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Recovering a Nugget from Bedrock
CHRIS GHOLSON
“Some of the best gold
was recovered at or just above the bedrock…” These are words I have come
across time and time again when researching old placer mining districts. The
size and purity of the gold in these districts varies, but one thing they
almost always have in common is – the best values were found near bedrock.
The purpose of this article is to inform you (the electronic prospector) on
the most effective methods for recovering gold from bedrock while using a
metal detector. But before moving ahead, let’s first talk about the bedrock
itself. What is it?
Bedrock (also called country rock) is the outermost layer of the Earth’s
crust; and it comes in many varieties. The composition of the bedrock
(granite, schist, slate, etc.) will most certainly change depending upon the
geological conditions that are prevalent in the area you are detecting, as
will the color and texture. The texture of the bedrock is important for gold
prospectors, and we can describe it as being either rough or smooth.
Rough bedrock is highly regarded among nugget hunters because of its
excellent gold trapping ability. Jagged outcrops full of deep cracks and
crevices form a natural sluice box making it virtually impossible for the
gold to escape. If a nugget becomes wedged within one of these cracks it
will remain there until the bedrock breaks down or a lucky hunter comes
along and removes it. Whenever you encounter areas such as this, slow down
and focus your efforts on the cracks.
Smooth bedrock will have a slick polished look; almost as if someone has
taken an electric sander to it (and in a sense this is what has actually
happened). Smooth bedrock started out as being rough but because of the
sheer amount of water, sand, rocks, and boulders that have scoured its
surface it has lost its original texture. Usually smooth bedrock will be
found in the lower ends of a wash or at the edges of drop-offs; like
waterfalls. Most of the time, nuggets will hit these areas and just slide
right on by. Gold is occasionally found on smooth stretches, but it is a
rarity. Therefore, if time is of the essence, your best bet is to bypass the
smooth stuff and concentrate on the rough sections.
Now
that we have a better understanding of what bedrock is, the next question we
must address is, “Why should we metal detect the bedrock?” One of gold’s
amazing natural properties is its high specific gravity. When comparing gold
to most other elements found in the environment we notice that it is
extremely dense and heavy. Gold is 19,000 times denser than air, 19 times
denser than water, more than 3 times denser than quartz, and twice as dense
as lead!
Placer gold can be defined as free pieces of gold (i.e., dust, flakes,
nuggets, etc.) that have eroded away from the original lode, and have been
deposited elsewhere by the forces of nature. By far the most powerful agent
for moving gold is water. Pieces of eroded gold will be dispersed down a
hillside by rain storms, snow melt off, wind, etc., until they eventually
find their way into a river or other water channel. The gold will then be
swept up by the running water and redistributed downstream. Throughout this
entire process the gold is continually working its way downward through the
gravel. It is heavy and it wants to sink to the bottom; which is the
bedrock. Once a nugget hits bedrock it must stop there.
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This is VERY important for the detectorist because in many goldfields the
bedrock is shallow or even exposed. Since all metal detectors have a limited
depth range, it is beneficial for a person to hunt areas that are close to
bedrock, because he/she can be confident that if nuggets are present they
will be within detectable range. Not to mention, after millions of years of
erosion, the gold has become highly concentrated on the bedrock. Some
prospectors have been lucky enough to recover several pounds worth of
nuggets from a single bedrock pocket!
Recovering a nugget from the bedrock can be a tedious task; especially if it
is deeply wedged or very tiny. Occasionally you can see them shining
brightly on the surface, however most require some coaxing to retrieve them
from their hiding place. If the bedrock is highly weathered it will
typically break apart easily. If it is composed of a harder rock, it can be
a real chore.
There are three items
I always bring along when targeting bedrock: 1) a sturdy pick, 2) a strong
rare earth magnet, and 3) a flathead screwdriver. A good pick will allow you
to clear away any boulders, gravel or brush that may be covering the
bedrock, and chip away at deeper pockets. A powerful magnet is brilliant for
quickly removing ferrous junk like fragments of wire, boot tacks and bits of
decomposed cans. It is a fairly inexpensive bit of equipment that can really
save a lot of time. The trustee flathead is another tool that can be put to
good use. It is much easier to maneuver in tight bedrock cracks than a pick
head, plus you can take your time making sure a nugget does not get damaged.
Don’t use an expensive one, instead go for a “junker” in your toolbox or
pick up a cheapo from the hardware store. Another inexpensive device you can
use while bedrock hunting is a straw. That’s right – a straw! Grab a few
from a local fast food restaurant the next time you swing in for a meal.
They are great for blowing out sand filled cracks.
The
first thing to do when you receive a signal with your detector is to
pinpoint the location of the object as accurately as possible. Sweep the
coil in a horizontal motion listening for the strongest signal, then sweep
vertically; once again listening for the strongest signal. The object (or
target) should be located somewhere towards the center of this imaginary
“X”. You should also try tilting the coil on edge, using its side to help
determine the location. Once you have a general idea of where the target is
hidden, use the side of your boot to kick away any materials that may be in
the way, and pinpoint the target once again.
At
this point you can get down on your knees for a closer look at the bedrock.
Use your mouth or a straw to blow away any excess material and hopefully
expose the nugget. Be sure to close your eyes while blowing; there’s nothing
worse than an eyeful of sand! If you still don’t see the nugget, use the
screwdriver to pry apart the cracks and blow it out again. If the signal
remains, we can assume it is still in the bedrock and will require further
digging with the pick.
Gold nuggets only have a hardness of about 2.5-3.0, and are extremely
malleable. They can be scratched, bent, or even punctured by a sharp blow.
Therefore, if you get a signal and believe it is gold; never strike that
area directly with your pick. Instead, begin digging around the target,
loosening up the ground. As you’re digging, periodically rub the magnet into
the hole or crack. If the target is a piece of ferrous trash it will quickly
be removed, saving you from unnecessary work. I attach mine to the end of my
pick, so it also works as I’m digging. Just be careful if you carry your
pick on your side and your wallet in a back pocket. I’ve wiped out more than
one credit card this way!
Fortunately, if you are digging up the bedrock and the signal persists, your
chances of it being gold greatly increases. You may also notice
concentrations of black sand (magnetite) in these cracks. Black sands are
heavier than ordinary sands and accumulate in much the same way as gold. The
presence of black sand in a crack is a good indicator of gold, but not a
definite guarantee.
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Once you finally get the target out of the hole and into the pile, you can
then use your hands to recover it. I call this the “Back & Forth” technique.
Grab a handful of dirt and wave it across the coil. It doesn’t matter if it
is the bottom or the top of the coil; either side will work. Once you have
the target in hand, pour half of the material into your other hand and wave
that across the coil. The material in the hand that doesn’t trigger a “beep”
can be discarded. Continue splitting the material in half until nothing is
left but a small handful; now you should be able to see what is causing the
signal; hopefully it will be a gold nugget! This same process can be
accomplished with a plastic scoop, which is often a better choice if you are
working around cactus.
Learning to quickly recover a nugget from bedrock is not something mastered
overnight. Just like every other facet of metal detecting it takes practice,
but the more you do it, the faster and more efficient you will become.
Finding nuggets with a metal detector is challenging, however, by working in
a known gold-bearing area and focusing your efforts on the exposed bedrock,
you greatly improve your chances of success. I wish you the very best of
luck! |
