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“161 outstanding video segments provide visual demonstrations to support 24 of the most important stories and articles on the 49’er web site”

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Watch valuable real life examples of pay-streaks forming during the raging 1997 “major flood storm” on the Klamath River in California. You can actually see the flow dynamics of how a major storm creates pay-streaks within a waterway!

Now you can watch visual demonstrations of all the important theories and techniques as they are explained in the text of my how-to articles. You can read about it and look at the images; but actually seeing it play out on video should vastly improve your understanding of the most important principles and techniques!

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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.

 

 
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This story first appeared in Gold & Treasure Hunter Magazine May/Jun, 1997 on Page 16.
This issue is still available! Click here..

By Marcie Stumpf/Foley

The Great flood of 1997 – “Larry Ogborn found himself in a situation where if he should leave his boat and dredge, he would surely lose them to the river!”

97 flood

“An, exhausted but relieved, Larry waves to Dave McCracken,
his boat ( right center of photo) and dredge safe, and the water on its way back down.”

Larry Ogborn was not born a gold miner, but a number of years ago he visited Happy Camp for the first time and fell in love with gold mining. He bought a 5-inch dredge; and during the summers while his son was visiting, they would dredge for gold together. Soon, however, Larry was extending his dredging time beyond the limits of his son’s visit. And, in time, the five-inch dredge just wasn’t large enough to satisfy Larry. So he bought a 6-inch dredge and invested a great deal of time into customizing it. Once Larry’s 6-inch dredge was completed, he was very proud of it. Larry joined The New 49’ers to gain access to more mining property than he could prospect in a lifetime, and soon became a lot more serious about mining gold.

By this time, Larry had moved to Happy Camp, bought a home, and had been living there for several years. He bought two dogs to keep him company, and all was right with his world.

Larry was finding one to two ounces of gold every single day. You just don’t walk away from that if you can help it.

Larry derived great satisfaction from his dredging; and in time he added to his equipment. Since many of dredging sites Larry preferred were in deep canyons along the Klamath River, he mounted a winch on a separate floating platform, and also purchased a jet boat so he could gain better access to the more remote locations.

In the fall of 1996, Larry was working on a rich claim in the canyon below Independence Creek, approximately 20 miles downriver from Happy Camp. He was just about to run out of one pay-streak when he discovered an even richer one just upstream. It was fall by this time, and almost all the other New 49’ers had quit dredging for the season. It was cold! But, Larry was finding one-to-two ounces of beautiful gold every single day. You just don’t walk away from that if you can help it! So Larry devoted another two weeks working the pay-streak with really good results. He was recovering a lot of gold! Thanksgiving came and went; and with it, the first heavy rain of the winter wet season in Northern California.

Soon, the water was so swift, that Larry was unable to dredge in his pay-streak. So he moved his prized dredge downriver to calmer waters and did some sampling in that area to see if he could pick up an extension of the same pay-streak. It was something productive to do just until the rains let up enough so he could get back into that original pay-streak in the swifter water further upstream.

Larry continued sampling in areas that he could get to without endangering his dredge, but rising water levels in the river due to persistent rains were making it increasingly difficult to find a place to dredge. The rains grew heavier, and the water became muddy and extremely fast. Soon, Larry was spending a lot of time making trips downriver to check on the condition of his dredge and boat in the increasingly-bad weather.

Up until the week before Christmas, Larry was still able to negotiate his boat over to the dredge, which was tied off on the far bank of the river. But that week, the river grew too dangerous for any further boat trips. He had the dredge riding in a very good spot, it was tied well, and there should have been no further problems with it. For years, Larry and many other dredgers in this area have left dredges in the river (including the canyons) during the winter months, and there had never been problems before. Leaving dredges in over the winter, mining could be done when weather allowed, giving a break to cabin fever. In this canyon, the only way to get any dredge out was to float it over to the highway side and hire a crane to winch it up the mountainside and out of the canyon. This would be an expensive exercise, if not necessary. Once the river becomes so treacherous, it is impossible to safely cross it with a dredge.

Larry’s jet boat was tied off on the roadside bank where there were many large rocks. It took a pretty constant watch of the river and its level to keep the boat off the rocks. Rising water meant Larry had to keep adjusting ropes and using different tie-offs along the side of the river.

Larry had attached tires to the side of the boat that was against the rocks, to help keep the aluminum sides from getting all banged up. But it was a treacherous bank for a boat. As the rains increased, water had to be bailed out of the boat to keep it from being swamped and overwhelmed by the river.

As rains steadily grew longer and harder, Larry spent most of his time every day of the last week of the year running upriver and down, checking on the boat at least four times a day. It was continuously necessary to shorten the ropes as the water climbed, and adjust them to keep the boat off the rocks.

Soon, bailing water from the boat several times a day was not enough. On Monday, December 29th, as the rains increased in intensity, the river grew wilder than Larry had ever seen it. Tremendous waves roared through the canyon, churning masses of water, mud and violent whirlpools which were washing right past the boat. It made Larry dizzy to watch down on the river. Entire trees were washing by! He knew then that the situation had become critical, and the only way he would be able to save the dredge and boat would be to camp down there in his truck so he could do whatever was necessary as river conditions continued to worsen.

So Larry made a quick trip back up the canyon to town, picked up his two dogs, some food for them, sandwich-makings, coffee and some snacks. He took enough for a couple of days, worried that the river could take some time to drop back down to normal winter flows. Then he rushed back downriver. The rain was still coming down in sheets, and he was concerned about the two hours that he had been gone. Larry invested the remainder of that day making the journey down the bank every hour and a half, bailing out the rainwater that was rapidly filling his boat. He had to adjust the tie-off lines every time to compensate for rapidly rising water.

Larry found it necessary to use seven different tie-off lines to keep turbid river currents from smashing his boat on the rocks.

As it grew dark, he parked his truck so that the headlights were shining on the trail that led down to the boat. Larry continued his vigil all throughout the night. He would turn on the lights every hour and a half, lock the dogs in the truck and follow the trail down to the river. As the truck was parked some distance away, Larry used a small flashlight to guide himself down the treacherous, slippery mountainside in the dark.

Down on the river, the boat was pitching two feet or more with each wave. With only the small flashlight to help him see, Larry had to negotiate his way onto the boat from the slippery bank, bailout the water as rapidly as possible, adjust all of the ropes, check to make sure his tires were still in place along the side to buffer against the rocks, and then fight his way to the shore and back up the mountainside in the driving rain. There wasn’t anything Larry could do about his dredge which was tied off on the far side of the river.

Larry had had no sleep when Tuesday morning dawned, but his dredge was still riding the water well, and the boat was still floating. He kept to his schedule. At in mid-morning, another miner arrived on the scene who also had a large dredge on the opposite bank of the river. This other dredge was in trouble.

When Larry first saw the other miner, the guy was already launching a raft into the turbulent canyon and was preparing to attempt a crossing to the other side. Larry was stunned that anyone would attempt to cross the incredibly turbulent river in anything! But even before Larry could go talk to the guy, the other miner climbed into the raft on his belly, pushed out into the river and started using his hands to try and paddle himself across. This had worked for the man in calmer water, but Larry was convinced that nobody could paddle a raft across the Klamath River under those conditions.

This particular miner had not been dredging very often during the winter. He had a firewood business in town. The late fall and early winter months found him busy cutting, splitting and delivering wood to the residents of Happy Camp. That work, strengthening his arms, probably saved his life this day; because the raft, when it reached the tremendous waves out in the swift current away from the bank, immediately capsized and the man was tossed out into the raging river. And the guy wasn’t even wearing a life preserver!

As Larry watched, stunned that anyone would attempt to cross the river, the miner launched the raft into the raging river. Using his hands to paddle, he headed for his dredge across the river…

Even though the miner was a large man in good physical condition, he still had a formidable task to ford that river in a narrow canyon, with raging 40-degree water roaring through at breakneck speed. As Larry watched, with tremendous power born out of fear for his life, the man swam for the opposite bank. Even in the violent storm-tossed river, the man actually made it to the other side, pulling himself up onto the rocks to rest near his dredge. There, the man quickly secured his dredge where it would be safer. Then he hiked up over the mountain and followed Independence Creek down the other side, so he could cross the Klamath River over the Independence Bridge. One swim across that river was enough!

A passerby immediately called 911when the man first capsized into the river. As is the way with small towns, not only did the local sheriff’s deputies and ambulance respond, but a goodly number of others in the mining community also showed up to help wherever needed. Many residents in Happy Camp keep a scanner on at all times to remain informed, and to be able to provide assistance to others when needed. So it was only a matter of minutes from the 911 call before a bunch of New 49’er members and others were on their way down there to provide assistance.

Dave McCracken interviewed the man who swam across the river on camera just after the ordeal:

Then Dave captured the river conditions which the man actually swam across. Isn’t it a miracle that that the guy actually survived it?

Late Tuesday afternoon, Connie and Dave Rasmussen, residents of the only nearby home, stopped by to tell Larry that a big slide had closed Highway 96 between there and town. Larry did not say much. He was feeling pretty depressed by this time. His large floating winch platform had been dragged away by the storm that morning. Now with the news of being cut off from town, it looked like he was going to go hungry, too. Larry was just about out of the food he had brought down there with him. His dogs were also hungry. He had not planned on being there for so long. But the rain was increasing in intensity; it was not letting up! He had had no sleep, little food, and things were not going well at all.

Larry thanked the Rasmussens for the information and got back into the truck to rest. At least he had the dogs for company. Larry was worried about friends in town who lived along the river and creeks. He was wondering just how bad it was back there. What he was seeing here was unbelievable!

Just as Larry was sinking into a pit of depression, a truck appeared. It was the Rasmussens again, and he couldn’t believe his eyes! They had a tray that held a big bowl of steaming hot, home-made stew, fresh-hot homemade biscuits, a soda, and some candy for dessert. They even brought dog food for his dogs! He just couldn’t believe it. They were so supportive, it really cheered him up. After he ate a hot meal, Larry’s faith was restored that things might work out all right after all.

Larry maintained his vigil throughout the night again, going down every hour and a half as the water continued to rise and grow evermore turbulent. It was becoming very difficult to get onto the boat. When Wednesday (New Year’s Day) came, the river was the worst he had ever seen it. Down in the boat, Larry found that he could not look out onto the raging river without becoming so disoriented that he could no longer keep his balance as he tried to board the boat.

Larry spent New Year’s Day watching all the trees and people’s belongings pass by on their headlong rush for the sea. He saw several dredges pass by, along with many bits and pieces of other manmade things. Larry could not imagine what things looked like upriver, given the tremendous amount of personal belongings that were washing past him downriver.

That night, as it grew dark again, and the waters became even more turbulent, Larry watched the boat rising and falling violently on the waves, and he decided that he simply could not attempt the trip in the dark again that night. He had less than three hours sleep since Sunday night, he was numb to the bone with cold, and he was totally exhausted.

So Larry climbed into the truck with his dogs and quickly fell asleep. Six hours later, Larry woke up to the early hours of the 2nd of January. With dread in his heart, he shined a flood beam down where the boat was supposed to be, and it was actually still there! The seven lines that he had tied to the boat were not in the best of shape, but the boat was still there and in one piece. Larry tried to see if his dredge was still across the river, and thought he could see the blue of the canopy, but decided it was just his own wishful thinking.

When Larry woke up, it took him 20 minutes to get up the nerve to get out of the truck and look to see if his dredge and boat were still there.

Overnight, the boat had risen to within 10 feet from the final mooring spot where he had left it on the previous day. There was nowhere higher up that the boat could be tied off to a firm anchor. What would he do if the water continued to rise? Larry felt numb by this worry, and he just couldn’t think anymore. Finally, he climbed back into the truck and slept for several more hours. There was nothing more he could do.

It was just beginning to get light when Larry awoke again. It took him 20 minutes or more to get up the nerve to go over to check on the boat and dredge. He was so afraid they would be gone that he could hardly look. What a great surprise when he found that the water had already dropped quite a bit, and both the dredge and boat still there!

Larry rushed down to bail the boat and give slack on the tie-off lines. Two of the ropes had been secured to the windshield frame, and the frame had been ripped out completely by the heavy pulling of the storm. Luckily, he had also secured the ends of both lines to the side rails of the boat. If not for just that little extra security, Larry would certainly have lost the boat. From then on, it was just a matter of adjusting the ropes to keep it off the rocks as the water rapidly receded.

On Thursday, Dave McCracken braved it through the two feet of water across the road at Oak Flat, and then carefully crossed over the slide-area to check on Larry and anyone else who might be stranded downriver. Here follows a video segment that Dave captured where the river was crossing Highway 96:

After that, others also cautiously crossed the submerged road when they saw the tracks which Dave had left behind. The mountainside above had slid down from the top to block one side of the road, and the outer 17-feet of the roadway had slid away into the canyon to be washed away by the river. First one on the scene from the outside world, Dave took the opportunity to interview Larry on camera:

Friday, the Rasmussens had arranged with friends to meet them at Rattlesnake Rapids, and walked across the slide-area where they were picked up. They then rode into town to pick up supplies for themselves and for Larry.

Leroy Hardenburger arrived with more food and supplies for Larry on Friday, as did other New 49’er members, Gary Wright and Bill Seifert. The river had receded from the road by this time. They brought news of everyone in town, and Larry was happy to learn that everyone was okay, although some had sustained heavy property damage from the flood.

How great it was to have good friends. And the Rasmussens; they were not gold miners and he had hardly even known them before the storm. They provided continual moral support for Larry and all his necessities.

Even though he went through an ordeal he hopes never to have to repeat, Larry still feels life is really good. “If you can live in a place like Happy Camp with friends and neighbors like this, life just couldn’t be better!”

 
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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!

 
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This story first appeared in Gold & Treasure Hunter Magazine May/Jun, 1997 on Page 22.
This issue is still available! Click here.

By Dave McCracken

“It takes a huge amount of streambed in motion to cause large portions of the river to form new high-grade deposits.”

Dave Mack

It only takes a small amount of water force to move sand-sized particles downstream in a riverbed. It takes more water force to move pea-sized gravel downriver, and even more force to move baseball-sized rocks, and so on. It also takes a greater amount of water force to move larger particles of gold, than it does to move smaller ones – just like other streambed materials.

There is a massive amount of gold in gold-bearing waterways which is so small in particle-size that it floats in a state of suspension in the river-water itself. Some amount of gold is moving downstream in any gold-bearing river at any given time. An increase in water-flow increases the amount of streambed material and gold that is moved downstream.

Normal winter storms, for the most part, can move large amounts of fine and ultra-fine gold down the gold-bearing rivers. But this gold is likely to be so widely dispersed throughout the overall river that it is of little value to the modern river-prospector.

Today’s modern river-prospector is mostly interested in that gold which lies inside and underneath naturally-formed streambeds. For the most part, this gold will remain locked in place until a storm of major proportions comes along. Such a storm can cause so much water force in the river that large sections of pre-existing streambeds, and the gold that is within them, are swept up and washed downstream.

When a storm or snow-runoff of huge dimensions comes along and creates so much force of water flow that large portions of the riverbed are torn up and washed down along the bedrock, large portions of the bedrock will also get pounded loose, and any gold which was trapped in that bedrock will become washed further downstream along with the rest of the streambed material.

“Rough bedrock makes the best gold traps.”

The amount of gold still sitting inside streambeds of proven gold-bearing rivers is incalculable; there is a whole lot of it! Much was left behind in low-grade deposits which the early miners were not capable of mining at a profit. While there may been a lot of gold in some sections of river during the gold-rush years, it might also have been too widely dispersed or sitting underneath too much overburden to make the gold worth mining in those days. Other very rich deposits were missed because they were out of sight. Without processing every bit of streambed (which they did not have the capability to do), the old-timers simply could not find all of the gold deposits that existed during their time. A lot of gold that was excavated was never recovered. It was washed out of the high streambed deposits, through sluice boxes, and right back into the present rivers and creeks. This was particularly true of hydraulic mining, where an estimated 59% of the gold was missed by many of the large and small operations alike.

Also, the last 150 years of erosion has washed more gold into the present rivers and streams out of higher and older streambeds, and out of some lodes that are still in existence.

In taking all of this into consideration, we are talking about a lot of gold still existing in these gold-bearing rivers. In some cases, there is more gold present now than the amount that has already been mined out of them.

When a major storm occurs in a gold-bearing area and tears up large portions of streambed, a great deal of gold is set free and put into motion downriver. A fair amount of this newly-released gold, because of its superior weight, will be deposited in common areas along the riverbed. This is the type of gold that the modern gold prospector should be sampling for. The same major storm which causes enough force to tear up large portions of streambed material will also deposit most of that material into newly formed natural streambeds-even in those same areas which were once mined by the early miners.

During full flood stage, when streambed material and gold are moving free in the waterway, because it is so heavy, most of the gold will travel along a rather narrow path. This path is often referred to as the “gold line” by prospectors. Almost all high-grade pay-streaks will be located along this specific path. Therefore, the first step in prospecting is to locate where the common gold path is within the waterway. This very important principle is demonstrated by the following two video segments. Please take careful note of how the gold is attracted to the common line in the simulated river, regardless of where it is fed into the waterway:

For the most part, normal winter storms occurring in gold country do not create enough water force to do this. A winter storm might be enough to sweep up small portions of streambed in faster-moving sections of river and redeposit new streambeds in those areas, but this small amount of movement is not likely to put paying quantities of gold into play in the riverbed. It takes a huge amount of streambed in motion to place substantial amounts of gold into movement. This causes large portions of the river to form new placer deposits. Such storms occur occasionally, and are the main cause for a streambed cutting deeper into the earth as time goes along. Most gold-bearing areas have had at least one of these major storms since the early 1960’s. Alaska has major storms along with massive snow runoffs. So flood forces like this happen more often there.

When millions and millions of tons of rocks, cobbles, and boulders are being swept downstream along the bedrock foundation during a huge storm, the ground shakes and vibrates, and the river rumbles like a huge loaded freight train. After a major storm has been through an area, the plant growth, underbrush and weeds which normally grow along the river gravel bars, will be washed away. This will also be true with a lot of the growth, including trees, along the riverbanks.

It takes an incredible amount of water force to cause an entire riverbed to move downstream, but this is what it takes to form many new placer deposits in the river.

The following video was taken during the major flood storm that took place along the Klamath River in Northern California during early 1997. If you watch the footage closely, you will see places where the river is flowing down river with the full force of the storm, and you will see other places right alongside where the water is flowing in a reverse direction. This is important! Take note of the incredible amount of boiling which takes place between the different directions of flow. These are pay-streaks in the making; places within the waterway at flood stage where the river is not really flowing in either direction; but rather is boiling like a kettle of superheated water between opposing forces. Gold concentrates within these areas because there is not enough water velocity to keep it moving along. Each place along the common gold line within the waterway that a boil like this is created by the interplay of reverse-flows is where a prospector will find the high-grade pay-streaks. See how big the boiling areas are?

The earlier idea that gold drops into the river and simply is vibrated down through already formed streambeds to eventually reach bedrock and form a placer deposit is very limited in its workability. This theory does not lead a prospector into paying deposits of high-grade gold

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

Streambed layers caused by different flood storms are referred to as “flood layers.” Flood layers within a streambed are easily distinguished, because they are usually of a different color, consistency and hardness from the other layers of material within the streambed. Sometimes the bottom of a flood layer will contain more gold than is present on bedrock. Sometimes, when more than one flood layer is present in a streambed, there will be more than one layer of flood gold present, too. Gold deposits can often be found in the contact zone between the layers.

Flood layers that are caused by major flood storms are almost always found in a compacted state where the rocks and material hold together tightly and require tools to help pry them apart. In mining, we call this “hard-pack.” There is a big difference between hard-packed streambed and tailings from earlier mining activity or loose streambed material. Almost all high-grade pay-streaks will be found at the bottom of a layer of hard-pack. So it is very important that you know what it is. Please note how hard I have to work to break apart the hard-pack in one of the following 2 video segments:

The larger that a piece of gold is, the faster it will work its way down toward the bottom of a flood layer as it is being washed downstream during a flood. The finest-sized particles of gold might not work their way down through a flooding layer at all, but might remain dispersed up in the material.

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

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

Some of the best areas to test for paying quantities of flood gold are where the stream or river widens out, or levels out, or changes the direction of its flow. Such places always cause the flow of water in a storm to slow up in certain locations. This can allow concentrations of gold to collect either on bedrock or in the contact zones between layers. These following important videos demonstrate the most common areas where pay-streaks are formed:

Gravel bars, especially the ones located towards the inside of bends, tend to collect gold. Flood gold in bar placers is sometimes consistently distributed throughout the entire gravel bar. Often the lower-end of a gravel bar is not as rich as the head of the bar, but the gold there can be more uniformly distributed throughout the material.

 

 

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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.

 

 
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By Dave McCracken

Under many circumstances, it is wise to first verify that a viable deposit exists on a property before a substantial investment is made into production equipment.

Dave Mack

 

How to outfit a suction dredging project, to a large degree, comes back to how you would answer the following questions:

1) What am I trying to accomplish; (sampling, production, or both)?

2) Where?

3) In what period of time?

4) How much of a budget is available for acquisition of equipment and for operational start-up costs?

A gold (and/or gemstone) mining project basically should to be looked at in two separate steps: First you sample to locate a viable deposit. Then you launch into a production program to recover the gold or other valuable minerals from the deposit. Generally, the idea is to minimize investment into a particular mining property until a viable deposit has been located and verified.

Production-equipment is commonly larger and is more expensive to purchase and move around. The logistical infrastructure to support a production operation is usually more substantial and costly than what would normally be required to just go in somewhere for a short sampling program. . So generally-speaking, a production operation costs more to set up and involves more gear and supplies to move around and put into place. Therefore, under many circumstances, it is wise to first verify that a viable deposit exists on a property before a substantial investment is made into production equipment. The idea behind sampling is to minimize risk.

Prospecting Equipment & Supplies

The following video sequence will provide you with a visual demonstration of this very important point:

A typical camp to support a preliminary sampling operation usually would involve just the basic necessities.

The answers to “Where?” and “For how long?” also impact upon your decision about what kind of gear to buy. For example, if you are not tied to just one mining property, and you are prepared to launch a sampling program onto different properties until you find what you are looking for, then it would be a good idea to invest in good sampling equipment that is portable enough to move around the properties which are available to you. In this case, the capital expenditure is not tied to a single property, but rather into a portable sampling infrastructure that can be used for an extended period of time in many different places.

While sampling-gear is more portable, the smaller the size of a dredge, the less volume of streambed material it will process (in the same experienced hands), and the less-deep it will effectively excavate a sample into the streambed. Therefore, you trade-off productive effectiveness and the capability to make meaningful, deeper samples as you reduce dredge-size and gain in portability.

Two Pro-Mack 5-inch dredges were used to find rich deposits on this river in Cambodia, before a 10-inch production dredge was brought on line.

As an example of this, a 4-inch dredge can effectively sample down to around 4-feet deep in hard-packed streambed material). A 5-inch dredge can excavate about twice the volume of a 4-inch dredge down to around 5-feet of material. But the bulk of gear to move around is about twice as much.

A 6-inch dredge can excavate about twice the volume of a 5-inch dredge down to around 6-feet of hard-packed streambed. But the bulk of gear to move around is about twice as much.

An 8-inch dredge can excavate about twice the volume of a 6-inch dredge down to around 8-feet of material. But the bulk of gear to move around is about twice as much.

Here follows a video segment of a typical commercial dredge operating on the Klamath River in Northern California:

Ten-inch Pro-Mack dredge operating on New 49’er properties in Northern California.

A 10-inch dredge can excavate about twice the volume of an 8-inch dredge down to around 10-feet of material. But the bulk of gear to move around is about twice as much. By now, we are talking about a pretty substantial platform. But it still remains portable enough to place inside of an ocean shipping container, and can be towed around on wheels behind a small truck. For example, watch how this recovery platform for a 10-inch production dredge can be moved around by a normal-sized truck. This particular platform was built to ship overseas inside of an ocean shipping container:

These are just guidelines, because conditions change from one location to the next. It does not mean you cannot dredge deeper into the streambed using smaller-sized dredges. You can! But it generally does mean that the deeper you go beyond these guidelines, the less effectively your time will be invested. This is mostly a matter of over-sized rock management. All rocks that are larger than the intake-size of the dredge’s suction nozzle must be moved out of the way by hand. When dredging in an average hard-packed streambed, at the point where an experienced operator gets down through 5-feet of material using a 5-inch dredge, he has so many rocks to get out of the dredge hole that he is lucky to spend half his dredging-time operating the suction nozzle!

Bigger dredges get more accomplished primarily because they will suck up larger-sized rocks.

Under most circumstances, there are a proportionate greater number of smaller-sized rocks in a hard-packed streambed, than larger-sized rocks. So this is really a discussion about effective time-management. Since a larger dredge will suck up a larger rock, it means the operator will not have to move smaller-sized rocks from the excavation by hand. So he or she will spend his time moving even larger rocks out of his way, of which there are proportionally-fewer. This means he will get more done faster, and be able to dredge deeper into the material, before he reaches the point that there are just too many rocks to move out of the way.

Using a 5-inch dredge will mean having to move many, many more rocks by hand that would more-easily be sucked up the nozzle of a larger dredge.

This important reality cannot be overcome by positive thinking or an abundance of enthusiasm (as important as these are to have). We are talking here about the physical reality of how an excavation is accomplished. The size of the dredge-nozzle determines what size of rock can be sucked up (which is fast and easy), and what must be moved out of the hole by hand (which takes more time and effort).

The following video sequence demonstrates this very important point, and also explains why you must be very careful about projecting the true volume capability of different-sized dredges during feasibility planning:

By the way, when conditions allow for it and you want to increase the productive capacity of your equipment, you can also organize two or three separate teams to take shifts using the same production equipment. As demonstrated in the following video sequence, lights can even be set up to do a night shift:

So when deciding what to acquire for sampling or production equipment, it is necessary to balance the desire to get more productive activity accomplished (bigger dredge), with the necessity to remain portable (not so big that you cannot move it around to find what you are looking for). This must be decided on a case-by-case basis.

Here is my advice: Go as big as you are able to without forfeiting the portability that is required for your particular situation. I suggest these important decisions can only be wisely made after at least a preliminary evaluation of the project-area is completed.

Once you have proven-out your deposit(s) by sampling, you can feel more comfortable investing in production equipment and support-infrastructure to develop the project. In that case, bigger is not always better. Sometimes it is. A lot will depend upon the depth of water and streambed where you will be dredging. For example, a 10-inch dredge might not be as productive as a 6-inch dredge in a shallow-water and shallow-streambed area where a larger dredge cannot be floated around easily.

Another example is where shallow streambed material is made up largely of boulders that must be winched out of the way. In this case, some of your money might be better invested into a good mechanical or hydraulic winch, rather than a larger-sized dredge.

A well-done preliminary sampling program should result in a good production plan, based upon what type of equipment will be required to obtain optimum production under the conditions which exist where the gold deposit is located.

I am not going to discuss sampling, production or recovery systems here, because they have been covered in other articles. But since the type of equipment you should acquire is directly related to these subjects, I suggest it is a good idea to review that material very closely.

Some dredges are made to operate from the surface with the use of an automated cutter-head device at the nozzle. These are generally ineffective in hard-packed streambeds that are mostly made up of oversized rocks.

Some dredges are available with hydraulic-powered cutter-heads to help with the excavation. These 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. Hard-packed streambeds which are made up mainly of oversized rocks and boulders will usually destroy a cutter-head device in short order.

Here follows the normal steps in the development of a mining program:

1) Preliminary evaluation: This is where you take a hard look at the available information about a potential project. Then you go out and have a direct look at the specific location(s) and surrounding area. You are looking at the potential for commercial gold (and/or gemstone) deposits. You are also looking at what it would take to accomplish a preliminary sampling program, based upon all of the information and observation you can bring together. A preliminary evaluation will often result in a preliminary sampling plan.

2) Sampling Program: Depending upon what the objectives are, sometimes sampling is accomplished in several stages. Generally, the purpose of a sampling program is to locate and verify the existence of a commercial deposit that is valuable enough to justify a production operation. Sampling should work out the recovery method upon which the deposit may be developed efficiently. A sampling program can evolve into feasibility planning to develop a mineral deposit.


3) Production Operation: Is full or partial development of the deposit.

While there can be some overlap, equipment needs are usually different in each phase of a mining program.

While each project is different, during a preliminary evaluation, I personally always at least bring along a face mask (so I can have a look at the underwater environment where we would sample), a gold pan and classification screen, zip-lock sample bags and marker pen, map, GPS, camera equipment, local money in small denominations (to buy mineral samples from local miners), a dozen bright-colored ball-caps (gifts for local miners), a bottle or two of whiskey (gift for the village chief in non-Muslim communities), and the other basic things I will need to visit that particular environment.

A sampling program will basically require the same things as will be required in a full production operation, but usually on a smaller and more portable scale. Here follows a basic outfitting list:

Dredging Equipment:
Dredge
Boat (and motor?) and ores
Winching gear and rigging?
Pry-bars
Rope (floating)
Fuel containers
Complete set of tools needed to service the gear

Diving Equipment:
Face mask
Air reserve tank and fittings
Air line(s) & regulator(s)
Wet-suit?
Weight belt & weights
Protective foot ware (steel tips?)
Rubber work gloves (bring spares?)

Clean-up Gear:
Wash tubs
Classification screens
5-gallon buckets
Scraping tool and/or hand scoop
Final concentrating equipment?
Gold pans
Steel finishing pans
Magnet
Portable gas stove
Weight scale
Zip-lock sample bags and marker pen

Support Gear:
Vehicle-support?
Shelter
Cooking & eating utensils
Wash tub for kitchen
Cook stove
Toilet facilities?
Portable chairs & table
Medical kit
Waterproof bag(s)
Ear infection preventative
Maps, GPS and camera equipment
Electric generator?
Camp lights
Paper and pens
Communication equipment?
Flashlights & batteries
Knife
Firearm?

Supplies:
Drinking water and/or filters
Food supplies and containers
Fuel & motor-oil for all motors
Dish washing detergent
Chlorine for sanitizing cleaning water
Laundry wash tub and soap
Hand-wash soap
Tissue paper
Cook stove fuel or canisters
Duct tape
Nylon line (plenty)
Plastic trash bags
Zip-lock bags & plastic containers for food

Spare Parts (priority often depends upon how remote the project location is):
Tune-up replacement parts for all motors
Extra water pump seals and bearings
Extra compressor & alternator belts
Rebuild kit for air compressor
Extra air compressor?
Rebuild kits for dive regulators
Extra dive regulators?
Repair kits for diver air lines
Extra diver air lines?
Extra air fittings
Extra water pressure and intake hoses
Extra water hose fittings
Extra rubber hose seals (each size)
Extra foot valve(intake for water pumps)
Extra suction hose?
Extra face mask(s)
Extra starter & alternator & fuel pump for dredge motor?
Spare tire (if dredge has removable wheels)

 

 
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By Dave McCracken

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

 

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

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

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

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

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

Is the political situation stable?

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

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

7) Travel to the potential project area and:

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

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

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

    

 

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

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

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

    

 

    

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

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

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

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

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

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

    

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

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

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

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

  

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

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

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

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

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

 

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