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Don’t walk away from a weird target.

I went back to a spot I found late last year that left me somewhat confused. This small area of exposed bedrock sounded off as a strong target with my GPX4500 but not a peep with my Eureka Gold VLF. At first I thought it was a strange hot rock area, but with no response from the VLF (a notorious hot rock detector), I was perplexed. To make matters worse, no matter what timing setting I tried on the PI, it still registered as a target in solid rock. The fact that the VLF didn’t respond made me think the target might be beyond the depth sensitivity of that machine so maybe a second look at this spot was in order. …Turns out that this was correct.

The target was located in a small garnet-laced seam (about 6 inches wide) sandwiched between limestone bedrock. I managed to convince my much more “motivated” son to chip away at this garnet seam with a mallet and chisel for a few hours until he broke through to a small, red clay-filled cavity located underneath; about 7-10 inches down. There we found many delicate, paper-thin pieces of gold locked in the clay. To date, we recovered about 3 grams of the good stuff but I’m still panning out the clay from the hole.

I’ve never seen this type of leaf-gold in this area. I wonder if it was originally formed in a hydrothermal event with the gold being deposited between cracks in the garnet rock. But over the years, maybe the rock in this pocket deteriorated into this red clay stuff leaving the gold still trapped in it?

Here are some pictures of our finds, and my son’s handy excavating work.

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That is a very interesting hole in the ground, not kidding. I'm talking about the strata around the hole. very cool looking leave gold too. I dont know why but for some reason that photo just struck me. If I figure it out I'll let you know. AzNuggetBob

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LabYankee I think you are correct. It appears to be an old Hydrothemal vent. They are formed under the sea when the land was covered by ocean. Just hot fluids, mineral rich (solutions)coming up out of an old volcanic vent under water from below and precipitating minerals at the surface as they hit the cold alkaline ocean water..

Two things are happening here to form this.

First hot solutions hitting cold water.

Second the PH of the solution is instantly changing from acidic (from iron) this free's up the metal from below to alkaline from ocean water. both can cause precipitation of the metals back out of the solution in a confined area. this can also cause pockets with no real vein structure. sort of a pipe.

AzNuggetBob

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  • 3 weeks later...

LabYankee I think you are correct. It appears to be an old Hydrothermal vent. They are formed under the sea when the land was covered by ocean. Just hot fluids, mineral rich (solutions)coming up out of an old volcanic vent under water from below and precipitating minerals at the surface as they hit the cold alkaline ocean water..

Two things are happening here to form this.

First hot solutions hitting cold water.

Second the PH of the solution is instantly changing from acidic (from iron) this free's up the metal from below to alkaline from ocean water. both can cause precipitation of the metals back out of the solution in a confined area. this can also cause pockets with no real vein structure. sort of a pipe.

AzNuggetBob

I spotted this today and thought you may find it interesting.

http://www.bbc.com/news/science-environment-27158883

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Hey Guys,

Brings back a memory of a nuggethunting friend about 15 years ago that discovered a vein of "foil gold" around the same depth with a Minelab metal detector here in Arizona. He was hunting along some ridges since he found wire and nugget type gold in the gulches and ended up getting a good target on solid Granite bedrock. Hours after digging through the solid rock, he had several ounces of foil gold. He ended up sweeping up the area and panning a bunch of smaller foil pieces he couldn't detect. It was a strange discovery since the area wasn't known for foil gold, more so wire nuggets and specimens.

Thanks for sharing!

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AzNuggetBob,

Thanks for the geological tip. This area was underwater at one time, so your theory on the formation of this pocket makes sense. We’ve recovered a bit over 5 grams of leafy stuff from that hole, and are following the seam up the hill. I keep finding small, garnet/quartz/calcite (tactite?) outcroppings laced with this type of gold in the bedrock.

No “bonanza” yet…but hope springs eternal!

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Labyankee

Ive worked at a lot of small mines and some large ones too. I still love hunting with a detector. prospecting can start with a small discovery, but can also turn into a large mining operation too. :) Good luck, AzNuggetBob

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