By Dave McCracken
Getting pinned solidly to the bottom by a huge hunk of bedrock that
Crumbled off the Side of the River!
Dave Mack
It was a judgement call. Obviously I made it wrong because it almost killed me. But it was the first time I had ever run into this sort of situation before. I was not sure what to do about the fractures in the bedrock wall that was hanging over me. Should I have put the chisel edge of my five-foot pry bar into it to see if it’s loose? I finally decided that might loosen it up even further and make it more unstable if I was not able to break it loose using the bar. This was a guessing game. I knew it, and I guessed that the bedrock wall would hold together if I left it alone. I simply guessed wrong this time, that’s all.goldIn dredging for gold, there are a lot of things you are not sure of, so you have to use your best judgment to make a guess.It all started several years earlier when we discovered a very rich pay-streak on the Klamath River in northern California near the confluence of Thompson Creek, about 10 miles upstream from the town of Happy Camp. We were performing a sampling contract for a company out of Salt Lake City. They were looking for a special type of gold deposit, mainly very consistently high-grade for long term production. This particular deposit did not qualify because it did not produce at least a pound of gold every day. It did produce a pound on some days though, sometimes as much as two pounds. But there were also quite a few two and three ounce days which disqualified the deposit as far as the principals were concerned. So we moved on to sample in other locations for the remainder of that season, and we located several other semi-rich deposits which we left behind in our hunt for the real motherlode.

Several years then quickly passed by while the deposits we found during the sampling program could not be touched, in case the company which paid for the sampling decided to exploit the deposits according to their option. They were waiting for the gold prices to skyrocket as we all have been waiting. But instead, the price just slowly kept edging downward. The company finally dropped its lease. So several seasons ago, my partner and I went to work at the head of the deposit where the amount of gold is more inconsistent, but pays quite handsomely in the pockets. Because of other commitments we both had, my partner and I were only able to dredge on a part-time basis, but the deposit did appear to be getting better as we dredged forward. We were getting more excited, and trying to squeeze more and more time in as the season went on.

The biggest problem we had was the huge boulders! We were working in an average of ten feet of tightly packed virgin hard-packed streambed material. The bottom had a layer of boulders most which we were able to shift around to dredge the gold off the bedrock. But there were occasional huge boulders up in the material, sometimes sitting right on top, just waiting to fall into the hole on top of us. It was a very dangerous hole!

The gold was coming from the bottom two or three feet of virgin hard-pack, and on bedrock if it was rough and irregular. To make the gold really add up in our recovery system, all we had to do was move the volume through and uncover a bunch of the bottom layer. When the bedrock was right for it, we would get a handsome bonus. Sometimes the pockets contained so much gold, we could stir our fingers in it! The bonuses were getting more often as we moved on, and we were really synchronizing our effort to move the material. We were also working really hard!

Since we were not using a winch at the time, it was a constant challenge to move the boulders out of the way safely. The two of us together could roll many of them out of the hole. This would allow us room on bedrock to roll the really big ones. When a big one was uncovered in the top layer, which we knew we would not be able to move once it was dropped into our hole, we would try and safely make room for it on the bedrock so we could undercut the boulder and drop it on a spot where the gold had already been dredged. This is a very dangerous method of dredging which I do not generally recommend. It requires you to be constantly on guard; and even so, your life is on the line all the time!

Still, underwater mining can be a dangerous business. Sometimes where you find the richest gold deposits prompts you to take personal risks. You find yourself in situations where every decision you make can directly affect the final outcome.

Dredging under a five-ton boulder (underwater estimated weight) and trying to calculate just how much you can take out to loosen it up enough to roll, without taking so much that it rolls in on top of you, is also a dangerous game. We call these boulders “Loomers.” It is a very high-risk job, because it is difficult to tell what material is holding up the boulder, or what affect the current is having on the boulder or the face of your excavation. You can never take your eyes or some part of your body off the boulder even for a split second. You have to be poised to jump out of the way at any given instant; because sometimes, the boulder will come crashing down with no warning whatsoever!

But the worst part of this type of dredging is cleaning the bedrock when there is a loomer hanging over you way up in the material. It is another judgement point (guessing game) as to how much of your “working face” (side of the hole that you are dredging) that you can dredge without undercutting the boulder too much. Most of the time, my partner and I were managing this with me running the nozzle deeper in the hole, and my partner watching the boulder while holding onto my shoulder, ready to pull me out of the hole quickly if the boulder started to move. Needless to say, this was very high-stress for both of us, and confirms the sensibility of a winch.

With a winch, you simply hook onto a boulder before it becomes a “loomer” and you pull it down and out of your hole.

Needless to say, we went home feeling queasy at the end of nearly every day we were working this pay-streak without a winch. I was having nightmares about not being able to move out of the way fast enough, or taking my eyes off a loomer at the wrong moment…

It was becoming apparent that my partner thought I was crazy to take such chances! Actually, I was being very careful; we did not have any near misses. But I knew it was just a matter of time. The odds were against us.(me)

We could have moved to any number of other mining properties if we wanted to. But the gold was so rich on this property, I decided to assume the calculated risks that were involved.

So I did not have my full attention on the state of the bedrock wall that was hanging over me. I noticed that it was fractured and the cracks were big. The problem was that we were dredging under a cave-like overhang of bedrock on the side of the river. We just had our best production days right behind us. I was watching out for big rocks on the working face, and I was paying a lot of attention to the gold I was seeing on the bedrock!

There had never been any time in the past where a bedrock wall had collapsed into one of our dredge holes!

It was time to take another cut off the top-front of our working face; and as I took material off the top six or seven feet, I noticed (again) that I was removing support from the hanging bedrock wall. The thought crossed me that I should do something about it, but what? Perhaps try prying on it to see if the bedrock was loose? It was hanging menacingly right over where I was dredging. I also was keeping my eye on a good sized boulder up in the material that I was going to have to do something about pretty soon.

After we moved the loomer, we were down in the hole underneath the cracked bedrock overhang watching the gold go up the nozzle. Then we uncovered a “two-roller” sitting on the bedrock. A two-roller is a rock that takes two persons to roll. Just as we finished rolling the rock to the back of the hole, with no warning, the bedrock slab came down on top of me in two pieces! The first hit me on the back and shoved me forward, ending up on my right leg. The second piece landed on top of the first and drove my foot hard against the bedrock.

The pain was almost unbearable, but was quickly replaced by panic as I realized that I was pinned solidly to the bottom. The hunks of broken bedrock on top of me had me pinned face down on my cobble pile, and I was not able to turn around to see how big they were; this was terrifying! And it hurt real bad which added to my severe discomfort. My first impulse was to try and pull myself free; and there was no way. This just sharpened the pain as the movement caused the heavy weight to settle more firmly on my foot.

My partner was not hit by the falling bedrock, but was obviously very upset about my situation. He told me later that he thought my leg must have been crushed into pulp by the sheer impact of the slabs when they came down. Both our heads had been in the same position as my leg only seconds before. If the slabs had come down on our heads or backs, we would have been killed instantly. We were both stunned by this reality.

I gave my partner the sign that I was O.K. and signaled for him to try and lift up on the slabs so I could pull my foot out. I still had no idea of how large the slabs were, but was getting a better idea when my partner was not able to even budge them when he put his full weight into it. This added to my panic. I knew we were towards the end of a three hour dive and there was not much gas left in the dredge. The pain in my foot was killing me! I was not prepared to wait while he went up to gas the dredge; I wanted out from under the slabs now!

There is also some risk to gassing up a dredge while it is running. We have caught a few dredges on fire that way! Shutting down a running engine creates a situation where you might not be able to get it started, again. There was only a minute or so of air reserve for me once the dredge shut down. So gassing it up while I was pinned to the bottom was very risky! But what if the dredge ran out of gas while I was pinned?

I signaled to my partner to go get the 5-foot pry bar. Neither of us knew exactly where it was. We had been allowing two other New 49’er Members to dredge in the outside of our hole, but they had taken the day off. They had used our 5-foot pry bar the day before and we had not seen it all day. My partner went off to look for it. As my partner went off to look for it, I really started feeling trapped like I was close to the very uncomfortable end of my life, and it was out of my hands. Very few times in my life have I been in a position where I certainly was going to die within a very few minutes if someone else did not perform exceptionally well! I still had no idea if the slabs were so big that even the 5-foot pry bar would not budge them. The full weight of the slabs were slowly crushing my foot flatter and flatter to the bedrock.

My partner’s airline was tangled in mine. So, as he reached the outside of our dredge hole, his line pulled against mine. He spotted the bar outside of our hole, on the very outside edge. He felt his airline go tight against something; but in his panic to get to the bar, he lunged forward against the tug on the line. When he lunged, it yanked the regulator right out of my mouth! This really panicked me. With all my might, I pulled him back by our airlines. I had no idea he had even located the bar, much less gotten that close to it. When he came back, he did not have the bar; my foot felt like it was being crushed off; and he thought I was certainly dying by the violence with which I had reeled him in. In desperation, I had him try and lift the rock off me again even though I knew it wasn’t going to work! I guess I was starting to get a little delirious in my pain and panic. This time, I tried pulling my leg out with all my strength. The resulting pain was excruciating! Man, was I pinned solid!

There was no alternative. I gave my buddy the signals to first untangle our airlines, and then continue to look for the bar. You don’t know what patience is until you have had to wait for someone under this condition! All I could do was wait and hope. It did not take long before he was back with the bar. I set the point of the bar, myself, to make sure in his own panic, my partner did not get my foot between the bar and the slabs. My whole beingness was in a state of hope that the pry bar would give the necessary leverage to move the slab enough that I could pull my foot free. There was one sincere voice from somewhere telling me that the slabs were too big and heavy even for the pry bar.

Once the bar was set, I positioned myself to pull with everything I had, to break free and gave the signal. He pried; I pulled; and my leg came smoothly free. What a wonderful relief! Then I grabbed my foot to get an assessment of the damage. Possibly a bad bruise, maybe a mild break, I was thinking. My partner misread the action, grabbed me around the waist, and was going to help me get to the surface. I signaled him that I was okay, and then gave him the signal to please go gas up the dredge. I was going to remain down to dredge for awhile longer.

I sincerely believe that if it is at all possible, it is best to stay in the immediate vicinity of a location in which you have suffered severe injury or fear until the immediate shock wears off. I feel the body and mind will heal itself faster, and I also don’t like to leave right away because it leaves me feeling like I am running away. I could see by the look in my partner’s eyes that he did not approve, but I insisted.

So we dredged for a few more hours directly in front of the slabs. They were too big to move, so we dredged around them. I made it a point to make sure they were left well behind in our cobble pile before knocking off for the day, even though my foot hurt and I was not able to put very much weight on it. As it turned out, nothing was broken except my boot. The steel tip was crushed so tight that I could barely squeeze my toes out! This was further confirmation of the value of steel tipped boots! Without the steel tip, I surely would have lost some toes or perhaps my whole foot!

And now? I have dropped back on the pay-streak and have incorporated a floating winch into my dredging program.

My partner of that time quit shortly thereafter. The experience, I believe, was harder on him than it was on me. When I told him to go gas the dredge after the accident, I could see that he knew in his own mind that he was not going to dredge along side me, no matter how good the gold was.

And now? I watch out for the bedrock! What am I going to do next time I find a fractured overhang like that? I’m not sure. But one thing I won’t do is turn my back to it!

Here is where you can buy a sample of natural gold.

Here is where you can buy Gold Prospecting Equipment & Supplies.

This story first appeared in Gold & Treasure Hunter Magazine Mar/Apr, 1993 on Page 13. This issue is still available! Click here.

By Dave McCracken

“Covering the Basics of Suction Gold Dredging”

Most gold mining today is done in small operations — one or two persons working at a time — often with the use of suction dredges. A suction dredge is a powerful underwater-type of vacuum cleaner. It sucks up streambed material (rocks, sand, gravel, silt, gold and other minerals), passes it up through a suction hose, and runs it across a recovery system floating at the surface. Pieces of gold, which are very heavy, are separated from the other streambed materials and trapped, as the gravel and other material wash through the recovery system and are then washed back into the stream to fill in the hole as the dredge moves forward in the waterway.

Most intermediate and larger-sized gold dredges come with built-in hookah-air systems. These attach to the same engine that powers the water pump. As demonstrated in the following video segment, air for breathing underwater is generated by an air compressor, passes down through an air line, and provides air to a diver through a regulator, similar to what is used by SCUBA divers:

Dredging is usually done in ten feet of water or less, but some work is done at greater depths. The following video segment demonstrates how modern suction dredges are constructed with the use of venturi jet systems. These allow gravel and streambed material to be directed into a gold recovery system without having to pass through the pump:

Using a dredge, an (experienced) operator is able to process a much larger volume of streambed material than with any other small-scale hand-mining apparatus. Most of the gold-bearing river-bottom streambed material is sucked up as quickly as the operator is able to feed it into the suction nozzle. Rocks that are too large to pass through the suction nozzle are moved out of the way by hand.

The early miners who came to California (and elsewhere) during the 1849 gold rush (and later) did find and recover many of the easy-to-find gold nuggets and rich deposits. During those early days, the deposits had to be easy to find and recover; because recovery methods and processing capabilities were very limited. Suction dredge technology allows modern-day gold and gemstone miners to prospect and mine for mineral deposits in places where earlier miners were not able to go. This is true in the deeper rivers (3-meters or more of water depth) all over the world. It is especially true in remote locations and/or within developing countries where modern technology is generally not available to village-miners.

Because a modern (experienced) dredger is able to process substantially more volume of streambed material with better gold recovery, the gravel deposits of today do not need to be as rich in gold as was necessary during the past.

One of the main advantages of having the capability to process more streambed material is that an area can be more-effectively sampled. Therefore, the success-rate in modern underwater mining is much greater than it has ever been using other technologies. This has caused a lot of interest in suction dredging equipment, which has resulted in a competitive market. At present, very good equipment for suction dredgingcan be obtained at relatively low cost. Just to give you some idea, a top-of-the-line five-inch gold dredge and the miscellaneous gear needed to run a small dredging operation can be obtained for less than $6,000.

The size of a gold dredge is determined by the inside-diameter of its suction hose–usually anywhere from two to ten inches. A single person customarily can operate a four, five or perhaps even a six-inch dredge. Two men commonly operate six, eight or ten-inch units. Sometimes, when streambed material is deep, and there is a lot of oversized material (large rocks and boulders) that needs to be moved out of the way, as many as four or five persons can be utilized underwater to operate a production gold dredge.

A single, experienced operator who is sampling with a four-inch dredge can process multiple times more streambed material than could be processed at the surface using conventional pick & shovel methods. A six-inch dredge in experienced hands can process about four times as much material as can be accomplished with a 4-inch dredge — and can also dredge several feet deeper into the streambed material while remaining efficiently-productive. An 8-inch dredge can about double the production over a 6-inch dredge and excavate even deeper into the streambed material. And a 10-inch dredge can double production over an 8-inch dredge and excavate even deeper holes.

The other side of this equation is that each larger dredge-size about doubles the bulk and weight of the equipment that must be moved around and managed. Because of this, some locations may be too remote to support a larger-sized dredge. The limiting-factor on a suction dredge is not the horsepower or the size of the suction hose. It is the size of the suction nozzle opening. Please trust me on this one: It is all about the size of rock that will go up the suction nozzle. Once again, I invite you to closely watch the underwater video segments on my videos and see what is happening underwater. It is almost all about moving the oversized material out of the way. The size of the nozzle-opening determines what can be sucked up, and what must be otherwise moved out of the way by hand.

A cutter-head will just get bogged down (and damaged) in a normal hard-packed streambed.

Some dredges are available that are operated from the surface with hydraulic-powered cutter-heads at the nozzle. Cutter-heads are mechanical devices that help feed material evenly into the nozzle. They are most-productive in doing channel-work in harbors or making navigation-channels deeper or wider (where the material mostly consists of sand or silt). Cutter-heads cannot replace the need for divers when mining in hard-packed streambeds which are made up mainly of oversized rocks and boulders which must be broken free with pry bars and moved out of the excavation by hand.

If you want to do serious excavations with a suction dredge, you must leave the opening of the suction-nozzle as large in diameter as possible, while still reducing it enough to eliminate un-necessary plug-ups inside of the suction hose or power jet.

Streams, rivers and creeks in gold-bearing areas are constantly being replenished with fresh gold. During the last 150 years, natural erosion has caused a substantial amount of new gold to become deposited in today’s waterways. Some rivers and streams that were once thoroughly mined by the old-timers are presently paying gold dredgers in very handsome deposits. Rivers that ran too deep for local miners to gain access to the bottom during the past are also producing rich, virgin gold deposits for suction dredgers.

Gold found in streambeds is called “placer gold.” Placer gold is most commonly found in flake form, usually about the size of flattened grains of rice and smaller. Some deposits carry a larger amount of such flakes and fine-gold. Other deposits carry substantial amounts of larger pieces and nuggets. Gold nuggets can be worth more than actual weight-value, because of their uniqueness as jewelry or specimens.

Gold is one of the heaviest metals. It has a specific gravity of 19.6, meaning that it weighs 19.6 times more than an equal volume of pure water. It is about six times heavier than the average sand, gravel, rocks and other materials which normally make up a streambed. So it takes a substantially-greater force to move gold, than it does to move the other streambed materials. This principle is used in gold recovery systems. The same principle is also used to predictwhere high-grade gold deposits are most likely to be found in a streambed.

Because of its enormous weight, gold tends to follow a certain path of its own when being washed down a waterway, and it will concentrate in common locations where the water force lets up enough to drop gold. One example is the inside of a bend where a stream makes a turn. Another example is at the lower-end of a section of white water. Gold will form “pay-streaks” in areas such as this–where the water slows down on a large scale during large flood storms.

The nice thing about gold dredging is that you can actually see the gold as it is uncovered when you are looking for it. This means that you should pay close attention when you reach the locations where gold is most likely to be, like in the contact zone between different flood layers and on bedrock. Because they are also heavy, lead and iron objects also commonly follow the very same path inside of the waterway as gold, and they deposit inside the same places.

As demonstrated in the following video sequence, with just a little practice, you can learn to look for these positive signs and can follow them right into the high-grade gold deposits:

Once a rich gold deposit is located, as long as there is time, the best thing to do is continue the sampling process long enough to establish the downstream boundary of the deposit. As demonstrated in the following video segment, if the deposit is developed from the lower-end, cobbles and tailings can be deposited further downstream without worry of dropping them directly on top of the rich deposit where they will just have to be moved again at some later time:

A gold-dredger has an advantage, in that he or she is able to float equipment where he or she wants it to go, sucking up gravel (sampling) from various strategic areas. This is much easier than having to carry equipment around and set it up in each new area, as is required in conventional mining.

Most gold dredgers use just two types of knots to secure their dredges in the waterway: (1) several half-hitches, or: (2) a bowline knot. The bowline knot is used where a non-slipping loop is needed at the end of a line. Here follows a demonstration of how to tie a bowline:

There is some amount of gold to be found just about anywhere in a gold-bearing waterway. The important key is to find it in paying quantities. Most commonly, experienced dredgers locate rich pay-streaks by systematically sampling various locations where it seems that gold should have been deposited. Sometimes it takes numerous sample holes to locate a pay-streak, and sometimes it only takes a few. This often depends upon an individual’s understanding of where gold gets hung up in a stream, and upon his or her familiarity with the area that is being sampled.

To accomplish the most from your effort, usually the best way to dredge a sample hole is to move it forward and downward at the same time. This way, you can move steadily away from your growing pile of cobbles (rocks that must be moved out of the hole by hand). Since you usually do not know which way the positive signswill lead you when you begin a sample hole, if possible, it is best to toss your cobbles downstream from the excavation, rather than off to either side or to the front. The idea is to move the same cobbles as few times as possible. The following video segments demonstrate how to obtain optimum production for your effort:

In fact, most of the work associated with suction dredging involves the organization and movement of cobbles and (sometimes) boulders.How well a person can organize and move the oversized material out of the way will determine how deep and fast the samples can be dredged efficiently. Consequently, this will also determine how quickly your sampling activity will lead you into high-grade pay-streaks. The following video segment further demonstrates this very important principle:

For the most part, you want to avoid dredging sample holes straight down into the streambed material. This is because dredging straight down will soon have you off balance. It is much more difficult to remove cobbles from the excavation when you are upside down in the hole.  As demonstrated in the following video sequence, if you cannot toss the cobbles far enough out of the excavation, they will just keep rolling back in on you.

Depending upon how deep into the streambed your sample goes, it can sometimes be difficult to get cobbles far enough out of your sample hole on a single toss. In this case, as shown in the following video segment, it can be sometimes be more efficient to relay them out with 2 tosses, rather than try and carry each rock all the way out of the hole. Each situation is different and requires independent judgment on the part of the dredge operator(s).

Dredging can be an exciting and remunerative activity if you are willing to work hard at it. It takes a bit of study and persistence in the beginning–just like any other activity. Anyone contemplating suction dredging as a commercial activity should be aware that there is a learning curve involved, and they should plan on it.



By Dave McCracken

“When lots of gold starts coming into play, everyone gets excited and in a hurry!”

Dave Mack

At the beginning of a recent season, my partners and I were sampling a promising section of our properties along the Klamath River for new pay-streaks. We had dredged several holes and were onto a deposit. Since we did not know if it was high-grade enough for us to work, we were dredging more holes up and down the deposit to get a better idea. On the fourth or fifth test hole, we uncovered a section of bedrock which had gold lying all over it; it was truly rich!

Something always happens in the dredge hole when dredgers start uncovering lots of gold! It does not matter how professional or experienced the operators are. When lots of gold starts coming into play, everyone gets excited and in a hurry. And it was no different on this occasion.

There was a pretty good sized boulder in front of us, slightly up in the streambed material. It was too large for one of us to move. But we thought both of us, working together, could probably roll it to the rear of our hole. Hurriedly, because we were anxious to see more gold on the bedrock, we made room behind us for the boulder by throwing a bunch of smaller rocks and cobbles further behind. Then we climbed upstream of that big rock and gave it a shove. The rock moved more-easily than we thought and slammed into the hole—right on top of my airline!

divers under waterWe use extra heavy-duty airline, the kind that does not kink under normal working conditions. I have tossed cobbles onto it hundreds or thousands of times; I have rolled boulders over it; and I have never had an instance where the airline was damaged in any visible way. That is, until this time.

As soon as the boulder stopped moving, I lost all my air supply. That is when I realized the boulder had pinned my airline underneath. I was already winded from the exertion of shoving on the boulder. So quickly, my partner Rob and I put our shoulders against the boulder, propped it up, and I pulled my airline out just far enough to see that it was split almost in half. We set the boulder down to deal with this new problem, but the boulder still had my airline trapped from behind.

These kinds of emergencies unfold very quickly when they happen underwater. One moment everything is fine. And the next moment, your life is hanging in the balance of what you do! I had a similar event once where I got pinned to the bottom by a slab of bedrock that fell on top of me from the side of the river.

First I thought I might be able to get air by holding the airline together and compressing it in my hand. This did not work and I was really starting to hurt for air; the second stage of panic was just starting in. What is the second stage of panic? It’s when you are on the verge of a psychotic break!

I looked to Rob and signaled him to cut my weight belts loose. We were working in fast water and I was using a second 25-pound belt to keep me in the hole. Instead, Rob handed me his regulator. Good idea, I had not even thought of that! So I took five long, deep breaths from Rob’s regulator. I would have taken more, but he had that “growing worried” look in his eye. The air was a big help, but far from satisfying; my body was demanding more.

However, the air did reduce my emotional state down to first stage panic—which is non-careful, frantic action. I signaled for Rob to release my belts again. The reason I was asking Rob to remove them is that a face mask prevents a diver from being able to see his or her own belt, so it is much easier for a second diver to release them.

I had one heavy belt which carried about 60-pounds of lead. And my second belt, with about 25-pounds, was connected to my airline. Rob released my heavy belt, not seeing that the airline was still connected to me.

This was all happening very fast. Rob was having panic problems of his own, because he was desperate for air while I was breathing off his regulator. When I handed him his regulator back, he was having trouble removing the water from it. So Rob cut his own weights loose and was gone with his own airline. With my heavy belt gone, I floated up into the current and reached the end of my airline (which was still stuck under the boulder), stuck about six feet from the surface. I immediately reached second stage panic; I was dying for air!

We use a boom on the front of our production dredges to help support the suction hose. A cable extends from the boom down to the suction hose. Looking up from my suspended position, I realized I was in reach of the boom cable. I had already frantically tried to find the quick-release buckle on my weight belt. But the belt had shifted around somehow; and with my heavy rubber gloves on, and in my panicked state of hurriedness, I could not find the buckle. I snapped into third stage panic, grabbed onto the cable and started pulling myself to the surface with everything I had. It was an inch at a time.

Finally, when my face was about one foot from the surface, the airline would no longer give. So close, but so far! In a last ditch adrenaline pull, I managed to get my mouth just above the water’s surface; I got a breath of air and water. I did it a few more times. Then I pulled my glove off the right hand, stuck it under my left armpit (no use in throwing away a good right-handed glove), and reached around to release the weight belt. It fell away and I was quickly on top of the dredge. Rob was up there hoping I was going to make it.

That one was close!

While I was catching my breath on the surface, without any delay, I asked Rob to go down and recover our belts and my air line. We repaired the line with some parts in our tool box, fueled up the dredge, and went right back down to finish the sample hole. I immediately went back down to finish the dive because I believe it is important to get back on the horse that throws you without delay, especially when you are feeling emotional trauma from a harrowing experience.

The pay-streak turned out to be a good, rich one!

I learned a few valuable safety lessons that day—the primary one being to not roll heavy rocks across my airline. This means knowing exactly where my airline is, along with everyone else’s in the hole, at the time when boulders are being moved.

fast waterHere are a few other pointers we have learned about airlines from our experience: Stay aware of where your airline is. Do not allow it to get wrapped and tangled around objects, the suction hose, tangled with other divers’ airlines. Immediately untangle your airline if it does get caught up in any way that might prevent you from getting quickly to the surface or the stream bank in an emergency.

I am a true believer in extra heavy-duty, non-kinking airline. Not only is it non-kinking, but it is also a safety line. We run several wraps around the frame of our dredge before plugging our airlines into the air system. This way, if we need to pull ourselves up the airline in an emergency, we are not pulling directly against brass fittings.

Airlines generally float when being used under normal circumstances. This means you have to watch out that yours does not get tangled around the underside of your dredge. Airlines usually sink to the bottom when they are being used in conjunction with a hot water system, which pumps hot water down to the dredger through a second line that is fastened to the airline. In this case, you have to watch what the airline might get tangled around on the bottom of the river. And, spoken from hard-won experience, you have to be careful not to roll boulders on top of it. You also have to watch that you do not bury your air line with cobbles being thrown behind your dredge hole.

Avoid using longer airlines than are necessary. Ten or twenty feet longer than the suction hose is just fine. Longer airlines tend to get caught on more objects and set up more drag in the current.

When we are working in fast current, and the heavy drag on the airline is a problem, we pull our airlines up onto the back-side of the dredge hole and put a cobble on top to hold it there against the fast water. The cobble must be large enough to hold the airline down, but not so large that you cannot jerk it free in an emergency rush for the surface or stream bank.

We always untangle and unwrap our airlines on our way to the surface at the end of every dive. This gives us a free airline to coil up on deck at the end of the day, or to use again at the beginning of the next dive.

two guys dredgingAnd we always replace or repair a damaged or defective airline without delay. Murphy (as in Murphy’s Law) lurks behind every corner! There are so many details to get right in a dredging operation of any size. There are many things which can possibly go wrong. We try to do everything right to avoid problems. But one thing we should never get lazy about is maintenance action on our air systems. If it even looks like it could be a problem, fix it now! And use quality repairs! Clamping copper tubing between two pieces of airline is not the way to do it!

All in all, I believe safety is a personal matter. This is all about having the right approach in the first place. Different people have different levels of ability doing different things. While one person may have trouble walking across the street without encountering grave personal danger, another person can stay out of personal danger while pursuing hang-gliding or sky-diving activities.

Still, it is true that the more adventuresome the activity, the less margin there is for error. And in adventuresome activities, when things do go wrong, it often turns into a life-threatening emergency. So it is very important to cross all your “T’s” and dot all your “I’s” when it comes to your air system.

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This story first appeared in Gold & Treasure Hunter Magazine Jan/Feb, 1992 on Page 21. This issue is still available! Click here..

By Dave McCracken

“Team dredging is very similar to playing music, except that you are playing little notes of effort in unison, so that all of the effort combines together to achieve optimum momentum.”

Pro-Mack Team

The amount of streambed material that you are able to process through a gold dredge will determine the volume of gold which you will recover. Actually, this is true of any type of mining operation, whether it be a large-scale lode mine or a small-scale gold prospector using a gold pan.

The smaller the amount of material which an operation has the capacity to process, the richer the pay-dirt must be in order for the operation to recover as much gold. Consequently, a smaller operation often needs to sample more to find the higher-grade pay-streaks which are more scarce. So smaller-scale operations generally spend more time sampling and less time in production.

To summarize this, gold mining on any scale is a volume game. If you can move twice the volume, not only can you recover twice the gold, but you will find more than twice as many lower-grade gold deposits which you can make pay adequately enough to meet your minimum standards. You can also reach deeper into the streambed to find more pay-streaks.

This is why we always advise beginning gold dredgers to go find an easy location and practice their basic gold dredging production techniques for a while to bring their speed up to par, before they get very serious about sampling for pay-streaks. A beginner will sometimes be so slow in volume-production that he or she will likely miss valuable pay-streaks simply for lack of being able to process enough gravel during sampling. This is because when you dredge a sample hole, you have to evaluate how much gold you recover against the amount of time and energy that it took to complete the test hole. If you are only moving at 20% of your potential production speed, you are likely to walk away from excellent pay-streaks just because you will believe they are not paying well enough.

When we run larger-sized gold dredges, eight inches or larger, we almost always have at least two men underwater. The reason for this is that operating an eight-inch dredge in six feet or more of streambed material requires that a large number of oversized rocks must be moved out of the dredge hole by hand. This varies from one location to the next. But generally, in hard-packed natural streambeds, somewhere between 60 and 75 percent of the material is too large to process through an eight inch dredge. This is where the second person comes in. A sole operator in this type of material, when the material is deeper than five or six feet, is going to spend a great deal of time throwing rocks out of the hole, rather than operating the suction nozzle. Some hard-packed streambeds require that most of the oversized rocks be broken free with the use of a pry bar. This further decreases the amount of nozzle-time on a single-person dredging operation. This extremely important concept is demonstrated in the following video segment:

In the final analysis, it is the volume of material which is sucked up the nozzle that determines final gold production. However, it is how efficiently the oversized material is moved out of the way which determines how much gravel and gold is sucked up the nozzle.

If a rock-person is added to the operation, he or she must increase the efficiency of the operation at least as much as the percentage of gold which the added person is going to receive.

If I am running an eight inch dredge in two or three feet of hard-packed streambed, chances are that a second person would not increase my speed enough to justify paying the second person a fair percentage of the gold for his or her time. The reason is that I do not have to toss the oversized rocks very far behind me when dredging in shallow material.

If I am dredging in five or six feet or more of streambed, I can literally bury a rock-person with oversized rocks and make the person work like an animal all day long. I also have to work like an animal to accomplish this. The result is a good paying job for my helper and a substantial increase in my own gold recovery.

And when we start talking about working in ten, twelve or more feet of material, I absolutely must have a rock person to help me. Otherwise, I myself am completely buried with cobbles all day long and get very little actual nozzle-time accomplished.

As we move our hole forward, and as we dredge layers (“top cuts”) off the front of the hole, we try to leave a taper to prevent rocks from rolling in on top of us. This is an important safety factor. Also, since the nozzle operator’s attention is generally focused on looking for gold, the rock person should be extra vigilant in watching out for safety concerns. As demonstrated in the following video segment, any rocks or boulders that potentially could roll in and injure a team-mate should be removed long before they have a chance to do so:

One main advantage to a two-person team is the enormous emotional support which a second person can add to the operation-especially when you are dredging in deep material, or when you are sampling around for deposits and have not found any in awhile.

On the other hand, the wrong person can inhibit the operation. So you must be especially careful to find someone who has a similar work, emotional and moral standard as yourself.

In my own operations, we have found that the key to good teamwork is in establishing standard operational procedures for almost everything. This takes quite a bit of planning and communication, and is an ever-continuing process. We have standard procedures for removing plug-ups from the suction hose and power jet. We have standard procedures for moving the dredges forward and backward during operation. And, we have standard procedures for every other facet of the underwater work of moving the material from in front of us, to placement of the tailings and cobbles behind our dredge hole.

The following video segment demonstrates a well-orchestrated underwater dredging team. Notice how the rock-persons are working to free the very next over-sized rocks that are impeding progress of the suction nozzle:

Most importantly, we have standard underwater communication signals. These are demonstrated in the following important video segment:

As we discussed earlier, volume is the key to success — or the degree of success. We take this quite seriously in my own operations, to the point where every single second and every single physical effort is important to the operation. You will seldom find the members of my team socializing or goofing off during the underwater production hours. During the rest of the time, maybe. But during production time, we are entirely focused upon the needs of the operation. We treat the dredging-portion of the operation kind of like competitive team athletic sports. We don’t compete against each other. We compete against the barriers that Mother Nature has constructed for us to overcome to recover volume amounts of gold.

We try to spend a minimum of six hours doing production dredging each day. In our operation, this is done in two 3-hour dives. Other commercial operators prefer three or four shorter dives. I know one commercial dredger in New Zealand who prefers a straight six, seven or eight-hour dive. What an animal!

Personally, I like lunch. But I do agree with the concept of long dives; the reason being that it takes a little while to get a good momentum going. Every time you take a break, you need to then get the momentum going again. What do I mean about momentum? Momentum in dredging is very similar to the beat of the drum in rock n’ roll. It is the continuous flow of gravel up the nozzle, with the oversized rocks being moved out of the way in their proper order at just the proper time so that the flow of material into the nozzle is not slowed down.

In fact, team dredging can be like an art form. It is very similar to playing music; only instead of notes being played on several instruments to form a harmonious melody, you are playing little notes of effort using your bodies to move the suction nozzle, or the oversized rocks, in unison, so that all of the effort works together to achieve optimum momentum.

An inexperienced rock-person will often move the wrong rock, which will cloud the hole out with silt, rather than move the next rock which is immediately in the way of the nozzle operator. In this case, the nozzle operator is slowed down because of the decreased visibility, and is further slowed down because he or she must then move the proper rock out of the way. This is similar to playing off key, or playing the wrong tune, in music. Everybody else is playing one song, and the new person is doing something else. This all amounts to less volume through the suction nozzle.

On the other hand, there is enormous personal and team-satisfaction to operating within a well structured team-dredging system. This is where the nozzle-operator is the conductor, and the rock-person or rock-persons make the extra effort to stay on the nozzle-operator’s wavelength, to play his tune at his pace, to do everything possible to contribute to his momentum. This is where the rock-person is always paying attention to the needs of the nozzle-person in order to keep things moving along; not just the next rock which is in the way, but moving the dredge forward a bit when necessary to give the nozzle-person a little more suction hose when it is needed, and the hundred other things that are necessary to keep the flow going with minimal restrictions upon the effort being expended to get the job done.

We treat it like a team sport. Everything in dredging is physical. When I give my rock-person the plug-up signal, he or she races to the surface to do his part to clear the obstruction. He doesn’t just mosey on up there like he is on vacation. He goes like he is running for a touchdown or home run. And he gets back to the hole just as fast, once the plug-up is free. When he sees that rocks are stacking up in the hole, he doubles his pace to catch up. When caught up, he will look around to see where other cobbles might be moved out of the way without clouding the hole. Or, he might grab the bar and start breaking rocks free for me. At the same time, I am doing my job, which is to get as much material through the nozzle as humanly possible, with the minimum number of plug-ups. And I don’t stop for anything if I can help it. If something else needs to be done, I delegate it to my rock-person so that I can keep pumping material up the nozzle. That’s my job! Everyone’s gold share depends on it.

Every effort counts in production-team-dredging. This requires everyone to pay attention to what is going on in the dredge hole. Rock-persons particularly must be able to remain flexible and be able to switch gears quickly. At one moment, there may be a pile of rocks which needs to be thrown out of the way. The next moment, even before the rock-person has moved several of those rocks, he may notice something else which is directly impeding the nozzle-operator’s progress-like a boulder that needs to be rolled out of the way, or a particularly difficult cobble which needs to be broken free with the pry bar.

The main objective in everyone’s mind must be to support the nozzle-person’s progress. Whatever the next thing in the way is, deserves the most immediate attention.

When things get too confused, sometimes the nozzle-person needs to put down the nozzle and help organize (move cobbles and boulders out of the dredge hole). But everyone should have it in mind that actual production-momentum (gravel through the nozzle) has stopped and needs to get going again as soon as possible.

We take cuts off the front of the dredge hole in production dredging, and take the material down to bedrock in layers. We do this because it is the fastest, safest and most organized method of production dredging. Sometimes, when conditions are right for it, a rock-person may be working directly at the nozzle, breaking the next rock free and quickly throwing it behind the hole. However, on every cut, there comes a time when the nozzle-operator decides to drop back and begin a new cut to take off the next layer. The rock-person has to pay close attention to this and follow the nozzle-operator’s lead. Otherwise, he or she may finish breaking free a rock up in the front of the hole when there is no nozzle there to suck up the silt. In other words, the rock-person has to keep one eye on the nozzle-operator all the time. Because if he is a dynamic and energetic nozzle-operator, he certainly will not be following the rock-man around the dredge hole.

Teamwork extends up to dredge tender, as well, if you have one. A dredge tender should always immediately attempt to remove a plug-up when the water velocity slows down through the sluice box. Many times, this effort is done for nothing, because the nozzle-operator has set the nozzle down over a large rock in the hole for one reason or another. However, on the occasions where there is a plug-up, it is great teamwork to have a tender handling the problem immediately without having to be told. Volume through the sluice box should also be heavy on the tender’s mind. When gravel stops flowing, something is wrong.

And the same thing goes for other support activities. When the tender sees that the dredgers are moving forward in the hole, he or she should be also making sure the dredge is being moved forward proportionately to insure the nozzle-operator has a comfortable amount of suction hose to work with. Good teamwork minimizes the number of orders that need to be given. Most of the activity is handled by standard operating procedures which require a bit of planning and coordination in advance.

There are different opinions about all of this. Some people are simply not running any races. This is fine, but they must understand that they do not have nearly the same gold recovery potential as others who are working at a faster pace or with a more organized system.

I hear the occasional comment that I am a slave driver. Slaves do not last very long with me because they have too little personal judgment and require constant orders! I choose to work with hardworking, ethical, highly-motivated individuals who enjoy the challenge of optimum physical team production. I prefer to think of myself more as a production manager. And, generally, you won’t hear those on my team complaining, especially during split-off time.

There is not anything difficult to understand about successful gold dredging techniques. The process is quite simple. However, the activity, as a commercial endeavor, is a lot of hard work. The faster, deeper and more efficiently you can dredge the sample holes, the faster you will find the pay-streaks, and the better you will make them pay.

Even when you are not finding commercial amounts of gold, there is at least a satisfaction to knowing that you are accomplishing optimum momentum. And, when you do locate the deposits, the sky is the limit!



Helpful Tips on Dealing with Big Rocks Underwater

Dredgers underwater

Every experienced dredger has had at least one close call with a rock that decided to ruin his (or her) day, despite the precautions he was, or thought he was using. It comes with the territory. Just like a close call in traffic, you have a while of silent thankful prayer vowing to never let that happen to you again, and then you get on with things like nothing ever happened.

If you have ever been trapped by a boulder while dredging, and are still alive to tell about it, then you will likely have a tale to tell that would make people sit up and listen.

For those of you that have never experienced it, let me try to tell you what it is like:

There is no noise, and very rarely is there any warning. A horrible, crushing weight comes down on you, like “Jaws,” and you get a sick feeling in the pit of your stomach as you instinctively try to pull yourself free. You try to tell yourself to keep calm, but the shock of the pain as the boulder crushes your leg or arm, joined with the realization that you have very few escape-options, makes you hyperventilate. You cannot seem to get enough air through your hookah regulator.

If your airline is also pinned under the rock, you might find yourself with no air at all! You try to pull yourself free, but there is no place to push against; and the rock is not moving. If you have not already drowned by now, or been so badly hurt that you can no longer function; reason will slowly return, and you will start thinking hard about what your resources are and what remaining options you have. “How much gas do I have left?” “Am I caught, or is a piece of my equipment caught?” “Can I use the dredge to suck away a channel to free myself?” “Where the heck is my diving partner?”

The biggest danger facing the trapped diver is time. How long until the air runs out? Your whole life is tied to your hookah airline and the dredge motor. This is a good reason to take suction dredging on with the right approach in the first place, making sure to keep all your dredging gear in a good state of maintenance and repair.

Dredgers moving bouldersA trapped diver needs time. As long as he has air and has not sustained a fatal injury from the accident, he can wait it out underwater until he starves to death. Here follow some good ideas when you find yourself dredging around big rocks. Some of these ideas will buy you time. Some will help you avoid serious problems in the first place. Some will help get you out of trouble if you are having a bad day:

1) It is always a good idea to work with a buddy.

2) Your buddy should have a source of air. If you are dredging in water that is too deep for your buddy to stand waist deep, how else can the person stay underwater to help you? This could involve an extra hookah line on the dredge and/or even a scuba tank with regulator which is ready to go in the event of an emergency.

3) Unless your buddy is the incredible hulk, you should have the basic tools for moving large rocks. At the very least, a long pry bar and a few wedges. Few people realize the great advantage that a wedge can provide. Wood and plastic wedges can sometimes be hard to use underwater, because they try to float away. I suggest having a metal wedge or two on the dredge site.

The difference between freedom and drowning can be a fraction of an inch. A wedge, hammered alongside a diver’s trapped limb, could lift or move the rock just enough for the person to break loose. A wedge can be used to prop-up the rock as you try to dredge some material away to create more room under the boulder. A wedge can be used to create a pivot-point for your pry bar. I have even heard that a wedge was used once to break-up a large rock that had trapped a gold miner. This was on dry land, but it would work underwater, as well.

4) Never leave a large rock above you in the open working face of a dredge excavation. This is a rule Dave McCracken promotes in his books and videos; it is one of the best safety tips that you can have. As long as that rock is up there hanging over you, it can work loose and do you harm. If you expose a large rock in your working face, and you do not have the ability to winch it out, then you will have to drop back and clear some bedrock where you will place it in the back of your dredge hole. Then you can dredge away material so that the rock will roll down the face of the cut and end up back in your previously-dredged hole. Follow number 5 when cutting this rock out.

5) If you must dredge away material from around a large rock that has the potential to move, then work from above the rock if possible. This can be awkward; but if you can float on the surface and move material away, you know the rock will fall down away from you. If you are above it, the rock cannot swim up and get you. Put one hand on the rock as you work around it. If that thing even moves a hair, you can feel it and will have a better chance of moving back out of range. If you have to move, move fast upwards and downstream letting the current help carry you out of range. The rock will be going forward and down. Drop the dredge nozzle! Trapped dredge nozzles cannot drown, but they can anchor a diver that is trying to get clear of danger. Keep in mind that you should not have any section of the dredge hose over or across your body when working around big rocks.

6) If you are working a cloudy hole, and you expose the large face of rock, let the water clear so you can get a good look at the thing. Alert any other divers in the hole with you to a possible dangerous rock! You might not get caught by a falling boulder, but your cobble-man further down the cut might get caught.

7) Rig up an emergency signal with your buddy up top. There are all sorts of ingenious setups for controlling the throttle on the dredge from the dredge nozzle. This is a practice which I personally believe is detrimental to fine gold recovery as a rule, but that is another article altogether. It would not be difficult to rig up an electronic or mechanical alarm system to alert someone topside. Tugging on your air hose is a common signal sys- tem, but is impractical if your buddy isn’t holding onto the hose or in view of it at all times. I have seen floating buoy systems used that do have a potential, as long as you can reach it in an emergency. It is good practice for the top-side person to put on a mask and snorkel every once in a while to check on the dredger.

Slinging Boulders 8) When winching a rock, never stay near it, especially lower in the hole than it is. Sometimes a pry bar is needed to help move the rock while winching. This is a dangerous practice. But if you think you have no other choice, then try to stay above the rock while prying. Do not winch or pry blind. Keep your eyes on that rock. If it shifts in any manner whatsoever in a way you didn’t expect, back off and wait for it to settle.

9) Sometimes a dredger will expose a section of a large rock and feel it is too risky to work around until later, when the hole is clearer or whatever. This is good common sense; but if you are in fast water, keep in mind that by exposing a portion of the rock, you have opened it up for increased erosion. You have also removed some of the structure that was holding the rock in place. The fast current could eat away the critical portion of the gravel you left to hold the rock up. If you turn your back on the rock, you could be wearing it! Always treat an exposed rock like a loaded gun. Keep your eyes on it, and unload it as soon as possible by moving it safely or working around it in such a way that it will not come down on you.

10) Never try to prop up a boulder and work under it. I have seen where a diver will dredge out sections of gravel from under a large rock, and then stick a cobble under the rock so it won’t drop as he continues to dredge away more of the supporting material. It is better to dredge a ramp down into your cut that you can roll the boulder down or winch it into. Propping boulders was a specialty of the Chinese miners in the old days, but even they lost sometimes. And, they weren’t working underwater while they took risks. The added risk is just not worth it.

11) Quite often, when working with a large dredge in shallow gravel on bedrock, a dredger will just rest the nozzle on the rock and let the face of gravel cave in and flow to the nozzle. It is easy to get so involved in watching the material flowing into the intake and trying to keep large cobbles from flowing onto the nozzle that you forget to look up at the face you are working. A large boulder stuck part way up the face can be exposed and drop in on you as you dredge away its support. Always watch the full face of your cut.

12) In some deep dredging operations, lift bags or 45-gallon drums are used to lift rocks and float them downstream out of your excavation. A 45-gallon drum is common because of the low cost. One end is cut out and cables are strung down from the open-end. When moving a rock, the drum is filled with water and allowed to sink down to the rock. The cables are attached and the drum is set up so the closed-end faces the surface. Air from an extra hookah rig is fed into the drum, and the lift created by the air-filled drum lifts the rock and floats it downstream.

It sounds easy; but in practice, it can be a lot harder than it reads. An air-filled drum will lift at least 300 lbs. It is supposed to lift 400-plus if you use mathematics. If you lift a 300-pound rock from the bottom, you have a couple of problems. How to keep it from getting away from you as it heads downstream, and how to stop it once it gets where you want it to drop — and how to do this all very safely. First, tie a line to the drum and anchor it to shore. The line may act as your steering system and will pull the drum in an arc towards the shore. This may or may not be the place you want it. To drop the rock, you want the safest way possible, and in my experience, that is a stop cock valve on the closed end. When you have the rock where you want, just crack open the valve, and the trapped air will leak out, allowing the drum and the rock sink to the bottom. You are well out of the way by floating on the surface or at least above the drum. Never swim directly above a drum full of air, as it has enough power to hurt you if it gets loose.

13) When placing the cables around the boulder for lifting, use a length of wood to push cable ends under the rock. Do not risk being caught by placing your hands down there. You may have to dredge away a couple of channels under the rock to pass cable through. Follow the above rules when doing so. When lowering the rock into place, try to set it down so you can pullout the cable. You may have to set the rock down on a couple of cobbles, but keep in mind the support may be wobbly as you try to remove cable. Post a warning sign at your dumpsite to warn divers away from potential loose rocks at least for the first season. The spring floods will have a tendency to settle the rocks into more stable configurations. The air-filled drums are great as long as you have deep enough water, and are not fighting the current as you wrestle them into place. If you have any sort of current, you will have to winch boulders. Post your pile of winched rock too, as it can be unstable for the unwary. When working underwater around your rock dump, keep the potential for instability in mind. Do not stand on any rock that could slide or move or you could be right into the situation which you were trying to avoid.

The above rules are a few that I have used and I have not had a problem, yet. Close calls do not count! There are others that could apply to specialized dredging situations, and it would be a real benefit to hear other people’s ideas for good safety practice. If we had enough input, a small manual could be compiled which would benefit all of us dredgers.

For those of you foolish enough to work around big rocks solo, the question is: “Why the heck didn’t I bring a buddy?”


By Dave McCracken

Raw gold creates an impulse inside of you that makes you want to possess it, to own it for yourself, to hoard it away, to treasure it as your own!

Dave Mack

Not too long ago, while dredging with partners on the Klamath River in northern California, we located a very rich deposit, sometimes recovering as much as 24 ounces of gold per day. This was one of the best gold deposits I personally have ever located!

While some people are skeptical about the subject, the condition of “gold fever” really does exist. I know, because I have felt the heat and confusion on more than one occasion. I have written in the past that gold fever affects different people in different ways, depending upon the basic nature of their/your personalities. How much gold that is being uncovered also can determine the degree to which gold fever strikes. Some people get excited over recovering just a few flakes! What would happen if they uncovered untold riches out of a bonanza deposit; how would these same people react?

When my partners and I uncovered this very rich deposit, we started by finding about two ounces during the first 30 minutes of sampling. Because it looked so good, we decided to drop back on the pay-streak several hundred feet and dredge another sample hole. We recovered a pound of gold the first day we uncovered bedrock. There were pockets of gold deep enough and big enough that we stirred our fingers in it! We undoubtedly could have doubled our production if we had chosen to dredge efficiently, rather than spend most of our time googooling around together on the bottom, screaming at the top of our lungs, patting each other on the back, and uncovering the gold as slowly as possible to prolong the incredible excitement of uncovering a real treasure.

After all, in the end the gold gets traded for money and spent or locked away. And all you have left is the memory of having found it. That is a memory I personally will never forget. It is a memory of an adventure that few people on this planet ever get a chance to experience. It is an experience that gets into your blood, goes directly to your heart and soul, and gives you a case of gold fever that will probably never be cured!

I have heard people, after locating rich deposits, express the wish that they did not have partners with whom they had to share. For me, I am really glad I had partners to share this experience with. Because the experience was so powerful, with so much generation of emotional energy, that it is almost impossible to express it to others who were not there.

More recently, while consulting in Central America, I had an opportunity to get my first look at real gold treasure! I have spent some time looking for it during the past and spent a lot of time thinking about being in the big treasure hunting game, but this was my first chance to see the real thing as it had come out of the ground. Wow!!

I saw gold and jade artifacts which had been created five, maybe six, centuries ago by people who had not even discovered the wheel! Artifacts so rich in detail, beauty and antiquity that they made my heart pound so hard that I could actually hear it. My body-heat came up enough to run sweat down my back. And my emotions energized to the maximum limit just at the thought of owning such things. No gold deposit ever affected me in this way!

I am told this is called “treasure fever”.

Just like many people who get into gold mining, but never experience a really significant gold deposit, I think perhaps a lot of people get into treasure hunting, but never get a chance to really experience “treasure fever” the way it can really be. It is one thing to think about it, speculate over it, plan on it, and experience it on a subjective level. It is entirely another thing to confront priceless treasure head on, to find it unexpectedly—even when you were planning on it. Then you have to deal with the reality of having uncovered incredible riches.

There is something excitingly-beautiful about the aesthetic wave-length of gold as you locate it in its natural from. It creates an impulse inside of you that makes you want to possess it, to own it for yourself, to hoard it away, to treasure it as your own.

But finding gold which has been refined, perfected and crafted into artistic, beautiful, rich artifacts which were valued and hoarded and lost by people long ago, adds a value of antiquity which intensifies the personal emotional desire to keep the pieces for yourself. This is treasure fever!

I sympathize for treasure hunters or gold prospectors who are not prepared for it, who have not organized their program well, and who are (un)lucky enough to stumble upon real treasure!

I say “lucky,” because most treasure hunters today who find really significant treasures are very well organized, utilize modern equipment, and follow proven techniques. They generally are prepared for treasure when they find it. But, even the most successful and experienced treasure hunters will readily admit that they generally were not prepared for the amount of confusion and greed which resulted from uncovering real treasure!

Gold and treasure will test your personal integrity in a serious way!

While treasure fever, or gold fever, can have many negative connotations, it can also have a very positive affect upon people. Treasure fever adds spice to life, gives you purpose and makes life more interesting.

As gold prospectors, we actually experience the adventures most others only touch on lightly by watching the television!



Family Finds Gold — And Fun While On Vacation


There I was seven feet deep in the Merced River, staring at a human skull. Was this a watery grave for some murdered miner from the 1800’s or an early native Indian from the Miwok tribe of the Sierra Nevada foothills?

As I wondered about the origin of my latest find, I remembered what happened to me the year before on a similar trip with my father, brother, and sister. We were finding gold crowns on the bedrock, and I found one in the sluice box that had a partial tooth in it. My dredging partners and I believed we had a body or skull minus a few teeth close by. It wasn’t until the end of the weekend that my family had a good laugh and admitted they had planted the gold teeth in my hole. For the complete story read “The Toothless Miner” in the October, 1992 issue of Gold and Treasure Hunter Magazine.

On this particular trip, I was dredging with my father, my Uncle John Bard, and his son Michael. My Uncle John was an experienced diver who also had some experience at gold prospecting. It wasn’t until I had started dredging on the Merced River that I found out about John’s prospecting experiences. During the 1960’s, John had dredged the American River and had done some prospecting in Alaska.

After talking to John about his gold prospecting experiences, I found that we shared a special bond. It was the love of hunting and finding gold, and sharing your experiences with other prospectors. My Uncle John had it, I could see it in his face and hear it in the excitement of his voice. It didn’t take much for me to talk my uncle into joining me on a dredging trip to the Merced River.

I pulled into East Bagby on the Merced River on a Wednesday in mid-August. I was working a hole upriver and had uncovered a few crevices with nuggets showing. I cleaned the bedrock and left the gold so that my relatives who were arriving later in the week could enjoy crevicing the gold. They arrived Friday and had a great time picking the gold nuggets out of the bedrock. Unfortunately, the gold played out in that location and we decided to move downriver and try a new location. We opened up our new hole and attempted to locate bedrock. We were about seven feet down, which is a little deeper than I like to work with my 4″ dredge. We were working two-man crews. My father and I were in the dredge hole working through about six feet of overburden without hitting bottom. I was getting a little discouraged because of the possible depth of the bedrock and lack of gold in the overburden.

I was working the nozzle when my father tapped me on the shoulder and pointed at something in the bottom of the hole. As I took a closer look at the object, I saw a white cap peering through the overburden. I began to fan the sand and gravel away from the object when suddenly, two eye sockets looked out at me. Well, I almost had a heart attack right there on the spot, and I think I went into a slight state of shock. I jumped out of the hole and started screaming about a dead man. My Uncle John and Michael looked at me in a funny way when I explained that I was moving my dredge because there was no gold, and there were dead people in our hole.

About a half hour later, the shock began to wear off. I decided that I just had to have some pictures of my new discovery, so I went back down into the hole and uncovered the skull. When I lifted it out, I realized something was wrong– it was very heavy. Once I took a closer look, I found out why; it wasn’t bone, but a fake plaster, skull. My relatives from hell had struck again!

I went crazy and popped out of the water screaming obscenities, that would offend most Christian people. They all stood around laughing and enjoying themselves because they had put one over on me again. They had all done a good job setting me up for it. The night before, we had been discussing the history of the Merced River–it was very interesting how they kept talking about all the dead miners who had lost their lives on the river. Needless to say, I was totally embarrassed. To this day, I can’t believe I fell for the old “Hide a skull in the dredge hole” trick. I can hardly wait to see what they have in store for me next year. Maybe I’ll find an arm, a leg, or possibly a full cadaver.



Have you ever seen gold in a hairline crack and reached for your crevice tool, screwdriver, or rock hammer; and then spent the next 20 minutes prying, scraping, and/or prodding to get it out of that crack, wishing all the while that this tiresome process wouldn’t take quite so long? Well, the answer to quick gold removal from hairline cracks as suggested and demonstrated by veteran miner Dan Fifer is to go to your local auto parts store and purchase a muffler/tailpipe air chisel. Prices vary from $39.95 to $89.95, chisel included.

Using an air chisel, you can rip up a four-foot crack containing gold in one to five minutes, and then move on to either pumping more overburden or to the next uncovered crack. The amount of time spent depends on how deep the crack is and/or how hard the bedrock is.

My partner Chuck and I found that the speed of our operation dramatically increased when we began using our air chisel. If you do decide to use a chisel, be sure to oil it once every day. We use Marvel Mystery oil each evening after we’ve finished dredging. In our dredging operation, we use a Pro-Mac 8-inch dredge with VW power plant, two pneumatic 100 PSI air compressors as standard equipment, and have two divers down at all times.

We added one additional air tank and 50 feet of air line to power the air chisel and provide extra air for the divers when the chisel is not in use. With the extra tank, we have yet to run out of air. The only draw back in using the chisel underwater is that the noise is quite loud, but you get used to it. So save time and bring in more of the yellow stuff each day; invest in an air chisel. You will be glad you did!


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By Dave McCracken

“It is vital that you design your recovery systems from the beginning to make certain they will actually do the job!”

Dave Mack

 Rubies and sapphires from Cambodia.

Over the many years, my various partners and I have experimented a lot with secondary recovery systems to catch fine gold and gemstones that get sucked up the suction nozzle of a floating dredge. There are numerous issues involved, each which must be carefully resolved to make it all work out right. I strongly advise you to study these issues for yourself as much as possible before deciding how to acquire accurate samples, and what to do for a production dredge if you decide to move forward with a mining program.

If these problems are not carefully considered and resolved in the construction of the equipment, the problems will definitely have to be dealt with in the field, where it becomes much more difficult to fix them!

Since the purpose of sampling is to accurately determine the real value of gold (and/or gemstones) in the river gravels, it is important how you acquire the samples. And if the samples turn out well, it is vital that you design your production dredge and recovery system from the beginning, to make certain they will actually do the job. The reason I stress this point so strenuously is because my team has been called in so many times to help with projects that did not acquire equipment that would efficiently recover fine gold and/or gemstones in the first place.

I also advise you to please not take for granted that gemstone-dredges advertised by various dredge-builders within the industry will recover diamonds or other gemstones efficiently just because the builders advertise that they do. I encourage you to review the points that I will outline here. Then you will have a foundation of understanding from which to ask questions and make your own judgments at the time when you will need to make pivotal decisions.

Gemstones are not heavy like gold. Therefore, they are much more difficult to recover.

Conditions must be set up to near-perfection to effectively recover gemstones from the volume of sand and gravel which passes through a dredge nozzle. This is especially true of production dredges in the hands of experienced operators!

Any enquiry into gemstone-recovery on suction dredges should certainly lead you to the subject of “mineral jigs”. A mineral-jig is a mechanical device that can be adjusted to create a specific suspended medium inside. As raw material flows into a jig which has been set up properly, different minerals are separated according to their specific gravity. Minerals that are lighter than a specific weight-range are allowed to flow off the top of the jig as tailings. Minerals that are heavier are allowed to settle to the bed, or to the bottom of the jig. The heaviest finer-sized materials (mostly gold and iron) are allowed to (flow) bleed out the bottom of the jig to keep it from concentrating with heavy material. Heavier materials are then collected elsewhere, or are directed to even more finely-tuned recovery systems.

The following video segment will demonstrate a mechanical suspension medium that can be created by a mineral jig:

Any and every enquiry into suction dredges and jigs should prompt a series of important questions:

1) classify and separate the smaller-sized raw material that is sucked up through the dredge’s suction nozzle?

2) What size-classification and how much volume of material will feed the jig?

3) How much volume and velocity of water will be included with the feed to the jig?

4) What will you do with the heavier material that is bled from the bottom of the jig?

Let’s please take these important questions up one at a time:

1) Classification: You cannot direct large-sized materials (rocks) into a mineral jig and expect it to perform well. This is actually true of any recovery system being set up to recover gemstones or fine-sized gold. Some method of screening is necessary to “classify” the size-range of materials that you want to direct into each type of recovery system. The more that different size-fractions of material are separated from each other, the easier it is to separate gold or gemstones from the other materials by their differences in weight.

Since dredges have limited space to work with (usually on a floatation platform or two), classification systems must be kept reasonably simple and portable.

Most suction dredges are set up with a fixed (not mechanical) classification screen which material and water flow across inside the sluice box. Riffles and various types of traps are constructed below the screen to trap gold and other valuable minerals out of the flow of water. All of the material that passes over top of the classification screen, or that is not trapped by the riffles under the screen, is allowed to flow out of the box and be discarded as tailings. For lack of a better term, let’s call this a “hydraulic classification and recovery system,” because it depends entirely upon water-flow to move raw material across the classification screen and through the riffles. This is the type of system that you can expect to receive as standard dredging equipment on today’s market.

Hydraulic classification and recovery systems have evolved over the years to the point where they generally recover gold and platinum with a reasonable degree of efficiency down to size-fractions relatively small in size. How fine in size depends upon various factors, like the purity of the gold, its average shape (round, flat or crystalline), and the nature of the material (slurry) that is flowing through the recovery system along with the gold or platinum.

It is reasonably safe to say that any recovery system is efficient down to a certain size-fraction of gold or platinum in any given area. The size-fraction might vary from one place to another. The reason for this is that the specific gravity of gold and platinum is generally 5 to 6 times greater than the average of other materials which commonly exist within a streambed. This incredible difference in weight will generally allow pieces of the heavier metal to penetrate the screen and drop behind the riffles in a sluice box – even though there is a strong force of water present to wash larger-sized material (rocks) over top of the screen.

It is also reasonably safe to say that the smaller a piece of heavy metal is (gold or platinum), the more it will be influenced by the fast, turbulent flow of water that is required to wash larger-sized material through a sluice box. For example, it requires a violent force of water to wash 9-inch rocks over top of a screen in the recovery system of a 10-inch dredge. So the smaller it is, the less likely that a piece of gold will drop through a hydraulic screen and get trapped behind a fixed riffle. Therefore, hydraulic classification and recovery systems lose efficiency as the particle-size of a heavy metal becomes smaller.

It is important to understand this: Because gemstones are only slightly heavier than quartz, and are within a similar weight-range as the average materials generally found in a streambed, hydraulic classification systems on dredges are not an efficient method of sizing raw material. This means that probably more gemstones wash across the top of a stationary classification screen (into tailings), than drop through it into the recovery system.

Furthermore, hydraulic recovery systems (fixed riffles and baffles) are actually designed to discard gemstones.

Because gemstones are light, it is unreasonable to expect them to drop through a classification screen that has a torrent of water passing over top. And then, because riffles will quickly accumulate a concentrate of material behind them that is heavier than the average specific gravity of a gemstone, you should not expect to recover gemstones efficiently using fixed riffles.

As far as I know, Pro-Mack is the only dredge-builder that has accomplished mechanical classification on a suction dredge. We do it by placing a shaker-screen (powered by a hydraulic pump) in place of the sluice box. Raw material from the suction nozzle is directed onto the shaker-screen. Minus-size raw streambed materials drop into a hopper under the screen and are then pumped to a recovery system – usually on a second platform. The following two video segments demonstrate this very important principle:

Summary: On suction dredges, there are basically 2 kinds of classification systems:

(A) A fixed screen which a flow of raw material is washed across by the force of water, with some portion of minus-sized raw streambed material dropping through. This system works relatively well on heavy metals down to a certain size-fraction. Efficiency is lost below that size, and there is poor efficiency on gemstones (they are too light).

(B) Mechanical classification, when set up properly, can be depended-upon to provide nearly 100% of the size-fraction that you want to separate out from the raw material, then to be directed into a recovery system. Please take a look at the following free video segment to see how we recently worked this out on a Pro-Mack commercial dredge system that is being used on a diamond recovery project in India:

Since it is impractical to refit smaller-sized dredges (which must remain portable for sampling) with mechanical classification, 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.

2) Size and volume: Jigs are available in different types and sizes. Generally, a certain size of jig is designed to process a given volume of material. Each manufacturer will have their own set of guidelines.

I say “guidelines” because there are variables that will change from one location to the next. The main consideration is the difference in weight between the mineral you are trying to save, and the medium that it is mixed with.

For example, because the weight-difference is so great, it is relatively easy to drop a particle of gold (19.6 times heavier than water) through a suspended medium of pre-sized quartz crystals (only 3 times heavier than water), because the difference in weight is more than 6 times. Therefore, with heavy metals, there is greater margin to introduce a larger variation of size-fraction (different sized material) into the jig, or a larger volume of pre-sized raw material, without forfeiting recovery.

If you are trying to drop gold particles through a raw material made up of iron (8 times heavier than water), you will be required to tighten-up the sizing and slow down the feed to the jig. This is because the weight-difference between what you want to retain and what you want to discard is only around 2 ½ times.

Sizing and volume are critical in the recovery of gemstones (usually only around 3.5 times heavier than water), because there will be only the smallest weight-difference between the valued material and the other streambed materials which must be rejected by the recovery system.

Summary: Sizing and volume requirements for jigs are largely affected by the difference in weight between the type of material you are trying to recover, and the raw material you want to discard as tailings. This becomes critical as you try and recover gemstones with efficiency.

3) Water feed: Most suction dredges operate on a “venturi” system, where a stream of high-pressure water is pumped into a power-jet at an angle to create a vacuum through the suction hose and nozzle. In this way, gravel and rocks can be sucked up from the bottom of the river and directed to a screening or recovery system floating at the surface, without having to pass them through a water pump. This allows a suction dredge to be manufactured at a small fraction of the cost to produce a dredge of the same size which must pass rocks and material through a pump.

But venturi-dredges are limited, in that they cannot lift streambed material and water more than about a foot (or less) above the water’s surface. Therefore, anything that is going to initially be done to raw material excavated by a suction dredge must be accomplished directly at the water’s surface. This is the reason why almost all standard suction dredges are equipped with hydraulic classification and recovery systems; because there is very little room at the water’s surface to do much else.

Men installing the Catch-hopper which mounts under the shaker-screen on a 10-inch commercial Pro-Mack dredge.


Classification systems used on a suction dredge almost always drop the minus-sized gravels into a sump or hopper that is located below the water’s surface. Therefore, to get the classified material up into a recovery system, it will need to be pumped.

Any jig is designed to allow only so much water-flow with the feed. The reason is that too much water velocity can wash sized-material across the top of the jig before the suspended medium has an opportunity to place particles where they should go.

Water-flow through a jig is highly critical in the recovery of gemstones because they are so light.

Therefore, important consideration must be given to how classified materials will be directed into the feed of a jig. We use hydraulic-powered gravel pumps on the Pro-Mack design, because we have found that venturi-elevators (using a high-pressure water flow) usually deliver too much water volume with the feed. For example, check out the water and raw material feed into the rougher jig (Preliminary jig) on one of the commercial dredges we were operating in the following video segment:

4) Bleeding off the heavy material: One of the reasons why jigs work so well, is that they are allowed to keep bleeding off the heaviest materials from the bottom. These otherwise would accumulate inside the jig and alter the suspended medium which creates the desired separation of your target-mineral from the other streambed materials. For example, if your target mineral is an average weight of 3.5 (times the weight of water), you must bleed enough heavy material from the bottom of the jig to maintain a suspended medium that is lighter than 3.5. Get the idea? If the suspended medium in the recovery system is heavier than your target mineral, the system will then be set up to discharge your target mineral along with tailings.

What you should do with the heavy materials from the bottom of a jig depends entirely upon what they contain.

On the production dredges we build at Pro-Mack, it is common to have a series of three jigs. The first (called a “rougher”) accepts the classified raw material from the sump under the dredge’s screen. The rougher accepts a larger classification of material at volume speed. Its purpose is just to make an initial classification and trap the largest gemstones and heavy metals on top of a bed (smaller classification screen) inside the jig. Large materials and the lightest small materials flow off the top of the rougher-jig as tailings. Heavier, classified materials are bled off the bottom and directed into a “secondary-jig.”

The secondary-jig can be more finely-tuned to further separate a finer-classified, slightly-heavier material at a slower speed. Then the finer-classified, heavier material from the bottom of the secondary jig is fed into a “finishing-jig” – which can be tuned to complete a final separation.

The following video sequence demonstrates how these systems harmonize together:

Most or all of the gemstones will become trapped on top of the jig-beds (classification screens) inside of the jigs. If there are fine-sized heavy metals present, the bleed from the bottom of the finishing-jig usually is directed into a final concentrating device – commonly a centrifugal bowl. The final concentrate is then separated in camp, often with the use of a mechanical shaker table. This final step is demonstrated by a video segment included in an article that I wrote about a sampling project we performed in Cambodia.

As all of these mechanical recovery systems are very sensitive to sudden jerking movements, changes in water pressure and other factors, we have found that it is much better to set up the recovery system for a production dredging operation on its own independent flotation platform. This includes the water pumping system that supports the recovery system(s). Here are a few reasons why we have found this works better:

1) Dredge platforms jerk around a lot as the suction nozzle is managed underwater. The suction hose is flexible, so there is an accordion-affect when varying amounts of suction are used at the nozzle. This causes the dredge to bounce around. The bouncing can throw off critical settings on mechanical recovery equipment.

2) Demands made upon the dredge’s main water pump fluctuate widely, depending upon how much suction is being used at the nozzle. If the dredge’s water pump is being used to supply water to mechanical recovery systems, the pressure-fluctuations can throw off the criticle suspended mediums that make the systems work.

3) A production gold dredging platform has a constant parade of divers, managers and tenders moving about while doing their various jobs. Most recovery systems are designed to be fastened down to a level, stable platform. The movement of numerous people around a dredge platform can throw off important settings.

4) Security: The final product(s) on a commercial mining operation should accumulate in a safe location where traffic can be carefully controlled.

5) These mechanical recovery systems have a lot of moving parts. It is better to keep wet, slippery divers and all their gear clear of the machinery.

In my view, the best way to do it is to set up two platforms:
A) A dredge platform that you can move around, put divers and tenders on, pump raw material to; and pump classified materials from.

B) A recovery platform that receives the classified materials and processes them. This system needs to be carefully engineered, and large enough to manage the volume of raw, classified material that is directed to it from the dredge. You only need to have one or two operators on this platform, so as to not upset the delicate balances that can be easily offset by people walking around changing the way the platform is sitting in the water.

Please take a closer look at the point I am trying to make here by viewing the following video sequence. See how much more organized it is to have a separate platform to contain an advanced recovery system. Just picture trying to combine all of that equipment onto a single platform and still retain some mobile flexibility:

I have found that when you try and put it all on one platform, you are forced to ignore several vital factors which can ultimately add up to a dredge-package that does not do the job very well.



By Budd Salsig


CartoonThe day is just beginning–you and Carl are in the dredge hole. Carl is on the nozzle, and it is your turn to heave cobbles and boulders downstream and out of the hole.

Next hour, you will manage the nozzle while Carl gets to bust his back on boulders. Throughout the day, you will swap around like this. Except when you have to shut down; because it takes two to winch-out a three-footer like the one just upstream that is sitting right inside of the pay-streak. Winching is slow and dangerous work because of rigging, fast water and other challenges which must be overcome.

By now, you and Carl know a lot about boulders and cobbles, in the water or out. Your experience is practical–learned the hard way. But maybe it would help to know, say within ten percent, what a boulder weighs in the water and out. So let’s look at a formula to calculate the weight of rocks in and out of water, by rock diameter. You can easily estimate diameter underwater using hand-spans. You already know that a boulder you can lift underwater just buckles your knees when you try to lift it above the surface. So how much weight is added by lifting it clear of the water? This matters when you are winching, too.

We can figure out rock weights both in and out of the water using a concept called Specific Gravity. We don’t have to weigh the rocks in the air and then in the water. But you could check our results if you want to. Plenty of work has been done on rocks and weights, so we will use existing tables and equations rather than re-invent the wheel.

The definition of Specific Gravity (SG) is: The ratio of the density of a substance (rock) to the density of some pure substance (water), taken as a standard when both densities are obtained by weighing in air. As an example, if one cubic centimeter of gold weighs 19.3 grams, and one cubic centimeter of water weighs 1 gram, then:

Weight of 1 cm3 of ~old SG gold / Weight of 1 cm3 of water = 19.3 gm /1gm = 19.3gm

Or, we say that gold is 19.3 times heavier than water. Water is our standard, and the SG of water is 1.

Now we find from a geology handbook that the SG of most rocks runs from sedimentary (sandstone) (where SG = 2.50); then granite (where SG = 2.73); to basalt (where SG = 3.00). These are typical rocks which you handle all the time while dredging.

Then from Dana’s Manual of Mineralogy, we can find an equation relating Wa (the weight of rock in air), to Ww (the weight of a rock submerged in water), and the specific gravity of that rock:

Or we can rearrange this equation showing the ratio of Ww over Wa, and separate-out the sa-factor, which reveals the weight of the rock underwater:

~ = SG-1 or Ww = ~Wa Wa SG SG

Using our three SG rock numbers: 2.50 for sandstone; 2.73 for granite; and 3.00 for basalt, then:

Ww = 2.50- 1 = L2Q = 3/5 = .6 for sandstone

Ww = .6 Wa SG 2.50 2.50 ~= 2.73- 1 = ill= .63 for granite

Ww = .63 Wa SG 2.73 2.73 ~ = 3.00- 1 = 2/3 = .66 for basalt

Since most rocks end up with SG a little greater than granite, it is reasonable to use the .66 or 2/3 ratio as a general rule. That generally means that Ww = 2/3 Wa.

If Wa is a 10-pound rock above the water, it should weigh around 6.6 pounds when submerged underwater. If Wa is a 300-pound boulder, it will weigh about 200 pounds underwater. Looking at it another way, it is the water which supports one-third of the rock’s weight.

Going back to the knee-buckling maneuver; when you try to lift that 100-pound submerged rock out of the water, it suddenly weighs 150 pounds. Knees buckle! Your winch has the same problem.

Bad back and all, you now have a handy 2/3 rule of thumb!

Let’s go a step further and put together a Table of Average Rock Weights submerged and above the water. For simplicity, we will assume all boulders are river-worn to round-shaped objects (spherical). This way, we can list them by diameter in inches. That will be close enough. You can estimate rock-diameter underwater by hand-spans; that is, from tip of thumb to tip of little finger with your fingers spread. Yours will be around 8 or 9 inches; very easy to check with a ruler.

Let’s do one case in detail to show how it is done: Water weighs 62.5 pounds/cubic foot. The SG of water is 1. The SG of an average rock is 2.75. The rock weighs 2.75 times what the water weighs. Remember, that’s our definition of SG. So, (SG rock = 2.75 x 62.5 pounds/cubic foot (weight of water in air) = 2.75 x 62.5 lbs/cu. ft. (weight of rock in air) = Wa = 172Ibs/cu. ft. (weight of rock in air) Using our handy rule of thumb: 2/3 x 172 lbs/cu. ft. (weight of rock submerged) = 113 pounds while underwater

So a rock which is about 15-inches in diameter will weigh about 113 pounds submerged and 172 pounds above the water’s surface. About the best you can with a rock this size is roll it around underwater. It will take you and Carl both to roll it out of the hole, and a winch to get it out of the water.

That 10-footer in the bottom of your dredge hole is a pretty serious boulder–30 tons in the water, and 45 tons at the surface!

This next hour, Carl is going to be heaving rocks and you will be on the suction nozzle. But before you two get back in the hole, let’s consider if there might be a way to improve the efficiency of rock-removal. Especially on rocks that are too big to roll out of your dredge hole. Can it be done by a single person? The marine salvage people use inflatable air bags to lift loads. Bags are lowered deflated. Then they are connected to a basket-load from a single-point suspension, like a pelican hook. This allows for a quick-disconnect. The bag is inflated with compressed air, just enough to lift the load. A tether guides the load’s rise. There must be an air-bleed to prevent too-rapid ascent. What happens when the air bag reaches the surface and loses lift? This would be a major problem in a shallow river with a swift current. If the air bag can be kept underwater while helping to move rocks out of a dredge excavation, it might work. For example, A15-inch diameter air bag should lift about 60 pounds when it is fully submerged.

Well, I guess you guys (and gals) are ready to get back to that pay-streak under all those rocks. Oh yes, if you and Carl think this specific gravity business is piddling, consider this: The difference between the SG of magma (2.74), and the SG of country rock (2.97), is enough to produce a volcano. With a few additional facts like the depth of the magma, as determined by seismic readings, the resulting height of the volcano can be reasonably estimated. Now that’s a very big deal!

Have a happy 2/3!