Log in

View Full Version : Thoughts on hand mining flour gold



overtheedge
09-14-2012, 02:49 PM
This is just my thoughts based upon the last decade or so of reappraising the hand mining of flour gold based upon experiences. This ramble is directed at fine/flood gold. No doubt I've overlooked something.
----------

Let's face it, today's hand miner faces a set of obstacles.

1. Most deposits of hand mine able nugget gold have been mined out long ago

2. Remaining deposits typically require heavy equipment to get through the over-burden.

3. The few remaining mine-able deposits tend to be quite remote requiring goodly capital to get to them and be able to remain in the field for a lengthy period of time.

4. Any known deposits that still have hand mine-able tenure will cost a good deal to buy the claims.

So where does this leave the hand miner?

Low tenure deposits of flood/flour gold still remain. Many of these are too small in size to attract equipment miners. The size and character of these deposits create a problem for mechanized recovery. Many of these small deposits have hot-spots that can earn a decent rate of return for the labor expended.

Fine/flood gold is often found directly below and on the same side as areas that are being actively eroded.

The hand miner has new sluice bedding materials that can be used to increase the recovery rate.

With the internet and availability of books, researching an area is far easier than a just few decades ago.

Still the hand miner is limited to the amount of material that can be shoveled a day.
---------------

So what is the best course of action for the hand miner?

1. Thorough research of mining areas and their history. When, where and how. Current and past claim history as well as what little can be determined of the recovery. Pay particular attention to access routes.

2. Then you have to be able to put boots on the ground and conduct a concerted sampling effort. Take aerial photos, maps and mining/geology excerpts with you in a water-proof container. Take a notebook and several pencils. I like the "Rite-in-Rain" water-proof notebooks but anything is better than none. Take a GPS with you. Your maps should have at least the section corners identified with Lat/Long.

3. Both of the above demand time. This almost mandates a means of self-financing. With learning to be frugal and living out of a rucksack, it can be done on the cheap. However, you must have enough financial resources to pay the bills back home while you are in the field.

4. If you are married or in a relationship, your other half must be supportive of your efforts.

5. The only mining equipment you should be taking with you is what you need for panning: pan, shovel, snuffer bottle and a container for the gold once you have cleaned it enough. If you aren't a proficient panner, get busy becoming one.
------------------

So once you have found a likely location and got there, what should you do?

1. Set up a base camp that is dry and comfortable. You will be exhausted at the end of every day leaving little time to improve your living conditions. High calorie nutritious meals and a good night's sleep are mandatory.

2. Find high ground and get above the area to ground-proof the maps and aerial photos. A digital camera with spare batteries will pay dividends. Take plenty of pictures.

3. From #2, set up a sampling program for areas that appear to have the most potential.

4. Sample near the heads of these likely spots and close to the banks of the stream. Try at least 3 pans per sampled spot to reduce the nugget effect. One good pan could be a fluke, but three reduces the probability of the nugget effect to close to zero. If the tenure is low in this area, move on. The tenure rarely gets better further downstream of the head. Digging deeper than a foot or so is usually a waste of time if the gold isn't available in the top foot. Remember, flood gold is the last to be deposited and only under low river flow conditions when the water flow transitions from turbulent to laminar.

5. If the sample has potential, only then do you transition from fast and dirty sampling to detailed sampling. So what is potential? From my experience, a 15" pan of straight bank run minus the bigger rocks should show at least 100 flecks or about a dozen flakes that can be picked out with tweezers. Any less is too low for the hand miner.

6. For detailed sampling, I move a couple of meters and pan again. Again, three pans per. By doing this, you are delineating the dimensions of the deposit that could be profitable.

7. NEVER fall in love with the deposit. If the tenure isn't there, more effort on your part won't make it better. I try to spend a hour or two at the end of each day sampling another location. Not only does it help work the kinks out, but each deposit only will last so long.

8. Remember, this is a sampling effort. You aren't going to make money mining with just a pan. Don't let yourself start production panning any prospective deposit. The intent is to determine whether or not an area is worth claiming. One small deposit in a 40 acre area is not worth the expenses and effort to claim it. Several spots in a 40 are.
--------------------

Once you have found an area worth claiming. Do the paperwork and put in the claim posts. Continue the sampling effort for prospective areas up and/or upstream. Get it recorded once you leave the field.


While you are in the field, keep you eyes open for access routes so you can haul in more equipment and supplies.

----------------------------
Hand mining is a tough way to go. In many cases you are faced with either improving the access for ATVs or hauling the equipment in on your back.

Remember, every thing you will need for an extended stay MUST be delivered to the site. Never overlook hiring delivery out by boat, ATV, snowmachine, or the potential for air drops. Helicopters can sling-load a lot of stuff in minimum time although it may cost several thousand dollars counting ferry time. A months worth of groceries can weigh half a ton easily. Add in equipment, a month's fuel and support equipment and now you could be close to a ton.

In most areas, the mining season is limited. Every day you spend ferrying in supplies is one less operating day.
-------------------
Mining equipment is where many get themselves jammed up.

Stream sluices are a waste of time although they may be applicable as a recovery device.

High-bankers need fuel and take time to move and relocate. Failing to move them results in time wasted moving the material to them. Never move NOT-gold any further than is absolutely required.

In decent ground, you might be able to shovel 5-8 yards a day. That is just shoveling into boxes. If you have to take more than a step or two per shovel load, cut that figure in half. Same goes for classifying into buckets and hauling them to your recovery device.

One possibility that I have used is classifying at the shovel site and hauling the classifieds to a large piece of plastic at the recovery device location. I do this for 4-6 hours and only then fire up the pump. Then I spend an hour or two just feeding the highbanker.

Every yard weighs roughly 3300 pounds. Therefore, never move anything that doesn't need moved any higher or further than it absolutely must be moved. This is why moving a highbanker results in higher efficiency. Only operating the pump once you have stockpiled an hour or two worth of classified material means less fuel weight that must be delivered to the site.
-----------------------

Another option that should be considered is modular recovery device design. All of us have seen the old photos of lengthy sluice boxes used by the old hand miners. The reasons were multifold. Among them was low recovery per sluice-foot, transporting tailings and water delivery.

Most of these reasons are still valid. Consider wooden flumes for water delivery to a classification stage that uses a rod grizzly with rods about 1/2" apart. Then use a narrower aluminum roof flashing lined flume to deliver the classifieds to another classifier near the sluice that is set at 1/8"-1/4". Plastic pipe could be a good substitute for delivering the -1/2".

Why two classification stages? Water and tailings. It takes lots of water to move large material. Why move the grossly over-sized any further than is absolutely required? Why not wash the over-sized and drop it back into the area you just cleaned out?

Keep everything as close to the ground as possible. Why lift gravel any higher than is required? It is reported that a person in extremely good shape can expend 1/10th Hp for several hours with their legs. 1 horsepower is lifting 33000 ponds 1 foot per 1 minute. But we are shoveling. So better cut the 1/10 HP to 1/100th at most. We don't walk on our hands now do we? So this is means 330 pounds per foot/minute. Yet we know that under the very best conditions, 15 yards a day is about the absolute limit of endurance for someone in great shape. That equates to roughly 100 pounds per foot minute. Lift two feet under the same conditions and the person in exceptional shape can only do 50 pounds per minute.

A fully loaded #2 shovel load runs about 10-11 pounds. I'm in very good shape and can only average about 4 shovel loads a minute or roughly 4.5 yards in a 6 hour day under the conditions I face. When faced with the larger rocks at the head of a bar, I can barely manage 3 yards a day.
-----------------
As you can see, the physical limitations restrict the hand miner to only the best flour gold deposits.

This absolute mandates that we move no material any higher or further than must be done. The only way to accomplish this is by moving the recovery device often.
---------------
Recovery of flour gold sets up a whole new set of requirements.

1. It is physically impossible to get high recovery when we need to move large material while retaining flour gold.

2. In order to retain the maximum amount of gold we have to reduce the size of the material to 1.5-2X the size of the largest gold we expect to recover.

3. Classifying to -8 mesh presents the problem of throughput. This is due to a couple of factors. One is actual classifier size as the smaller the opening, the greater the number of openings required for the material to get through. The other limitation is water has viscosity. The smaller the opening, the greater the probability that the water will just run over the screen carrying the smaller material with it.

4. From experience, I've found that the classifier openings should be no smaller than 1/8" with 3/16" better to keep classifier size to a reasonable dimension.

5. Riffles are not a good idea. Riffles need water depth and velocity to work. This induces turbulence to an environment when particles have very little mass that would overcome the turbulence and drop out. Either use small expanded over the bedding or go to one of the newer rubber mats currently on the market.

6. Because these flour gold particles have such low mass, deeper water columns and higher water velocity can set up the conditions where the gold hasn't settled to the bedding before the current takes them off the end with the tailings. We only need enough water depth and velocity to keep the bed active and move the lights away. I keep the water depth to under 1" and preferably 3/4". I adjust the slope to keep the black sands bouncing just a bit in the bedding.

-------------------
Dredges are of limited use for flour gold. The water velocity and quantity makes recovery difficult to lousy at best. However if a person were to use 2 stages of classification and set up the conditions to slow the water and get rid of excess water, a recovery system could and does work.

My highbanker with 1/4" screened classifier fed with a suction nozzle powered by an under-sized pump gets reasonable recovery. The only advantage is the ability to recover gold from bars that are slightly under water.
-------------------
Some may argue the points I've presented and I'm open to disagreements. These forums give all of us the opportunity to present new ideas and arguments that should be considered if we are to move the craft forward.

I have no doubt that I missed something.
eric

Jrreyboi
09-14-2012, 09:06 PM
Eric,
Excellent post, very informative. I have some comments that I would like to make on it but I am heading out the door for a week of business travel in China. I'll work on it while I am gone. Thanks again and I'll be in touch.

auldrider
09-15-2012, 03:17 AM
Very interesting stuff .... what are your thoughts about the amount of material one can shift with a #2 shovel compared to say a 3 inch dredge nozzle on a combo unit?

Personally I really enjoy shovelling into my highbanker, it is good therapy and if I don't get too much gold, at least I get a good days exercise!

I find the dredge both uncomfortable and damned hard work by comparison!

Maybe I am doing it all wrong!

overtheedge
09-15-2012, 11:01 AM
Somewhere I ran into a figure of dredge capacity running 7% solids to water ratio as its maximum capacity. So if we figure 150GPM pump for a 3" dredge, we get about 1245 pounds of water a minute. 7% solids means 87 pounds of material a minute.

This translates out to about 1.5 yards per hour maximum under the best conditions aka loose sand, gravel and small pebbles. My 2" dredge has trouble averaging 0.5 yard an hour. This figure is considered about maximum practical for a 2" with 1.0 yard average for a 3".

A full #2 shovel full weighs 10-11 pounds. However it is not limited to material smaller than 3" diameter. I can almost always shovel 0.5 yard an hour even under the worst conditions. 0.5 yards weighs 1650 pounds divided by 60 minutes equals 27.5 pounds a minute. 27.5/10 pounds per shovel load equals 1 shovel load every 22 seconds. So if a 3" dredge will average 1 yard an hour, you would have to shovel about 1 shovel load every 10 seconds to equal the average capacity of a 3" dredge.

Under average conditions I think a person in good shape can shovel the same or more material than a 3" dredge can move, but not much more.

I can run my 2" dredge as either a stand-alone dredge or as part of a cobbered together combo rig. It does have the advantage of getting material from underwater. BUT, I am bent over for hours and this kicks my posterior right proper. I've tried squatting and it is hard on my knees. I wind up taking 10-15 minute breaks every hour or so. This is unproductive time for me.

So I'm with you. I prefer a #2 shovel. But shoveling is an art too. We all have heard about lift with your knees, not your back. Another one we don't often hear about is NEVER lift and twist. This means we should be shoveling straight into the highbanker, sluice or whatever to avoid lower back rotational injuries.

I like a D-handled shovel for sampling, but for production I stick with a long handled shovel for the added leverage.

If a person is gonna handle a shovel, they need to be in good physical shape to begin with and figure your gonna have Popeye arms after awhile. I like shoveling in. Not only do I get good exercise, but I sorta go into "zen" like trance and the day seems short.

I also like shoveling in because I can keep an eye out for bears. I haven't had any bear encounters on the river, but I have had them approach within about 35-50 meters before turning around and leaving. I think they were just curious about the noise from the pump. Once they got close enough, the noise was too much for them.
-----------------------------
All things considered, I think a combo rig is a great choice. It has portability and flexibility. The cost of a new one is still not that high considering gold prices. Fuel economy is reasonable. The only drawback is the sluice bedding/riffle design being so-so at best for flour gold. But I would suggest picking up another riffle tray and modifying it for flour gold. Another option that I used is to remove the tray completely and replace the bedding with rubber mat. I hold it in place with a thumb screw and a piece of that aluminum carpet edge material. I just drill a hole in the sluice bottom and use a thumb screw topside and a wing nut underneath.

If I change back, I cover the hole with duct tape or use a round head screw with the same wing nut.
-------------------------------------------
Adding to the original post, the better deposits of flour gold are often replentished during each high water episode. Last year on the bar I was working, I could average 1/2dwt per 4 hour period with a pan. Same area this year produced just over 1/8dwt in 4 hours panning a couple days ago. This is too low for me to continue working. So I get to haul everything back today.

Yah, I violated one of my rules by hauling in a highbanker before I had checked the tenure. If your gonna be in the placer gold game, you have to be the eternal optimist. I was sure that the deposit would replenish; it just didn't replenish enough.

When you do find a workable deposit, take pictures under varying water height conditions. Keep notes. It may be too small to bother claiming, but it may replenish after a year or two. With good notes and pictures, you can farm these deposits year after year or two.
------------------------
Many books and videos show gold moving in a circular path towards the inside of the curves as it flows downstream. Here is the rest of the story.

There are 2 of these circular paths. One on each side of the stream. The water moves from the bottom center of the main current towards each bank. Then up the bank and across the top of the stream to the center again.

The outside of the curve is erosional while the inside of the curve is depositional. Where it gets interesting is immediately below the outside curve, as the velocity drops, big boulders stop moving. Material begin to build up behind these boulders. Once the material builds up enough and the water begins to get shallow, the turbulence drops and becomes more laminar. Flour gold remains suspended in turbulent water, but once this gold gets into laminar flow, gravity takes over and the gold will start to drop out.

Because the water flow along the banks is up-bank and down stream, part of the flow is peeled off where the boulders pile up. Any gold that was eroded and carried in the flow against the bank will get peeled off too.

Just because there is mud on a bar is NOT a good reason to overlook it as a potential deposit. Silt and sand drops out under low flow/low velocity conditions. As the water drops, material with the least mass will settle out. Dig down through it. You might be surprised by what you find at the head of the deposits.

I do all I can to dispel the nonsense about low pressure/ high pressure zones in a stream. IT IS NONSENSE. There is high energy and low energy. Energy is velocity, plain and simple. There is turbulence and laminar flow. The water flowing over the inside of a curve can be high and gold will still drop out due to the laminar flow where gravity can be the major player.

Depending on the size/character of the gold, turbulence can either keep the gold in suspension or greatly lengthen the wavelength of the saltation process.

Another bit of nonsense is gold working its way down. Gold will settle deeper in a dilated material. Once the material settles, gold movement stops. So in order for gold to drop deeper, there MUST be a gap for it to fall into.

Remember those boulders piling up? Nuggets are moved by saltation during high flow conditions. That boulder pile has lots of hidey-holes for the nuggets to fall into and out of the main current. The turbulence in the circular paths against the banks isn't enough to lift the nuggets (high mass) very high and they return to the bottom and bounce along until they find a hole to fall into.

Even for flour gold, the above holds true. Look for flour gold where the rocks run about fist sized. On average the smaller the rocks, the smaller the gold. There are exceptions, but the hand miner needs to play the averages.

In known gold-bearing streams, pay attention to the quantity and size of magnetite and other high S.G. material in your pan. More and bigger is always good for additional sampling.
eric

auldrider
09-15-2012, 01:25 PM
Thats terrific Eric but I am on a tight reign at the moment! (lol)

Will have to come back and read it more slowly later today! Thanks, John.

PS: I like you posts!

Gold Seeker
09-15-2012, 04:11 PM
Eric,

Great post!

Being a dredger I have always heard that with a dredge you should go for 10% material and 90% and I try to maintain that when dredging to keep from overloading the sluice and it seems to work well for me and my 4" dredge, which would up your figure for a 3" dredge a bit, enough on that though.

I would love to see a diagram of the 2 "circular paths" you post above if you can do a drawing of it to help clarify it in my mind's eye?

Skip

overtheedge
09-15-2012, 06:53 PM
1661
This shows the lateral currents (red arrows) in a hard curve cross-section. I'm not much of an artist.

The hump in the stream surface is grossly exaggerated.
eric

auldrider
09-16-2012, 01:23 AM
I have an area that looks just like that but there is a Y above it where a fine gold bearing stream joins into the slightly larger main stream. (from the left, looking at your diagram)

After the floods have subsided there is a shoal of sand gravel and rocks on that left side and it always gets recharged with fine gold!

Unfortunately not enough to make much money on but certainly is worth it's weight in gold as a learning tool.

The creek then cuts back across to the left side making the shoal a long tear drop shape.

I was washing too much gold barren sand but now,

(thanks to an incredibly kind and sympathetic miner friend from the West Coast)

I am learning to use my pan to tell me which material is bearing gold and which isn't! (I.E. pay streaks)

Unfortunately I am a bit of a slow learner but at least the pan knows more about reading the river than I do!

I think your diagram explains what takes place there during a flood, perfectly!

Thank you for your post Eric. Cheers, John.

overtheedge
09-16-2012, 12:24 PM
Some more thoughts.

The one question that must be answered about streams and there being two lateral currents is, "How does gold entering the stream on one side get to the other side?"

For the answer, we have to look at the hydrology from the gepmorphology angle.

Geomorphology is just the land-shaping process over time.

Streambeds aren't stable and the main channel can and does swing from side to side. It can cut a new channel through what was high ground during periods of severe flooding. It is this swinging back and forth of the main channel that can make what was a right side of stream deposit wind up on the left side.

It is difficult to imagine what happened to the stream several decades ago and attempting to look back several thousand years ago can strain even the most imaginative mind.

One trick I learned a few decades ago was aerial photos. These can be a big help. Even though the old channels may now be covered with vegetation, they are still obvious due to the type of vegetation.

In forest management, there is a term known as forest succession. This is nothing more than what was a bare gravel bar first get vegetated with grass and small brush. After a few years, the taller brush takes over with some of the fast growing hardwoods such as aspen and cottonwood keeping up. After a couple of decades softwoods, such as spruce in Alaska, get strated under the aspen/cotton wood canopy. One the spruce gets high enough, it shades out the hardwoods and the die off.

Each type of vegetation gives an idea of how long the old gravel bar has been high and dry.

If you have access to the complete flight line that the aerial photos were taken on, you can put two adjacent photos together and view the area in stereo. This makes elevation camparisons easy and was an important method for making topographical maps.

If your area doesn't have any aerial photos covering it, you have another option. Hire a small plane and use a digital video camera to film the ground under the flight. Then using a computer, you can grab individual frames from the video and print them. You want to take frames that have a 1/3-1/2 over-lap.

There are cheap stereoscopes available on the market. Some folks can learn the knack of twisting their eyes so they are looking at a distance, but focused up close. I learned how by holding a card vertically between my eyes. Once I focused on the photos, I removed the card and whola, stereo. Another option is crossing your eyes. This makes thing a bit wierd as the lowest ground appears to be the highest. Yeppers, the creeks appear to be perched on top of ridges.
--------------------------
Typically the tenure of flour gold ground is low. Only the best can be mined by the hand miner so we need to use every trick in the book to find the ground with the highest potential.

Our sampling time is limited and labor intensive.

We hand mine because we can't afford the expenses of leaping to earthmoving equipment. If we can keep our enthusiasim and optimism under control, we won't make expensive investments that flour gold deposits can't provide us with a return on our investment.

With today's gold prices, I can almost always stay in beans after expenses. Often enough, I can return home with a couple three pennyweights. Ten years ago, that wasn't happening. Four or five grains was a great day. Now that is a bad day.

I credit a bunch of my sorta success to taking a course in "Physical Geology" at the community college by a practicing geologist. The rest was getting selective with my book purchases. These made me start looking at geomorphology as the key to success. By looking, I mean observing the terrain, watching the river and keeping digital photos taken on most every trip as well as keeping track of water levels.

My best choices for books were:
"The Modern Goldseekers Manual", Tom Bryant (Best I've found on flour gold and recovery)

"Fists Full of Gold", Chris Ralph (Not only a great overview of gold, but Part III, Basic Geology for Prospectors, is the best I've found.)

"The Elusive Pocket Gold of South Western Oregon", Tom Bohmker (Although the book is somewhat site specific, the geologic aspects are definitely need to know.)

"Handbook for the Alaskan Prospector", Ernest Wolff (Again somewhat area specific, there is enough in it to make for months of reading and re-reading. Currently out of print. Hey MIRL at UA Fairbanks, reprint it!!)
eric

Lonetree
09-22-2012, 06:30 AM
Eric,

I think you should write a book. I bet others would have it on their list at the end of post's. I really enjoyed reading this, and think I may have learned something.

Thanks.

overtheedge
09-22-2012, 03:50 PM
There are already plenty of books out there. My posts are just a matter of my interpretation based upon my experiences and the books/posts I've read.

I've thought about writing a book and in the past picked up a few shekels doing technical writing. However to feel more confident with the content, I need to spend a lot more time working a more diverse number of deposits. I'd also need to go back to college to gain more disciplined education on ore and placer deposition.

Another factor that enters into the picture is that as I gain experience, my opinions change (unlike politicians). I contend that once a mind is made up on a subject, the mind is effectively dead.

You might consider doing what I do. I keep copious computer files on the subject and re-read them over and over again. Then I run them through the sieve of my own experience and knowledge base. Often enough some make sense later once I gain more experience.
eric

goldmann
09-23-2012, 01:43 PM
Thank you for the great information. I would like to discuss more about a flour gold recovery highbanker set-up(catching area, etc.). You already said:

All things considered, I think a combo rig(highbanker) is a great choice. It has portability and flexibility. The cost of a new one is still not that high considering gold prices. Fuel economy is reasonable. The only drawback is the sluice bedding/riffle design being so-so at best for flour gold. But I would suggest picking up another riffle tray and modifying it for flour gold. Another option that I used is to remove the tray completely and replace the bedding with rubber mat. I hold it in place with a thumb screw and a piece of that aluminum carpet edge material. I just drill a hole in the sluice bottom and use a thumb screw topside and a wing nut underneath.

There is small(1/2", 1/4", and 3/16") expanded metal over miners moss, the Popandson style, and also the new Gold Hog matting in their highbankers. Some like the lighter-weight plastic highbankers, GMS and G1 for flour gold.

You also mentioned that a dredge is not so good for flour gold recovery because of too much water, and you suggested getting rid of some excess water and also a 2 stage recovery.

I will add Keene has the 3 stage over-under dredge. Also previously Steve H. had a thread on designing a flour gold dredge.

auldrider
09-24-2012, 07:08 PM
Hey there goldman,

all you need is a California Sluice Box GMS and you can catch all the gold you can find!
(zero up to to 3/8 inch at least). Cheers, John.