Hot Rocks, page 5

Here are a few methods that can help you lessen negative effects of the most troublesome hot rocks:

• 1) If you are running a VLF metal detector, a Double D (DD) search coil will be your best choice of the coil type for dealing with hot rocks. The DD configuration, with its narrow "blade" of transmitted electromagnetic field, will substantially help muffle some signals generated by the positive hot rocks, and reduce the ground noise. A small search coil, especially a "sniper" coil of 5", 5" x 3" or 6" x 4" in diameter, will work best in the hot-rock-infested search area. The Double D search coil always gives a better target separation in any target-clustered environment but does not detect targets as deep as a Concentric and Monoloop coils of the same size in areas with light concentrations of detectable targets and iron trash.
• 2) Implementing high levels of Reactivity (also called Speed of Response, Recovery Time or Recovery Speed) will ensure excellent Target Separation in the positive-hot-rock-clustered areas. If you combine the high Reactivity setting with the sniper search coil, you will have a quite capable metal detector, and be able to detect desirable targets that lie underneath the positive hot rocks, and therefore, are partially masked.
• 3) You may want to lower the maximum acceptable level of Manual Sensitivity a few units down. In most cases of detecting on the highly mineralized ground, lowering the Sensitivity level actually allows for greater Detection Depth (see details in my article - Busting Myths About Metal Detector's Sensitivity, Discrimination and Depth) while silencing the negative hot rocks positioned at depths.
• 4) If your detector incorporates adjustable Signal-amplifying and Transmit-Boost controls, reduce their setting and elevate a search coil slightly above the ground when searching. This will cause a loss of some Detection Depth and Sensitivity, but also will quiet many "zips" coming from the positive hot rocks.
• 5) Simply increasing the Conventional Discrimination level or amount will just not work as many desirable targets with VDI values below and above a selected rejection level will be silenced (see my note below). However, if the Notch Discrimination is available and potent enough (not cutting off adjacent VDI values of desirable targets), it may help eliminate the detector's audio responses to the most redundant positive hot rocks. Just make sure that conductivity ranges of desirable targets are not included in the rejecting notches, or "clipped" by them. Also keep in mind that the Notch Discrimination is a type of Conventional Discrimination and, therefore, can reduce the Detection Depth (more info and details are given in my article - "Less Discrimination Lets You Find More").
• Also the Two-Dimensional Dot-Discrimination of the Minelab FBS metal detectors may help mute the signals generated by the most redundant positive hot rocks. Just like in a case of the Notch Discrimination, make sure that the Fe-Co portions of the 2-Dimensional Discrimination pattern, that contain Fe-Co values of desirable targets, are not "clipped" by the rejecting "squares" in the Disc pattern. The Dot Discrimination is also a type of Conventional Discrimination and, therefore, can reduce the Detection Depth.
• NOTE: When setting a level or customizing a pattern of Conventional Discrimination to detect with less incoming audio noise, one should always keep in mind that often small and/or deep targets, when being detected in the highly mineralized ground, emit electromagnetic fields that get suppressed by mineralization and become very weak by the time they reach the search coil's receive windings. These weak signals do not manifest real Conductive or Ferrous-Conductive (FE-CO) properties (phase values) of detected targets, and are rather registered as electromagnetic fields corresponding to ferrous targets with certain conductive properties by the metal detector's Discriminator. In the worst case, if these conductive properties are within a rejecting range set by an operator, the valuable non-ferrous targets will be silenced. This is the best way to miss the deepest coins positioned within the detector's Operating Depth Range.
• 6) If you encounter and recover a few positive hot rocks, including the ones lying on surface, in the search area, and noticed that they are homogeneous, memorize what the rocks look like in this particular location. At least when you get an audio response to a hot rock lying on the surface, you will immediately recognize it and ignore. The hot rocks of both negative and positive types are fairly homogeneous in any given area, so you should only have to memorize a few different types. This simple practice will help you maintain a good time efficiency in the field.
• 7) If you attach a small Rare-Earth magnet to your pickax, you will be able to quickly identify most hot rocks which will be attracted to the magnet. However, for example, some meteorites are magnetic too and could be easily confused with the hot rocks if one does not know how to ID the meteorites. Fragments of iron junk and other ferrous objects will always be attracted to a magnet. Only gold will not be attracted to a magnet. But this is a different story...

Advanced Pulse Induction (PI) type metal detectors effectively ignore both types of hot rocks as well as the pockets of concentrated mineralization in the ground. Unfortunately these detectors do not have a Discriminate function, i.e. they can not reject targets, and therefore would be impractical to use at the trashy hunt sites.

The VLF metal detectors that are specifically designed for the gold-fields will respond to the positive hot rocks as well as all the common VLF machines. All but one - XP Deus, which is the only VLF metal detector that incorporates a revolutionary feature called Notch Ground. This feature easily takes care of all positive hot rocks as if they do not exist, and do not compromise the detector's Ground Balance, Depth Penetration ability and, therefore, the Detection Depth. More information and details are given in my article on the XP Deus' Manual Ground Balance Mode - Function and Effects.

I hope that now you know how to deal with the hot rocks and improve your detector's performance. Please keep in mind that encountering both types of hot rocks in a search area happens quite often, and if to add the annoying effects of mineral salts to the "soup", it may take you some time to fine-tune your machine to these adverse metal detecting conditions, i.e. to determine an optimum combination of the search program settings. Make sure you know your metal detector well, and it is a capable machine. And always remain patient.

"Hot Rocks"

Happy Hunting!

In case you have seen some terms in the article and do not know what they mean, soon there will be my inclusive "Glossary of 1,700 Metal Detecting Terms" available on this website, and you will be able to easily find definitions to all terms unknown to you.