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Methods of Gold Recovery - Arizona Outback

Methods of Recovery

CHRIS GHOLSON

Placer gold is believed to be one of, if not the first, metal to have been mined by early humans. Placer gold can be defined as free gold that has eroded away from its original lode, and has been deposited elsewhere by the forces of nature. The size of placer gold varies from microscopic dust up to large nuggets weighing several thousand ounces. Although the type of equipment used to mine placer gold has changed over the years, the basic principal has not. The most popular methods currently in use by recreational prospectors are the gold pan, sluice box, metal detector, drywasher, dredge and highbanker, all of which have their strengths and weaknesses. Some methods that work well in a stream type environment will be of little use in the arid dryplacers of the southwest, and vice-versa. The type of equipment you choose will be dependent upon the conditions in the area you are working, the size of the gold particles, and your budget. If you are a new prospector, or thinking of becoming involved with gold prospecting, take a moment to familiarize yourself with the information listed below. It is meant to provide you with a better understanding of how each piece of equipment works and in what environments they are most likely to prove useful.

Gold Pan

The gold pan is probably the oldest method in existence for recovering placer gold. The first pans were made of woven baskets or wood, then metal, and most recently plastic. Whatever the material, the pan is still one of the most valuable tools used by modern prospectors.

Pans are like a shallow bowl with riffles built into one side. Gold-bearing material is placed inside, and then the entire pan is submerged in water. Once the material has been covered in water, the pan is vigorously shaken. The object is to get the heavier materials (i.e., black sand and gold) to sink to the bottom. The pan is then titled at an angle; water is allowed to move in and out of the pan sweeping away the lighter material. The heavier materials are trapped behind the riffles and remain inside. The pan is then filled with water, shaken and dipped back into the water again. This process is continued until all that is left behind is a streak of black sand and hopefully gold!

NOTE: Gold pans, especially those made of plastic, are incredibly cheap; most cost less than $10.00.   They are fairly easy to learn and can be used anywhere with water. Their low weight and lack   of hoses and motors make them the most portable piece of prospecting equipment. Pans are also used in conjunction with dredges, drywashers and highbankers in the final clean up procedure. The size of gold particles recovered and the amount of material processed with a pan will be dependent upon user experience. Every gold prospector should own this essential tool.

Sluice Box

A sluice box is a trough-like device that is fitted with riffles along its bottom edge. The sluice has been in use for well over 100 years. Some of the original sluices developed by the 49’ers were actually carved into the bedrock itself; a method called ground sluicing. Eventually they were handcrafted out of wood. Most sluices available today are made of either metal or plastic. A sluice, when properly set up, can process anywhere from 10 to 200 times more material than a gold pan. A sluice requires a steady flow of water for maximum efficiency. A sluice is placed in a swiftly flowing stream or creek, with the box placed in such a way that the water is directed through it. Gold-bearing material is then slowly shoveled into the sluice. The riffles in a sluice mimic the natural bedrock cracks in a stream allowing it to capture and retain gold particles which pass through it. The lighter materials will be washed away, but any gold will drop behind the riffles and remain there. Some experimentation will be needed in order to determine the optimal flow of water and angle of the sluice.

NOTE: Sluicing is one of the most popular methods for recovering placer gold. The sluice has several advantages such as 1) low weight and portability, 2) affordable; most cost under $200, 3) excellent recovery when properly set up, and 4) easy to operate. If you are new to gold prospecting and live in an area with gold-bearing creeks, streams or rivers, the sluice is a good choice.

Metal Detectors

As its’ name implies, a metal detector is a device used to locate metallic objects. The three main components are the control box, shaft, and the search coil. The control box houses the "brains" or electronic components of the detector. The shaft is the frame which supports both the control box and the coil. The search coil is the part of the detector which is swung over the ground. It is comprised of many windings of wire that are used to transmit and receive the generated electromagnetic field. Whenever this field passes over a metal object it causes eddy currents to flow on its surface. This in turn distorts the field causing the detector to produce a signal, usually audio.

There are many different types of detectors available on the market. Some are used for working underwater, seeking out coins and relics, others for hunting gold. If you are going to be primarily looking for gold you should invest in a machine designed exclusively for nugget hunting. These machines are able to handle high levels of ground mineralization and are designed to be extremely sensitive towards tiny metallic targets. The most popular types in use today are the VLF (Very Low Frequency) and PI (Pulse Induction). VLFs achieve excellent sensitivity and are preferred for chasing small, shallowly buried gold. They do, however, struggle in areas of severe ground mineralization. PIs are not as sensitive as the VLFs, but they provide more depth penetration and will outperform any other type of detector in mineralized or "noisy" ground. Unfortunately they carry a price tag of several thousand dollars. You will discover that there are many different types of metal detectors out there, so before making a purchase take some time to research which one is right for you. Whatever machine you decide on buying make sure it is designed exclusively for gold prospecting.

NOTE: The metal detector is the most versatile of all the methods. It can be used virtually anywhere under any conditions. Metal detectors can recover gold from hard to reach areas where bringing in other types of equipment is an impossibility. They are most effective on pieces of gold at least several grains in weight; they will not recover fine gold. Metal detectors can be expensive, however they are fairly easy to operate and can be packed into virtually any gold-bearing location. Aside from nuggets, metal detectors are also able to locate meteorites, coins, and historical artifacts. The metal detector is quickly becoming a favorite among recreational placer miners.

Drywasher (or Dryblower)

By far the most popular piece of equipment used in the recovery of desert gold was, and still is, the drywasher. Arid regions presented many new challenges for the early placer miner. The first prospectors used or needed very little equipment other than their eyes, as most of the nuggets were lying on the ground in plain view. Early prospectors could simply walk along a wash and inspect the bedrock for exposed nuggets. However, these rich surface bonanzas quickly played out, and the miners needed a devise that could effectively process and recover coarse gold from dry gulches without the use of water; hence the evolution of the first primitive hand operated drywashers.

In its simplest form a drywasher consists of a grizzly (mesh size varies) supported by a frame that is fitted with an adjustable riffle tray. Hand cranked models typically use a system of bellows to move or vibrate the material across the riffles, while blower-motor powered models are equipped with a fan offset by a spinning counter weight. Air is pushed through a hose by the blower which then causes the unequally weighted fan to spin, effectively shaking the riffle tray. Basically all models do the same thing, it’s just a matter of how they accomplish it. As dirt is shoveled into a drywasher, the larger overburden is immediately screened off while the smaller material passes through and enters the riffle tray. This process leaves two distinct piles, which we will label as either coarse or fine. The coarse pile forms at the front of the drywasher; this is where the larger rocks and nuggets that wouldn’t fit through the screen will be located. The fine pile will be produced towards the back of the drywasher; this material has already been processed and should not contain any large nuggets.

NOTE: Aside from the metal detector, the drywasher is the most effective method for recovering gold from a dryplacer environment. They are portable, easy to operate, and usually cost a few hundred dollars. Gold recovery is best when the material being processed is free of moisture. It is recommended that a metal detector be used in conjunction with a drywasher to ensure that no large nuggets are lost amongst the coarse tailings.

Dredge

A dredge is a device used to suction up gold-bearing gravels from a creek or river. It is essentially a glorified vacuum cleaner consisting of a sluice box, nozzle, hose, water pump and a gasoline-powered engine. The sluice box may be floated upon a set of pontoons or set alongside the bank. Dredges are very effective in the amount of gold they will recover; however they require an ample supply of water. Commercial dredging operations have been used successfully throughout the United States, most notably in California, Alaska and Montana. Other states such as Arizona, New Mexico, Utah, and Nevada have seen some large-scale operations, however their arid climate has always made this type of placer mining a difficult endeavor.

Dredges are usually classified according to the diameter of the hose attached to it (i.e., 2, 3, 4, 6"+). The larger the hose diameter, the bigger the dredge and motor. Large dredges are capable of moving more volume, so gold recovery is usually greater. While they are capable of shifting more gravel, large dredges are expensive, bulky, and require a considerable amount of water. Small dredges cannot match the capacity of their bigger siblings, but in areas where the bedrock is shallow and running water is scarce, a small dredge may outperform the "big boys."

Dredging can be loosely classified as either deep water or surface. Deep-water dredgers are usually experienced divers, as they often dive to depths exceeding 20 feet. Dredging in deep water can be dangerous! The biggest threat comes when suctioning gravels beneath large boulders. Careless undermining can cause these boulders to shift, possibly trapping the operator underwater. Experienced deep water dredges nearly always work in teams of 2-3 men. On the other hand, surface dredgers rarely exceed 4-5 feet in depth, so diving knowledge is not a necessity. They need little equipment other than their dredge, a few tools and perhaps a mask. The type of dredging you do will be determined by the location and the amount of money you are willing to invest in equipment.

NOTE: Dredges are very efficient, being able to recover gold of all sizes including fine gold and dust. They are capable of processing large amounts of auriferous material and are the best means of working gold in a stream type environment. Dredges vary in both size and price. Small backpack dredges can be purchased for a few hundred dollars, larger models can cost upwards of several thousand dollars. As mentioned above, dredges require water and are therefore not suited for dryplacer areas. Always consult with your local BLM, State Land, or Forestry department before doing any dredging.

Highbanker

A highbanker is basically a cross between a drywasher and a dredge. A highbanker is similar to a drywasher because material is shoveled in. The difference is, that water instead of air, is being used to separate out the heavy concentrates. A hose runs to the creek or river through which water is drawn up to the highbanker via a water pump. This water is then released over the sluice box. Gravel is shoveled into a hopper which rests over the head of the sluice box. A titled mesh screen allows gold-bearing gravel to fall through into the sluice for processing. Rocks too large to pass through the screen roll off onto the ground. Highbankers are used to recover gold from bench-type deposits, or to process material that is a short distance away from a water supply. Like dredges, highbankers require a decent amount of water. They do, however, offer more flexibility as a prospector is not confined only to working the creek or river.

NOTE: Highbankers use water as a means for separating gold from worthless material; therefore recovery is good. Highbankers vary in both size and price. Some of the smaller versions appearing on the market are actually battery powered, a nice alternative for those wishing to sample a perspective placer. Highbankers are capable of processing large amounts of material and can be used some distance away from a water supply. Like dredges, they depend on water and will be of little use in an arid environment.

 

Dry and wet methods of recovering placer gold.
Methods of Gold Recovery - Arizona Outback

 

             
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