Catching Fine Placer Gold – Part 2

Written by DOC

In this second article we’ll talk about your sluice, catching fine gold, the importance of understanding proportional force, and other impacting adjustments you can make. PART 3 coming later this week.

WARNING… This article will seem INCOMPLETE if you don’t watch the proportional force video.  I know, it’s a bit long, boring, tech stuff, but worth the watch. (Put it below this article) 

Everyone’s Heard it Before
The more you classify the easier it is to catch fine gold. Let’s face it; if you classified all your pay to 50 mesh (smaller than table salt) then catching fine gold would be easy.  The problem is that the labor cost ratios (as well as time) would sky rocket.  How long would it take you to classify one YARD / TON of pay down to 50 mesh?  Considering a cubic yard has about 40 five gallon buckets, I’d say days and days. KEY TO PF IS THE ABILITY TO CHANGE THE CAPTURE BEHAVIOR OF OUR SLUICE WITHOUT CHANGING THE CLASSIFICATION LEVELS.

“Mining Math” is something I’ve LONG talked about.  A yard of material has “X” amount of gold in it. Nothing you do will increase that. Your goal is just to capture a REASONABLE / ACCEPTABLE percentage. Of course that varies from person to person, but the ultimate goal of operations is to find a BALANCE of good recovery rates with the highest production possible.  After all… if a yard / ton of dirt only has $30 of gold in it, that’s all it will ever have.  You can take 2 days to process it, 2 hours, or 2 minutes. So… for most of us…  CLASSIFYING TO VERY SMALL LEVELS ON A LARGE SCALE is out of the question.  This is KEY to understanding the PURPOSE of PF and how we can use it to our benefit.  Using and understanding PF will help us not only run more material but capture different size gold including the fine stuff that often is lost.

Big gold takes care of itself.

Every once in a while every prospector will find that “dream nugget”. For some that dream nugget might be a piece of gold 1/8” in size.  For others it might be a ¼ ounce nugget.  Big gold is easy to catch if you PLAN for it.  That’s why EVERY piece of equipment should have some larger aggression near the top of the system. Whether that’s a few big riffles, aggressive matting, nugget trap, etc, it should be there.  You should also be aware that large flakes like to GRAB water flow and flip down a sluice.  So making sure you have different capture zones is important regardless of where you work.  In our highbankers we usually see “nuggets” in the reverse ramp riffle area or in the top 2 mats.  However if you have nothing but FINE and SMALL profiles in your sluice, you do run the risk of missing bigger gold. The image you see to the left is from an actual field run when we shut down. Caught by the RiverHog mat. 

Starting to understand PF (Proportional Force)

Doc’s Definition: A combination of factors and settings (other than classifying) that impact the requirements of energy in a sluice to both remove waste and rocks and retain the size gold one desires.

BASIC images for your mind.

Starting with a pan, picture you just filled it with a bunch of raw pay dirt and bank gravels.  You start to pan it.  What do you do during the first few minutes?  You reach into the pan and pull out large rocks. WHY?   Simple… the amount of PF required to move these larger rocks out of the gold pan will also carry out fine gold.  Get it?  If we simply relied on PANNING ONLY to move them out, the force we created would also force fine gold out of the pan.  That’s lesson one and very simple to understand.  The amount of force to move something BIG will also move something small. Even if it is HEAVY.


The right hook size?

I spent a LOT of time fishing in the ocean in my younger years and always had a good laugh.  I’d spend at least one day a week at the local pier and watched the tourist come down with fishing poles rigged up with HUGE hooks and BIG pieces of bait.  They were going after fish that had a 1/2 “wide mouth using 2-3” long hooks and a piece of bait that could choke a dog.  Once in a while I’d be nice and hand them a tiny little hook and say “try this”.  Minutes later they’d be reeling them in one after another.  (The right size hook for the right size fish.)
The same applies for fine gold. If all you have is large riffles in your sluice… you’re trying to catch a minnow with Marlin hooks.  Capture zones, matting, and riffles should vary in a sluice creating multiple exchange and capture environments.  The best commercial ops the in the world TOTALLY understand this point and some have as many as seven different stages.

It’s settled… Gold WANTS to settle.
A 1mm sphere of gold will drop roughly 36” through water in one second.  GOLD IS HEAVY… it wants to settle. It travels to the bed load of your slurry quickly (read this article) but often gets thrown back up by large riffles and lots of turbulence.  Balancing a good exchange, with minimum turbulence, is critical. It’s the number one reason for losses of fines in commercial ops.  After any “aggressive matting” near the top of a unit, you should start to decrease the aggression and allow things to be SMOOTH.  Again, that’s the whole point to most of our “flaring units” and varying mattings.

What can you change?   

  1. Sluice Width – (Widening will lower water depth.)
  2. GPH and Water Depth
  3. Flow Interruption – (Riffles and their height)
  4. Pitch / Angle of the Sluice.
  5. Lastly… Classification, which is usually not an option.

Proportional force is probably best described by looking at a dredge. Why a dredge?  Because YOU ARE LIMITED TO THINGS YOU CAN CHANGE.  When you’re running a 4 inch dredge what are you sucking up?  All kinds of material including 4-5” rocks.  These large rocks must be moved through the system, sluice, without hanging up and clogging the sluice.  So the water inside a dredge is deep and fast.  It MUST BE deep and fast in most dredges to move the larger rocks out of the system.

Below, we use a large tub to catch all our 6″ dredge tailings to check for losses of fine gold. 

Because it’s deep and fast, larger riffles and large expanded is usually used.  This combination of big water and big riffles is kind of like using that 3” hook to catch a tiny fish.  It just doesn’t match the job at hand or the fish that are biting. (Fine gold running through your sluice.)

Proportional force helps you understand variables that are “changeable” and those that are NOT. In a dredge… there is very little we can change.  After watching the VIDEO… you’ll understand that.  Basically we can reduce the riffles and expanded, replacing those with exchange matting and this will reduce the flow interruption and turbulence.  This allows the fine gold to settle more and stay in the BED LOAD (watch the video) and have a better chance of being caught.  Otherwise the fine gold will be constantly thrown back up into the fast turbulent waters and lost.

I like to use a dredge as an example because you’re “handcuffed” in a sense.  You can’t classify which is what most people will tell you to do in most water based systems.

What Gets “ENGAGED” and What Does Not

There’s a critical point in the PF video. It’s about 19:30 into the video.  I start to talk about “rules of engagement”.   The larger your “riffles” or flow interruption, the larger the ENGAGEMENT with material running through it.  In BASIC terms look at this picture.

If larger rocks are “engaged” then the proportional force to keep them moving needs to be increased.


That… is the greatest example of how proportional force impacts your fine gold capture. You are FORCED to increase water speed, depth, or pitch to keep them moving. When you do this what happens?  You got it.  The overall exchange rate / energy increases greatly and FINE GOLD will be carried out of your sluice.  GOT IT?

If you read this article and watch the PF video… I think you’ll quickly understand the key points of catching fine gold WITHOUT… classifying to extreme levels.  THAT my friends… is our ultimate goal as miners.  Working larger amounts / volumes of pay / material EFFICIENTLY.

In the next article we’ll look at how we used all this to design the SuperHog 

PF Video below…