Hot Rocks
How To Eliminate Hot Rock's Response
Hot Rocks are pebbles or rocks that contain more nonconductive mineralization than the surrounding ground to which the metal detector is balanced. When hot rocks are in the detector's electromagnetic field, they disturb the ground balance of metal detector so intensively that the machine reads them as metal targets, i.e. the hot rocks produce a positive or false metallic responses which slightly vary in pitch tone from one area to another. Hot rocks can contain either a mineral density (pebbles) or mineral quantity (large rocks), or both.
The Full Band Spectrum (FBS) system found on the Minelab Explorer series, Minelab E-TRAC and Minelab Safari automaticly adjusts the ground balance every time it gets affected by a more concentrated change, caused by the hot rocks or black sand deposits, in nonconductive mineral intensity. But in case of the high SENSITIVITY setting in MANUAL mode, and SOUNDS set up on FERROUS (pitch tone is based on the targets inductance), the hot rocks can drive you crazy.
They would give you a distinctive "screaming" signal with a solid "silver-like" high pitch tone but without any sound imperfections. One way of determining whether the signal is produced by a hot rock or a good target is to dig a few hot rocks in the area and train your ear to their response. Another way is easier: when a hot rock is pinpointed, it always gives a pulsating signal as if it is a deep target.
"Hot rocks" as well as the areas of highly nonconductive ground may "null" the threshold audio in the All Metal mode depending on their intensity. These are the only things that can null threshold in an All Metal mode of detection.
To get rid of unwanted responses from hot rocks, you can do one of the following changes of settings:
1) Slightly reduce the level of SENSITIVITY setting and switch it from MANUAL to the SEMI-AUTOMATIC mode.
2) Reduce the level of SENSITIVITY and switch SOUNDS from FERROUS to COND (pitch of tone is based on the target's conductivity).
3) If you do not want to reduce the reasonably high level of SENSITIVITY (your metal detector is stable) and change SOUNDS from FERROUS to COND, you can simply discriminate hot rocks, but only if they do not register in the "silver" area on the SmartFind display.
For example, once I extended the black (rejected) crowncaps column up just one square - that was where all hot rocks at one particular metal detecting location registered. And I was not bothered with annoying signals coming from hot rocks anymore.
But on a different occasion, when I was treasure hunting with this discrimination pattern in a different area, I missed a good coin. My treasure hunting partner found it while walking behind me with his less advanced metal detector. I had to quickly change the discrimination pattern on my Explorer not to miss another valuable coin. So, this option should be chosen carefully.
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