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Recovering a Nugget from bedrock - Arizona Outback

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.

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.

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!

Recovering a Nugget from bedrock while metal detecting for placer gold.
Recovering a Nugget from bedrock - Arizona Outback

 

             
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