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Date Posted: 09:41:11 10/14/02 Mon
Author: Jim McCulloch
Subject: Quickly identifying hot rocks with the MXT and GMT

For those of you who use the GMT or the MXT to find the Most Happy Yellow Metal, here is how you can easily identify most varieties of hot rocks without digging them: once pinpointed, swing your coil off of the target zone a couple of passes so that the ground balance number on the VDI meter ("Ground Balance" on the GMT, "Ground" on the MXT) ID's the the ground balance number of the soil matrix devoid of the target/hot rock. Once you have noted the ground balance number for the soil near the target, repeatedly pass the coil back over the target zone (short passes) and do two things: listen to the threshold response (i.e. signal produced) and watch the VDI meter. If the ground balance number on the VDI meter remains constant, and, the signal repeats with the same intensity with each pass of the searchcoil, then you have a metallic target (hopefully AU), OR, in my area at least, a "zipper" hot rock, i.e. one of the red/black high-iron garnets. If the signal abates with 3 to 5 passes, and the ground balance number drops 5 to 10 points, then you have a hot rock. In short, what you are doing is tuning out the hot rock (which explains the reduction/cessation of the signal) AND the drop in the VDI number reflects the new ground balance setting due to the presence of the hot rock. Once the hot rock is ID'ed, pass the coil off of the target zone, pump it up and down a couple of times to restore proper ground balance (to the soil matrix) and continue hunting. Saves lots of time, and unneccessary digging. In my area the weaker grey hot rocks drop about 5 points on the scale, the darker grey ones 7 to 10 points, and the red "volcanics" fully 10 to 12 points. Naturally, you will have to experiment to see how things react in your area. Hope this helps; horray for cooler weather in the Mojave, lots more "Mojave Midgets" are now being deposited in my safe deposit box. HH Jim

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