Searching for the source

[Twobrothers]

Ive been hard rock prospecting a particular known gold bearing area for a couple months now and would like the opinion of more experienced hard rock prospectors/ miners on the photographs of a few samples.

The area is a known placer gold producer with the bulk of production taking place between 1890's and 1930's. Some large nuggets were recovered. An 8 ounce-er, to one over a pound made quite a stir. Most of the creek bed is covered by active current placer claims. There are some historical hard rock claims in in the area. Most produced at least some gold as a commodity. The few historical assay and smelter reports I've found indicate some representative ore material with 1-3 oz/ ton of gold. A few high grade shipments to smelters indicate material with 14-29 oz/ ton of gold. I've visited a few of them and they are not easily accessible. Ive taken some samples from the most promising lead which I sent off for a silver/gold fire assay about a week and a half ago. The ore material is a quartz vein finely layered with oxidized iron and limonite after sulfides. The material I am interested in occurs in thin sheets. Here are some pictures of the material.
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The first picture is a piece from a 15 pound piece of the vein I sampled and quartered. I sent off two opposing quarters of the chunk for Ag/Au fire assay. This is one of the two quarters still in my possession and is fairly representative of what I sent in for assay.

The second picture is a thin flake off of an exposed section of the vein. About 1/4 in thick with many thin layers throughout.

Third picture is the same material opposite side.

Fourth picture is one of the first pieces of material I found in the vein structure that got me excited about this location as a prospect.

Feedback welcome. Eagerly awaiting assay results.

 

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[Twobrothers]

So I got the assay report by email this afternoon. I had two samples assayed.
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Site 1 has lots of shiny material on the contact between the hanging wall and the vein material. Additionally the host rock has a lot of manganese oxide dendrites throughout. It is the most accessible point of the vein and I figured I would get a sample assayed. The sample I sent assayed very low in gold. I did not include a disproportionate amount of the shiny material in the sample I sent for assay. I kept it pretty representative.
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Site 7 had what I consider low-medium qualitative material based on my visual assessment of the visible 'shiny'. I sent an average representative sample of only the vein material. I did not include any foot or hanging wall because there really wasn't any. It had all rotted away from the quartz vein.
Site 7 sample assayed the highest, but not nearly as high as I hoped.
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Now the question is where is the gold traveling? Is it the 'shiny' apparently golden material traveling in the layers? Or is it microscopic particles in the oxidized pyrite box works that was only revealed by the fire assay? Interesting to note the apparent constant ratio of gold to silver between the two sample locations. If the 'shiny' layers are indeed where the Au-Ag is traveling I know of sources on the vein where more concentrated material exists.

 

[Twobrothers]

This is what a concentrated section the 'shiny' looks like under the microscope.
View attachment 1469296

 

[bobw53]

Half gram a ton..

I guess the question is.. Can you get that half gram a ton??

did you crush it and pan it?? Is it free mill gold?

IF you can free the gold with nothing but crushing, then it might be worth chasing to find higher concentrations..

IF that gold is bound up and will require all kinds of funky processes to free it, it probably won't be worth chasing.

 

[Assembler]

Hello
Anyone finding 'High grade' today?

 

[Twobrothers]

That raises the two big variables that make mining economics.
"Ore" Material and Process.

As for the potential ore material I know at the very least I can reduce the amount of gangue material I am working with. I am becoming more and more acquainted with the vein system and have identified hot spots where I know I can get to better material than what I sent in for the site # 7 sample. I purposely selected an area where I knew there was average representative material on the vein and randomly picked the first piece of vein material I saw. But that still leaves the question of the process and where the gold is traveling.

Is it traveling as microscopic bits in the vugs left behind by decomposing pyrites only revealed by fire assay? Or is the shiny material indeed the gold? I am pretty sure the shiny material is gold. My reservations come from its physical properties. I did my homework and tried the typical physical tests (testing malleability with a pin, scratching it with a knife, looking at it under a microscope). Under a microscope there are undeniably very gold colors. But its not consistently one color. Its a spectrum of silvery-yellow, to yellow, to yellowish-red(gold). My homework leads me to understand that hardrock gold almost never approaches 24k in purity. So its always alloyed with a little silver more or less. But does it occur in such a dynamic spectrum within one piece? My understanding of nature and natural processes says yes its possible but Ive never found a research source that confirms this. The physical tests are what throw me for a loop of doubt sometimes. I cant get a conclusive result on a scratch test because of how thin the layers are. Inevitably it powders off every time I try because I cannot press it without gouging up the soft limonite layer underneath. That kind of leads into a discussion on the extraction process

Here is what Ive tried so far. It not pretty or civilized but I took every environmental and PPE precaution I could so don't jump down my throat. First thing I did to a sample rich in shiny
was to crush it down with my improvised stamp mill. Screened it down to about 140-200 mesh (metal screen door sheeting). Panned it down. Visible shiny but still stuck to quartz particles. Not free. Needed to crush more thoroughly to free gold. Had some mercury so I tried a crude "pan amalgamation". Basically I put the crushed material in a plastic washing tub with water, a little lye, jet dry and mercury, and ground the mixture with a glass bottle. Did that on and off for a couple days and recovered an amalgam ball.
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Retorted it, didnt look like gold.
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Melted it with some borax, got a leady prill with something goldish underneath.
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Hit that with more borax and tried to draw off the slag and lead.
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While still hot i was able to draw off the slag and a couple lead prills, leaving a little gold-ish prill.

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Under the microscope the leady prills still looked like they have some gold-ish material on them and the gold prill was very soft and appeared to be a little leady. I made that indentation on the top with my finger nail. So I cooked it one more time with more borax and potassium nitrate flux.

Made a slaggy mess couldnt tell what was going on so I put the spoon in a glass of water to soak for a couple days. Checked it today and a lot of the slag dissloved off. Still a mess but a delightful buttery yellow gold-ish mess.
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Crudest of processes executed by someone without experience and it worked! Amazing! Gold from a rock I found! A lot of work this process. Building a pan mill. Ive got a test batch of material I am experimenting with a carbon in pulp chlorine leach solution. So far the Stannous Chloride says its not worked yet. Plenty of free chlorine in sloution. pH is a little low. Lots of iron hydroxides, and oxides. Lots of experimentation needs done there. Write up for another time.

 

[Eu_citzen]

Looks like sulphides to me.

Try using hydrogenperoxide and it'll eat up the sulphides. Do so outside. Gold will be unaffected, sulphides are oxidized. Useful for small test batches.
In my experience, any gold can then be panned out if it's been locked up in sulphides.

Be weary the solution may boil if a high percentage is used. So mix up with water if your solution is above 17%.

 

[Twobrothers]

I will test a little sample with some 3% H2O2. Anything in particular make you think they are sulfides? It looks to me like the iron sulfide pyrites (FeS) rotted away long ago. My impression is that sulfides dissociate at a similar rate. Except for Galena (PbS) which forms a passivation layer. In my expereince freshly exposed PbS will begin to decompose but once the surface layer of sulfur is gone and a healthy layer of native lead is exposed it tarnishes inhibiting any further decomposition of sulfide underneath.

 

[arizau]

A couple of things for you. Commercial window screen mesh size is typically closer to 20 mesh than 140 to 200. 20 mesh gold is pretty easy to pan/separate/concentrate even if it is stuck to a lesser sized amount of gangue since it will still be two or more times as heavy as pure gangue providing the particles are of the same relative size eg. screen it to half size differences such as minus 20 plus 40, minus 40 plus 80, etc. An important thing to remember for visual identification.....gold still looks like gold when it is in shaded light while a pyrite's color dulls out and/or becomes dark in shaded light. I am guessing that your color descriptions are under full light and they are pretty classic for pyrites of what ever ilk.

Good luck.

 

[Twobrothers]

Try using hydrogenperoxide and it'll eat up the sulphides.

So I treated a piece with some 3% H2O2 for 4 hours. I changed the solution twice for fresh solution on account of the low potency. Didn't do much. A little bit of bubbling on and around the oxidized iron, but by the second solution change no more bubbling and the shiny was as shiny as ever.
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I took a known iron pyrite/ iron sulfide sample and flaked some into the H2O2 and its bubbling pretty strong
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[Twobrothers]

Ah...its is the number of openings in a linear inch. Thought it was in a square inch for some reason. Yeah about 14 mesh then.

 

[Twobrothers]

So I took a little sample and cooked it with a MAPP gas torch. Got to be careful though MAPP gas does burn hot enough to vaporize gold. Got it hot enough to get the corners on the quartz glowing orange. The result: The iron oxide colors got darker but the shiny still remains shiny. No sulfurous odors detected.

 

[Twobrothers]

roasted sample

 

[Eu_citzen]

I will test a little sample with some 3% H2O2. Anything in particular make you think they are sulfides? It looks to me like the iron sulfide pyrites (FeS) rotted away long ago. My impression is that sulfides dissociate at a similar rate. Except for Galena (PbS) which forms a passivation layer. In my expereince freshly exposed PbS will begin to decompose but once the surface layer of sulfur is gone and a healthy layer of native lead is exposed it tarnishes inhibiting any further decomposition of sulfide underneath.

Just guessing from the pic under the microscope.
There's around 4000 minerals known to man, so...

If you're not sure it's gold, I would be to try doing a streak test.

 

[Twobrothers]

The search goes on

The search goes on.
Did some more prospecting on the primary vein structure of interest.
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Some visually interesting material. There are about a dozen workings from adits to prospect pits along the half mile of exposed vein.

Did some prospecting on a vein structure on the other side of the mountain.
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An old working mine. Copper Silver Gold. Currently unclaimed on public land open to mineral entry. Lots of iron and copper minerialization. Some as oxides, some as pyrites. Mineral Land Assesment reports show samples taken with up to 0.7 oz/ ton of gold

It was a nice rainy day so we were able to do a little fire setting. ( https://en.wikipedia.org/wiki/Fire-setting ) It still works. Made about 6 inches of progress in a couple hours.
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[Eu_citzen]

I gotta say, to me that looks like some fine material.

 

[Assembler]

Hello
Maybe it is best to go after the Silver?

 

[Twobrothers]

I think I found what I am looking for. Its traveling in at least two separate and distinct vein structures.
In one vein structure it occurs as streaks and sheets sandwiched in layers of quartz and oxidized base metals (mostly lead, and iron).
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In the other vein occurrence it comes as blebs and nuggets mingled in oxidized iron masses from old rotten vugs.
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[nadavis]

Something that usually works for me if i want to test some sulfides for gold is to crush it as well as you can, pan off the light stuff, use a magnet to remove magnetite etc, and then use a hot plate or camp stove and an old ( never to be used for food again ) small pan to roast it. Just mix the sample with some non iodized salt and cook on high stirring and mixing occasionally to make sure all of it gets exposed to oxygen, and cook for 45 min to an hour. Keep in mind that you are probably releasing some very nasty stuff- arsenic sulfur mercury etc, so only do a small amount outside, downwind, and do not breath in when stirring. When done cooking, empty the hot stuff directly into a bucket or pan of cold water to further shock it, then just pan it out and look at it with a loupe.

 

[Assembler]

Testing time.

I think I found what I am looking for. Its traveling in at least two separate and distinct vein structures.
In one vein structure it occurs as streaks and sheets sandwiched in layers of quartz and oxidized base metals (mostly lead, and iron).
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In the other vein occurrence it comes as blebs and nuggets mingled in oxidized iron masses from old rotten vugs.
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Now that you may have found what you are looking for time to do a test say of a hundred pounds or so. Let us know and thanks for posting.