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Gold ní Clay

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As others have said there are different types of clay.
We generally tend to lump any sticky ultra fine deposit as "clay" but because clay can form under different circumstances it is an unfair generalization.
just some quick comments and then maybe some more depth later.
General clay as geologists seem to lump it is linked to ultra fine particles settling out of still water or being left as water evaporates away leaving layers of fine silt that would never have settled even in still water. This type of clay represents an energy level that is not conducisve to depositing anything but sub micron gold.
If that was all there was to it you could say forget about clay BUT.
That type of clay can act as false bedrock, it can act as a gold trap, and there is some suggestion that under certain circumstances gold can be preciptated out of solutions into clays in the right environment.
Chuck pointed out that clays will grab gold and I have seen that first hand as clay balls formed by incomplete washing in a trommel rolled down a sluice and came out the other end coated with fine gold and in a bit of a support to people who say that they find gold in that kind of clay the tumbling action through the sluice caused the clay to flatten and then roll and like plasticine grab gold and then fold it into the ball so that gold was all through it. The clay has an affinity for the gold like grease does and gold will stick to it like glue.
A reworked false bedrock clay could do this. In the beginning it was a layer left by calm water and a more modern stream cut into it - that modern stream carried gold and as the stream slowly cut into the clay the soft clay resists the erosion because the water can't get a good bite in it and rocks are mushed into it. The rocks and sand that get mushed into the surface not only carry gold that cannot penetrate the false bedrock clay but as the grainy texture increases with the added junk the river can get a better bite and will sometimes tear out chunks of this clay, sand and stone mixture to be incorporated into the general placer gravels as the deposit forms.
When a placer miner comes along and complains about all the clay balls in the gravel they had better be paying real close attention to those balls.
The action also enriches the upper layer of clay that is acting as false bedrock.
Next - the "different" clays

One clay that could for sure carry gold in big quanitites is actually weathered bedrock. All the "glue" of the host rock is weathered by time and chemicals in groundwater. Never enough energy to rework the rock or move it so the more resistant minerals are left behind even as the host rock breaks down into finer and finer particles. You can find whole gold veins suspended in this weathered rock/clay like a fossil of the original vein. The original rock just rots in place leaving behind a clay like seam that is all that remains of the resistant minerals. The gold in this case is often rough edged and sometimes pristine like you had used hydrofluoric acid on quartz to liberate leaf and wire gold. Rough edged and strange shaped nuggets of intricate form are often associated with it. The nuggets found in some areas of Australia using metal detectors are a good example. Some are barely "placerized" as they have hardly moved from where they formed - just sluffed down with the rotting bedrock.
One other deposit that fits the clay profile is "fault gouge".
Underground miners know this stuff. Some faults move over and over through their history as the earth shifts. The crack between the rock faces of the fault represents the contact point and like taking two pieces of chalk and rubbing them against each other. The rubbing action breaks down the rock faces into fine powder and breaks chunks off that are ground fine between them as well. Sometimes the fault pulls apart and the mobile action stops creating so much fine stuff but allows bigger chunks to survive as a breccia of mixed fine and course rock and sometimes the rock faces just keep working away grinding the faces finer and finer till there is a seam of clay bound by two solid rock faces.
Now if a gold bearing vein happened to be on that mobile fault Mom Nature would have ground the rock to liberate the gold and then erosion could move that material down into the placer environment. beyond that however is the possibility that a modern prospector discovers a strange cut in the local rock (usually the claylike fault gouge" will erode away faster when exposed). Looking deeper into the cut to the back they find a clay seam that they write off as perhaps fine materials that have settled into a bedrock crack. That ain't what they are looking at.
It can fool ya sometimes too because with other processes like groundwater invasion this fault gouge now resembles shale - so its not clay in the prospector's mind and that is where you have to have your millenium eyes in. Its not what it is now -its what it was then that you have to see.
That material could have major amounts of gold floating in it already liberated from its bedrock host and ready to recover by a savvy prospector.
The interesting thing about this deposit is that it is also linked to major hardrock gold deposits of hydrothermal nature as the mobile fault acts as a conduit for hydrothermal fluids and those fluids invade the fault gouge and fault gouge breccia and replace some of it with silica (quartz) and minerals like gold. TA DA!! A brand new gold vein. The still clayey stuff the prospector might find is just part of the process of mineral deposits being deposited and reworked over and over by different agents. Each one linked in the cycle.

Here is A picture of gold weathered out of green stone by chemical erosion.......A large area of the mountain has turned to clay an slowly moving with gravity to the creek.. <-yes_>

GPEX admin:
Excellent insight into the nature of clay, guys.    More please !

A few further questions:
1/ When one views a significant amount of clay in a deposit location, are there any specific key indicators that might suggest if the clay is more apt to comprise fine gold, nugget gold, both, or none?

2/ Is one type of clay more prone to possess gold than other types?

3/ In regard to the colors of clay, such as light gray, dark gray, blue, red, green, etc, which one/s is/are more apt to bear the presence of precious metals?

4/ Clay and the Gem World - - are the principles the same for mothering gemstones, as exists for harboring precious metals?

5/ Is there reasonable grounds in which to rank the varied clay types as to their potential of bearing precious metals, and/or gemstones?

6/ To what consistency would one have to maintain the slurry before the finest of gold particles could be liberated, and with next thing to zero loss?  If thatís possible.

7/ I presume in working a clay deposit, one would be better off if employing a re-circulating water system, whereby a detergent could then be used to over-ride the buoyancy of the float factor?


I would say that the red clay would be your best bet for coarse gold.  One, because that is the clay in which I found the most, and two, because the red colour comes from fine iron (magnetite, hematite) particles decomposing and colouring the rest of the trapped silts.  Iron is most certainly an indicator mineral.  I have only seen the red clay in small crevises in iron rich zones of the benches I work so it is not that common, and it rings my bell everytime I see it.

I am not up on chemistry or geology enough to know what gives the blue clay its colour, but that would be my second favourite, again based upon my own finds.

It seems to me that in order to ensure getting the fines to settle out of a clay slurry you would have to work it down to where its SG would be the same as water, and even then if there is any clay sticking to the fines you would have some float off.  Perhaps a small angle on a long sluice with the outflow from the slurry box controlled and a pure water source entering the head to further delute the slurry.

I have heard about the soap thing, does it really work?  I understand it breaks the surface tension of the water, but if the water had a high SG because of a high particulate concentration, would the soap be enough?


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