to keep my coil as close to the ground as possible, and to avoid making my coil an antenna for interference from other detectors. However; that Mono was so sensitive on its edges that it detected a nugget beside and above it in the wind row. I got the original signal and started digging in the flat push area, beside the wind row. The signal got fainter and by accident I swung the coil over the wind row and got a decent tone. The nugget was probably 4 inches above and 2 inches to the left of my coil when I first detected it.

That experience aside, running the Mono at Moore Creek requires some sacrifice in detector sensitivity. As I have mentioned, on the 4000, the most stable settings were Sensitive - Smooth, Audio - Quiet, with a gain of between 8 and 12. Some piles had more hot rocks than others, hence the 8 setting. Even with that, you're still getting hit with a fair number of hot rocks. Minelab's own user manual suggests that by using the Sensitive Timings you "might" be sacrificing some depth cabability. I experimented with leaving the timing in Normal and was bombarded with hot rocks, had to take the gain down to 6 to get anywhere near a stable tone.

It stands to reason that a DD coil would allow the user to operate at higher settings and to perhaps avoid the Sensitive Timings. Is there a balance point in there, where switching to a DD and avoiding the Sensitive Timing would compensate for its general reduction in depth and sensitivity?

I should point out that the ground at Moore Creek is not "hot" per se, that is, the soil is not the problem the Aussie's experience. The problem there is the volume of hot rocks. I'm no geologist, but these things were buff colored, very grainy and were generally rust stained on the wet, bottom side. The rounded, fist sized ones seem to pose the greatest challenge. Reno Chris did a trip up there, maybe he can comment on the origin of these rocks.

This is all moot unless there is a new generation of DD coils that is as "bump resistent" as the new "goldstalker"? I don't think I could go back to the assault on my hearing I experienced from some of my old coils, and I've had them all. Sooner or later, and sometimes right out of the box, they are bump sensitive and ruin the ability to get absolutely low and slow.

[Jonathan Porter]

Assuming the hot rocks were of a similar make up, I would try Ground Balancing the machine to the hot rocks and detect in Normal timings assuming your ground matrix is benign. This way you would be getting maximum senstivity and depth without the hot rock problem.

JP

[sdf527]

Assuming the hot rocks were of a similar make up, I would try Ground Balancing the machine to the hot rocks and detect in Normal timings assuming your ground matrix is benign. This way you would be getting maximum senstivity and depth without the hot rock problem.

JP

JP,

You're knowledge and understanding of the workings of the ML machines far exceeds that of ordinary prospectors and I'm sure I speak for everyone out there when I say how much I appreciate your contributions. Bravo Zulu

Stephen

[nuggethunting]

Hello Steve,

The Sesitive/Smooth mode on the GPX-4000 is a huge hit. There were places that were loaded with ironstones and volcanics here in Arizona that I could never hunt with prior Minelab's. I was able to go back to these spots with the 4000 and mono coil and hunt using the Sensitive/Smooth timing. However, you do loose some depth. It comes down to being able to hunt the spot or not. I would rather be able to hunt the location with minimal amounts of ground noise and find what I can within a certain range rather than not being able to hunt the ground due to the amount of ironstones and volcanics.

There was and still is a lot of debate on the Senstive/Smooth timings. I've done enough testing to conclude you will loose some depth, but then again you can do other things to bring some of the depth back. Many of these areas that require Sensitive/Smooth timing are very noisy and almost un-huntable with other timings such as Normal. If you were able to use Normal to some degree, you would probably have to turn the Gain down to maybe below 8 to somewhat hunt these areas. With the Sensitive/Smooth timing I was able to hunt these spots with a mono and turn the Gain up to 11-12. Yes, I might still be loosing some depth, but for the most part I'm getting all the smaller and medium sized nuggets at depth from what I've seen.

One of the new settings on the GPX-4500 is the Enhance timing. This timing is somewhat similar to the SS, but you don't sacrifice all the depth you would in SS timing. At Moore Creek the "Enhance" timing was a huge hit. I was still able to get the same mineral immunity as the SS timing, but able to get much more depth, almost the same depth as in the Normal timing from what I seen. For the last 4 years many of those mounts where hit by all type of Minelab's and different users. We went back with the Minelab GPX-4500's, Goldstalker Mono Searchcoils in the Enhance Mode and found over 15 ounces in a week working old pounded ground. To me, that is a pretty good testimony!

The nugget/specimen below was 1.65 ounces. Before I dug more than a few inches I played around with the settings a bit. I couldn't hear this nugget in any of "Special, which includes Sensitive/Smooth" timings on the GPX-4500. I was using the Enhance/Deep timing and toggling my audio from Quiet to Normal. My audio was in Quiet when I found this specimen. I also tried the Normal timing and it also heard the specimen a bit better than Enhance. However, I probably wouldn't of heard this piece in Normal timing due to the amount of basalts scattered throughout the tailing piles. Never hurts to experiment with your setttings, but you must find something that is stable and immune to the mineralization if you're looking to hear those faint targets like below.

Talk with you soon,

Rob Allison

[kamikaze]

Great info guys! Thanks for the input!