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The gold miners had a problem with gray clay and it was always in they way.

Well, not really.

What the Comstock miners found was certainly not blue clay, nor did they think it was blue clay - it was actually black. So comparing your blue gumbo clay to the residual sulfides of Virginia City is not accurate.

From Dan DeQuille's History of the Big Bonanza:in talking about the original find of O'Reily and McLaughlin at the site of what later became the Ophir mine:

"What our miners found, was not glittering native silver, but a great bed of black sulphuret of silver a decomposed ore of silver filled with spangles of native gold."

The miners found that the black dirt concentrated with the gold in their sluice boxes because it was so heavy - and that was because the black stuff was sulfides, not clay. They were frustrated because it made collecting the gold (which was very light colored and high in silver) much harder. Blue clay is not a heavy material like sulfides or iron oxides that gets concentrated in a sluice box. They may not have been mineral geniuses, but they knew that the black sandy stuff they were processing was not clay.

But... What is the blue Gumbo?

I've dealt with clays like this a number of times. Remember that shales, slates and schists are normally formed from what was originally mudstones - lithified clay and silt. If they are exposed to heavy weathering, they can convert right back to clay and silt. Most blue gumbo type clays I have had experience with were weathered slate or shale. Since you say shale is present, this also might be the source of your clay. Can volcanic rock or ash weather to clay? Sure it can, but shale can also. If the blue clay layer was once broken slate gravel, that would explain the gold in it.

The Aussie miners have had experience with gravels converted to clays that contain significant gold. One cannot just put piles of clay into a sluice because unless the clay is fully washed into a slurry, clods of clay will carry any gold they contain right out the sluice. The Aussies developed a device called a puddler to fully mix clay with water and break it up to the point it could be processed in a normal sluice. Clays can be broken up in trommels, but may need a lot of time rolling around getting sprayed before they are fully washed and release all their gold. For grins, you might look up puddlers and see what the old time Aussie miners did.

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I've no quibble about calling it black, dark gray, or blue (many silver sulfides can have a blueish sheen). The reference that you noted that called it clay seems to be a recent summary. Dan Dequille (real name William Wright) came to Virginia City in the first few months after the big discovery and knew "Old Virginny", Comstock, O'Reily and McLaughlin as well as all the other early day pioneers of that area personally. He got the tale right from the horse's mouth so to speak. He was also friends with Mark Twain (Sam Clemons) from the time they worked together at the Territorial Enterprise newspaper. The guy who was the paper's editor liked both Wright and Clemons, but figured Wright had a much brighter future as an author (Boy was he wrong!).


I still think you might check out the Aussie puddler device - seems like at least some of that clay has enough gold to be worth working.

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You might consider taking a sample and processing it to remove the coarse free gold in the clay. As large as the gold is according to your comments, and with a small 10 gram sample size you are going to have a serious potential nugget effect. Removing the coarse gold first then doing an AA analysis will give you a more meaningful result as to what the blue clay itself actually is. The other thing is that separating out the coarse material from the clay will allow you to examine the coarse material and see what is in it - does it contain bits of volcanic rock, or bits of slate, or bits of quartz, etc. Those are important clues as to its origin.


Personally, I would not expect any significant precious metals values in the blue clay itself - but that's why you are testing - to see what it really is and what potential it has.


So if the clay is mineralized volcanic ash, what numbers would you expect to see from the AA?


If it is unmineralized?


If it is actually weathered slate / shale?


Looking forward to seeing the results.

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