The confusion over coils
Which coil is the best for you? Will they help you get more gold?
The advantages and disadvantages of the various coils presently available.
FOUR BASIC RULES
There are four basic rules involved in understanding the different types and sizes of coils available.
1. The bigger the coil, the deeper it will detect the bigger nuggets, but the shallower it will detect tiny nuggets.
2. The smaller the coil, the shallower it will detect big nuggets but the more sensitive it will be on tiny nuggets.
3. Double D wound coils are far more stable and create minimal ground noise but they are not as sensitive. This gives them a disadvantage in quiet (low internalization) soils but an advantage in noisy (high internalization) soils.
4. Monoloop wound coils are more sensitive, but they create far more ground noise and are less stable.
This gives them an advantage in quiet soils and a disadvantage in noisy soils.
The Monoloop design coil has a single winding of wire on the outside edge of the coil. The double D design has two loops of wiring which overlap in the central area of the coil.
DOUBLE D COILS
1. Produce far less ground noise and require much less tuning.
2. Give considerably less false signals on mineralised patches or hot rocks.
3. In highly mineralised soils, nuggets can be detected at greater depth.
4. In very highly mineralised ground, they can be used when monoloop coils become too noisy.
5. They have a full width search pattern at depth.
6. They are less sensitive to electrical interference coming from nearby detectors, power
lines and thunderstorms.
1. They don’t penetrate quite as deeply in quiet ground (low internalization) as the Monoloop coils.
2. They will not detect smaller nuggets as well as the Monoloop coil in quiet ground.
3. They are slightly heavier in comparison to an equivalent sized mono coil, due to more wiring.
4. The audio signal produced is not quite as sharp or loud as a mono coil.
5. They don’t pin point targets as well.
1. They have an edge in sensitivity over double D coils. They penetrate a bit deeper than an equivalent sized DD coil in light to moderately mineralised soils.
2. They are slightly lighter than the same size DD coil.
3. They are capable of detecting slightly smaller nuggets than the same size DD coils.
4. They pin point more accurately.
1. In heavily mineralised soils, they create quite a bit of noice and will not detect nuggets as deeply as the equivalant DD coil. In extreme internalization conditions they cannot be successfully used.
2. With manual ground balancing, they need to be tuned more frequently.
3. They will create many more false signals in heavily mineralised soils, and be more sensitive to hot rocks.
4. The search pattern is much narrower at depth, so the ground cannot be scanned as quickly.
As can be seen from the above, one cannot say that either coil configuration is better than the other. It depends on the particular goldfield, the soil types, and even the size of the nuggets. It also depends on whether one is prospecting old previously detected ground or new ground. Also with the larger heavier coils, the condition of your back can come into the decision-making process.
Let’s examine different types:
LARGE MONO COILS,
Large mono coils of around 14 inch and upwards give the best depth on the broadest range of nuggets in most soils. With an 18 Inch mono coil I have detected a 4-ounce nugget at 90 centimeters. Large coils should be used in deeper ground where gold has either been detected before or it is likely to be found. A round coil will detect deeper than an elliptical coil of the same length because of its symmetrical shape, but elliptical coils will fit into tight places and are lighter for their length which gives an advantage in ground coverage speed.
SMALL MONO COILS,
By very nature of their size, they will detect tiny pieces of gold but may miss the deeper bigger pieces. I remember detecting two small nuggets with a large mono coil. I scanned the immediate area and could find nothing else. I then thought I would try the little 8” mono on exactly the same patch, which was only room sized. There were signals everywhere! In all, I collected about 40 nuggets totaling about 14 grams. Having the right coil for the job can make a big difference. Little coils are good for detecting creek and gully beds among the bedrock crevices and boulders where only small coils can fit. They are also ideal for detecting between tall clumps of long grass where you can’t fit the bigger coils.
LARGE DD COILS,
Are best used where the ground is highly mineralised and deep, with the possibility of larger nuggets being found at depth. They are not very sensitive on very small bits of gold, so you wouldn’t use them in shallow ground which has been detected before, as it is mainly small bits that have been missed you are searching for.
SMALL DD COILS,
Are best used where the ground is highly mineralised and you are looking for small bits of gold in shallower ground with little likelihood of striking a big nugget at great depth. .
MEDIUM SIZED COILS,
from 14 Inch to 17 Inch are the most popular by far, as they are a good compromise, and are not heavy.
A good coil choice for most amateurs would be: A Medium sized Mono and a Medium DD coil. If you want an even better range of coils, add a 10 Inch elliptical mono and a 24 Inch elliptical mono to your kit.
Having the right coil for the job can make a difference of thousands of dollars worth of gold in many situations. I would hate to think that for the sake of saving a few hundred dollars in coil money that I had to give up early on that productive patch of gold, just because the ground became too deep to detect in or many of the nuggets were too small to detect. It would be frustrating to give up on that likely looking rocky ground, because you couldn’t fit a coil between the boulders. To some hobbyists who only spend the occasional weekend on the goldfields, buying too many coils might be a bit of overkill.
For most serious seekers, having the best range of coils will mean more gold, particularly if they visit a variety of goldfields and meet up with varied situations.
See you out there!