Hi Dave. Yep, it's addictive. Hmmm.... my suggestion would be either a PI capable of very short delay, with either a litz wire, tinned copper stranded, basket weave, or spiderweb coil, of small size.....or a 15-50kHz VLF or IB. The best bought ones I have is the Garrett Infinium (PI), and the Whites GMT E-series (VLF 50kHz).
The GMT has a black sand meter, which is handy, because where the black sand accumulates most is the best chance of gold. But the black sand will drown out the gold signal.
Older 100kHz IBs, like my Compass 94B, can also "detect" black sands, in that the threshold tone will disappear over iron or black sands.
The best idea with this is to then dig the black sands, then pan it to take off the light stuff. A magnet can then be used to remove the sands from the gold.
Another handy machine is the Falcon MD20, which can detect gold you can't even see.
A PI with an adjustable threshold and delay may be able to discern a small nugget over the black sands signal. A GMT with the SAT (self-adjusting threshold) turned off, and gain up, may also.
For a homebuild, you are best to start with a PI, as VLF/IB coils are very hard to get right. The most documented are the Whites Surfmaster/surfpro, the Baracuda, the Minipulse, and the Hammerhead, which are all extensively covered on the Geotech forum, as is building a "fast"coil for these.
Sven at Treaurelinx has a machine called a Mirage PI, which is a souped up Hammerhead, but boards are hard to get and expensive, and he has never documented his modifications, to my knowledge.
My Surfpro I purchased the completed board from Tacoma56 on Ebay, and assembled the detector from it using a Minelab 10x5DD coil.
It will see 1.7g of flour gold at 4-5 inches in an air test. The surfpro has variable delay, sensitivity, and threshold, and automatic ground balance.
My Baracuda was purchased as a bare board from Silverdog UK. I now have it working well, but am still experimenting with coils.
Currently my best is 3-4 inches on 1.7g flour gold air test. It has variable delay and threshold.
I have the Minipulse board and IDXpro(VLF) on the way from Silverdog also. He is the best value for homebuild boards, and can supply all components also.
But my best performer so far is the Surfpro(made for a DD coil).Not to be confused with the Surf PI 1.2 that Silverdog sells, but apparently that is good also.
For creekbeds with black sand, I would probably first try a PI.
I'm really only a beginner, so Goldigger or other more experienced members may disagree or contradict some of my statements here- hopefully my post will spark some more replies for you Dave.
I suggest you sign up to Geotech also, if you're not already. Most posting on similar subjects here will be members there also.
Here's some project pics.
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