Clay... friend or foe!

 

Red clay, brown clay, gray clay and the dreaded slimy yellow clay… reminds me of an historic Deadwood newspaper article.

Historically, Rapid City and Deadwood were bitter rivals. Rapid City billed itself as the gateway to the Black Hills and therefore mining.

Deadwood eventually took offense and retorted that Rapid City was “miles” from the heart of mining and their only claim to mineral fame was gypsum: powdered gypsum, granular gypsum, crushed gypsum, lump gypsum… the list of varieties continued for an entire column in the newspaper!

This runs true for varieties of clay throughout the Black Hills. It’s a tough foe, potentially robbing your sluice of every fleck of gold!

So why this love/hate relationship? Why would you want to even run material if it might rob you?

Superficially you would think all clay is a gold robber.

So let’s take a closer look. Wikipedia defines clay as, “Clay minerals typically form over long periods of time from the gradual chemical weathering of rocks, usually silicate-bearing, by low concentrations of carbonic acid and other diluted solvents… In addition to the weathering process, some clay minerals are formed through hydrothermal activity. There are two types of clay deposits: primary and secondary. Primary clays form as residual deposits in soil and remain at the site of formation. Secondary clays are clays that have been transported from their original location by water erosion and deposited in a new sedimentary deposit.^[2] Clay deposits are typically associated with very low energy depositional environments such as large lakes and marine basins.”

So what we see, digging placer material, would be classified as Secondary clays. They eroded during major flood events and deposit a layer in the creek/stream. Large fires can play a role also, depositing inches thick layers of ash.

Now back to prospecting! We’re digging, exposing layers of eroded out rock. If the material you are digging is wet, clay is pretty obvious! It’s that stuff that sticks to your shovel and doesn’t go through the concentrator screen. If your material is dry, it would prbably be a very fine, talcum powder consistency.

We usually call a halt to digging any deeper. Your best bet, and I know all you guys hate this, is clean your sluice and recover existing gold. If you’re not ready to do that, keep running material from above the clay zone! If you introduce clay lumps into your sluice, you can just kiss your gold goodbye as the lumps roll over it, collect and dump out the end of your sluice!

Back to the same old mantra… test pan! My advice is run a test pan of material directly above and resting on the clay layer. Here’s where your power of observation comes into play. When you get the material thoroughly saturated, does the clay break down or do you have lumps of slimy clay in your pan? Is the clay saturated with tiny pebbles or does it smear across your fingers?  Break it up as you pan and see what you’ve got. If there’s gold there’s no way you want to sacrifice it, right?

If the clay breaks down you can run it, carefully, in your CLEANED sluice.

If it doesn’t break down, you’d better either resolve yourself to really working it over while panning or throwing it out!

If the clay band is relatively thick, the gold would probably only penetrate into the top layer and a whisk broom might release it. I’ve found, as hard as I find being patient, to let the clay dry then whisk it clean. Otherwise, you need to whisk it AGAIN when it dries. If you have a fairly wide area exposed and the weather is cooperating, you can whisk from one end of your diggings to the other. Then go back and start removing material again, starting from the same end you started whisking. By the time you have run that material, it’s ready to whisk clean again! I’ve done this time and time again and didn’t miss a beat feeding the sluice… well except when I take a self-imposed break!

A stellar example would be our claim where we get to bedrock and hit a clay layer right on top of bedrock. We had avoided running that material until I test panned it and found nice, bigger gold! I took a bucket of it home and panned it out gradually, finding good gold. We now try to sluice all but the really nasty stuff, which I continue to bring home in a bucket as a “bonus”.

Historically, here are a few examples:

Yellow clay, in the Tinton area is well renowned for 60-ounce per ton from clay seams.

The Hayward/Rockerville area also reports deposits of high-yield yellow clay.

We run into a grayish-blue clay in the Northern Hills that has a yellow clay layer below it. We get some great little pickers out of it.

We also find red clays covering whitish clays in some local creek channels. That’s where I test panned and we started running the material except the really nasty stuff that I pan.

An example of how this all breaks out would be…

Teresa: “Think I hit a layer of clay!” About the same time:

Bob: “Be careful, looks like clay in the sluice!”

Teresa: “I’ll run a test pan.”

Bob: “What have you got?”

Teresa: “ It’s breaking up pretty easy,” or “it’s baby-(poo) clay,” or “we gotta run this!”

Be cautious, test pan for solubility. A good soaking sometimes breaks down clay. Sometimes it’s better to run the dry powdered material!