Did you ever wonder?
We talk about magnetic viscosity and all the side effects like the need for ground balance and then we can take a PI to a saltwater beach and often to a running stream and have no ground effects. Yes, you can hunt with a PI with no GB. In fact, the most common pi's used on saltwater beaches are straight PI's.
Why is this? Well, the answer isn't that simple and to be honest, I can't give you an ironclad response except to say that what I have found is washed beaches (washed by the water) or washed streams are basically free or nearly free of any form of clay type materials.
I remember when I first began using a PI and how it was so sensitive to the typical ground. Then I went to a claim owned by the GPOC here in Colorado and there at or near the active stream bed, I could use that same PI and get no ground response. Move up the bank and the ground signal was back.
I found this to be true on other streams, so before I knew how to develop a ground balance feature, I spent a lot of time using my knowledge which allowed me to hunt areas where gold could be found.
Later I found that some drywashes displayed this same condition, so there was places where I could hunt even in AZ with no GB.
Once I figured how to build a ground balance system, I pretty well forgot about the ability to hunt certain areas without the GB feature.
Extensive studies have been made about clay type materials and even papers have been written on the subject as to how clay based materials cause responses on both the VLF and the PI. In fact, in one study by the the US government, they went so far as to state that clay type materials create opposing signals that basically fight back and limit the potential depth in such materials. I haven't seen that article in years, unfortunately, so posting a link is not available at this time.
On a little different note, there are many active streams and even some saltwater beaches that are not free of signals and thus require a GB feature. Generally, the reason is the beach or stream bed is comprised of a basalt (volcanic) base and this is what is causing the ground effect.
The point of this post is to point out that there are other less obvious reasons for ground signals.
Reg
PS: "A rather rare effect, but one which can occur,
particularly in clayey soils, is that of induced polarization.
Rapid termination of the transmitter current can charge up
the minute electrical capacitors in the soil interfaces
(induced polarization). These capacitors subsequently
discharge, producing current flow similar to that shown in
Figure 4-27, but in the opposite direction. The net effect
is to reduce the amplitude of the transient response (thus
increasing the apparent resistivity) or even, where the
effect is very severe, to cause the transient response to
become negative over some range of the measurement
time. Since these sources of reverse current are localized
near the transmitter loop, using the offset configuration
usually reduces the errors caused by them to small values"
This is a quote from the article I mentioned that discussed what can happen within a clay environment. So, now induced polarization is a new item to review.
The above added info came from;
http://en.openei.org/wiki/Time-Domain_Electromagnetics
Just drop down to the bottom of the page and select 6 under the references. The above info is located at or near page 39.
