Wednesday, July 22, 2009

Working Clay Layers

2


(A productive clay layer rests only inches below shallow overburden in this photo taken along the N. Yuba River in California.)

 I spoken about the general characteristics of clay layers elsewhere in this blog. Now I will provide you with some direct information and suggestions about working these potential gold-bearing locations.

Gold Pans
Gold Concentrators

Process the Overburden

Generally clay layers will be covered by overburden (assorted small boulders, rocks, and gravel). At times this overburden can be quite shallow with a depth of only inches while in other instances it's thickness can be measured in feet.

Your task is to "run" or process this overburden (where feasible) because assorted gold values are typically distributed throughout this material. Obviously, if you are highbanking or sluicing you'll probably want to sort or classify and bucket up this material first before running it.

Fines, Flakes, and Small Nuggets

In my experience however, your best gold values will come from the material sitting just above and on the clay layer itself (the "false" bedrock aspect...). This will include everything from fines, to flakes, to even occasional small nuggets.

For example, the clay layer I mention in the photo at the beginning of this post provided some excellent sluice box runs over the course of 10 days or so, including the recovery of 5 small nuggets (the largest weighing .70 troy grams).

Work Obstructions and Keep Your Eyes Open

When working an auriferous clay layer pay particular attention to large obstructions such as medium to larger-sized boulders. Some of your best recoveries may be found directly behind these and underneath them to some degree.

Additionally, as you've probably read in other posts in "Bedrock Dreams," when you begin uncovering old rusty nails, bits of wire, lead shot, and similar artifacts on or above a clay layer, your gold recovery potential has just gone up a notch or two. Keep your eyes open because these items tend to follow the same similar deposition patterns as placer gold and share a similar specific gravity.

Should You Work Into Clay Layers?

Now the question arises as to whether you should work into clay layers themselves. I have read a number of first-hand accounts from miners during the California Gold Rush that state in many instances excellent gold values were retrieved from clay layers themselves.

However, I myself cannot recall one instance where I found much, if any, placer gold locked inside clay layers. This doesn't mean that there can't be gold in clay layers, so it doesn't hurt to sample into the clay itself to see what might turn up.

But overall I suspect that most "modern" clay layers act as impermeable, "false" bedrock. One exception to this rule was a Northern California creek I once worked that carried fines, coarse gold, and yes, nuggets locked inside a hard dry clay layer containing moderately cemented gravels that was situated high and dry some yards from the present-day streambed.

That's it. I hope this has proven useful to you.

If you liked this post, you may want to read: "Gold in the West: Idaho (Part 1)"

(c) J.R. 2009

Questions? E-mail me at jr872vt90@yahoo.com

No comments:

Post a Comment