Need help with ID on copper nuggets

[Idaho Jim]

Yes...the reason for this thread is they don't look like the others I've found either. One more interesting thought on these. The more I look at them, the more convinced I am that they formed in a cavity in the host rock. The black "rind" may be a layer of that rock. I'm certain these eroded out of a rock outcrop  that is currently not visible at the surface, and they didn't travel far. Dave and I covered a lot of ground last week. These were the only natural metal we found. They were both in the same dry wash, and 208 yards apart. Both were about the same distance from the bottom of the wash. I assume where they were was where the wash bottom was once located, but moved. So now the problem is finding the outcrop. You've been a big help, Morlock, and I appreciate it.

Jim

 

[Desertpilot]

3 hours ago, Idaho Jim said:

None of those really look like what I found. These nuggets are metal...not mineral. They do have a very thin mineral coating, but under that is metal. The thin coating is black, with here and there some copper oxides, or maybe sulphides. But under all that is metal.

 I like your specimens in any case...especially the next to last. We don't have much like them around here.

Jim

No worries,

I guess you can take it to a rock shop or maybe a gem/mineral club? When I get stumped I take my stuff to the University of Arizona in Tucson. They have a pretty good mineral collection.  

[Morlock]

7 hours ago, Idaho Jim said:

Yes...the reason for this thread is they don't look like the others I've found either. One more interesting thought on these. The more I look at them, the more convinced I am that they formed in a cavity in the host rock. The black "rind" may be a layer of that rock. I'm certain these eroded out of a rock outcrop  that is currently not visible at the surface, and they didn't travel far. Dave and I covered a lot of ground last week. These were the only natural metal we found. They were both in the same dry wash, and 208 yards apart. Both were about the same distance from the bottom of the wash. I assume where they were was where the wash bottom was once located, but moved. So now the problem is finding the outcrop. You've been a big help, Morlock, and I appreciate it.

Jim

 

There's a possibility that the "rind" could  be the result of chemical weathering.

That's a nice find and it would great if you could find the source. Good luck.

[Idaho Jim]

6 hours ago, Desertpilot said:

No worries,

I guess you can take it to a rock shop or maybe a gem/mineral club? When I get stumped I take my stuff to the University of Arizona in Tucson. They have a pretty good mineral collection.  

DP. the one rock that has the gray, sawcut side, with the yellowish inclusions looks similar. is it metal, or mineral? You  might put an ohmmeter across that and see how conductive it is. The gray color is close to the metal color on the ones I found.

Jim

[Idaho Jim]

1 hour ago, Morlock said:

There's a possibility that the "rind" could  be the result of chemical weathering.

That's a nice find and it would great if you could find the source. Good luck.

I guess it's also possible the "rind" was the "junction" where the solution was pulling chemicals out of the host rock to form the metal. I forget the term for that. Too old...LOL

I'll go back down sooner or later, and do a more exhaustive search. Years ago, Dave and I were in a gold area, riding our Rokons, and happened on a crew that was surveying an old site. They were laying small wires on the ground, and surveying them in lines V'd out from a source transmitter/receiver of some sort. The wires went, out 1/2 mile or more. They said they could put signals on various pairs of wires, and by the return signals, they could locate the lode they were searching for. Once located, they'd bring in a drill, and do test holes. Apparently it worked, as they eventually found and worked a lode using a heap-leach process, open pit. The lode lasted about 8 years. I would sure like to know the type of gadget they were using to do that initial survey....especially if it's now outdated, and could be bought fairly cheaply.

Jim

[clay]

On 6/14/2020 at 1:19 PM, Idaho Jim said:

I heated it to dull red. All it did was melt the copper out of the matrix metal.

Jim

Cuprite is an oxide of Copper Jim.  The flame testing green shows the presence of copper.

You can't convert an oxide of a metallic element to the pure element by heating it in air. That just oxidizes the mineral form being heated. Since Cuprite is already fully oxidized copper the best you can hope for from heating in air would be melted Cuprite - not copper metal. Cuprite melts at about 300 degrees higher than copper so heating the sample to red won't melt  the Cuprite. More heat would be needed.

To get metallic copper from Cuprite you will need to heat it to about 2,400 degrees F in a reducing atmosphere to free the copper from it's oxidized state. Lots more heat with no oxygen. Then you can extract copper from Cuprite or other copper oxides. That reducing atmosphere and heat and a fair amount of an appropriate flux should allow the copper prill to form on the bottom of  the crucible. No flux and you end up with little copper prills trapped throughout the resulting slag.

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Now for some pure speculation. What you have may not be Cuprite or a natural mineral. When copper sulfides are processed the basic process is to heat the ore in the presence of oxygen to convert the sulfide to an oxide. At that point you have created a copper oxide. That roasted and oxidized result is known as matte.

To continue the processing to extract the copper the matte is heated further in a reducing atmosphere. The resulting product from reducing the matte is known as slag. Free copper will be found in little prills inside the slag mass if no appropriate flux was used in that last step.

Now if the matte was created in a small batch with minimal heat control small portions of the inside of the matte can become oxygen deficient and be reduced to slag with the trapped copper prills intact. Mostly oxidized matte (no free copper) with some slag (free copper).

Imagine a prospector was doing some quick roasting in the field for analysis and the oxidized matte produced was left behind after investigation. The copper in the matte would continue to convert to Azurite as it was exposed to the carbon dioxide in rain water. As you know this happens fairly quickly when copper rich minerals are left exposed on the surface.

Far fetched? I've seen stranger things in mining areas and I'm sure you have also. Just a possibility to consider.

 

[Idaho Jim]

That's a pretty good conjecture. Could very well have happened. It's certainly strange that those pieces of copper are in there. Let's say that's what happened. There's obviously copper there. You'd think there'd be evidence of excavation, like prospect holes, etc. If there are, Dave and I didn't see any. We did find some a mile or so away, but not  close to where I found the nodules. I guess we'll never know for sure. I guess it was too much to hope for, that there was a metallic vein closeby....LOL I'm still going to go back and check the area with the TM808. Maybe lightning will strike...Ha!

For the record...I wasn't trying to get copper from the nugget by heating. Desert Pilot suggested it, so to give every opportunity for a solve, I tried it. I had zero ideas about what would occur.

Jim

Edited June 16, 2020 by Idaho Jim

[Idaho Jim]

OK, guys. The XRF gun said it's 96% copper. A bit over 1% lead. 1/2% nickel about 1% Tin 1% iron 1%manganese If they add up to more than 100% it's because I'm approximating. There was some other trace stuff. I expected the copper to be lower. Obviously I got a false reading on the SG....will have to redo that.

Jim

Edited June 17, 2020 by Idaho Jim