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BHNugget
05-10-2011, 05:10 PM
Hello,wondering if I could hear from some experienced users on how the GMT handles high mineralization with quite a few hot rocks? This areas mineralization seems to change by the square foot.My brother runs a VSat with the manual ground balance and is constantly fighting to keep his ground balance in this area.

ddmk6
05-10-2011, 07:03 PM
Hello BHNugget,

I'm not sure if your question is about the earlier VSAT goldmaster or the current version?

I have the current version of the GMT. I can tell you that high mineral/hotrock is not the funnest experience. It will work but if the ground is really hot you lose considerable performance (depth). With the auto ground balance it's not near as painful as with manual. The GMT does a great job of auto balancing. I will run in auto with a really slow sweep speed if the ground is bad, then when I find a target switch over to manual to pinpoint. If the target turns out to be a good one, I will keep it in manual and use the grab button frequently. I also keep a test nugget handy so I can make sure I have the machine tuned correctly to get the best possible signal for the ground I am working. Whenever I start twisting knobs I always do a quick check with the test nugget. I haven't found a way around the hot rocks with the GMT. You just learn what they look like and kick them out of the way.

Hope this helps,

Kenny

BHNugget
05-12-2011, 07:51 PM
Thanks Kenny, I was asking about the GMT.I think I got my dealer as low as Im going to get him,price wise,so I'll be picking it up tommorrow and starting the learning process this weekend.If the rain breaks,that is.

ddmk6
05-12-2011, 08:14 PM
The GMT is a great machine. It will find some really small pieces when you get it tuned correctly. And of course, if you can find the small stuff...you will easily hear the big stuff!

After you get a chance to play around with it for awhile. Post up and let us know how you are doing. Do some searches on this and other forums. There are some great threads out there on getting the most out of the GMT.

Post up any questions as well. There are some awesome people on here to help out.

Good luck.

Kenny

Sent from a Thunderbolt ;-)

FedFire
05-14-2011, 12:21 PM
The GMT is notoriously bad in highly mineralized ground especially when andesite &/or rhyolite if there is either of those rocks in any concentration where I am detecting I pretty much pack it in and head somewhere else. However, if I am searching on exposed bedrock or very shallow bedrock I have had good luck... Very very good luck. It only took me a year to find a suitable spot and once I did I pulled out around 5 oz between Dec '10 and April '11. But the area had a lot of andesite and Rhyolite so i had to strip the bedrock clean before my detector would pick anything up. Once it was clean I would systematically go through an area and dig all the crevices that I got hits on. It was a blast!!!

If you do a search on here you can read some of my other posts about the settings I used....
1.5oz
http://i1101.photobucket.com/albums/g434/jobadiahg/6b8aefb8.jpg

fish5050
05-16-2011, 08:17 PM
Wowza Fed, you do great work with that GMT. Beautiful specimens too say the least. Thanks for sharing the picture of your results.
All the Best
Fish

ArcticDave
05-17-2011, 07:06 AM
Wowsa is right!!!.........Great job Fed! Glad persistance is paying off for you. I bought a new GMT from AMDS this spring, for running over the bedrock on my claims. I can finally use it in 3 weeks.:D
Beautiful gold Fed:cool:

drydiggins
05-20-2011, 07:00 PM
Nice job Fed! Just wondering, was that out of ancient river dry diggings, or were you in the water?
I also beep in ElDoCo :)

Steve Herschbach
05-20-2011, 08:39 PM
Very nice! Beautiful gold!!

BHNugget
05-21-2011, 05:57 AM
Great haul out of the bedrock FF!! Ive only made it out to one spot so far due to being busy at work.After I ground balance and get my threshold set, my threshold keeps dropping out and coming back in while Im searching.Ive tried raising the SAT.Is this an indication of the initial gain position being to high for the area?

Steve Herschbach
05-22-2011, 07:56 AM
Are you running in automatic or manual ground balance?

BHNugget
05-23-2011, 04:51 AM
Ive tried both methods and it seems to do it in both,but is slightly more pronounced in manual.Im pretty well convinced its something Im not getting yet as the machine is brand new.

Steve Herschbach
05-23-2011, 06:04 AM
For bad ground the key is to use automatic. Then experiment with higher V/SAT settings and lower Gain settings until you get the smoothest response.

Jimmy Sierra refers to this mix of V/SAT and Gain as the "salt & pepper" settings. You have to find the proper amounts to suit your taste. The key is to get over fears over reduced sensitivity and seek the smoothest response from the ground. this will allow nuggets signals to stand out better. A sample nugget really helps out in getting this right.

Small coils can also help.

Some ground is very difficult for high frequency VLF units. The only answer sometimes is a lower frequency VLF detector or in worst case scenarios a PI. That is why we have so many different detectors on the market. No one unit fits the bill in every scenario. But careful tuning should allow you with patience to find gold with whatever detector you have providing there is gold to be found.

Jim Hemmingway
05-31-2011, 11:23 AM
Hi BHNugget…the posts above pretty well cover it off but I’d like to elaborate on Steve’s comment about using small coils in bad ground. There seems to be some misunderstanding or controversy regarding the use of various coil types or sizes with VLF units within the hobby.

Small coils, while more sensitive to small targets, see less ground mineral than do larger coils… resulting in better bad ground handling performance. This may be an overlooked advantage particularly when using high operating frequency units such as the Goldbug II or in this instance the White’s GMT.

Below are some excerpts from an excellent book Gold Prospecting with a VLF Metal Detector by Dave Johnson, Chief Designer, First Texas Products & Fisher Research Labs. You may find his comments a useful future reference… all emphasized text is my doing...

“Most gold machines are available with at least two different sizes of searchcoils.

Advantages of small searchcoils: higher
sensitivity to the smallest nuggets, ability to get between rocks and bushes where larger searchcoils won’t fit, lighter weight, reduced interference from ground minerals, easier to pinpoint the exact location of an object and less electrical interference.

Advantages of larger searchcoils: broader
sweep (covers more area), slightly more depth (but not as much as you’d think).

Some gold machines can be purchased with searchcoils in either the concentric and double-D (DD) configuration.

The big advantage of DD’s is that they penetrate ground minerals deeper than a concentric. Minor advantages of a DD compared to a concentric of similar overall size and shape are a broader sweep (wider coverage) with tighter target separation.

However, DD’s have numerous disadvantages:
greater vulnerability to electrical interference, confusing multiple signal responses on shallow objects, inferior shallow iron discrimination when used in discrimination mode, greater manufacturing cost and often less sensitivity to the tiniest nuggets.

For gold prospecting the advantages of the DD
usually outweigh the disadvantages. However the situation is not so clear-cut with small searchcoils where concentrics are often more sensitive to the tiniest nuggets.”

Jim.

BHNugget
06-01-2011, 05:35 PM
Thanks for the information Jim,Im ordering the little 4X6 shortly.