Hi Joe,
There tends to be some confusion regarding PI (pulse induction) detectors and VLF (induction balance) gold nugget detectors. Both are reputed to handle mineralized soil well, and so they would seem to have similar capabilities.
Induction balance gold nugget detectors, often referred to as VLF detectors, are good at compensating for mineralized soil conditions. However, because they are very high gain, higher frequency units, they easily detect low conductive items. Salt water or wet salt sand is a low conductive target. You would find that the Goldmasters and Gold Bug would just signal on the wet salt sand constantly, and so be virtually useless on a salt beach. If you stayed to bone dry sand you could use them to find tiny earrings and such that other machines would miss, but basically these just are not machines for a salt environment.
The CZ detectors are among the best available induction balance (VLF) detectors for a salt environment. Single frequency induction balance detectors have a problem compensating for both salt and ground mineralization at the same time. Units processing two or more frequencies are better able to work in a saltwater environment. They do this by adjusting out the low conductive signals from saltwater, but you are therefore unable to pick up tiny gold items a gold nugget detector would easily find. It is a Catch-22 situation. Extreme small gold sensitivity equals salt sensitivity.
Pulse induction detectors, like the White's Surf PI and others, are often advertised as having "Automatic Cancellation of Salt and Ground Minerals". This is somewhat misleading. A PI unit properly designed for a salt environment does not cancel out salt per se. The machine is just designed to not pick up something that is as low conductive as wet salt sand or salt water. This means that you also cannot pick up small gold items that would give a similar low conductive reading.
Most non-ground canceling pulse induction detectors also tend to be less adversely affected by ground mineralization than induction balance detectors, but they are indeed affected by it. Still, in saltwater/black sand environments pulse induction detectors generally will get better depth that induction balance detectors. The price you pay is that in general they pick up all metallic targets, whereas a detector like the CZ-6A and others can eliminate most iron and steel items, and even some conductive items like pull tabs (and rings!) if you choose.
Pulse induction detectors do not totally ignore ground minerals, and if you run into bad "hot rocks" you have problems. A hot rock is a rock that varies significantly in its magnetic or conductive properties from the surrounding soil, and so which read as targets on metal detectors. Induction balance detectors like the most common nugget detectors have huge issues with hot rocks. Most PI units like the Surf PI or Goldquest work well in an environment where the background mineralization is roughly the same. But put a nice basalt cobble in quartz sand and you will get a good signal as the basalt varies so much from the sand.
This problem is worst in prospecting locales, and so ground compensating pulse induction units like the Minelabs were developed. These machines do actually compensate to a very high degree for the ground mineralization. Some here will point out that by properly detuning their non-ground balancing PI units they can work in mineralized environments. But there is a difference between detuning and proper ground balancing, and a ground balancing PI units will get better performance in the worst ground mineralization.
But, these ground balancing PI units are designed specifically for prospecting, and so are designed to detect very low conductive targets. They also have problems with wet salt environments, just like induction balance gold detectors. Some do have "salt" settings, however, which adjust the machines to ignore low conductive salt... but once again there goes the small gold!
As Eric has said, designing a detector is quite the balancing act. Concentrating on one type of performance tends to take away from another area of performance. The abilty of a Goldmaster to hit tiny gold hurts it in a salt environment. And what makes a PI unit good on a salt beach hurts it on tiny gold.
It is certainly possilbe to pick a "best" detector for any given task. But if detect in many different environments for different types of targets, any one detector will be a compromise. Which is why I have four metal detectors, and some people have many more!
Steve Herschbach
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