Strange "hot bedrock outcrop" or something else?

[leviterande]

Hi!

So I am in what I believe is a possible potential creek where I found many rusty quartz rocks with small bits of pyrite(also, other rocks where the pyrite is sandwiched between the quartz and the rust; none of them gave any signal). Only things otherwise that gave signal in the entire creek are nails, metal trash, coins found in crevices.

Big red/rusty(?)stained rocks are also here and there but they never give any signal.


Now, here I was scanning a big bedrock outcrop when all of the sudden I got a pretty strong signal on one point on the bedrock where there are no crevices. It is clearly something metallic inside the bedrock. Thus wonder if it is a hot rock. How do I know? No reaction from a magnet and the entire creek is filled with similar huge rocks that have the same color but that dont give any signal. It is only on that bed outcrop that I get a very strong signal when I pass over a point of perhaps 3x3 inches. I halfed the sensitivity and the signal is still there. I swapped from all directions and the signal is as strong on that spot


I tried to break the rock but that seemed fruitless as it was very hard, I really want to know how to find out if it is a hot rock. Any methods on how?

1st pic is the bedrock outcrop. Red circle is around the "hot spot"
2nd pic is the hot spot after trying to break through it w/o success

Thank you for your time and patience
Best Regards

 

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[kcm]

Pyrite will often set off MD's, even if there is no other metal in the rock. I have some sulfide ore from South Dakota that will set off my MD, but my friend who owns the mine says that sample is 100% metal-free. However, LOTS of glittery gold stuff in the sample - just nothing worthwhile. However, that's not saying there's NOT metal in your rock!! Only one way to find out - keep at it with the hammer and chisel!

 

[Jim Hemmingway]

Hi Leviterande… I’m not a goldhunter but do hunt silver in Northeastern Ontario. I’ve run into similar signals on bedrock outcrops when out float hunting while using a VLF unit. Such signals were broad and much less distinct than a signal produced by native silver. If your signal leaves you in any doubt, you will have to break it out of the bedrock.

These type of signals in my area were invariably produced by a dramatic difference in iron minerals (that resulted in quite different ground phase and magnetic susceptibility readouts) that exist between the host mafic (rich in iron minerals here) bedrock and the anomalous felsic (quartz, feldspar for example, normally poor or devoid of magnetic susceptible iron minerals) material that produces your signal.

Use the motion all-metal mode with a small sniper coil, and preferably use the autograb feature if your detector has it. Do a ground balance over the bedrock and note the readout. Then ground balance over the spot producing a signal and note the difference in readouts. If the ground balance over the spot falls much lower on your ground balance scale, it indicates a comparatively more conductive material… hence a signal is produced.

Now if the above explanation is incorrect and there is actually metal present in a former crevice that has sealed over, a signal should continue to be present even after you’ve ground-balanced over it. Signal interpretation is a bit tricky in this instance because that spot by itself is quite different in its chemical make-up from the host bedrock. Again… if there is any doubt about it, then you will have to break it out with a small sledgehammer and chisels to know for sure.

It seems likely that similar-looking rocks in the stream don’t produce a signal because they are not embedded in that host bedrock. If you happen across one that produces a signal, it could contain metal, or it could be a result of embedded iron pyrite oxidizing to a rusty-looking material that could be a highly magnetic susceptible iron-mineralized substance named maghemite… which could very well generate a positive (hotrock) signal.

The commonplace rusty appearance on most rocks present in the stream is likely a very weakly magnetic, highly oxidized iron mineralization generically described as limonite or otherwise known as nature’s rust. It doesn’t have much or any effect on metal detectors with respect to producing hotrock signals. Hope this helps a bit, good luck with everything…

Jim.

 

[Lucky Eddie]

18 V Lithium Ion battery powered angle grinder and diamond blade. Slice it and break it out with a crow bar, until you get to whatever sett off the signal.
At least you will know one way or another what your dealing with!.

Or

Drill it with tungsten drill bit and blast it with a heavy cover of conveyor belt rubber to trap the debris for further analysis!.

 

[leviterande]

Thanks a lot for the replies!

I have considered using a magnetometer(which I dont have) but if it is indeed a big lump of pyrite than the magnetometer wont react since its also paramagnetic as the gold. I have found many pyrite filled rocks that wont give a signal but it perhaps because the pyrite amount in the smaller rocks is small..

But still, a magnetometer would signal if it is just a piece of some iron and not gold.

I have unfortunately not that autograb feature.
I am sure it is just a false signal coming from a some kind pyrite, magnetite etc(actual gold trapped in bedrock is very rare?) but 1% of me is saying the signal "sounds good" hehe

Doing it the hard way is the only way. I tried with a sledge hammer and chisel, could barley do anything since this is a very hard rock. I tried an 12v electric drill with a cutting wheel and it barely makes a scratch. I either need a huge sledge hammer or a very powerful battery driven drill/angle grinder. But I will now try to simply drill holes around the target today and use the chisel.

Best Regards
Levi.

 

[leviterande]

Just wanted to let you know that I didnt crack the rock, found out it was pyrite/trash and just left the thread . the score is till 0:1, couldnt crack the thing, its mighty tough so I gave up. I scanned a huge portion of the entire creek and no other rock/bedrock gave any signal except this one.. hmm. Wonder if there is any cheap powerful portable drill machine somewhere.

 

[GreyGhost]

My guess is it's just a hot spot in the rock. Throw a nickel down next to it and find a hot rock around the same area and swing over both with your detector. Get the sound of that solid metal target in your head then swing over the hot rock and swing over that hot spot. Sometimes we just want a signal to be good and real but it isn't.

 

[63bkpkr]

leviterande, lots of good responses here though I thought I'd comment on the Grey Ghost's offering - a metal detector reacts to a Nickel the same way it reacts to gold. I've no idea what you know of metal detecting and you may know this already but in case you are not aware of this, then now you do. From your description of the area you are in it has possibilities for the soft yellow metal. Best of success with your hunt..........63bkpkr

 

[meMiner]

One other thought before you move to a larger hammer. Clean off the spot and look at it with a jeweler's optic. If there is gold, hopefully some will be visible on the outside. Especially, look at where you managed to chip some of the rock and where your detector said was the sweet spot. If it has been a few weeks, also look for new stain on the chipped area. If the new stain is brown = hot rock.

 

[dave wiseman]

Possibly graphite as mentioned many times in posts by Steve Herschback....http://www.detectorprospector.com/forum/topic/2498-detecting-bedrock/

 

[jadocs]

Someone is going to encounter that rock in your second pic and think it's a map or the work of Jesuit Priests.

 

[bug]

If the signal is very intense like a real metal target, from the looks of your bedrock, there is likely a conductive iron sulfide seam/pocket below, or graphite like dave mentioned.
If the bedrock is solid- no crevice cracks visible, or no quartz seam, that is usually the case. Just my experience after encountering hundreds of these in the Motherload

 

[Lanny in AB]

I've encountered lots of spots like that with a VLF. Is that what you're using?

The way I remove all doubt is to get a hammer and chisel and break out the signal. Lots of iron with various accompanying combinations where I detect. Ran in to some ones that pegged on the meter just like gold, but when I broke them out, meter went high and low. But, that way I knew for sure it wasn't gold, and that's what I have to do with signals that mimic the real thing.

Invest in a good masonry chisel, a small hand sledge, and some safety glasses.

All the best,

Lanny