Background: I started Coin & Jewelry Hunting in march of '65, and took on Relic Hunting in ghost towns, homesteads, encampment sites, etc., etc. in May of 1969. Since then my primary detecting activities are based around Relic Hunting, primarily. But doing so got me hunting a lot of old gold mining camps and gold mining towns, so as an aside to Relic Hunting gold mining towns I also worked a bit of Gold Nugget hunting into my adventures.
I started Gold nugget Hunting in the summer of '77 and, while it was an off-and-on activity for me, I did enjoy some success. Nothing you'd call a big money maker find, since most of my Nugget Hunting time is in Western USA areas that mainly have smaller-size gold. That's one reason I also am glad to have the excellent LF range Makro Gold Racer in my arsenal working at 56 kHz. It is a nice complement to my other regular-carry detectors. But through the years I think the biggest gold nuggets I ever detected were a 5 dwt and 8 dwt with the rest being smaller.
Now that you have that background and know I am not a totally dedicated Nugget Hunter, I'll share my opinions, and my 'opinions' are based on actual in-the-field performance and results I have enjoyed through the years. Here are my answers to your post:
mick64 said:
Thank you for the information, but could someone please advise whether a concentric coil 10x5.5 on a Nokta Fors Relic, would be better for nuggets than a DD 10x5.5 on the same machine.
I have found, long ago, that search coil size, shape and internal winding design [size=small]
(Concentric or Double-D)[/size] are only part of the overall detector and coil performance.
Other things must be considered, such as:
Ground mineralization
Detector operating frequency
Detector search mode
Detector Gain or Sensitivity as it affect the search mode
Circuitry design being Analog or Digitally-based ..
and how it is made to perform!
Presence of any 'Masking Effect' caused by: Nearby metal debris, Hot Rocks, or challenging ground mineral make-up
Operator's choices of settings used
Operator's sweep speed and search coil presentation
Back in the latter '70s most detectors used Coplanar/Concentric search coils, but some Double-D's were used and often touted as
"being better in highly mineralized soil." This was when some of the early rush started we called "Electronic Prospecting" and in that early era there was some merit to that claim. But it was especially tied to the particular make and model detectors used, and not necessarily to the search coil design. There seemed to be more interest in figuring out how different operating frequencies compared and, for Gold Nuggets and other lower-conductive targets [size=small]
(such as the US 5¢ coin or for gold jewelry)[/size], we found models working ± 15 kHz worked a lot better on the small, lower-conductive targets than those in the lower frequency range which was usually about 4 kHz to 7 kHz.
I have friends who lived in Australia for many years during the gold rush or the latter '70s and through the '80s, and they used models that operated from 6.59 kHz to 10 kHz, which wasn't the 'fashionable' frequency range, and they used only Concentric search coils. In the end they did quite well! My 5 & 8 dwt nuggets were found with a 13.77 kHz detector and an 8" Concentric search coil. Most of my Gold Nugget Hunting was handled with models operating ± 15 kHz and most of the time with Concentric search coils for one reason. The detectors just happened to perform well for me, and better than most units with a DD coil I tried.
So, from experience, I have enjoyed very good success with some Concentric coils on some detectors and Double-D coils have also worked OK, if the detector design also happened to work well with it. I have been a devoted fan of good working Concentric coils for decades ....
as long as the detector design they were affixed to also performed well with them. The same holds true of models that are, by design, able to provide me the performance I want and need with a DD type search coil.
It seems to have been a trend since about the 2000 to 2006 era for manufacturers to compete with new detector or coil designs, promoting all kinds of models that are now more digitally designed, and also come standard with a Double-D search coils. That, plus many that came with a Concentric are hyped/promoted to do well with a particular DD coil or two. Very trendy, and I have owned and evaluated several of them and very few impressed me much for the hunting scenarios I generally encounter.
Then, along come January of 2015 and I get a Nokta FORS CoRe Pro Pack in my hands.
Well balanced ... check.
15 kHz operation ... check
Ample but simple adjustments ... check
Digitally designed circuitry ... check
Double-D coils standard ... Okay, but how is the operation for all my hunting site encounters?
I was impressed overall for all my usual hunting needs, especially after evaluating it with some gold nuggets in higher unrealized environments!
December, 2015: I got the 19 kHz FORS Gold + in-hand with the 5½" round DD, 5½X10 DD and 5½X10 Concentric. Great! Now I can compare the Gold + performance to the 15 kHz CoRe, and even better, compare the same-size DD and Concentric search coils.
In January of this year I got the FORS Relic prototype and worked with the same search coils on the Gold + and Relic units, prototype and production, and came to a very simple conclusion.
Both search coils work very well for any of the hunting needs I might have. I opted to keep the 5½X10 Double-D on my Gold + and the 5½X10 Concentric on a Relic simply because I prefer the Discrimination performance and TID read-out with the Concentric. I can quickly swap lower rods and coils if I want to, but for Gold Nuggets, of those I used to sample, it was a very touch choice to make. Maybe,
just maybe, the DD had a slight edge over the Concentric on the smaller-sized specimens I tested. But on the 3 dwt and 5 dwt nuggets used, the Concentric gave me a little better audio response and depth. Slight, but there.
mick64 said:
The area I would be in wouldn't have much trash
If you do get into a trashy environment when Gold Nugget Hunting, mount that round 5½" DD and work it slowly and methodically. If the gold potential site is free of a lot of trash, either 5½X10 coil will do.
If I was limited to only one of them, however,
for my hunting needs, it would be the Concentric coil.
Monte
