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Do You Consider Your Soil Highly Mineralized And Where?


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For the most part all my permissions or sites that i have detected on over the years are pretty mild mineral content,i do almost all my detecting just north of roman Londinium and never really have any major issues ground mineral wise,but i/we have access to a roman trading villa sites that has been detected for i guess just over 12 years,this sites was a active roman trading site for 400 years,so the amount of coinage that has been found with detectors without exaggerating must be approaching a 5 figure amount its been that prolific.

Only trouble with this site the ground is basically just like black sand from the beach,very highly mineralised but just natural occurrence and not man made,the only machines that will really work on the site and produce finds is multi freq VLF and Pulse machines ,the current king and will be ongoing is the Equinox,and also CTX and Etrac's.

This one of unique site is possibly the hardest site that i have detected,but it still keep producing finds on a regular basis even after all these years.

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On 8/12/2019 at 10:41 AM, GB_Amateur said:

It's worth noting that the map shows iron concentrations totalled over all chemical forms, not just the insidious (to detectorists and other gold recoverers) magnetite.

Interesting... I hadn't considered that some iron compounds might not sway the detector.  I was thinking that most iron compounds had some (varying) degrees of magnetic susceptibility.  Perhaps not.  However, one particular clip from that excellent Fisher reference you cited said something that made me wonder, again, if elemental iron is a problem.  Here's it is:

Quote

Most iron-bearing minerals exhibit magnetic effects similar to that of magnetite (i.e., low loss angle), but with much lower magnetic susceptibility.

I appreciate Steve's comment that localized variations can be dramatic and multifactorial.  Now, I'm back to wondering if that map reveals any generic trend in detecting difficulty.

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I agree with Gerry in regaurds to Montana being very very hot. The best areas I hunt are impossible with a vlf, but the monster is in fact capable if you reground balance often when it gets too noisy. Some areas you can't even move your coil an inch in any direction. This isn't just for a few feet or yards but 1-5 miles. You can see the black sands on the surface and if you dig down 5 inches, 10 inches, 1.5 feet, 3 feet, it is the same thing. Not tell tale signs of black sand but the dominant regolith is black sands and  granodiorite.

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18 hours ago, Skookum said:
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Most iron-bearing minerals exhibit magnetic effects similar to that of magnetite (i.e., low loss angle), but with much lower magnetic susceptibility.

 

Pretty sure the 'low loss angle' refers to the phase shift (related to target ID).  I think that shows up as the ground reading (phase) and setting.  But the magnetic susceptibility is the property that leads to loss of depth.  Maghemite also has high magnetic susceptibility.  When your manget picks up black 'dust', that's magnetite.  When the attracted dust is brown/tan it's maghemite.  At least that's my simple minded view.  BTW, I could never remember the word 'maghemite' until I just read (while researching my above post) that its first two syllables are 'mag' (from magnetite) and 'hem' (from hematite):  mag-hem-ite.

I don't mean to downplay the presence of iron as causing problems.  Even "mildly ferromagnetic" material can affect things if enough is concentrated.  It's the ferromagnetism that is the issue.  Iron in some compounds isn't ferromagnetic.  It just depends upon the form (compound) of iron, and there are many different types in nature.

 

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  • 1 year later...

 I would have to agree with Jerry on Montana. There are areas I detect that a vlf is 100% unhuntable and when you use a pulse induction detector you will still have hot rocks come through every couple feet. I have found the only thing you can do with the 5000 is hunt in high mineralization in order to wipe out all the hot rocks. It isn't just the hotrocks though. If you dig down in the sides of these washes you will hit a layer of black sand about 3/4 of a foot down and I tried to dig past that layer, only to never reach the bottom of the black sand layer.  It wasn't black sand mixed with lighter sands, but solid layer of pure black sand.

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Just a couple of site-specific notes on the Pacific Northwest based on some limited initial VLF detecting.  In the Oregon Cascades, the Quartzville Mining District appears to be an area of mild mineral content.  In eastern Washington, the area about 10 East-Southeast of Spokane, in the Spokane Valley area is also of mild mineral content.  In both instances I have focused on small areas where I had permission to use a detector.  Other areas nearby may be different.

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On 7/8/2019 at 9:24 AM, AllenJ said:

The PI won't see small gold nearly as good as the VLF

IMHO, the SDC is as good with small gold as the GB2 or GM1000, especially with the SP01 combo. And yes, where I hunt the soil is highly mineralized (Motherlode). Especially with the ultramafic Serpentine outcroppings that are part of the Motherlode belt. However, the worst soil I have encountered in some areas of the Mojave desert in Southern CA. Some of these areas are so rich in iron that the compass doesn't even work (magnetite, iron-rich basalt, iron ore, etc..). Go figure....

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  • 1 year later...
On 7/8/2019 at 9:24 AM, AllenJ said:

I'm in Northern California and yes, that is my experience up here.  Our soil is all over the place, to the point that VLF's can be pretty much useless in certain areas due to mineralization.  I ended up getting a PI and the difference was unbelievable.  The PI won't see small gold nearly as good as the VLF but at least you're looking for gold and not digging up hot rocks and ghost signals!

I'm up in Northern California as well. While still a novice, this has also been my experience. It's tough ground to learn on!

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If anyone in the US can find a spot where you can actually weld the soil into pig-iron, you are getting into semi-Australia type conditions. I haven't seen or heard of anything remotely similar there? 

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2 hours ago, Aureous said:

If anyone in the US can find a spot where you can actually weld the soil into pig-iron, you are getting into semi-Australia type conditions. I haven't seen or heard of anything remotely similar there? 

So true…… the next time I see an ironstone outcrop (here in WA) that has been struck by lightning, I’ll be sure to take a photo. It can look like a small solidified lava flow 😳

 

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