By Dave McCracken

You have a substantial prospecting-advantage with a modern gold detector!

Dave McCracken

 

 

woman with a gold nuggetI highly recommend The Fundamentals of Electronic Prospecting be read before reading this article.

All the rules of placer and desert geology apply to gold nugget hunting, and this knowledge should be utilized to establish where gold deposits and nuggets are most likely to be found.

Particular attention should be paid to locations which have little or no streambed or other material present, so the detector’s coil can search as closely as possible to bedrock or false bedrock layers. Also, exposed tree roots along the edges of the present streams, rivers and dry-washes have been proving successful, especially along the smaller tributaries in the higher elevations of known gold country.

Some of the most productive areas for electronic prospecting in the dry regions are in the near vicinity of old dry-washing operations. The old-timers were only able to make dry-washing work in very high-grade areas. They seldom recovered all the high-grade gold out of an area, because they did not have the means or equipment to prospect extensive areas. You have a substantial prospecting-advantage with a modern gold detector. Natural erosion over the years has likely uncovered more high-grade in the immediate area, or concentrated other spots into new high-grade gold deposits.

When prospecting old dry-wash workings, it is always worth a little time to rake back some of the old tailings piles and scan them with your detector. Dry-washers, today and during the past, almost always used a classification screen over the feed area. The screen was commonly around half-inch mesh. An operation shoveling onto the screen at production speed in dry high-grade gravel might have missed larger nuggets as they rolled off the top of the screen. Sometimes, when working a layer of caliche, if the material was not broken-up well enough, it would roll off the screen with nuggets still attached. A metal detector reads out strongly on these kinds of targets. Make sure to ground-balance to the tailing pile. One nice thing about prospecting in these tailing piles is that they usually are not filled with iron trash targets.

When dealing with natural streambeds above the water, you generally do not find too many other reading metallic objects besides gold, unless the spot which you are scanning is near an inhabited location, like a park or an old dump. So it is reasonably safe to dig any target that gives off a metallic reading in a streambed.

However, some locations have lots of trash and small iron targets. Sometimes, iron targets seem to accumulate heavily in the same areas as gold. This presents a big challenge! Once you have been scanning a particular area for a while, you will gain an understanding of how much “trash” (metallic objects of no value) exists within the vicinity. With some experience on gold objects, you will learn to distinguish the different tone changes between most gold objects and most trash targets. Pay particular attention to the very faint readings, as is often the case with natural gold targets.

One of the main keys to successful electronic prospecting is to slow down your sweeping action. You cannot do it fast like when hunting for coins. You almost have to crawl across the ground. Remember, you are listening for even the faintest whisper of a sudden increased threshold hum. A gold target may sound like a coin—only a quieter signal.

Different types of detectors have special non-motion or pinpointing settings which allow the coil to be moved very slowly and still pick up targets. This means you are able to slow down your sweep to almost a standstill and still hear a target as the coil moves over it. On the other hand, these settings may be too sensitive to use for nugget hunting on some detectors, depending upon field conditions and how fast you are sweeping. When in doubt, experiment while using a test-nugget on or in the ground you are searching.

Another important point is to overlap your coil sweeps. The area covered by the search-field under your coil is similar to a triangle. Directly underneath the coil, the search area is about the same size as the diameter of your coil. The search area becomes narrower as it penetrates the ground further away from the coil.

However, the size of this triangular search-field is not constant underneath the coil. It changes as mineralized conditions change in the ground below your search coil. If you do not overlap your search strokes, you can leave as much as 50 percent or more of the area below the search coil behind, without being adequately searched.

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You have to use your own judgment about how to discriminate between which targets to dig, and which to leave behind. This comes with practice and experience. Discrimination of any kind, whether by electronic circuitry or the audio sounds given off by the target, has limited accuracy. The depth of a target and the degree of ground-mineralization in that particular location can confuse any discriminator. In some places, you will want to dig every target. In other places, where there is lots of trash, you may find it more productive to discriminate your targets by sound and/or in combination with electronic discrimination features on your detector. In this case, you have to balance the need to leave some small pieces of gold behind, with not wanting to dig a bucket full of trash and valueless iron targets; and therefore, less gold.

When in doubt, dig! Or at least toss your sample nugget down and get a comparative reading.

With lots of practice in the field, you will eventually reach the point where your metal detector is like an extension of your arm—like an extension of your perception and knowingness. You will gain the ability to look down into the ground and have a pretty good idea of what is there.

Big nuggets are generally not too difficult to find. In most areas, however, there are hoards of smaller gold targets in ratio to each large nugget found. Small pieces of gold are your bread and butter! Most gold is small gold, but it has to be large enough to be worth your while. Some of the modern gold detectors will pick up pieces of gold so small that you could be finding them all day long; and at the end of the day, not have accumulated very much gold by weight. In this case, you may want to move to a different area.

Just like in other forms of gold mining, electronic prospectors have to set standards for themselves. Someone pursuing the activity to make money will be motivated to recover volume-amounts (by weight) of gold. Another person pursuing electronic prospecting as a part time activity may receive his or her best thrills by recovering the smallest-sized targets.

One interesting development in the electronic prospecting field, which I have not seen happen in other gold mining activities, is the tremendous emotional success gained from finding extraordinarily-small pieces of gold. Normally, in gold prospecting, we get excited to find a big nugget or a rich deposit. These are easy to locate when scanned over by a metal detector. The big challenge with a metal detector is in locating the smaller pieces. Experienced prospectors know that if they are finding the small pieces, they will easily-find the big pieces.

When scanning, keep your coil as close to the ground as possible. It takes a coordinated arm and wrist-action to keep the bottom of the coil parallel and close to the ground throughout the full sweeping action. Allowing the coil to move one or two inches away from the ground during the outside of a sweeping motion will also reduce depth-penetration by one or two inches. This will certainly result in lost gold targets. You have to practice keeping the coil close to the ground. Shorter sweeps is usually the answer.

Sometimes it helps to kick rocks out of the way, or use a garden rake to remove multiple smaller obstructions before you search an area. This allows you to keep the coil close to the ground with minimum obstructions.

During your prospecting activities, it is possible that you may find occasional targets which could potentially be classified as artifacts. The Archaeological Resources Protection Act defines just about anything you might find as a “protected” artifact. There are criminal penalties for disturbing or removing artifacts. What constitutes a protected artifact is primarily up to the judgment of local bureaucrats. Searching for natural gold targets is legal. Messing around with old junk and trash may be illegal. Sometimes, it is better to just leave old items where they lie. You will have to decide.

The main suggestion I commonly give to beginners about electronic prospecting is to not give up. With practice and by working in the right area, you will surely find some gold!

PINPOINTING

When you do have a reading target, its exact position in the ground should be pinpointed. This can be done by noting when the detector sounds out while scanning over the target in fore and aft and left to right motions. A steel or iron object can be often be distinguished by noting the size and shape of the object during the pinpointing process. Sometimes trash objects are large and/or lengthy in size.

Sometimes a stronger-reading target will seem to cover a larger area than it actually does. If you are having trouble getting an exact location, continue to lift the search coil higher off the ground while scanning with an even back and forth motion. As the coil is raised higher, the signal will become fainter; but the position of the metal object will sound-out at the very center of the search coil.

PINPOINTING WITH THE GOLD PAN IN WET AREAS

Once you have pinpointed the exact position of a target in an area near water, one way of recovering the object is to carefully dig up that portion of ground, using a shovel or digging tool, and place the material in your gold pan. Here is where a large plastic gold pan comes in real handy. Be careful not to cause any more disturbance or vibration of the streambed than is necessary while you are attempting to dig up a target. It is possible to miss the target on the first try and cause it to work further down into the streambed because of its greater weight in the wet environment. Sometimes you can lose the target, and not be able to locate it again with the detector.

Sometimes the ground is hard and needs to be broken up or scraped with a small pick. Keep in mind that a sharp blow from a pick can destroy a coin or disfigure a gold nugget, reducing its value. Digging and scraping is better than pounding, if possible. In hard ground, sometimes it is easier to loosen the material up and shuffle it into several small piles. These can then be flattened out and scanned to see which contains the target.

Once you have dug up that section of material where the target was reading, place it in your plastic gold pan and scan it with your detector. If the contents of the pan do not make your detector sound-out, scan the original target area over again. If you get a read in the original location, pour the contents of the pan neatly into a pile out of your way, pinpoint the target all over again, and make another try at getting the target into your gold pan. Continue this until you finally have the target sounding out in your pan. If you cannot see the target, and water is immediately available, pan-off the contents until the target is visible.

There is a good reason why you should not ever throw away any material from the target area until after you know for certain exactly what the reading target is. If you are looking for placer gold deposits and it happens that your detector is sounding out on a gold flake or nugget, the chances are pretty good of additional gold being present in paying quantities within the material which has been dug out of the hole, even if it does not sound-out on your detector. Remember, small particles of gold often do not make metal detectors sound-out. Therefore, the possibility exists that there could be hundreds of dollars worth of gold in a single shovelful of material not tightly-concentrated enough to cause your detector to sound-out. So wait until you have seen the reading target before you start throwing any material away.

If you dig for a target and then cannot get any further reads on the detector from either the pan or in the original target area, quickly pan-off the pan’s contents. There is always a possibility of a concentrated gold deposit which is no longer concentrated enough to read-out on your detector. In this case, you are most likely to have some of the gold deposit in your gold pan, which will quickly be discovered when you pan off the contents.

There is also another reason why you save the material from a hole until you have recovered your target. Because of the shape of a gold pan, and depending upon the size and shape of the coil you are using, if the gold target (especially a small target) ends up in the bottom of your pan, your coil may no-longer be able to scan close enough to the bottom of the pan to sound-off on the target. Because of this problem, gold pans have limited workability as a pinpointing tool in electronic prospecting. Sometimes, you can have better luck scanning the bottom-side of a gold pan.

DRY METHODS OF PINPOINTING

There are several popular methods of pinpointing reading targets in the dry regions where water is not available for panning. Some prospectors use a plastic cup. Material from the target area is scooped up and passed over the coil. If the contents of the cup do not sound-out on the detector, the target area is scanned again until the target is located. Take another scoop, pass it over the coil for a signal, and repeat until the target is in the cup. Then pour some of the contents into your hand. Pass the cup over the coil, then your hand, until you locate the target. Put the rest away in a neat pile, and repeat the process until you recover the object.

One important point to mention is that most search coils have equal sensitivity to targets both above and below the coil. In other words, during pinpointing, you can pass material over top of the coil and obtain the same results as if you turn the detector upside down and pass the material across the bottom of the coil.

Your handy magnet can be a big help when you are having difficulty finding a faintly reading target. Sometimes it is just a small piece of iron.

There is also the hand-to-hand method of pinpointing a target. You can reach down with your hand and grab a handful of dirt or material. Pass your hand over the coil to see if you are holding the target. Continue until you have the target in one hand. Then pass half the material in that hand to your other hand. Use the coil to find which hand has the reading target. Discard the material from the other hand and pass half the material from the reading hand to the second hand, again. Keep up the process until you only have a small amount of material in the reading hand. Carefully blow off the lighter material to locate the target.

Another procedure is to grab a handful and pass it over the coil as explained above. Once you have a reading handful, toss it in a pouch for later panning.

Some prospectors prefer to sprinkle a handful of reading material slowly on top of the detector’s coil. There are different ways to do this. One effective way, which requires some practice, is to sprinkle material over a slightly slanted coil while you vibrate it so that material slowly sweeps across and off. When the target drops onto the coil, the detector will sound-off with a distinctive bleep. Then, all you have to do is gently blow the dirt off the coil, or recover the target from the top of the pile where the material is landing. This method is nearly impossible in wet material.

One important thing about using your hands to pinpoint and recover gold targets, is that some of today’s most sensitive high frequency gold detectors react to the salt (mineral) content on or in your hand. When this occurs, your hand will give a reading when passed over the coil by itself, sometimes even a strong signal. This makes hand pinpointing methods more difficult. In this case, the plastic tray or cup works just fine, or the method of pouring material onto the coil.

If you find a gold target, be sure to scan the hole again. Sometimes it is worth doing a lot of digging and/or raking, with alternate scanning of the immediate area. Gold targets almost never travel alone! I have seen dozens of gold flakes and nuggets come from within a one-foot square area on bedrock. Many times!

HOT ROCKS

Sometimes you get soft or strong signals from your metal detector when the coil is passed over rocks which contain heavy mineralization. These rocks are called “hot rocks.” This needs to be clarified. It isn’t necessary for a rock to have an extraordinary amount of mineralization to sound-off as a hot rock. It just needs to have more than the average ground which your detector is ground-balanced to. The opposite of this is also true. A rock containing less mineralization than the average ground will change tone on a detector in the opposite way. These are called “cold rocks.” A hot rock from one location could be a cold rock in another location containing higher mineralization in the average ground.

Put another way, when your detector is properly ground-balanced to the average ground, it will sound-off on rocks containing condensed heavier mineralization. Often, the signals given off by these hot rocks can be mistaken for signals which might be given off by gold targets in the ground. Some locations have lots of hot rocks. Naturally, since gold travels with other heavy mineralization, you can expect to find hot rocks in the various gold fields.

Hot rocks come in all sorts of colors and sizes. A big hot rock, depending upon the degree of mineralization over the average ground, can sound very similar to a gold target. The same goes for small hot rocks.

Quite often, most of the hot rocks within a given area will be similar in nature, color and hardness, but not necessarily in size. After searching an area for a while, you will know what most of the hot rocks look like. This makes pinpointing targets a little easier, especially when dealing with small hot rocks. When receiving signals from rocks which are dissimilar to the average-looking hot rock of the area, check them out closely, especially when they have quartz. Some of these may not be hot rocks at all, but gold specimens.

If you are finding hot rocks on top of the ground, you will almost always find them buried, as well.

Metal targets gradually lose signal-strength in proportion to the increased distance from the coil. Hot rocks rapidly lose their signal-strength as they are scanned further from the coil. Also, a metal target tends to create a more specific, sharper signal as the coil is passed over. The signal given off by most hot rocks is not as sharp. It is more of a mushy sound which doesn’t have as clear a change in tone-intensity as the coil passes over the target.

When uncertain about a reading target, one way that some hot rocks can be identified is by passing the coil over the target from different directions. If the target only sounds out when being swept from one particular direction, then it is nearly certain that the target is not a gold nugget.

Sometimes, when lowering the sensitivity on your detector a few numbers, the signal given off by a nugget will continue, but weaker. A hot rock signal will quickly disappear by lowering the sensitivity. You can get a better idea how your detector is reacting to sensitivity changes by running it over your test-nugget.

Another test is to slowly raise the coil further away from the reading target as you are scanning. The signal of a metal object will become progressively fainter as the distance is increased. The signal given off by a hot rock will rapidly die away as just a little distance is put between the target and the coil. Most hot rocks in a given area will have a very similar sound, the intensity depending upon size and distance from the coil. Sometimes, you will find that a gold nugget gives off a much sharper signal. But not always. Much also depends upon the size of a gold target, its distance from the coil, and the amount of mineralization interference in the ground that is being scanned.

Each area is different. The hot rocks in some areas are reasonably easy to distinguish. In other areas, it is necessary to dig every signal.

Larger hot rocks are easier to detect. Many can simply be kicked out of the way. It is the smaller pebble-sized hot rocks which create faint signals. In some locations, these signals are so similar to the signals given off by gold nuggets that you have no other choice but to dig them up.

If lots of hot rocks are making it difficult for you in a particular area, you might try experimenting with smaller coils. Smaller coils are more sensitive to smaller pieces of gold. Therefore, the sharpness of the signal over gold targets is also intensified. This may give you the needed edge in distinguishing the slightly-different signals being given off by hot rocks in that area.

Some gold prospectors go so far as to ground-balance over top of a hot rock until it no longer gives off a signal. This will eliminate a large portion of the hot rocks in the area, but it is also likely to eliminate a large portion of the small and marginal signals given off by gold targets. This procedure may work well in areas containing just large nuggets. However, most areas I am aware of have dozens or hundreds of smaller pieces of gold for every larger piece that you will find.

Since cold rocks are made up of a lesser-concentration of iron than the average material which your detector is balanced to, they give off a negative reading signal on your detector. Ground-balancing over a cold rock will cause your detector to react positively to the average ground within the vicinity.

PRODUCTION

Once you find a location which is producing gold targets, you will want to thoroughly work the entire area. This is commonly accomplished by carefully gridding the site. By this, I mean creating parallel crisscross lines on the ground, usually about four feet apart. You can do this by drawing light lines in the sand with a stick. Grid lines allow you to keep track of where you are, and what has already been searched.

If there are obstructions in the producing area (“nugget patch”), they should be moved or rolled out of the way if possible. The smaller rocks and materials on the ground can be raked out of the way. This allows you to keep the coil closer to the ground. In a proven area, this will surely mean more recovered gold targets.

Some areas produce quite well on the surface. Then, by raking or shoveling several inches off the surface and scanning again, sometimes you can find even more targets. I know of numerous small-scale mining operations in many different parts of the world, using metal detectors as the only recovery system. They use a bulldozer to scrape away material which has already been scanned, two or three inches at a time. A layer is removed; the area is scanned thoroughly with metal detectors to locate all of the exposed gold targets. Then, another layer is removed and scanned. This process is done all the way to bedrock. They make good money at it!

I have heard of others doing the same process on a smaller-scale by attaching plow blades to four-wheel drive vehicles. Some even do it using ATV’s!

While hunting over a proven nugget patch, be sure to keep your detector properly tuned all the time. Otherwise, you will certainly miss gold targets.

PROSPECTING OLD HYDRAULIC MINING AREAS

Perhaps the most productive areas of all to prospect with metal detectors are areas which were already mined by the old-timers using hydraulic methods. Many of these areas are left with a large amount of bedrock exposed. This allows immediate and easy access for search coils to get close to old gold traps. Sometimes, the exposed bedrock has been further-deteriorated because of direct exposure to the elements. Once a nugget patch is located, raking away decomposed bedrock sometimes can produce remarkable results.

While searching such areas, pay attention to the color of dirt which covers and surrounds nugget patch. You might discover a pattern. In our area of operation, it is a white powder which often signifies the possible presence of a good spot. Perhaps in other areas, it might also be this white powder, or something else.

PROSPECTING OLD MINING TAILINGS

It is usually possible to find piles and piles of old mining tailings throughout most proven gold-bearing country.

Many of the larger earlier gold mining operations (the ones that were set up to move large volumes of material), concentrated on recovering only the fine and medium-sized values from the material being processed. This meant that the larger material was classified-out so the smaller material could be processed through controlled, slower-moving recovery systems. On the larger operations, classification was usually done either with mechanical vibrating classification screens, or with the use of a “trommel.” A trommel is a large circular screening classifier which rotates and tumbles material through, allowing the smaller classification of materials to pass through the outer screen and into a channel which directs them to the recovery system. The larger materials are passed down the inside of the trommel to be discarded as tailings.

In many of the larger operations, there were no means to recover the larger pieces of gold which were screened-out along with the other large materials. As a result, larger nuggets were sometimes discarded along with the waste material as tailings.

Anywhere you see large tailings piles, especially near the present waterways, it is evidence of a large volume operation where it is possible that the nuggets were discarded with the waste and are likely to still be there. Some large tailing piles still have large goodies inside them, which sing out very nicely on the proper metal detectors. One way to distinguish the right kind of tailing pile to be looking through is there should be a pretty wide range of material sizes in the tailing pile. Tailing piles which consist only of the larger rocks (cobble piles) were most likely stacked there by hand during a smaller surface-type operation.

Scanning tailing piles with a metal detector is proving to be highly-productive in some cases, and should not be overlooked as a possibility for finding nice specimen-sized gold nuggets. VLF ground-cancelling detectors are usually best-suited for this, because tailings almost always also contain a large quantity of mineral content, which is likely to cause interference on a BFO-detector.

PROSPECTING OLD MINING SHAFTS

Even the most experienced cave explorers shy away from entering declining mine shafts because of the dangers involved.

CAUTION: The first thing to say about prospecting in old mine shafts is that they are dangerous! There are different things that can go wrong when prospecting around in such places, one main danger being a potential cave-in. The shoring beams in some of these old shafts may have become rotten and faulty over the years. So it is best not to lean up against or bump any of the old wooden structures situated in old mine shafts. Loud, sharp noises should also be avoided.

Shafts which extend down into the earth on a declining angle are particularly dangerous; because if the ladders or suspension systems are faulty and collapse while you are down inside, you may not have any way to get out again. It is never a bad idea to bring along a caving rope, and use it, when exploring declining-type old mine shafts. Caving rope is different than mountaineering rope in that it is made not to stretch nearly as much. But I suppose, when going down in dark holes, any rope is better than no rope at all!

Another potential danger involved with exploring old mine shafts is encountering poisonous or explosive gasses. Entire mines were shut down because of such gasses—even when they were good-producing mines. These, however, were usually caved in and closed off to prevent unsuspecting adventurers from entering at a later date and getting into trouble.

Before you enter any old mine and start sorting through its low-grade ore piles, or pecking samples off the walls of the mine, it is a good idea to make sure the mine is not already owned by someone else. Or, if somebody does own it, it is wise to get the person’s permission first. There is probably nothing more dangerous in a mine shaft, cave-ins and poisonous gases included, than some old cantankerous miner who catches you, uninvited, in his mine and thinks you are stealing his gold!

There is probably more danger in prospecting old shafts than in any other gold prospecting activity.

After all that, just in case I have not succeeded in scaring you out of the idea of entering old mine shafts in your prospecting adventures, here are a few pointers about how and where you might find some rich ore deposits, or rich ore specimens, with the use of your metal detector:

But first, let me recommend that if you do go into such places, you bring along a buddy and leave another one at the surface with explicit instructions to not enter the shaft under any circumstances, but to go get help in the event that you should get into trouble within. It is also a good idea to let a few others know where you are going, just in case your outside-man doesn’t follow orders and you all become trapped inside.

There are two main sources of possible gold and silver in an old mine:

1) High-grade ore specimens that may have been placed in the low-grade ore piles and left as waste material.

2) High-grade ore which has yet to be mined.

With the exception of the largest production hardrock mines, there is always a certain amount of rock (ore) which has been blasted away from the wall of the tunnel that was not milled and processed. This was because some ore is of such apparent low-grade value that it is not worth the expense to process.

Sometimes the vein being followed into the mountainside was not as wide as the tunnel needed to be in order to progress into the mountain. Therefore, that rock material which was not part of the vein itself, or the contact zone, that looked to be of lower-grade value, was also discarded into the waste piles.

Crushing and milling ore is, and always has been, somewhat of a timely and expensive process. For this reason, a good many mines only processed what appeared to be the highest-grade ore that was blasted from the ore body. The rest was usually piled out of production’s way inside or outside of the shafts.

In the smaller operations, the kind where the ore was crushed and milled by hand and then processed with a gold pan to recover the values, only the highest of high-grade ores could be processed at a profit. The rest was usually laid aside out of the way.

The sorting of a higher-grade ore from lower-grade ore has always been a matter of judgment on the part of the person who was doing that part of the job. And, until the more recent breakthroughs in electronic detecting equipment, sorting needed to be done by eye or by feel (weight). There simply was no other way.

The interior of mine tunnels was often poorly lit with miner’s candles during earlier days, and the air inside the shaft was often foul after the powder explosions used to blast ore from the interior of the mountain. As a result of all this, it is not difficult to imagine that some higher-grade ore was likely discarded as waste material in most mines.

How rich the ore was in a mine will have a lot of bearing on whether or not a present-day prospector will find high-grade ore in the waste piles of that mine. The size of a mine does not necessarily have anything to do with how high-grade its ore was, although it may have a bearing upon how much waste ore will be available to test.

County reports can be looked over to locate the old mines within an area. Many of these reports also include information about the grade of ore being extracted from some of the mines.

When you are testing ore samples from a mine with a metal detector, and you do not come up with any specimens, try a few different piles. If you still do not come up with any specimens, it was probably not a high-grade mine. Try another.

Keep in mind that the floor of a mine shaft is likely to have some iron, brass and other metallic objects which will cause your detector to read-out.

One of the fastest and most effective ways of thoroughly checking out samples of ore is to lay the detector down on the ground or upon a makeshift bench with the search coil pointing upward so individual ore samples can be quickly passed by the most sensitive portion of the coil. The 3-inch diameter search coils are probably best-suited for this kind of work, because of the increased sensitivity, and because there is seldom great need for increased depth-sounding when testing ore specimens.

The most sensitive portion of the search coil is usually located near the center of the coil. It can be easily pinpointed by passing a coin back and forth across the coil while the detector is in tune, and by finding that spot where the coin causes the loudest and sharpest reading. The most sensitive area should be marked brightly with a Magic Marker so it will be easier for you to move ore samples directly past it. It is worthy to note that the top of the coil should have similar sensitivity to targets as does the bottom.

Ground-balancing would probably best be achieved by tuning to the overall ore pile. But, you may need to experiment. A lot will depend upon the grade of ore you are looking for. High-grade gold specimens will require the surrounding mineral to be cancelled out. On the other hand, sometimes high-grade ore is full of fine particles of gold which would not sound-off on a detector. In this case, the high degree of mineralization in the ore specimen might sound-out like a hot rock. Therefore, you would not want to ground-balance out high mineralization. So, depending upon the nature of the ore in a mine, you will need to use your own best judgment regarding the proper way to ground-balance.

Bring along a bucket, canvas bag or a knapsack so you will have something to carry your specimens as you find them.

Both BFO and the VLF ground-cancelling metal detectors can be successfully used to locate high-grade ore specimens. For the individual who is interested in finding a wider range of high-grade ore specimens rich enough to be worth milling on a small-scale for the gold and silver values, perhaps a BFO is the better type of metal detector to be used for the job. This is because the BFO does exceptionally well at picking up highly-mineralized ore. When you are dealing with hardrock veins, high mineralization is a good index of gold being present, especially when you are working with the ore that was blasted out of a previously-successful gold mine. Ore which contains large amounts of locked-in values or lots of fine gold that is thoroughly dispersed throughout the ore is not likely to read-out as a metal on any kind of conventional metal detector, although the high degree of mineralization which usually goes along with such ore probably will sound-out on a BFO-detector as a mineral. So the BFO-detector is handy in finding rich ores which might otherwise be undetectable.

By placing a BFO-detector on its mineral setting and keeping the pieces of ore which sound-out, you can accumulate a lot of good-paying ore. With the use of a BFO as such, the perimeters of ore piles can be scanned first to find a pile that has a lot of mineralization.

Portable rock crushers and mills and processing plants are available on the market. Perhaps by combining these with the use of a good BFO-detector to pick out the highly-mineralized, discarded ore, a small operation could be quite profitable without having to invest the higher costs associated with developing a lode mine from scratch.

LOCATING RICH ORE DEPOSITS

When prospecting around in an old mine with a metal detector, don’t discount the idea of searching the walls of the various shafts to locate rich ore deposits which may have been overlooked by the miners who originally developed the mine. With today’s market value of gold and advanced milling techniques, a small-scale mining operation can be run profitably in ore producing about ½-ounce to the ton in gold values, or perhaps even less. Abandoned mines which will pay this well and even better are scattered all over the west. If a person were really interested in locating a lode mine that he could work at a profit, one way would be with the use of a BFO-detector to prospect the various abandoned mines within the area of his or her interest. In using the BFO to scan the walls of such mines, highly-mineralized ore deposits can be located, samples can be taken for assay, and a person could find the mines having the richer-paying ore deposits. When prospecting like this, it is a good idea to bring a can of spray paint, a pen and paper and some zip-lock bags, so samples can be accurately marked as to where they came from, along with their respective deposits being marked with the spray paint.

If you are not interested in starting up a lode mine, but are just prospecting around for a bonus, again, the VLF detector is good for looking through mineralization and detecting the richest deposits. If, however, you do locate a reading metal inside the wall of a mine shaft with a VLF detector, and you have determined that it is not some falsely-reading mineralization, it could be well worth your while to investigate further. This is because the chances are pretty good that you have located some bonanza paying ore. I know of one highly successful high-grade gold mine in the Mother Lode area of California that is using VLF detectors as its sole method of determining where to blast. At this writing, they have located and recovered millions of dollars in gold during the past two years, in a mine which was failing prior to the use of metal detectors.

MEDICAL

Bring along some mosquito repellent during electronic prospecting ventures. Otherwise, if bugs are around, sometimes it is difficult to put your full attention on listening to what your detector is trying to tell you.

In some areas, you also have to be careful of ticks. Some ticks carry Lyme disease. Some insect repellents will keep ticks off of you. DEEP WOODS, TECNU 10-HR INSECT REPELLENT, and OFF seems to work pretty well. Spread the repellent on your boots, pants and other clothing.

In the hot climates, you should bring along the proper sunscreen and apply it to exposed body parts.

It’s always a good idea to bring along a good first aid kit, and at least leave it in your vehicle in case of emergencies.

Extra clothing and water is also a good idea. You can leave it in your vehicle. You never know…

 

By Roy Lagal

 

Nugget hunting in the desert.The term “nugget hunting” is so ambiguous that no description of it could ever be complete. Countless books have been written about this method of searching. Weekend prospectors generally find their instructions too complicated. By condensing descriptions of target areas and summarizing the easiest searching methods for beginners to use, I offer you instructions that are simple but that employ methods proven successful the world over. Tools you may include:

  • Gold pan or gold panning kit
  • Waders
  • Gold tweezers
  • Rock hammer
  • Small bar
  • Shovel
  • Metal detector (suitable for use in mineralized areas)

The metal detector will unquestionably produce the best results in areas where gold abounds and large nuggets commonly occur, such as the western United States deserts, certain “mother lode” areas, Australia, New Zealand, China, Africa and other parts of the world where sizeable nuggets appear in nature. Fantastic finds with metal detectors are regularly reported.

Nugget Hunting Instructions

An electronic metal detector can be used effectively because gold is conductive and its presence will be indicated.

Unfortunately, so-called “hot rocks” contain an iron mineral content that is either greater than or less than the levels for which the ground-canceling detector has been adjusted. They present a constant nuisance to prospectors because they register as metallic (conductive) on a detector. Calibrated circuits used in modern metal detectors that allow easy identification and rejection of “hot rocks” are an absolute necessity in helping a prospector determine whether a rock contains gold or a predominance of iron. Make certain that your detector is a ground-canceling type that contains these special circuits.

In wet areas, start your search near water.

  1.  Adjust your detector to the magnetic iron content of the area according to manufacturer’s instructions.
  2. Pinpoint your target.
  3. Slip a shovel under the target and place it into a plastic gold pan. If the target is located in a bedrock formation, use your rock hammer and small bar to dislodge it. Then place the dislodged target into the pan for examination.
  4. Check the contents once again with your detector. If a “hot rock” is suspected, use the detector to determine if it is ore. If not, discard it.
  5. When the detector indicates gold is present, inspect the contents visually or follow panning procedures.
  6. When the detector indicates no gold in the pan, repeat Steps 3-5 until the target is located.

Metal detectors used for prospecting will also indicate large concentrations of black magnetic sand. Shovel the sand into your gold pan. Inspect for gold nuggets and save the black sand discards for later separation.

In dry areas, the procedure will vary only slightly. Locate the target with your detector, and dig carefully using your hands or a small tool, while being careful to not damage the nugget.

Metal detector headphones are an advantage in most areas, since small nuggets usually generate only a faint response. It is best to dig and visually investigate all targets unless they can be identified absolutely as “hot rocks.”

Electronic discrimination is a valuable aid but should not be relied upon entirely.

Dry areas with small, loose material make visual identification of targets more difficult. When searching such areas, shovel targets into a plastic gold pan or small plastic cup and check for electronic responses. When your detector indicates that a metal object is in the pan, use dry panning first to reduce contents. Then grasp a handful of the pan’s remaining contents with your hand (which must be free of rings and other metallic jewelry) and pass your hand across the search coil’s detection area. The material can be inspected in the same manner if you use a plastic cup. Make certain your detector is tuned correctly and move your hand containing the material across its coil. Continue until you get a response. Then place the contents which generated the response into another pan to avoid loss of the target.

Cracks and other sections of bedrock where gold may be trapped can be inspected in a similar manner. This is called crevicing.”

In desert areas where medium-to-large nuggets occur, and water for testing them is scarce, the metal detector provides the easiest method of recovery. The introduction of VLF metal detectors has brought with it fantastic success stories. Natural elements continually erode mountains, allowing rich deposits to surface. Once a gold nugget of sufficient size becomes exposed, it can be discovered by a metal detector. These nuggets are rarely detectable by sight alone and the absence of water leaves electronic detection as the surest and most effective method for small-scale prospectors.

Gold is too fine for electronic detection in some areas of the western United States, so dry washing machines or dry panning must be employed for recovery. Almost all areas where gold is now located once contained an original vein or concentration of ore that weathered over the ages into a placer deposit. This means that nuggets may still be present even in areas where the gold has been too fine to register on metal detectors. Presence of such valuable nuggets is continually proved as successful searches are conducted with detectors in the dry washes, arroyos and canyons of arid locations.

Streams can be a valuable source of nuggets. In heavily-mineralized areas where productive mines are located, rich ore specimens are often deposited in streams by natural erosion. All targets should be carefully examined before assuming that one is merely a “hot rock.” Valuable coins can often be found in streams of old mining districts. The silver- producing areas of Mexico also produce large nuggets that can be easily recovered from creeks and rivers. Small streams created by the melting of large glaciers in Alaska and western Canada often contain nuggets easily found with detectors.

Searching underwater for nuggets with a metal detector is often not as profitable as in above-water areas. Considering the small amount of labor required, however, especially in comparison with dredging or panning, underwater exploration can be well worth the time and effort. Search slowly and carefully. Even though metallic junk is usually present in streams and rivers, you pretty-much have to examine all target responses from your metal detector. Hot rocks are present in water just as on land.

Very often, companions of dredge operators use their spare time to search streams for nuggets. Persistence and patience are the keys to success here.

Large nuggets encrusted with a black or dark coating have been found particularly on mountain tops. It is believed that volcanic action or oxidation of other minerals and materials encrusted gold with the black coating.

Such discoveries commonly called “volcanic gold” or “black nuggets” represent a rare opportunity for the prospector, and are almost impossible to locate except by electronic detection.

Literally millions of dollars in gold nuggets are being discovered all over the world. Metal detectors enable gold-bearing areas to be searched in a manner never before possible. It is reasonable to state that more nuggets have already been discovered with metal detectors than were ever discovered in all the old gold rushes. The use of a metal detector will provide the weekend prospector with many enjoyable and rewarding hours of activity, and have the potential to detect riches beyond anyone’s wildest imagination.

Editor’s note: The preceding article is a chapter reprinted from WEEKEND PROSPECTING by Roy Lagal, used with permission of the author and Ram Publishing Company, copyright owners. For further information about the book, contact Hal Dawson, Editor; RAM Publishing Company, P.O. Box 38469, Dallas, TX 75238 (214) 278-6151.

 

By Dave McCracken

The water flow should be just enough to keep the concentrating action going behind each riffle, yet not so much that the riffles are being swept clean.

Dave McCracken

 

As a general rule, the optimum slope-setting of a sluice is around one inch of drop per linear foot of box. This can change, depending upon the volume and velocity of water being used, and/or the average shape, size, volume or weight (specific gravity) of material that you are processing.

There is no exact formula for setting the proper water velocity through a sluice box which will work optimally under all conditions for all the different types of riffles being used today. Therefore, rather than give you a formula, I will attempt to give you an understanding of what affects the proper amount of water velocity will cause in a sluice box, and also what the affects are of too much or too little water velocity. In this way, you will be able to act from direct observation to ensure that your, or anyone else’s, sluicing device will be recovering gold to the fullest extent possible.

In setting up a sluice, if feasible, it is desirable to have enough water flow to move the material through the box as fast as you can shovel (or dredge) it in at full production speed.

Most of the riffles being used today are designed so that a concentrating-action takes place behind the riffles. By increasing or decreasing the amount of water velocity over a set of riffles, the amount of water-action behind each riffle is also increased or decreased—which has an effect on the amount of concentrating action taking place. Water velocity can be increased by either putting more water through the sluice box or by moving the same amount through faster. Optimally, the water flow is just enough to keep the concentrating action going behind each riffle, yet not so much that the riffles are being swept clean (called “boiling”) of their concentrated material.

How much water velocity is directed over the box directly affects how much material will stay behind the riffles. When the correct amount of water force is being put through a sluice, its riffles will run about half full of material, and the material can be seen to be dancing and vibrating behind the riffles (concentrating) when the water is flowing.

If too little flow of water is directed through a sluice box, not enough water force can get into the riffles and they will “pack up” with material. In this case, little or no concentrating-action will take place and gold recovery will be poor. When this happens, little or no visible vibrating action behind the riffles will be seen and material will not be moving through the box fast enough to allow you to feed the sluice at production speed without loading up the entire box.

Too much force of water through a sluice box will put too much turbulence behind the riffles. This will cause some of the heavier concentrated material to be swept out of the box.

When this happens, gold recovery will also likely suffer, because the areas located behind the riffles are not calm enough to allow some percentage of the finer pieces of gold to settle. You will notice in this case that the dancing action is occurring behind each riffle, but less material will collect behind the riffles because of the increased amount of turbulence there. When you have too much water velocity, as material is shoveled into the box, it passes through very quickly and has little time to make contact with the riffles.

All the above points remain true when adjusting to get the proper amount of water flowing over an expanded metal-riffle system. However, when using such a system, it is necessary to remember that the riffles are very short. So it does not take very much water velocity to make them concentrate properly.

This means that the size of riffles affect how much water velocity is optimum through the box, how much classification of material is necessary and how fine in size your effective gold recovery will be.

The correct amount of flow is usually found to be just enough to move the material over the box to keep up with your feed of material. Since gold is around 6 times heavier than the average material that will pass through a sluice, there is usually some margin for error if velocity is a little faster than necessary. But a faster flow (than necessary) will affect how fine in size your effective gold recovery will be, if fine gold is present.

Once you have your sluice box set up the way you think it ought to be, it is a good idea to run a sizable portion of gold-bearing material through the box and then pan some samples of the tailings. If you do not find any gold in the tailings, you are set up properly. If you are finding gold in the tailings, some changes are in order. Another test is to mix some pieces of lead in with some material, run it through the sluice, and see where the lead stops.

Sluice boxes process material best when receiving it from a steady feed. Too much material dumped at once into a sluice box has a tendency to overload the riffles and choke off the concentrating-action behind the riffles. This will cause gold to wash right through the sluice box as if there were no riffles present at all.

On the other hand, it is not good practice to run volume-amounts of water flow over a sluice box without some material being constantly or regularly fed through. This is because the scouring-action from the water flows will continue to further-concentrate materials trapped behind the riffles, causing heavier materials to be washed out of the box. A sluice box operated for extended periods with no new material being fed to it has an increased chance of losing some of its fine gold values. How much gold loss will depend on a multitude of factors, such as the type of riffle design, how much water flow, the type and weight of concentrates and the size and purity (specific gravity) of the gold.

So if you will not feed more material into your sluice for a while, it is a good idea to cut your water flow back to reduce turbulence behind the riffles until you are ready to feed again.

Even when a sluice box is set properly, occasional larger-sized stones or rocks can become lodged within the riffles. These should be picked or flipped out of the riffles with minimum disturbance to the remaining portion of the sluice.

On most suction dredges, the volume of water being moved through the sluice continues at the same steady flow during production speed. So adjusting the water velocity to set up the dredge right is accomplished by changing the slope of the sluice box itself—which will speed up or slow down the flow of water over the box. Then, once you are dredging, if you will stop feeding streambed material into the suction nozzle for any period of time, it is wise to block the nozzle with a larger-sized cobble to slow the water flow through your sluice box.

When placing a sluice box within a stream or creek for its water flow, the water velocity can be adjusted by either changing the slope of the box, by varying the volume of water being directed through the box, or by placing the sluice at different sites in the stream or creek where the water is moving at different depths and speeds. Getting the right flow of water to pass through a sluice box out in the field is not difficult. But it is sometimes necessary to try different ideas until you find what works best in each situation. For example, in a location where the water is moving slowly, you might be able to direct more water through the sluice and gain the amount of water velocity that you need. In a stream where the flow is moving more swiftly, the water velocity through your box can usually be adjusted by changing the volume of water directed into it, and/or by varying its downward slope.

Usually, you will have little trouble arriving at the correct velocity through your sluice box when placing it in a fast stream of water. You can use river rocks to make a foundation within the stream so your box can sit level from side to side. By allowing different amounts of water volume through the box, and by changing its downward slope, you can work out a combination that does the job. It is good to have a length of nylon cord along with you for securing the sluice box to a rock or some other object upstream. This prevents the box from being moved off its foundation by the force of water. Sometimes it is necessary to pile a rock or two on top of the box to hold it in place. This is especially true when you are using a sluice made out of wood. You can shovel gravel into the box while trying the different combinations to see what effects the changes have on water velocity.

In a situation where you must set your sluice into slower water, you will find it is generally more difficult to get the flow you need, because you have to create more water velocity than is presently there.

If the flow of the stream itself is not enough to move material through your box, you will sometimes find that changing the slope of the box within the stream has little or no effect on speeding up the flow through the sluice. In this situation, there are several things that might be done to channel enough flow through your box so that you can run material through at production speed. Sometimes the flow of water within the overall stream itself is enough, so that by setting up a “water director” in the stream, you can move enough water through the box to give you the desired result. A water deflector, or barrier, like this can sometimes be built by throwing river rocks out into the stream to make more water flow into and through the sluice.

In this situation, there are several things that might be done to channel enough flow through your box so that you can run material through at production speed. Sometimes the flow of water within the overall stream itself is enough, so that by setting up a “water director” in the stream, you can move enough water through the box to give you the desired result. A water deflector, or barrier, like this can sometimes be built by throwing river rocks out into the stream to make more water flow into and through the sluice.

Sometimes you can get the water velocity needed by arranging a small water-elevator across the waterway. By doing so, and by placing your sluice where the moving water spills over the top, you might create more than enough water flow through the box to meet your needs. It really does not take very much volume of water through a medium-sized sluice box to get the right amount of velocity, if the water is moved through the box at speed. In the case of a short elevator (dam), the water level might only need to be raised up slightly to increase the downward slope of the box enough to create the needed water velocity. How high the elevator needs to be depends mostly upon how much water is flowing within the stream or creek.

A sheet or two of thin plastic, or a plastic tarp, or some old rice bags, can come in handy when you are arranging an elevator or water director within a stream. Such material helps prevent the water from pouring through the holes in your man-made barriers.

A water director or elevator can most often be used with good result wherever the water in a stream or creek is moving and is shallow enough that the barriers can be built easily.

If the water at the work site is moving too slowly, or for some reason a water director or elevator will not work in a particular location, it will be necessary to either set up your sluice in a different location where the water is moving faster, or use a motorized pump to feed water into your sluice. Or, in some situations, it is possible to siphon water into your box from a higher point upstream. Siphoning can be done effectively with the use of reinforced garden hose(es), other types of heavy-walled water hose or PVC.

 

 

By George Mullen

 

Desert tortoiseMost traditional methods for recovering gold from gravels require an ample supply of water. However, an old prospector’s adage has it that gold is where you find it. In the southwest, the “where” is all too frequently situated miles from even a trickle of water. Dry-washing of gold-bearing soil or gravel provides an effective solution to this dilemma.

Click here for a more thorough explanation of dry-washing techniques.

The Spaniards used a scheme similar to the winnowing of wheat from chaff and straw. Two men would grab the comers of a blanket, upon which a small quantity of classified gold-bearing material had been placed, and they repeatedly would toss it upward into the air. The wind would blow away the lighter fraction, and any gold and black sands, which are heavier, would fall back onto the blanket. Wool blankets worked best, because the static electrical charge generated by the wool tended to attract fine-sized gold on the blanket’s surface.

The modem prospector uses an efficient tool called a dry-washer to extract the ever-elusive gold particles from screened gravels or other material. Dry-washers can range in size and complexity from hand-shovel-fed models, to large machines serviced by wheeled or tracked front-end loaders.

All dry-washing machines require a low-pressure, high-volume source of air. At the low-cost end, this can be provided by a bellows which is linked to a hand-operated crank or motor-driven fly wheel. At the higher-cost end, the air source is typically provided by a gasoline engine-driven blower. The remaining components of a dry-washer combine to construct a sloped classification screen (or “grizzly”), which routes fine-sized material to a pneumatic sluice box, where a mechanically-modulated flow of air accomplishes the separation of gold from the lighter-weight material which contains no value.

Dry-washing for goldA dry-washer for small-scale prospecting might consist of a rectangular screen with 1/2 inch openings over a sloped trough. The screened material would pass from the lower-end of the trough to the head-end of a sloped riffle tray consisting of cotton fabric stretched over an inner frame. The tray includes sides to contain the flowing material, and its surface is interrupted by five crosswise riffles. Under the tray is a hollow box and the mechanism which modulates air flow through the tray at a rate of about 200 puffs per minute. The rate of air flow is designed to be sufficient to lift lighter material over the riffles, while the gold remains trapped. When everything is working right, the flow of material through the riffle tray resembles water flowing through a conventional sluice box.

My dry-washer was built from a plan published by Carl Fischer. It is mostly constructed of wood and is extremely portable. A small gasoline engine drives the air box via a belt and pulley speed reducer, producing the required 200 puffs of air per minute. The end result is an efficient separator which saves even the finest particles of gold. I have checked the tailings on numerous occasions and have yet to find any significant amount gold in them.

Prospecting for gold in the desert uses techniques similar to those that are used to locate placer gold on flowing streams or within old stream channels. You want to sample dry-washes on pediments to mountains, feeder-canyons in the mountains and ancient streambeds.

Another old prospector’s adage suggests that one should look for gold where it has been found before. This is still sound advice!

Very fine gold is abundant at many sites in the northwest, and the usual methods of final gold recovery do not always work very well. I have found that the screening and drying of dredge or high-banker concentrates, and then running them through my dry-washer, really works well. I use a metal detector to monitor both the feed and the tailings.

After processing pay-dirt material for about an hour, I suggest it is usually a good idea to clean-up the riffles to check your recovery. I use a plastic gold pan and small wash tub for the final clean-up and have operated all day on just a few gallons of water.

My wife, some friends and I operate suction dredges and high-bankers on the extensive New 49’er properties near Happy Camp, California during the summer months, where there is always an abundance of water. Our dry-washer allows us to remain active during the winter, usually around Quartzsite, Arizona. These gold prospecting and mining activities provide enjoyable activity, along with an extra source of income when we need it.

 
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By Dave McCracken

“Good organization always comes back to having some understanding in advance of what conditions you will encounter when it is time to complete the mission.”

 

Assuming legal access to the property has already been arranged, and company executives intend for us to proceed in this way, here are the primary objectives that we try and accomplish during the preliminary evaluation of a potential mining project:

1) Meet with company executives to gain an understanding of what the mining program is about, what the overall objectives are, the timing and the budget. Review the information which they have accumulated so far. Make plans for a departure-date.

2) Obtain the very best maps of the area that we can get our hands on.

3) Locate and study as much information as we can find concerning the mining history of the area, and the areas surrounding where the project will take place. Plot this information on the map. This includes finding out the type of mining methods that were being used, and what kinds of values have been recovered.

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4) Study background information about the geology, weather, culture, politics and economics of the area. This includes a look at the public information released by the U.S. State Department . Follow up with Internet research to see what others have to say about the people, events and mining activity within the area – and anything else of interest.

Is the political situation stable?

5) Establish a preliminary idea of how and where the potential project-area is located in relation to local communities, potential sources of supplies, emergency support, political structure and access. Bring together an early idea of what we want to see when we get there.

6) I always recommend that at least one representative (preferably one of the company directors) of the company accompany us through the full preliminary evaluation of the area where the potential project would take place. It is in the company’s best interest to have someone from existing management present to confirm our observations, and to help evaluate our conclusions.

7) Travel to the potential project area and:

A) Get a feel for the local politics in general, and in relation to the potential project. Will the locals ignore, support or object to the program? Are there pre-existing problems that will need to be fixed before beginning a sampling program? For example, the following video segment shows local campaigning on political issues within Madagascar that soon thereafter evolved into civil strife that disrupted all productive activity in the country for at least 6 months:

B) Find out the different ways of gaining access to the project site. Try and make contact with those people who would provide the transport service (if needed), and establish timing, cost and dependability. How can we make contact with them from the field? For example, the following video segments demonstrate boat transport services we needed to rely upon to support a dredging project in Cambodia :

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C) Locate sources of food, fuel, supplies and personnel to support the mining program. This would include any special needs, like local guides and boat operators out at the project-site. Establish the cost of things and dependability of the supply and/or services. Are there periodic shortages of supplies or services?

    

 

D) Locate the nearest place for competent medical assistance. Do they have any kind of emergency evacuation service? If not, perhaps they can provide a referral to the nearest large medical facility which does provide such a service. Develop a viable plan to provide competent medical care in the event that it may be needed, and how to mobilize the service from the field.

E) Establish support in local communities within the vicinity of where we would conduct the mining operations.

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F) Locate local miners and gain as much information as possible from them about what is being done, where and what results are being accomplished. Purchase samples of the values if possible and carefully log where they came from. Take a hard look at the gold, gemstones or other values being recovered. It is important to verify the activity and results. Look at how much value the locals are recovering, in relation to the volume of their production. Relate that back to what can be accomplished in production with suction dredging or other modern equipment.

    

 

    

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For example, the following video segment demonstrates a primitive hand-mining program that I stumbled upon along the border of western Viet Nam just a short while ago. These miners were breaking very small volumes of hard-rock ore free from the surrounding country rock with a hammer and chisel. The pieces of ore were being crushed by hand, and then surprising amounts of free gold were being panned in the river where we were sampling. While the amount of gold actually being recovered was not a lot, it was very rich compared to the very small amount of ore that was being processed by their primitive methods. Modern equipment and technology would turn this into an extremely valuable deposit:

The best local mining operations to observe are the ones that are actively processing the gravels within the waterway where our dredging would be done in a follow-up sampling operation.

For example, I captured the following video sequence where active gold mining was being done by local miners alongside and inside of the river where we were considering a suction dredge program in Africa several years ago. As the local miners were recovering a lot of gold in proportion to the volume of river gravels being processed, we decided that a follow-up dredge sampling program was justified:

G) Find out if there are special concerns about dangers in the water, within the surrounding area, sanitary problems, health concerns, or security worries. How will they be dealt with? Will there be any special needs for this?

For example, the following two video sequences were captured during a dredge sampling project that we completed in Cambodia several years ago at a time when there was an active (brutal) civil war in progress. The dangerous situation at the time required us to bring along a substantial contingent of security forces and also arm each of the specialists on our team:

Is the waterway full of big rocks that will require specialized equipment to winch out of our way?

    

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H) Free-dive in the river and/or probe from the surface to gain a good perception of what equipment will be needed to perform a preliminary sampling program. How deep and fast is the water? How deep is the streambed material to bedrock? Is there a lot of material too large to move by hand? Are submerged trees going to interfere with the sampling process? Are there excessive amounts of mud or sand that will overwhelm the recovery system?

It is often possible to bring up smaller-sized samples to pan from the bottom of the river, to get a better idea what a dredge sampling program will find.

I) Decide if special recovery methods will be required to perform a preliminary sampling program. If conditions present will mean that more portable equipment will be required, this may require a floating container be constructed to fully catch the samples, so they can be carefully processed on shore.

Or it may be that you can refit your sampling dredge so that it will effectively capture the fine gold from your samples. Here is a substantial explanation of the system which we have developed to effectively recover more fine gold on our conventional suction dredges. It combines two classification screens to more-effectively separate material-feed into three size-fractions, each which is directed into a different recovery system. The smallest gold particles (which are most difficult to recover) are directed into low-profile riffles along the bottom of the sluice box which have long been proven to be very effective at trapping fine gold.

  

J) Establish the potential for a commercial mining opportunity, based upon evaluation of pre-existing information and direct observation of ongoing local mining programs, along with whatever limited sampling can be accomplished using the resources that are immediately available.

K) Document all important details as well as possible by logging names, phone numbers (or email addresses) and locations of important contact persons, along with how much things will cost. Obtain digital images of everything important..

L) If appropriate, conceptualize a preliminary sampling program. This includes how the sampling program would be performed, supported, and how long it would take to complete. The concept should be consistent with the company objectives and budget.

8) Write a report which includes all of the important details of our findings. Include a photo-library with explanations for each image. The report should conclude with a recommendation. For example, Here is an example of the non-proprietary portion of a completed Report.

For a better understanding of why a preliminary evaluation is so important, I strongly encourage you to read about some of the sampling projects that we have accomplished in remote locations outside of America. The full list of the adventures I have written about can be found here . When reading these stories, it should become very clear to you that the potential success of any sampling program will largely come back to how well it is organized in advance. Good organization always comes back to having some understanding in advance of what conditions you will encounter when it is time to complete the mission.

 

 

Article & photos by David Lawler, Consulting’ Geologist

 

Placer deposits image 1Placer gold deposits represent the most attractive targets for small-scale miners and prospectors, since activities can be carried out with reasonably small costs, and encouraging prospecting results can be obtained rapidly. A small-scale miner has the opportunity to exploit small, rich accumulations of gold which larger-sized mining companies might pass by, due to reserve-size and overall ore-grade. In other words, because of the higher costs involved with a larger mining company, they will not be interested in some types of gold deposits which can be quite lucrative for a smaller-scale mining program.

Placer deposits have been exploited by man since early historic times and have remained an important source of gold on the world market into the 20th Century.

Placer deposits have yielded over 60% of the world’s gold production. Placer gold production in California alone during the height of the Gold Rush has been estimated at $81 million dollars. (Dollar-value in terms of $18/ounce in 1849, prior to 150 years of inflation).

While many texts and articles have been written on the subject of placer mining, the purpose of this article is to provide a brief overview of the subject and to introduce relevant facts which have practical application for the small-scale miner. The less common types of placers, e.g., Glacial, Aeolian, Bajada and beach placers will not be covered in this article.

Alluvial Placer Gold Deposits

Placer deposits image 2Definition: Alluvial deposits are the most common type of placer gold deposit. This category includes fluxial (river and stream) placers which formed in well-defined channels. It also includes “bench” or terrace deposits. These are older river or streambeds which formed on the elevated side slopes of drainage valleys. Both ancient (paleo placers) and modern deposits are included in this category and have produced significant amounts of gold.

Characteristics: Good sorting of sediment and gold particles by size and weight.

Sediments tend to be well transported, reflecting significant rounding or flattening of individual particles as a function of distance traveled from its source. The source of gold can either originate from a nearby lode deposit, generally leaving the gold’s surface with a rough texture; or the gold can have originated from distant sources, generally leaving it with smooth, flattened particles, flakes or nuggets.

Ancient Fluvial Placer Deposits

Placer deposits image 3Examples: (Ancient) Tertiary-age Ancestral, Yuba and Feather River systems, Sierra Nevada Mountains, California, Ancestral Klamath River system, Weaverville and Hornbrook basins Klamath Mountains, California. There are also widespread occurrences of other ancient gold-bearing channels in other western states in the U.S.

Prospecting Suggestions: Check areas where modem drainages (rivers, creeks, and gullies) have eroded ancient gold-bearing channel deposits. Many of these areas were worked by miners during the 19th Century, but there is still plenty of gold remaining for the modem-day small-scale miner.

For example, check side slopes of ridges which contain the ancient channel deposits, since these are areas that usually could not be exploited by hydraulic or ground-sluicing mine methods, due to lack of adequate water or water pressure. These virgin (unexploited) areas can produce eroded substantial pockets of placer gold.

Hydraulic Mine Pit areas often contain good prospects for small-scale mining. Check the exposed bedrock floor (representing the exhumed channel base) surfaces both for cracks and weathered cemented gravels. Gold may remain in small fractures and cracks in the bedrock. These areas can be particularly fruitful for electronic prospecting.

In addition, gold may be liberated from previously-cemented gravels after the long period of weathering on the pit floor. Check drain tunnels and tailraces that may have been cut into bedrock or the sides of the channel for several reasons: First, drain tunnels were driven through solid bedrock at the floor of a hydraulic pit to drain excess water and tailings from the working face of a mining excavation.

It is estimated that hydraulic mining methods lost between 30% – 50% of the gold that was liberated from the deposit. In addition, many of the drain tunnels were also used as the primary locations for the placement of elongated sluice box recovery systems. Thus, clean-ups were performed inside the tunnels. Although some of the drain tunnels have become choked with debris or collapsed from weathering, many still carry gold-bearing materials through the tunnels.

Testing and sampling of in-situ (in place) Tertiary gravel placers is one very proven method of locating valuable gold deposits for the serious small-scale mining operation today.

Modem Fluvial Placer Deposits

Placer deposits image 4Examples: Rivers and streams of the Sierra Nevada and Klamath Mountain areas in California.

Prospecting Suggestions: Prospect areas which are adjacent to known ancient channels or lode gold deposits, since modern river deposits will usually become more enriched close to those areas.

Gold-bearing stream and river channels must be examined and studied in detail in regard to their history, habit and special characteristics, in order to better-exploit the placers contained in them. Check available geologic maps of a particular river area or observe the different bedrock types which are present. This information will yield valuable clues to the location and manner of gold accumulation in various stretches of river.

Most modern-day small-scale prospectors are using suction dredges, sluicing gear, vack-mining equipment and/or gold pans to prospect for and develop these types of gold deposits.

Sample bench deposits adjacent to the active stream margin. Although these deposits are not as commonly reworked by stream processes, they often contain high concentrations of placer gold. Thick bench deposits containing gold-bearing material derived from hydraulic mines are still present along the margins of rivers and streams in the Sierra Nevada and Klamath Mountain regions of California.

Residual Placer Deposits

Placer deposits image 5Definition: Shallow mineral deposits forming directly from weathering and chemical disintegration of a gold-bearing quality vein near the surface. Residual deposits tend to be rich, but localized in occurrence, i.e., close to the vein or outcrop area. These are also termed “seam diggings” due to their occurrence in weathered gold-bearing quartz stringers contained in weathered schist and slate fracture-zones.

Examples: “Seam digging”s at Georgia Slide, Spanish Dry Diggings and French Hill areas, Georgetown Divide, El’Dorado County, California, Alleghany and Downieville districts, Sierra County, California, Humboldt Mountains area, Humboldt County, Nevada.

Prospecting Suggestions: Search in lode gold districts characterized by small high-grade gold-quartz vein pocket deposits. Focus your search into specific areas which are along the geologic trend of previously-exploited lode pocket deposits. Recent fires, landslides, or disturbance by logging operations are constantly exposing new virgin areas for prospecting.

Modern-day metal detectors may help in the exploration and exploitation of these deposits, due to shallow overburden and erratic distribution of the residual placer nuggets.

Eluvial (hill-slope) Placer Deposits

Placer deposits image 6Definition: Deposits representing the transitional stages between a residual and alluvial placer deposit (deposits which form in route between the lode erosion and drainage system). Residual gold tends to form accumulations in soil or colluvium by “creeping” along with material down a hill-slope.

Examples: Klamath Mountain region, California and Oregon.

Prospecting Suggestions: A metal detector can be the ideal tool for locating these deposits, since gold distribution tends to be spotty or erratic due to a poor degree of sorting and transportation. High-banking equipment can be very productive where an adequate water source is available nearby. Dry-washing equipment can be productive in places where there is no water available for processing. Mechanized earth-moving equipment is sometimes necessary to excavate thick eluvial deposits. In this case, small wash plants are being used to recover the gold.

Recommended Reading

Averill C. v: 1946, Placer Mining for Gold in California: California Div. Mines Bull. 135, 377 p.

Clark, B. 1965, Tertiary Channels: California: Div. Mines and Geology Mineral Inf. Service, Z 18

Clark, B. 1970, Gold Districts of California: California Division of Mines Bull. 193, 186 p.

Haley, C.S., 1923, Gold Placers of California: California Mining Bur. Bull. 92, 167 p. Jenkins, O.P., 1946, Geology of Placer Deposits, in Averill, C. Z Placer Mining for Gold in California: California Div. Mines Bull. 135 p, p. 147-216.

Lindgren, 1911, The Tertiary Gravels of the Sierra Nevada of California: U.S. Geol. Survey Prof. Paper 73, 226 p.

Whitney, J.D., 1880, The Auriferous Gravels of the Sierra Nevada of California: Harvard Coll. Mus. Comp. Zoology Mem. v. 6, no 1, 569p.

 
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By Dave McCracken

Any place along the gold path where there is protection from the main flow of water is a good location to sample for gold.

Dave Mack

 

Thorndike/Barnhart’s Advanced Dictionary defines “placer” as “A deposit of sand, gravel or earth in the bed of a stream containing particles of gold or other valuable mineral.” The word “geology” in the same dictionary is defined as “The features of the earth’s crust in a place or region, rocks or rock formations of a particular area.” So in putting these two words together, we have “placer geology” as the nature and features of the formation of deposits of gold and other valuable minerals within a streambed

The main factor causing gold to become deposited in the locations where it does is its superior weight over the majority of other materials which end up in a streambed. By superior weight, I mean that a piece of gold will be heavier than most any other material which displaces an equal amount of space or volume. For example, a large boulder will weigh more than a half-ounce gold nugget; but if you chip off a piece of the boulder which displaces the exact same volume or mass as the gold nugget, the nugget will weigh about six times more than the chip of rock.

As gold is eroded from its original lode, gravity, wind, water and the other forces of nature may move it away and downwards until it eventually arrives in a streambed.

Gold erodes from its natural lode and eventually 
is washed into an active waterway.

There are several different types of gold deposits that a prospector should know about, because they have different characteristics and are dealt with in different ways. They are as follows:

RESIDUAL DEPOSIT: A “residual deposit” consists of those pieces of the lode which have broken away from the outcropping of the vein due to chemical and physical weathering, but have not yet been moved or washed away from the near vicinity of the lode. A residual deposit usually lies directly at the site of its lode.

ELUVIAL DEPOSIT: An “eluvial deposit” is composed of those pieces of ore and free gold which have eroded from a lode and have been moved away by the forces of nature, but have not yet been washed into a streambed. The fragments of an eluvial deposit are often spread out thinly down along the mountainside below the original lode. Usually, the various forces of nature cause an eluvial deposit to spread out more as its segments are washed further away from the lode deposit. Individual pieces of an eluvial deposit are popularly known as “float.”

An eluvial deposit contains those pieces of ore that have been swept
away from the lode which have not yet been deposited by running water.

BENCH DEPOSIT: (Also “terrace deposit”) Once gold reaches a streambed, it will be deposited in common ways by the effects of running water. Most of the remainder of this article will cover these ways. During an extended period of time, a stream of water will to cut deeper into the earth. This leaves portions of the older sections of streambed high and dry. Old streambeds which now rest above the present streams of water are referred to as “benches.” Accumulations of gold and other valuable minerals contained in an old, high streambed are called “bench deposits.”

An eluvial deposit might be swept down to rest on top of an old streambed (bench), but it will still remain as an eluvial deposit until it is washed into a stream of water. A bench placer deposit contains the gold deposited within that streambed before it was left high and dry.

Many benches are lying close to the present streams of water, and are actually the remains of the present stream as it ran a very long time ago.

Some dry streambeds (benches) are situated far away from any present stream of water. These are sometimes the remains of ancient rivers which ran before the present river systems were formed. Ancient stream benches are sometimes on top of mountains, far out into the deserts, or can be found near some of today’s streams and rivers. Ancient streambeds, wherever found, can contain rich deposits of gold.

Most surface placer gold mining operations today direct their activities at bench deposits. The reason for this is that the presence of an old streambed is evidence that it has never been mined before. Any gold once deposited there will still be in place.

STREAM PLACER: In order to discuss what happens to gold when it enters a stream of water, it is first necessary to understand the two terms: “bedrock” and “sediments.” Many millions of years ago, when the outer perimeter of the earth cooled, it hardened into a solid rock surface–called “bedrock” (or “country rock” when discussing the subject of lodes). All of the loose dirt, rocks, sand, gravel and boulders which lie on top of the earth’s outer hardrock surface (bedrock) are called “sediments.” In some areas, the sedimentary material lays hundreds of feet deep. In other areas, especially in mountainous country and at the seashore, the earth’s outer crust (bedrock) is completely exposed. Bedrock can usually be observed by driving down any highway and looking at where cuts have been made through the hard rock in order to make the highway straight and level.

Streambeds are composed of rocks, sand, gravel, clay and boulders (sediments) and always form on top of the bedrock foundation (although they can be later covered up by volcanic activity). Bedrock and country rock are the same thing.

Streambeds are composed of sediments which lie on top of bedrock.

The following video segment will allow you a visual demonstration of these very important points:

A large storm in mountainous country will cause the streams and rivers within the area to run deeper and faster than they normally do. This additional volume of water increases the amount of force and turbulence that flows over the top of the streambeds lying at the bottom of these waterways. Sometimes, in a very large storm, the increased force of water is enough to sweep the entire streambed down the surface of its underlying bedrock foundation. It is this action which causes a streambed to cut deeper into the earth over an extended period of time. A storm of this magnitude can also erode a significant amount of new gold into the streambeds where it will mix with the other materials.

Gold, being heavier than the other materials which are being swept downstream during a large storm, will work its way quickly to the bottom of these materials. The reason for this is that gold has a much higher specific gravity than the other streambed materials and so will exert a downward force against them. As the streambed is being vibrated and tossed around and pushed along by the tremendous torrent of water caused by the storm, gold will penetrate downward through the other materials until it reaches something which will stop its descent-like bedrock. This very important principle is demonstrated by the following video segment:

With the exception of the finer-sized pieces, it takes a lot of force to move gold. Since gold is about 6 times heavier than the average of other materials which commonly make up a streambed, it takes a lot more force to move gold down along the bedrock than it does to move the other streambed materials.

So there is the possibility of having enough force in a section of river because of a storm to sweep part of the streambed away, yet perhaps not enough force to move much of the gold lying on bedrock.

When there is enough force to move gold along the bottom of a riverbed, that gold can then become deposited in a new location wherever the force of the flow is lessened at the time of the storm.

Bedrock irregularities at the bottom of a streambed play a large role in determining where gold will become trapped. A crack or crevice along the bedrock surface is one good example of a bedrock gold trap.

Streambeds are composed of sediments which lie on top of bedrock.

Many bedrock gold traps are situated so that the main force of water, being enough to move gold, will sweep the traps clean of lighter streambed materials. This leaves a hole for the gold to drop into and become shielded from the main force of water and material which is moving across the bedrock. And there the gold will remain until some fluke of turbulence boils it out of the hole and back into the main force of water again, where it can then become trapped in some other such hole, and so on. The following video segment further demonstrates these important points:

Some types of bedrock are very rough and irregular, which allows for many, many gold traps along its surface.

Some bedrock surfaces are very rough and
irregular–which allows for many gold traps.

How well a crevice will trap gold depends greatly upon the shape of the crevice itself and its direction in relation to the flow of water during a flood storm. Crevices extending out horizontally into a riverbed can be very effective gold-catchers, because the force of water can be enough to keep the upper part of the crevice clean of material, yet the shape and depth of the crevice may prevent gold from being swept or boiled out once it is inside.

Crevices running lengthwise with the flow of the stream or in a diagonal direction across the bed can be good gold traps or poor ones, depending upon the shape of the crevice and the set of circumstances covering each separate situation. For the most part, water force can get into a lengthwise crevice and prevent a great deal of gold from being trapped inside. However, this mostly depends upon the characteristics of the bedrock surface, and there are so many possible variables that it is no use trying to cover them all-such as the possibility of a large rock becoming lodged inside a lengthwise crevice, making its entire length a gold trap of bonanza dimensions. There is really no need to say much more about lengthwise-type crevices. Because if you are mining along and uncover one, you are going to clean it out to see what lies inside, anyway.

Potholes in the bedrock foundation of a streambed have a tendency to trap gold very well. These usually occur where the bedrock surface is deteriorating and some portions are coming apart faster than others, leaving holes which gold can drop into and thereafter be protected from the main force of water.

Bedrock dikes (upcroppings of a harder type of bedrock) protruding up through the floor of a streambed can make excellent gold traps in different ways, depending upon the direction of the dike. For example, if a dike protrudes up through the floor of a streambed and is slanted in a downstream direction, gold will usually become trapped behind the dike where it becomes shielded from the main force of the flow. A dike slanting in an upstream direction is more likely to trap gold in a little pocket just up in front.

Hairline cracks in the bedrock surface of a streambed often contain surprising amounts of gold. Sometimes you can take out pieces of gold that seem to be too large for the cracks that you find them inside of, and it leaves you wondering how they got there. Once in a while, a hairline crack will open up into a space which holds a nice little pocket of gold.

Hairline cracks can hold plenty of gold, and sometimes open up into small pockets.

How smooth the bedrock surface is has a great deal to do with how well its various irregularities will catch gold. Some types of bedrock, like granite for example, are extremely hard and tend to become pounded into a smooth and polished surface. Polished bedrock surfaces like this generally do not trap particles of gold nearly as well as the rough types of bedrock surfaces do. Also, polished bedrock, which sometimes contains large, deep “boil holes” (holes which have been bored into the bedrock by enormous amounts of water turbulence), is often an indication of too much turbulent water force to allow very much gold to settle there during flood storms.

Rougher types of bedrock, often being full of both large and small irregularities, have the kind of surface where many paying placer deposits are found. This kind of bedrock can be very hard and still maintain its roughness. Or it can be semi-decomposed. Either way, it can trap gold very well.

Rough bedrock surfaces tend to trap gold very well.

Basically, anywhere rough bedrock is situated so that its irregularities can slacken the force of water, in a location where gold will travel, is a likely place to find gold trapped.

Obstructions in a streambed can also cause the flow of water to slow down and can be the cause of a gold deposit, sometimes in front and sometimes to the rear of the obstruction. An outcropping of bedrock jutting out into a stream or river from one side can trap gold in various ways, depending upon the shape of the outcropping and the direction it protrudes into the stream. An outcropping extending out into the river in an upstream direction is most likely to trap gold in front of the outcropping where there is a lull in the water force. A gold deposit is more likely to be found on the downstream side of an outcropping which juts out into the river in a downstream direction, because that is where the force of the flow lets up.

LARGER GOLD TRAPS: PAY-STREAK AREAS

One of the most common locations within a stream or river to find a gold deposit is where the bedrock drops off suddenly to form a deep-water pool. Any place where a fixed volume of water suddenly flows into a much larger volume of water is a place where the flow may slow down. Wherever the flow of water in a streambed slows down during a major flood storm is a good place for gold to be dropped. And so it is not uncommon to find a sizable gold deposit in a streambed where there is a sudden drop-off into deeper water.

Any sudden drop-off into a deeper and larger volume of water is a likely spot to look for a sizable deposit of gold.

A waterfall is the extreme example of a sudden bedrock drop-off and can sometimes have a large deposit of gold at its base-but not always. Sometimes the water will plunge down into the hole of the falls and create so much turbulence that gold dropped into the hole during a storm can become ground up or boiled out. This is also potentially true of any other lesser sudden drop-off locations inside of a waterway.

On the other hand, sometimes large boulders can become trapped at the base of a falls and protect the gold from becoming ground up or boiled out by the turbulence. In this case the falls can become a bonanza.

In some waterfalls (or lesser sudden drop-off locations) the gold that has been boiled out will drop just outside of the hole, where the force of water has not yet had enough runway to pick up speed again-at least not enough to carry off much of the gold which arrives there.

Waterfalls are usually the territory of the suction dredger, because this type of gold trap usually deposits the gold underwater. Yet, this is not always the case. Sometimes during the low water periods of the year, some of the area below a falls can be exposed. There might be only a small amount of streambed to move in order to reach bedrock-where most of the gold is likely to be. The only dependable way to determine if gold will be present below a falls, or any other sudden drop-off location in a waterway, is to sample around and find out. Usually this is rather easy (unless you run into huge boulders); because if the area has been boiled out and swept clean of gold, often the bedrock will be exposed or have a layer of light sand and gravel on top. Again, this is not always true. Each falls has its own individual set of circumstances.

Another common location where a sizable gold deposit might be found is where the layout of the countryside causes the stream to run downhill at a rather steep grade for some distance and then suddenly it levels off. It is just below where the slope of the streambed levels off that the water flow will suddenly slow down during a major flood storm. This is where you are likely to find a concentration of gold. Areas like this are known for their very large deposits (pay-streaks).

The area just below where a streambed’s slope lessens often contains a good-sized gold deposit.

Boulders are another type of obstruction which can be in a riverbed and cause gold to drop out of a fast flow of water. Boulders are similar to gold in that the larger they are, the more water force it takes to move them. Sometimes during a storm, the force of water can pick up enough to sweep large amounts of streambed material and gold down across the bedrock. When this happens, the force may or may not be great enough to move the large boulders. A large boulder which is at rest in a stream, while a torrent of water and material is being swept past it during a large storm, will slow down the flow of the stream just in front, below and somewhere behind the boulder. This being the case, if the storm’s torrent happens to sweep gold near the boulder, some of the gold may concentrate where the slackening of current is at the time of the storm.

A boulder at rest in a streambed during a large storm might trap gold wherever it slows down the water force.

One thing to know about boulders is that they do not always have gold trapped around them. Whether or not a specific boulder will have a deposit of gold along with it depends greatly upon whether or not that boulder is in the direct path the gold took when it traveled through that particular section of streambed during earlier major flood storm periods.

THE PATH THAT GOLD FOLLOWS

Because of its weight, gold tends to travel down along a streambed taking the path of least resistance. For the most part, this seems to be the shortest route possible between major bends in the stream.

Gold tends to follow the shortest route possible between any major changes in the direction of the stream or river.

Take note that the route the gold is taking rounds each curve towards the inside of the bends in the river. While this might not be the route gold always takes in a streambed, it is true that when it comes to curves, the majority of gold deposits are found towards the inside of bends. In comparison, very few are found towards the outside. Centrifugal force causes a much greater energy of flow to the outside of the bend. This creates less force towards the inside, which allows for gold to drop there.

 

It is important for you as a prospector to grasp the concept that under most conditions, gold tends to travel the shortest distance between the bends of a stream or river, and it also seems to deposit along the inside of the bends. Your best bet in prospecting is to direct your sampling activities towards areas which lie in the path that gold would most likely follow in its route downstream within the waterway. This requires an understanding of what effects the various changes in bedrock and the numerous obstructions will have on changing and directing the path of gold as it is pushed downstream during extreme high water periods. For example, if you are sampling for concentrations of gold around and behind boulders, you are better off to begin with the boulders lying in the path that gold would most likely take. This is likely to be more productive than just sampling boulders randomly in the streambed, no matter where they are located.

WHERE THE STREAMBED WIDENS

Another situation within a stream or river where there is often a sizable concentration of gold (pay-streak) is where the stream runs narrow or at a certain general width for some distance and then suddenly opens up into a wider portion of streambed. Where the streambed widens, the water flow will generally slow down, because the streambed allows for a larger volume of water in such a location-especially during extreme high water periods. Where water force slows down is a likely place for gold to drop.

Anywhere that a streambed suddenly widens enough to slow the force of the
stream during high water periods is a likely place to find a deposit of gold.

Notice that some boulders will also drop where the water force is suddenly slowed down. Boulders are similar to gold in that it takes a tremendous amount of force to push them along. Wherever that force lets up enough, the boulders will drop. So boulders are often found in the same areas where large amounts of gold are deposited. But gold is not always found where boulders are dropped. This is because there are so many boulders within the waterway, and the majority of them probably do not continuously follow the same route that gold generally takes. Nevertheless, it is well to take note that those places where boulders do get hung up, which are on the same route that gold follows down the waterway, are generally good places to direct some of your sampling activities.

ANCIENT RIVERS

About two million years ago, towards the end of the Tertiary geological time period, the mountain systems in the western United States underwent a tremendous amount of faulting and twisting, changing the character of the mountains into much of how they look today. It was during the same period when the present drainage system of streams, creeks and rivers were formed, which runs pretty-much in a westerly direction.

Prior to that, there was a vastly different river system, which generally ran in a southerly direction. These were the old streambeds which ran throughout much of the Tertiary geologic time period, and so are called “tertiary channels” or“ancient rivers.” The ancient rivers ran for millions of years, during which time an enormous amount of erosion took place, washing very substantial amounts of gold into the rivers from the exposed rich lode deposits.

The major changes occurring towards the end of that period, which rearranged the mountains and formed the present drainage systems, left portions of the ancient channels strewn about. Some portions were placed on top of the present mountains. Some were left out in the desert areas. And some portions were left close to, and crossed by, the present drainage system.

Some geologists have argued that most of the gold in today’s river systems is not gold that has eroded more recently from lode deposits, but gold that was eroded out of the old ancient riverbeds where they have been crossed by the present river systems.

The ancient channels, where they have been discovered and mined, have often proven to be extremely rich in gold deposits. In fact, many of the richest bonanzas that have been found in today’s river systems have been discovered directly downstream from where they have crossed the ancient streambed gravels. Other areas which have proven to be very rich in today’s river systems have been found close to the old channels, where a few million years of erosion have caused some of the channel and its gold to be eroded into the present streambeds.

Ancient channels (benches) are well known for their very rich bottom stratum. This stratum is sometimes of a deep blue color; and indeed the rich blue color, when encountered, is one of the most certain indicators that ancient gravels are present. This bottom stratum of the ancient gravels was referred to by the old-timers as the “blue lead”, probably because they followed its path all over the west wherever it led them.

Ancient blue gravels usually oxidize and turn a rusty reddish brown color after being dug up and exposed to the atmosphere. They can be very hard and compacted, but are not always that way.

Running into blue gravel at the bottom of a streambed does not necessarily mean that you have located an ancient channel. But it is possible that you have located some ancient gravel (deposited there from somewhere else) which might have a rich pay-streak associated with them.

Most of the high benches that you will find up alongside today’s rivers and streams, and sometimes a fair distance away, but which travel generally in the same direction, are not Tertiary channels. They are more likely the earlier remnants of the present rivers and streams. These old streambeds are referred to by geologists as “Pleistocene channels.” They were formed and ran during the time period between 10,000 years ago and about a million and a half years ago — which was the earlier part of the Quaternary Period, known as the Pleistocene epoch. Some high benches that rest alongside the present streams and rivers were formed since the passing of the Pleistocene epoch. These are referred to as “Recent benches,” having been formed during the “Recent epoch” (present epoch).

Some of these benches, either Pleistocene or Recent, are quite extensive in size. Dry streambeds are scattered about all over gold country, some which have already been mined, but many are still untouched.

Usually, all that is left of a bench after it has been mined are rock piles. Notice in the picture that part of the non-mined streambed is in the background, behind the trees.

Usually all that is left of a high bench after it has been mined are piles of the larger-sized streambed rocks and boulders.

Most of the hydraulic mining operations which operated during the early to mid-1900’s were directed at high benches.“Hydraulic mining” was done by directing a large volume of water, under great pressure, at a streambed to erode its gravels out of the bed and through recovery systems, where the gold would be trapped.

A hydraulic mining operation. Photo courtesy of Siskiyou County Historical Museum.

So some bench gravels have been mined, but many of them still remain intact. While the Pleistocene and Recent benches are generally not as rich in gold content as were the Tertiary’s, it still remains true that an enormous amount of gold washed down into these old channels when they were active. They are pretty darn rich in some areas, and pay rather consistently in others. Also, any and all gold that has ever washed down into an old bench which has yet to be mined still remains there today.

FLOOD GOLD

A large percentage of the gold found in today’s creeks and rivers has been washed down into them out of the higher bench deposits by the erosive effects of storms and time. A certain amount of gold is being washed downstream in any river located in gold country at all times, even if only microscopic in size.

The larger a piece of gold is, the more water force that it takes to move it downstream in a riverbed. The amount of water force it takes to move a significant amount of gold in a riverbed is usually enough force to also move the streambed, too. This would allow the gold to work its way quickly down to the bedrock, where it can become trapped in the various irregularities.

Some streambeds contain a high mineral content and grow very hard after being in place for an extended period of time.

Sometimes a storm will have enough force to move large amounts of gold, but will only move a portion of the entire streambed, leaving a lower stratum in place in some locations. When this happens, the gold moving along at the bottom of the flooding layer can become trapped by the irregularities of the unmoving (“false bedrock”) streambed layer lying underneath. The rocks in a stable lower stratum can act as natural gold traps.

Flood gold is that gold which rests inside and at the bottom of a flooding layer.

Different streambed layers, caused by major flood storms, are referred to as “flood layers.” The flood layers within a streambed, if present, are easily distinguished because they are usually of a different color, consistency and hardness from the other layers of material within the streambed. That gold found at the bottom of or throughout a flood layer is often referred to as “flood gold.” Sometimes, the bottom of a flood layer will contain substantially more gold than is present on bedrock. Sometimes, when more than one flood layer is present in a streambed, there will be more than one layer of flood gold present, too.

The larger that a piece of gold is, the faster it will work its way down towards the bottom of a layer of material as it is being washed downstream during a storm. Finer-sized pieces of gold might not work their way down through a flood layer at all, but might remain disbursed up in the material.

So you can run across a flood layer which has a line of the heavier pieces of gold along its bottom edge, or a flood layer which contains a large amount of fine gold dispersed throughout the entire layer. You can also run across a flood layer which contains a lot of fine gold dispersed throughout, in addition to a line of heavier gold along the bottom edge.

Not all flood layers contain gold in paying quantities for a small-scale mining program. But in gold country, all flood layers do seem to contain gold in some quantity, even if only microscopic in size.

GRAVEL BAR PLACERS

Gravel bars located in streambeds flowing through gold country, especially the ones located towards the inside of bends, tend to collect a lot of flood gold, and sometimes in paying quantities even for the smaller-sized operations. The flood gold in bar placers is sometimes consistently distributed throughout the entire gravel bar. Sometimes the lower-end of a gravel bar is not as rich as the head of the bar, but the gold there can be more uniformly dispersed throughout the material.

FALSE BEDROCK

Once in a while a prospector will uncover an extremely hard layer of streambed material located just above the bedrock and mistake the layer for bedrock because of its hardness. A hard layer is often referred to as “false bedrock.” Such a layer can consist of streambed material, or of volcanic flows which have laid down and hardened on top of bedrock, or it can consist of any kind of mineral deposit which has hardened over time on top of the true bedrock.

There can be a good-paying gold deposit underneath a false bedrock layer. But when there is, it is usually rather difficult to get at.

Actually, for the purpose of sampling, the top of every different storm layer within a streambed should be considered a“false bedrock” and can be a surface-area for gold to become trapped out of the flood layer which laid down on top.

 

By Dave McCracken

There is always action and controversy of some kind going on in the gold mining business. I guess that’s why most of us like it so much!

One thing about participating in gold mining or prospecting, is that it is never boring. Nor is any part of the administration of the gold mining industry boring. There is always some action going on!

This is one of the things which makes our industry so interesting. People who participate tend to be non-conformists by nature, or at least on a temporary non-conformist quest of some kind.

Some people get involved in gold prospecting as an escape from the humdrum of their normal, everyday existence; get up early, go to work, come home, watch TV and go to bed, try and pay the bills on time, etc.

Getting out into the great outdoors on a quest for adventure, even on the most remote possibility that something of value may be found, is enough of a lure for many to pursue prospecting activities. In some cases, it is not the gold which is of primary importance. When found, the gold is just a bonus to many participants. The real treasure is the opportunity to get physically and emotionally free of our normal, everyday existence. This is refreshing and revitalizing. It gives us a chance to put things back in a more balanced perspective.

It’s been said that the best way to solve a problem is to get outside of the problem and view it from the outside. Sometimes it’s not enough to take a walk or go for a drive. Sometimes, the best way to get out of a problem, or to be able to view a whole existence from the outside, is to launch yourself into a new adventure or a new existence. After a few days on a quest, or in a complete new environment, or after a few days in a brand new dramatic activity, you can often look back at earlier problems, or your normal life, and see them far more clearly. Everyone can gain from an exciting vacation or experience.

Different people gain different things from being involved with our activity. While one person might get back in touch with the basics of nature, another might connect with the historical values of those who were there many years ago. Others enjoy the search and the excitement of the potential find. Some are emotionally disappointed in not finding what they are looking for. But everyone is touched in some way. These activities are never dull.

Even the guy that wasn’t able to find any gold this time, while perhaps disappointed at this moment, at the same time he is not all caught up in the problems at the office. He stopped thinking about the office last week. Right now, he is planning his next adventure in such a way as to improve the amount of gold he will find.

There can be more to life than normal survival routines, raising the family, earning the pension and paying off the house. This is where dreams come in. Take a person’s dreams away and you have destroyed that person. It is not only about how much gold the person finds. It is the fact that the person desires and is interested in going out looking. This is therapy; a person pursuing his or her dreams, no matter how silly or inconsequential those dreams may be to others with dissimilar interests.

Being involved with the administration of the industry is not dull, either! People associated with this business are either friendly and supportive, or they are out to do us in. The controversy over the 1872 Mining Law is just one example; those people who are against us will invent just about any lie or excuse why all mining should be stopped. There is no middle ground. There is no reason. But there is drama; plenty of it!

And this is the way our whole industry is. Some people are excited. Some people are disappointed. Some people like us. Some people hate us. Some people want to tell you the whole story about the rich gold deposit they are looking for. Some people are incredibly secretive. Some people want to share the gold deposit they located with all the other miners and friends in the area. Others want to keep all the gold for themselves. Some people want to argue and complain about what the problems are that face our industry. Others are willing to pitch in and give a hand to help resolve problems. But there is always action and controversy of some kind going on. Gold mining is never boring. I guess that’s why most of us like it so much!

 

BY STEVE HICKS

Placer miners at work

Placer mining is relatively simple as long as you don’t expect to make a profit; but it becomes much more difficult if your intention is to make some money. If you want to make some money, it’s a lot easier and cheaper to learn from other people’s mistakes, than to put yourself through the school of hard knocks. By far, the most common mistake I see is inadequate or improper sampling, which is often due to gold fever. Other mistakes are: not properly cleaning up bedrock, not researching the past mining history of your area, and starting a mining venture under-funded.

Placer miners diggingFirst, we will cover sampling. A common remark I hear is why put the time, effort, money, etc. into sampling when it can be better-spent on actual mining and making some money? All too often, individuals lose thousands of dollars on their mining ventures; but had they done some sampling and found out that the ground was too low-grade to mine profitably, they would have only spent hundreds of dollars. I have seen an individual go broke trying to mine ground containing less than $2 of gold per yard when there was un-mined ground about 300 yards away running slightly over $100 per yard. That is not a typographical error; it is one hundred dollars. This is, of course, an extreme example; but all too often rich ground is missed. Even before sampling, a literature-search is in order to get an idea of the ground’s value.

Another common mistake is not separating overburden from pay gravels. Novice miners frequently like to run low-grade overburden. This is because the more gravel they mine, the more gold they recover. While mining everything on a property will maximize the amount of recovered gold, it could bankrupt a person at the same time. If the overburden only contains $2 of gold per yard, and your mining cost is $5 per yard, then you are losing $3 for every yard put through the wash plant.

On the other hand, if you can strip low-grade overburden for $1 per yard, then you have saved $2 per yard which can be directed toward mining the pay gravels.

Gold sample in panOften, new miners leave a lot of gold values in the bedrock. Some highly-fractured bedrock may have values several feet below the surface. The deepest I have ever read about was a Canadian mine going down nine feet into bedrock to get all of the values.

Most often, the bedrock values will be in the top two feet of bedrock. Once you mine the top six inches, check the next six inches to see if there are still enough values to make it pay. Once again, you must evaluate your mining costs for ripping up bedrock to determine if the effort will pay adequate dividends.

Starting a placer operation under-funded is another common mistake of novice miners. It is a mistake to count on finding some profitable ground to pay off debts right away and carry you through the rest of the season. Unforeseen problems have a way of cropping up, such as equipment breakdowns or a severe water shortage later in the season.

Even though most individuals reading this article won’t be running a large-scale mining operation, these tips should help you toward a more profitable operation even on a smaller-scale. Maybe, with some increased sampling or more efficient mining, you just may find that big nugget this season!

About the Author: Steve Hicks is a geologist specializing in sampling gold placers. He has previously worked a number of years as a mineral examiner for the BLM in Alaska and Montana. Presently he is doing placer consulting work and residing in Livingston, Montana.

 

BY DAVID KAREJWA

 

 

Dredging is very hard and tedious work at its best. The more we dredge, the more we realize how much time is actually spent moving oversized material out of the way.

Some pay-streaks don’t have any large boulders at all. Then again, some pay-streaks have an abundance of boulders—many of which are too large to move by hand. When this is the case, gold production results no longer depend on how well you can operate a suction nozzle; they depend on how efficiently the boulders can be moved out of the way.

Many of us started by using two-ton come-alongs to pull the boulders out of the way. And while this may work fine on a very small-scale operation, or an operation which only runs across an occasional boulder, it does not work well at all on a commercial scale.

Pay-streaks can be time and energy-consuming to find in the first place. Being ineffective at moving the boulders out of the way can greatly lessen a dredger’s ability to succeed. I have been dredging on a somewhat serious level on the Klamath River during the past four or five years along with a number of other serious dredgers. Together, we have innovated new boulder-pulling equipment concepts which have improved our sampling and production capabilities to an enormous degree.

The most comprehensive demonstration of underwater dredging I have ever seen is contained in Dave McCracken’s video, ” Advanced Dredging and Sampling Techniques.” Detailed winching and rigging techniques are also fully laid out with diagrams in Dave’s book, “Advanced Dredging, Volume 2.” These are highly recommended for those of you who will get serious about winching.

We found that a winch can be mounted on a floating platform, and the platform can be anchored out in the river behind our dredge hole. We use an electric winch in most cases, but new designs are including hydraulic winches.

The platform is anchored to the rear—either by cabling it to a boulder or a tree on the bank, a boulder or a group of boulders in the river, or to a dead-man placed in the river with tailings from the dredge dumped on top to anchor it.

The winch cable and boulder-harness extends down into the dredge hole. Also, the winch controls, on a cable, are waterproofed, and extend down into the dredge hole. When a boulder needs to be winched out of the hole, it is just a matter of slinging it, and winching it back, with all of the winch controls directly at your fingertips. This greatly improves the situation over having to put an additional person up on the bank to operate the controls of a mechanical winch, having to give signals, etc. It allows for single-person operations. While I don’t advocate people dredging alone, a lot of people do. If you are one of them, with this system, you are able to dredge for awhile; and when a boulder needs to be winched, you can simply sling it and drag it out of the way—just like that.

The old way required single-dredgers to sling the boulder, then go up onto the bank to operate the winch. When the boulder got jammed against some obstruction along the river-bottom, the person would have to go back into the water, try to free it up, back to the winch, back and forth, etc., until the boulder was finally moved out of the water. It was a nightmare!

One excellent advantage to a floating winch, we have found, is that the pull is also in an upward direction on the boulder. This helps slide the boulder more easily because of less friction along the river bottom. It also helps get the boulders pulled up and over other obstacles. Consequently, there are fewer problems with the boulder being jammed up while it is being pulled.

Floating winch platforms are relatively inexpensive and easy to construct. They don’t generally need to have much more flotation and size than an average 6-inch dredge. They are not very heavy, and they are easy to float around in the river. In fact, we use the extra deck space on ours to store our extra dredging and cleanup equipment, extra gas, etc.; the things we don’t like cluttering up the decks of our dredge. We place a portable motorized electric generator on the winch platform to keep the winch battery fully charged while we are diving.

Some commercial dredgers on the Klamath River have taken this concept one step further by placing the electric or hydraulic winch on the front of their dredge platform. The dredge is directly behind the hole, anyway. This normally requires an extension of the dredge flotation platform in the front to allow for the additional necessary buoyancy. The advantage to this concept is not having to move around two separate platforms. The disadvantage is not being able to pull the boulders far enough to the rear when you are dealing with lots of boulders.

When you are winching from the front of a commercial dredge, it is also important to keep looking up to make sure you don’t pull the front of your dredge entirely underwater!

This can also potentially happen with a floating winch platform, but it is not normally a problem, because the pulling point is generally from the center of the flotation, as opposed to directly off the front of a dredge.

One local innovative dredger recently came up with the idea of mounting a winch on the front of his dredge in a backwards direction. By also mounting a snatch block under the center of his dredge, under the sluice box, then the pulling point of the winch is centered better on the dredge’s flotation platform. This helps eliminate the problem of submerging the forward part of the dredge.

One point to remember is to never tie off the rear of your dredge to a high point on the bank, or to a highline across the river, when you are planning to winch off the front of the dredge. This type of rigging will pull the back end of the dredge up into the air during rock pulling!

The biggest problem we have run into with floating winch platforms is in the electric controls. We have yet to find an underwater control box on the market which is designed for electric winches. So we have had to waterproof the standard control boxes. This is not all that difficult to do, but it is only temporary. Every few weeks, we find ourselves taking the box apart, and having to rework it.

There is also a potential safety hazard with the electric winches, in that if the controls short-out underwater, the winch can simply start winching! We have learned to create a quick disconnect on the electric cord near the control box. If we lose control of the box, we can unplug it, and the winch will shut down.

One important safety note on this: If you create a safety quick connect using extension cord plugs of some kind, make sure you put the female-side on the power cord. This way, the power cannot be shorted across once the cord has been unplugged. This lesson was learned locally the hard way when a dredger unplugged the control box and dropped the cord into his aluminum boat. He had the cord rigged with a male fitting. The male posts touched the aluminum of the boat, and he was winching!

While it is not particularly difficult to do, it is a bit involved to waterproof the control box to an electric winch—too involved to go into in this article. We use a fifty-foot #14 extension cord; we use a product called Dip-it, and we do a few other things to avoid making the modification so permanent that we cannot easily get back into it to re-do it when necessary.

The advantage to hydraulic winches is in having no problems with the control box. No electricity! This is why I believe the best future platforms will be utilizing hydraulics. For dredge platforms, it is not too difficult to mount a hydraulic pump directly to the dredge motor.

I hope this information has been of as much help to you as it has been to us dredgers up on the Klamath River.