Hi Yellow Hammer,
I apologize, as I have developed a bit of a knee-jerk reaction. I've seen way too many people with VLF nugget detectors ask for help, only to be told "your machine can't find gold - get a Minelab." If I had to own only one detector it would be my GPX-4500. A truly incredible piece of technology. But if all I had was a good old original Gold Bug I'd go out and find some gold.
I might have to work harder, and I might not find as much gold. But I'd still find more gold than the next guy more often than not. The secret is to research good locations. Put yourself on ground where gold nuggets can be found. Know the basic techniques (coil to the ground, etc.) and be patient. And put in the hours!!!!!
Finding gold is not easy. It takes time, dedication, and knowledge. Along the way the detector you use can make a difference, but after watching hundreds of people detect for gold I can swear to you it is not as important as the sum of the other factors. The detectorist finds the gold, not the detector.
Cork, on coils? The worse the ground, the smaller the coil should be on a VLF. The coil "sees" the ground, and so it is about separating the volume of ground seen from the target. The old snow in the headlights effect. High beams suck in a snowstorm because you see too much snow. Go to low beams. Too much mineralization, go to lower sensitivity or gain levels and reduce coil size. When comparing coils, measure the width, not the length. A 5' X 10" elliptical is closer to a 5" coil for performance than a 10" coil. Think of it as a "stretched 5". True measure is actually square inches of ground coverage. Mono (concentric) coils "see" more ground than DD coils and so DD coils are better in severe mineral situations.
So taking a W.A.G. I'd say given your mineralization indications (by the way the GB number is TYPE of mineralization, not AMOUNT) a 5" x 10" DD would be a safe bet. For places I hunt a 10" round DD has me intrigued. But it is all about balancing out factors. You have to try things and see what works best where you are. If it was "use this detector, and this coil, and tune like this" there would be no challenge in the sport.
Once you learn your machine and put yourself on the right ground, it really is all about hours. At the end of the day I do well compared to some simply because I am up earlier than them, I'm still detecting while they take a break, and when they've quit for the day I'm still detecting. Nothing beats sheer determination and ground coverage. I do not employ magic tuning tricks. I just detect more hours than most.
Steve Herschbach
Secret Tip - Sometimes a $5 gold pan is better than a $5000 metal detector!