The special focus of this
article is how to deal effectively with concentrates that pass through a #30 classifier.
The first step is to classify the concentrates after I have employed my primary means of
concentration. Panning is most efficient and most reliable directly in proportion to my
ability first to reduce my material to units of essentially the same size. This is so
because the existence of grossly unequal eddies is one of the worst enemies of maintaining
the relative stability of material while the mass is being worked by water action. One of
the causes of destabilizing water action consists of objects that are much larger than the
other objects near it. Large objects cause water moving over and around these larger
pieces to lose laminar flow, ie, the water gets diverted into different directions in the
local vicinity of the larger objects and this affects the ability of a panner to maintain
sufficient control of the mass. This degree of control is essential, especially during the
completion phases of each pan of concentrates, as will be seen. Ideally it would be more
effective to pan only the material that has passed through a #30, but not through a #50
classifier than material that only has been passed through a #30. But such attempts at
near perfection are quite labor intensive and the following procedures work quite well
even if a #50 screen has not eliminated the tiniest particles.
Drywashing is one primary means of initial
concentration, typically in a desert locale. Others involve water such as sluicing or
dredging in a creek or river. My technique for the initial classification of concentrates
is basically the same for wet or dry materials despite the fact that the shape of the
individual pieces and specks of gold itself is grossly different. Desert gold typically is
chunkier than river gold which frequently is hammered into extremely thin pieces. But
there are minor differences. I will go through each scenario in turn.
After a drywashing run in a desert locale I
empty the riffle tray into a rectangular plastic dishwashing basin that is the proper
shape and fit to catch all the concentrates and deep enough not to lose material in windy
conditions. I take this tub to the tailgate of my 4X4 pickup, which is a comfortable
height for me to work at without developing back spasms or neck kinks. I insert a #4
classifier screen into a green 14 plastic gold pan (I am describing the color of the pans
only to enable the reader to follow the process better). I begin with a #4
because anything that will not pass through easily can be located with a metal detector.
Thus, I always discard this material in the same spot and check it with the beeper prior
Next, I pour the contents from the green pan through a #8 screen that is
placed in a blue 14 pan. I use my gloved hand to rub the material briskly against the
metal mesh in an effort to break up hard, dry clay balls or caliche fragments. After
shaking through all of the loose material, I pour what remains in the classifier screen
into the empty green 14 pan. Then I bang the classifier screen down pretty hard into the
green pan. Doing this 3 or 4 times knocks out most of the little pieces that got stuck in
the grating of the classifier. The contents of the green 14 pan then are poured into a 10
finishing pan and set aside. I repeat this process through my #12, #20 and #30 classifiers
so that when I'm done I have five finishing pans ready to be panned, consisting of what
would not pass through a #8, #12, #20 and #30 plus what did pass through the #30). Panning
the first four of these five groups goes very quickly and the remaining gold is
transferred into a common vial with fingers or tweezers after counting the results. The
lead is picked out for proper disposal later. It is the fifth batch of concentrates
(composed of particles small enough to pass through a #30) that presents the greatest
challenge. Details on dealing with this very fine material is described in depth below.
Classifying wet concentrates only differs a
little in that everything must be done in water instead of dry and the volume of material
is much greater. I either set up a sufficiently large and deep basin on my tailgate and
fill it two-thirds with water or I set up at the edge of the waterway where the water is
fairly calm and I can comfortably sit or kneel and have a sufficient working surface to
place the pans, screens, etc. Material is poured into a classifying screen which, in turn,
is placed inside a 14 pan. I prefer to use low profile classifiers because these are
easier to grip and hold together against the inside surface of the gold pan. The pan and
the screen inside, while held tightly together, then are submerged. I proceed to agitate
the contents by swirling and jerking them, taking care to keep the bottom edge of the
classifier held tightly against the inside surface of the pan so that none of the
concentrates can escape. The smaller material quickly passes through. Then the bulk of the
wet remains are carefully poured into an empty 14 pan. The remaining particles that remain
adhered to the inside of the classifier then are banged into this same 14 pan so that now
all the concentrates that did not pass through the classifier are in this 14 pan. From
here I front pan some of the material down until I can transfer the remainder into a 10
finishing pan. A variation of the above, when dealing with substantial volumes of
concentrates, is to insert the classifier screen into a plastic bucket. If I'm in a
dredging production mode, then I only use buckets and set these aside for later processing
during my lunch break and after my evening meal.
Front Panning: Almost everyone has a front
panning technique. But first it is instructive to examine the different types of
underlying forces that are at play and to share some techniques and strategies that can
harness these forces rather effectively, especially when dealing with sub #30 fine
concentrates. The two primary forces I rely upon to reduce my concentrates are gravity and
magnetism. I will deal with each, in turn, as they relate to my panning strategy.
motion of objects has three measurable quantities: force, mass and acceleration. Mass is
different from weight. For example, the weight of any object is different when the object
is on the moon as opposed to the earth, but the mass remains the same. Since we do no
panning on the moon, for our purposes we can speak of the weight, the mass or the density
of objects interchangeably. Also, for our purposes we may refer to acceleration as speed.
Speed becomes important in panning when I create a momentary state of suspension because
some materials will gather speed faster than others. In a vacuum, of course, all objects
regardless of mass accelerate at the same rate. But in water, objects of greater weight
relative to the water can overcome the resistance of the water (and also the friction of
rubbing against other solid objects in suspension in the water) and accelerate faster than
lighter objects and thus are better able to slip downwards towards the bottom of the pan.
Finally, I will refer to various ways that kinetic energy (a type of force) can be
transmitted in the medium of water.
The idea of panning is to get the lightest
things out of the pan while keeping the heaviest things inside. This sorting process
depends upon creating conditions inside the pan that will permit gravitational influence
to allow some objects to behave differently than others. I can do so most effectively by
placing the solid objects in momentary suspension, ie, by creating a momentary separation
between the solid particles in my pan. By doing so we create a momentary opportunity for
the heavier, denser things to slip past other particles and fall faster than the lighter
things through the resistance of the water toward the gravitational pull exerted upon all
them equally from the center of the earth. If I am skilled at doing so, then I can control
the location of the heaviest things in the pan by forcing them to find their way to the
place in the pan that is closest to the center of the earth.
In the panning of
unconcentrated materials that consist of a wide disparity between light and heavy
particles I can fairly easily achieve a crude division of the particles by agitating the
contents of the pan such that the upper layers of material contain the least dense
particles. I then tilt the pan under water and skim this layer of light material off the
front of the pan a few times before resettling the remaining material and then creating
yet successive layers of light materials that are skimmed off, each time first by creating
some forward inertia and then by tilting the pan slightly lower in the front while
smoothly drawing the entire pan rearwards and slightly upwards back over the same angular
plane as the tilt of the pan. Each layer of lighter material becomes progressively thinner
as I work my way down. I call this process front panning.
The initial front panning of
concentrates, however, isn't so easy. This is so because much of the material already is
dense. Thus, I need to focus on a more efficient way to create the necessary momentary
suspension of the entire mass and I need to do this many, many more times per unit of time
than when panning unconcentrated material. The key to doing so lies in the principle of
the wave and mastery of its application to heavy concentrates.
Energy can be transmitted in numerous ways.
Think of how a bullet is forced out of the barrel of a gun. Or of how billiard balls are
broken up with an impact. Or how a screw is turned into a hole. Now think of a long,
coiled telephone wire (those of you old enough to remember fixed position telephones with
long curly cords) that you have stretched out somewhat while chatting on the phone. Note
that it takes very little energy for you to create a wave motion in this extended length
of curly cord. And when that wave motion reaches the other end of the cord, an incredible
amount of the original energy remains, ie, there is very little loss of energy when
transmitted over great distances by employing a wave. Note how far a tsunami can deliver
its energy. This exact same principle can be put to work in a gold pan.
I do this on the
tailgate of my pickup by employing an old fashioned porcelain, oval wash basin filled
about two-thirds with water (about two gallons). The 10 plastic finishing pan has about an
inch of empty space from side to side at the center of the oval basin. By banging the pan
repeatedly against the sides of the metal basin I create shock waves of energy that are
carried along through the water, momentarily putting the mass of particles in suspension
with each successive shock wave that I generate. First, I tip the front of the pan
slightly downwards as I move it forward and simultaneously bang it from side to side. Then
I gradually tip it back to near level as I continue banging. At this point I gradually
retract the pan rearward toward the center of the basin. In this way I have settled the
gold and I have created a gold-free upper layer of material in the finishing pan. After
repeating this process a few times I can begin skimming off this upper layer, but more
carefully than when working with unconcentrated material.
In a creek I can accomplish the
same effect by utilizing a pair of boulders or large rocks to bang the finishing pan
between or against. One difference, however, is that the oval shape of my metal basin
permits me to vary the frequency of the shock waves in a way similar to how the pitch of a
guitar string can be changed simply by varying the position of pressure application with
one's non-strumming finger along the length of the string. Higher frequencies are created
when the finishing pan is almost as far forward as it can go in the oval basin. It is here
also that I can create the greatest number of shock waves per second because the distance
of the edges of the finishing pan to the sides of the basin is shortest. Conversely, the
highest energy shock waves (and thus the greatest degree of suspension) can be created in
the middle of the basin because the extra distance permits a greater build up of speed
before hitting the side and reversing direction.
Front panning, of course, has its limitations
in that no amount of care can ever succeed in completely getting rid of all the black
sands while keeping fine gold inside the pan. The reason for this is because it becomes
virtually impossible to continue creating thin enough layers to scalp off the top by going
over the forward edge without pushing some of the gold over the same edge. A pan with
built in riffles, of course, completely rules out any possibility of getting rid of all
the black sand. Rather, a completely different strategy must be employed. This consists of
the art of back panning.
Back Panning: Back panning is a term I use for
the process of getting rid of unwanted black sand off the back edge of the pan while
keeping the gold pinned in the crease along the front, bottom edge of the pan. Some
additional forces are utilized -- magnetism and a phenomenon I refer to as capillary
cohesion, plus wave cancellation. I will explain how each of these come into play.
biggest problem at the end stages of panning down sub #30 material to pure gold is the
difficulty involved in avoiding swirl. The reason I say this is because one little mistake
will send your carefully panned concentration of fine gold spilling over a wide area and
toward the rear of your pan where you do not want it. Think of swirl as an unwanted,
rather overpowering horizontal wave of water that is strong enough to break up the fragile
web of cohesiveness that keeps the concentration of heaviest particles formed in the
crease at the forward edge of the pan from breaking up. The best way that I have found to
pan down to a point where almost all the black sand and lead is eliminated is by a gradual
drawing of the unwanted contaminants straight down to the bottom edge for disposal. After
many years of practice and experimentation I finally hit upon the concept of wave
cancellation as a potential solution to solving the swirl problem.
Wave Cancellation: Wave cancellation best can
be achieved in a simple gold pan. By this I mean a pan that has a single side sloped down
to a broad and flat bottom. Complex pans that are constructed with an additional straight
drop at the bottom and pans with a narrow bottom do not work well for my techniques. This
is because swirls and uneven waves result. Riffles are totally unnecessary for back
panning. Wave cancellation requires a careful balancing of the pan to maintain a level
axis upon which to backwash the unwanted black sands to the rear of the pan. The capillary
cohesion forces (related to surface tension forces) that allow your solid material (where
your fine gold is buried) to stick together are very weak, so our movements at this point
must be rather slow and careful. The proper way to position my body is the key to success.
This position is assumed immediately after I have eliminated as much unwanted material as
I safely can by front panning. I then reconcentrate the remaining material into the
forward crease of the pan by vigorously (but not overwhelmingly) banging or tapping it
quickly from side to side while under water. Then, very deliberately and very carefully I
tilt the rear of the pan lower than the front so that all the water drains back to the
back edge of the pan while capillary cohesion keeps the wet solid concentrates held
together in a bunch at the forward edge of the pan. At this point I dip the rear edge of
my 10 flat-bottom finishing pan into the basin and allow in about a cup or maybe a little
more than a cup of water.
When I back pan I hold the pan straight out
from my body as I lock my elbows at my sides and never move them, not even a little bit,
while I grasp the finishing pan firmly with both hands. The only movement occurs at the
wrists. They must work in synch in order to maintain the required level axis of movement,
ie, a perfectly horizontal plane held perpendicular relative to the center of the earth.
Once the proper position is established I begin dipping the pan forward so that the water
begins to advance towards the front of the pan.
By maintaining the pan perfectly level as
I continue to tilt the pan forward, the water advances against both curved sides at an
equal pace. Once the water reaches the mass of concentrates the water surface is split
apart. Each of these advancing water edges becomes a wave which carries with it a roughly
equal amount of energy. The curvature of the pan forces the advancing water to wash up
over and around the collection of black sand (and gold) concentrates and when they finally
‚kiss‚ at the very center of where the concentrates are
positioned, the energy they are carrying cancels, thus eliminating any significant swirl.
It is at this moment that I begin to bring the rear of the pan back down to allow the
water to backwash over the concentrates and carry some of it away. This drawing down
movement is executed at a somewhat brisker speed than when the pan is tipped forward. When
done properly the advancing flood of water does not break up the clump of concentrates.
But on the back dip movement the retreating water carries particulate matter straight down
towards the rear of the pan.
Doing this repeatedly gradually draws down a pile of black
sand to the rear of the pan. This contamination must be washed out occasionally by
carefully submerging the rear of the pan under water while tilting the front of the pan up
just enough to permit me to gently swish the unwanted black sands off the rear edge and
down into the basin (or into a water filled pan or bucket if I want to accumulate the
black sands for other uses). Now I repeat the process until I start seeing glints of gold.
That tells me it is time to use the magnet.
Use Of The Magnet: The biggest danger in using
a magnet is the accidental loss of gold that gets trapped between the particles of
magnetite. This happens when too powerful of a magnet is brought too close to the
concentrates. A large mass of magnetite that jumps to the magnet will carry with it
particles of gold. However, it is easy to avoid trapping the gold.
I take advantage of the
fact that both gravitational and magnetic forces act upon magnetite, while only gravity
acts on gold. Thus, no force is directly attracting the gold particles to the magnet,
while gravitational force is constantly tugging the gold away from the magnet toward the
center of the earth. By not allowing the magnet to get too close to the black sand, I
vigorously swirl the edge of the magnet just above the surface of the concentrates which I
previously have scattered across the entire bottom of the pan. The result is that the
resistance of the water prevents the particles of magnetite (which are too dispersed) from
trapping any gold.
Removal of the magnetite makes the remaining panning fairly easy,
albeit somewhat time consuming. I just keep drawing off more and more waste particles
until only gold and lead and a few specks of black remain. This is the time to employ the
Use Of A Pipette In Transferring Fines: I once
again bang the remains into the forward crease of the pan, but this time I then draw the
pan rearward and then thrust it forward with a short jerky movement. This causes the
majority of lead and black stuff to partially separate from the greater mass of gold which
tends to stay further forward in the pan. This fine gold then can be sucked into the
pipette and held there by adroitly tilting the pipette at an angle slightly higher than
level so that gravity keeps the gold particles inside until I am ready to deposit them
into a vial. This is done, not by squirting, but by inserting the tip of the pipette into
a water filled vial, then raising the pipette to vertical and simply allowing the gold to
fall down into the vial. This will occur very quickly the moment that contact is made
between the tip of the pipette and the surface of the water in the vial as long as no
bubble of air remains at the tip of the pipette.
The pipette also can be used to separate the
last remaining small stubborn black sand or lead contaminants from the gold. To do so I
employ the basic principle that heavier objects accelerate more rapidly through the
resistance of water than lighter particles. This nifty little trick is accomplished by
drawing all of these remains into the pipette, then immediately when the bulb has fully
expanded and the particles no longer are being drawn into the pipette, I quickly bring the
bulb end of the pipette up to vertical and simultaneously move the opening of the pipette
in a straight line under water across the bottom of the pan without applying any squeezing
pressure to the pipette.
This maneuver causes the heaviest things to accelerate and exit
first from the column of water remaining in the pipette. After the greater amount of gold
falls out the opening, then the lead and then the rest of the particles fall out in
descending order of density and weight. Thus, I now have a short line of mostly gold
particles which I can suck back up into the pipette in a much less contaminated state for
deposit into my vial.
Repeating this maneuver a few times, is effective at eliminating the
heaviest of the contaminates. Alternatively, I can use the pipette as a sort of pressure
hose to herd wayward gold particles together or, alternatively, to blow particles of
contamination away from the last of the gold with little puffs of water pressure. This
takes a little practice. With patience it becomes another valuable technique.
Additional Tips And Comments: Desert
gold, due to its chunky shape, occasionally presents a special problem even when the
pieces are smaller than #30. If the pieces are sufficiently round or log shaped, small as
they are, they will roll and migrate downhill along with the black sands. This means that
during back panning care must be taken because the weak force of capillary cohesion is
insufficient to hold these wandering rascals in the mass when the black sand layer gets
too thin. There are a few solutions. The easiest is simply to use your gloved finger to
push back the escapees each time they make a getaway. A better grade of tweezers easily
can pick these out if they are in the #30 to #50 range. The pipette also can be used to
isolate these in a separate pan for temporary holding.
While dredging it is important to keep
verifying whether I am in the pay zone and whether the gold is getting bigger or smaller.
Another important aspect of dredging applicable to me is that I need to force myself into
taking periodic breaks because I mostly dredge alone and I tend to get fixated, lose track
of time and not only over exert myself, but also get into a hypothermic state. So I use my
noon food break not only to eat but also to rest (aerobically) and warm up. This is when I
do some panning. I set up several 3 ounce glass vials and label each with a size
designation (#8, #12, etc.). As I work my way through the panning process I get a specific
result, already broken down in terms of different sizes and amounts of each that I easily
can see in the vials.