Index of topics:
Can I find gold nuggets with a metal detector?
How long are you talking about?
Do they detect only gold?
How small a nugget can I detect? How deep can I detect it?
What is frequency, and how does it relate to the performance of the
metal detector?
What is MPS?
What about Molecular Frequency Detectors (MFD's)?
What do searchcoils do?
Definitely! Whether you actually will or not depends on several things. First, you must have a detector capable of finding small gold nuggets in mineralized ground. Second, you must understand the operation of your detector thoroughly. Third, you must place yourself on ground that has gold nuggets reasonably close to the surface. Fourth, and last, you must be PATIENT & PERSISTENT! Successful nugget hunting requires skill and knowledge, and you must give yourself a reasonable amount of time to develop your skills. The first gold nugget is most often the hardest to find, but is also one of the most rewarding.
If you have someone guiding you, or you just get plain lucky, you may find gold on your first day. It is more realistic, however, to expect to put days of work into finding that first gold nugget with your detector. How many days depends on how closely you follow the guidelines in the item above. Remember, even the best operators will get skunked every once in awhile, especially when checking out a new area for the first time. Every area seems to have it's own little tricks.
Unfortunately, no. Gold nugget detectors are simply very sensitive metal detectors, and as such can pick up any conductive and many magnetic items. Almost any metallic item is detectable, as are iron ground minerals and iron mineralized rocks due to their magnetic properties. Wetted salt materials, such as beach sands or wetted desert salt flats after a rain are electrically conductive, and will therefor produce interfering signals on metal detectors. The high frequency detectors will actually detect a human hand, as the salt content of blood is conductive enough to produce a signal.
Coin detectors feature a discrimination system that is based on the target's conductivity. Less conductive targets, such as iron or foil, are tuned out as "trash". More conductive items, such as copper or silver, are accepted as "treasure". Unfortunately, gold nuggets, because of their varying size and purity, are impossible to place with any accuracy in this system. A small nugget does not have much conductive mass, and would commonly be rejected as "trash" at even low discrimination settings on these type detectors. However, many mining areas have a lot of trash targets, especially iron and steel targets such as nails and rusted metal objects.
Because of this, many nugget detectors offer a simple "iron rejection" circuit to tune out such items. Iron is a poor conductor, and so it is tuned out at levels that will accept most, but not all gold nuggets. Such "iron ID" circuits are best left off, unless the amount of iron trash is such that one is about to give up and walk away. In these instances, a few lost nuggets are preferable to quitting and finding none at all. This type of discrimination can also be helpful for identifying some types of iron mineralized rocks (hot rocks).
The Tesoro Lobo Super Traq and the Garrett Scorpion Gold Stinger offer full-range discrimination controls like those offered on most coin hunting detectors. While not normally used while nugget hunting, this feature makes these machines more useful as general purpose detectors. While in this mode they operate much like a common coin hunting detector. The other detectors made for nugget hunting may be used for coin and jewelry hunting, but they will detect so much trash that the patience required to operate them for long will elude most people. Those that persist, however, may be rewarded with deeper targets overlooked by those using regular coin hunting detectors.
The answers to these questions are related. A very sensitive detector can detect a piece of gold weighing less than a grain! This barely qualifies as a nugget.
However, such a small item would have to be at or very near the surface to be detected, and then only by a skillful operator. The larger the gold nugget, the deeper it may be detected. Detection depths are almost always measured in inches, not feet. To give a rough idea, a matchhead-sized nugget can be detected at two to three inches. A dime-sized nugget can be detected at six to eight inches. A nugget the size of a US quarter may be detected at ten inches or more. Only the very largest nuggets, measured in ounces, will normally be detected at depths exceeding one foot. Most nugget detectors can not detect even the largest metal objects beyond three to four feet.
These figures will vary depending on the detector, the size searchcoil used, the amount of ground mineralization, and the experience of the operator. Keep in mind that detection depth is measured from the bottom of the searchcoil, NOT the top of the ground. It is common for beginners to move the coil too high above the ground; each inch over the ground is usually a lost inch of detection depth, except in cases of extreme ground mineralization. Under these conditions, a little distance may be required to get smooth operation from your detector.
Metal detectors are based on radio technology, and are in fact are a type of radio transmitter and receiver, all built into one unit. They transmit on a given frequency or frequencies that could be heard on a radio receiver that had enough range in it's tuning. In general, it is accepted that lower frequency detectors are less responsive to ground minerals and have better depth of detection on larger items. Most coin detectors therefor operate at lower frequencies of around 8 kHz or less.
Higher frequencies are more responsive to smaller targets, but are also have a greater response to ground minerals and mineralized rocks. Gold nugget detectors available today operate in a range from 12 kHz to 71 kHz. Those at the lower end of the range tend to work well in mineralized ground, but are somewhat less sensitive to very small gold nuggets. Those at the higher end of the range are very sensitive to the smallest gold nuggets, but may be troublesome or impossible to operate in ground that is heavily mineralized or that has a lot of mineralized rocks (hot rocks). Some detectors offer selectable frequencies to work around this problem.
A related problem is that detectors operating at the same frequency will detect each others signal. They must be operated at some distance from each other so as not to produce interfering signals. This can be a good reason for groups to use different detectors, or models that can be set for different frequencies. The White's Goldmaster 3 and Goldmaster 4/B feature a frequency shift control designed to eliminate the interference of other nearby Goldmasters.
Multi Period Sensing, as offered on some of the Minelab metal detectors, is a variation on pulse detector technology. Most common detectors transmit and receive their signals continuously, and amplify the distortion caused in the electromagnetic field they generate around their searchcoil as a signal to the operator. Pulse detectors operate differently. They transmit, pause, and then receive, in a rapidly repeating fashion. They induce small electrical currents into metal items within range, and while in the receive mode pick up this electrical current before it fades. These types of detectors are fairly impervious to the effects of salt water and mineralized ground, and therefore are most commonly used as diving detectors.
Minelab has modified this technology for use in the goldfields and in areas of exceptional mineralization these machines can outperform any others on the market today. The reported depths at which large nuggets have been found in areas that other detectors have failed on are truly astounding. The downside is they they are generally less sensitive to small gold nuggets, but as other detectors are virtually unusable in severely mineralized ground, this is not really a concern in those areas.
In areas with moderate to lower mineralization the advantage of MPS technology lessens, and they may be out-performed by more sensitive, higher frequency detectors. In ground with low mineralization, most nugget detectors will perform as well as or better than the MPS units. MPS detectors are also much more expensive than transmitter/receiver (t/r) models.
These devices purport to be able to pick up specific types of targets a ranges vastly exceeding that of any detectors on the market today. Claims of "gold only" detection at ranges of a quarter mile or more are not uncommon. There is little evidence to suggest that these units are little more than dowsing devices dressed up with knobs and meters. That is not to say that dowsing may not work. There is a large body of anecdotal evidence that suggests it does for many people. However, whether these devices, which cost many hundreds or thousands of dollars, work any better than simple home-made dowsing devices is seriously in doubt.
These units have one thing in common; they cannot produce readily repeatable results under laboratory conditions in the hands of any operator. Only certain people, at certain times, and in certain places report results, and these results cannot be duplicated reliably by anyone in general. A metal detector, on the other hand, will always produce the same signal on the same target, for almost anyone who operates it. Repeatability of results is the key.
Extreme caution is recommended when evaluating these devices. If they did as they say, the sellers would never need to sell a unit, they would only have to use it! Note that none of the major metal detector manufacturers produce such a device.
The searchcoil (or loop) is an antenna that transmits and receives the detector's signal. It is surrounded by an invisible electromagnetic field. Any conductive or magnetic item that enters this field will produce a response from the detector. It consists of loops or coils of wire encased in a disc-shaped waterproof housing, hence the name. Searchcoils are generally round, or oval shaped on most nugget hunting detectors. They usually range in size from three inches to eighteen inches in diameter. Most detectors can use several different sizes.
Searchcoils ARE NOT interchangeable between most models of detectors, particularly nugget detectors. Each detector usually only works with the searchcoils made specifically for it. The most common are eight to ten inches in diameter, and are usually supplied as standard equipment with the detector when it is purchased. Each model will then usually have a smaller (four inch to six inch) and a larger (ten inch to eighteen inch) searchcoil available as accessory items. This is a generality, however, and is something to check into when investigating a detector model.
Accessory searchcoils are vastly underused, and should be in every nugget hunters arsenal. Simply put, small searchcoils produce a sharper response on smaller targets, but with an overall loss of depth and ground coverage. Large searchcoils produce sharper responses on deeper, larger targets, and cover more ground, but with a loss of sensitivity on smaller targets. The medium-sized searchcoil that comes with the detector is the best all-around solution.
The electromagnetic field around a small searchcoil is smaller and more intense, and more sensitive to small items. The field around a large searchcoil is larger and more diffuse. It reaches deeper but is less sensitive. A side effect is that the small searchcoil "sees" less ground, and is less subject to the false signals produced by iron ground minerals. The large searchcoil "sees" more ground, which enhances the ground response.
Envision the large searchcoil as the high beams on your car, the small searchcoil as the low beams. With high beams on, you can see large items, such as a deer, at a distance. Smaller items, such as a rabbit, directly in front of the car are less visible. When you switch to the low beams, you can now see the rabbit better, but the deer is dim or invisible. Now imagine it is raining heavily or snowing. The high beams (large searchcoil) reflect too much light back, and you cannot see at all. Heavy ground iron does the same to your detector with a large searchcoil; it blinds it. Now switch to your low beams (small searchcoil) and you can still see the rabbit in front of the car (or the small gold nugget just under your searchcoil). Small searchcoils handle mineralized ground better.
The ideal scenarios are these. When searching bedrock, with nuggets lodged in shallow crevices, use the small searchcoil. You will find smaller nuggets that you may have missed with the larger searchcoils, and the chances of missing a deeply buried large nugget are slim. You will also find the smaller searchcoil fits into depressions in the bedrock a larger searchcoil cannot fit into. When searching a tailings pile left by an old bucketline dredge, use a large searchcoil. Such dredges were very good at small gold recovery, but discarded most material over about two inches in diameter as waste. There is little chance of finding a small nugget in such a waste pile, and the extra depth obtained by the larger searchcoil may find the large nugget others have missed.
Finally, when in heavily iron mineralized ground, a smaller searchcoil will stand a better chance of producing gold while ignoring the false signals produced by the ground to a greater degree. The first accessory searchcoil purchased would normally be the smaller one, as there are far more smaller nuggets than larger ones. The simple advantage of being able to work in tighter areas will often produce nuggets others overlook.
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