Tuesday, January 29, 2013

Gus's Method for Processing Black Sand Concentrates (Part 1)

 (Small gold particles mixed with black sand material.)

"Gus" is a placer gold miner and prospector from Folsom, California who's had gold fever since he was little guy and recovered his first color in the panning troughs at Knott's Berry Farm. Since I've been talking a lot about processing black sand concentrates lately, I thought you'd like to hear how "Gus" goes about it.

 "My First Step"

"Regardless of the process (sluicing, highbanking, etc.) I use out in the field I always bring my black sand concentrates for further processing at my leisure. My first step in further concentration is accomplished by using a 'California Bucket Sluice Concentrator.' This inexpensive device employs a very simple 'drop riffle' design. However, it can take quite a bit of trial and error to understand the 'Bucket Sluice's' water flow requirements to prevent potential loss."

 (The "California Bucket Sluice Concentrator.")

"I place the bucket and the concentrator in a mortar pan and use plenty of 'Jet-Dry' rinse agent. Mine is a recirculating system where the water is delivered via a small bilge-type pump that I regulate using a Pulse Width Modulator (PWM). The PWM controls the water flow. I don't use a ball valve because the PWM is a much more granular and repeatable control method. Also, the PWM doesn't introduce additional turbulence into the water stream like a ball valve can. It also has the added bonus of making my 12-volt batteries last longer."

"Gold Down to Microscopic Size"

"The 'California Bucket Sluice Concentrator' can exchange material quickly and efficiently, capturing gold and black sands down to around 50 mesh. After my first run, I take the concentrates and dump them into a conventional gold pan for final clean up. When this step is complete, I classify the tailings from my 'Bucket Sluice' using a 30-mesh classifier. Anything that doesn't make it through the 30-mesh screen gets panned again. Next, I take the minus-30 mesh material and classify it again using a 50-mesh screen. I then take the 30-50 mesh material and pan it twice...usually I recover a little more color this way."

Gold Concentrates
Gold Concentrators

"Now I'm left with minus-50 mesh material and any jars of black sand derived from using a magnet out in the field. This is usually very heavy material containing gold down to microscopic size and lots of iron. To tell the truth, I've been surprised at the amount of very fine gold I've seen in this final group of material."

"This Approach Works"

"In the next step I take the minus-3-mesh material from the 'Bucket Sluice' and place it into one of my various sized, home-made fluid beds (depending on how much material I have, that is). I get the flow running in the fluid bed (FB) just enough to get the material moving, but not fast enough to make it exit. I then take a gold magnet and hover it over the top of the water circulating in the FB and occasionally dipping the magnet just under the water."

 (Gold particles under 50X magnification.)

"As the material churns inside the FB, iron is brought to the top and onto the magnet. This removes three quarters or more of the overall material, leaving behind any gold and other non-ferrous material. I've check what gets attracted to the magnet many times, but I've yet to find more than a microdot of color. The iron picked up from my gold pan or sluice box can contain quite a bit of gold still encapsulated among the black sand particles. However, the same material and magnet do not encapsulate the gold when used in conjunction with my FB. So, this approach works."

There's more to come from "Gus" on the subject of gold recovery from black sand concentrates, so stay tuned.

Good luck to one and all.

If you liked this post, you may want to read: "Gold in the West: Idaho (Part 4)"

(c) Jim Rocha (J.R.)  2013

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


  1. Good morning JR, the thing I have to wonder is, is it worth it to the small scale hobby prospector to mess with stuff that small? I understand about getting as much as you can out of your black sand, and it can be a real pain to do, but the super small pin prick stuff? I've always tryed to get it all, but it dosn't add up to much very fast. Every little bit adds up I know, but is it realy worth the trouble? It takes an awfull lot of the stuff that you can't even hardly see, to add up to just one small flake, let alone an ounce. The gold in my area seems to run fairly small, a big piece is about (0) this size, on down to about (.) and smaller. I have only a small sluice box and a gold pan, I don't take the consentrates home, I work it down to the end on the spot. When I clean the sluice, I can usualy do it in one or two pans. I did try a drop of mercury on the super fine stuff with good results, but I hate to use that stuff if I don't have to. Well this is longer than I ment to make it, have a great rest of the day! Gary

  2. Again, my take is that anytime you're processing large volumes of material you should run your black sands and derive the last bit of gold from those concentrates. What large volumes of material means to me may be different for others. I can say I don't mess with them at all when I'm only out for a day or only processing small amounts of gold-bearing gravel. But that's me...others will carry their black sands home no matter what. Best, J.R.