[meteorite-list] Re: Looking for Buried Iron-Shale with a Metal Detector

[Notkin]

Dear Paul, Dave and List:

I agree with my friend Dave Freeman's comments from yesterday but I'd 
like to add to them.


> If by some chance I had a hunch where I might
> find some buried iron-shale, is it possible to find
> highly weathered meteorite (iron-shale) with a
> metal detector?

As long as there is some iron remaining, and conditions are favorable, 
I would say very likely. When old iron meteorites decay into shale, 
small pieces may flake off over time, creating a three-dimensional 
"halo" around the original iron. This halo will often be larger than 
the volume of the original meteorite. In some cases this actually makes 
the signal easier to hear, as detector-sensitive flakes or fragments 
have been distributed over a larger area. I have some *extremely* 
weathered shale fragments that will still stick to a magnet and still 
set off a decent detector signal.


> If so, what is the approximate relationship between
> size of a piece of iron-shale and the maximum depth
> at which it can be detected?

I'm not sure that there's a hard and fast rule or equation for this. 
The maximum depth at which you can find something depends not only on 
the size of the target, but also the type of ground in which you are 
hunting (is it wet/is it dense/is it mineralized?), and the make and 
sensitivity settings of your detector. Without even trying I can think 
of six or seven people on the List who have much more expertise than I 
do with detectors. Perhaps one of them would have a better idea on this 
(good question).


> Also, are there any special tricks to using a metal detector to look 
> for
> buried iron-shale?

Shale can produce a curious signal. It may not be as loud or strong as 
the signal from a solid iron, but it may appear to emanate from a large 
area. You may also hear a very rapid "zip-zip-zip" sound as the 
detector coil reads multiple fragments of shale in close proximity to 
one another. If you are talking about a really large piece of shale in 
the ground, and your detector is properly balanced, I think it would be 
hard not to get a reading. If you are hunting deep targets, or targets 
with a weak audio signature, using headphones can help a great deal, 
but watch out for rattlesnakes -- you won't be able to hear them  : )

I would recommend practicing. Have some fun with it! Bury a piece shale 
in your garden at different depths and try different calibrations of 
your detector to see what works. I do this whenever I get a new 
detector, and jokingly call it Metal Detector School (yes, the wild 
part of my garden is full of holes, but it's the desert so who cares?).

You will also need a detector that responds well to iron. Certain 
detectors are intentionally made by the manufacturers to ignore iron 
(these might be used, say, for nugget or coin hunting). Some detectors 
that have proven popular with hunters on the List would include the 
White's Goldmaster III; White's Goldmaster V/sat; Fisher Gold Bug and 
Gold Bug II.

I'd be happy to send you a piece of meteoritic shale to experiment with 
if you don't have one handy.

Good luck, and keep us posted!


Regards,

Geoff N.