Yukon innovation increases gold recovery for placer miners

http://www.yukoncollege.yk.ca/research/post/yukon_innovation_increases_gold_recovery_for_placer_miners
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November 17, 2014

Yukon is home to a new innovation that has the potential to benefit placer miners around the world. Randy Clarkson, of Klondike Placer Miners’ Association has developed a simple method of removing fine gold particles from difficult concentrates in an economical, lucrative and environmentally-friendly way.

After two years of research, prototype development and field testing, Clarkson is able to upgrade difficult gold concentrates by taking advantage of the malleability of gold. This technique uses a small rod mill to grind the brittle waste minerals to powder in a few minutes while only flattening gold particles. The ground slurry is then washed through a fine screen capturing the flattened and polished gold particles.

“This method allows us to recover fine gold particles from labor intensive concentrates that are normally considered a waste to time, and apparently a waste of gold”, said Randy Clarkson, P.Eng., Klondike Placer Miner Association. “This technique recovered between 5 and 10 ounces of gold per day of testing this summer at a profit of over $5,000 per day – from concentrates that would normally be left behind”, said Clarkson.

Many Yukon placer miners have been storing these difficult concentrates on site in coffee cans, peanut butter jars and other containers for years waiting for an efficient method of upgrading to be developed. Previously the concentrates would have to be sorted by hand, one by one, a tedious and very time consuming process.

“This simple but effective method of separating gold particles from galena particles using a small rod mill and screens has allowed me to process concentrates that I have had in storage for some time. I didn’t want to throw them out because they still have gold in them and I don’t have the time to hand sort each particle”, said Claus Barchen, a placer miner from Mayo.

The procedure has been tested on many types of gold concentrates including those with high density minerals such as galena (mineral containing lead), cassiterite (tin), hematite (iron), illmenite (iron) and pyrite (fool’s gold) as well as more durable minerals such as garnet (used in sandpaper). The cleaned concentrates are generally 97% or purer native gold and are suitable for direct sale to a gold buyer.

The small rod mill can also be used to grind up gold furnace slag to recover any lost gold from smelting and to regrind concentrates which have become cemented together due to oxidation of the contained minerals. A small rod mill can be fabricated locally using a piece of steel pipe, rolled rods and an adapted portable cement mixer for a total cost of less than $2000.

A small shaking table with a magnetic separator (~$3500) was also demonstrated to pre-concentrate the difficult gold concentrates prior to grinding (if desired) and to separate out magnetic material such as magnetite and bits of iron more quickly than with hand magnets.

The concentration process does not use any chemicals or substances harmful to the environment and would have applications in any placer or hard rock gold mine using gravity recovery techniques such as sluiceboxes or centrifugal concentrators. It could also be used in the developing world at artisanal mines to help eliminate any harmful chemicals used to upgrade gold concentrates.

Clarkson will be making this technique available to all placer miners through a final report which will be available at the KPMA office and on the Yukon Geological Survey Website. This summer, a number of placer miners used this technique with great success. Clarkson will not be commercializing this innovation as he intends to share his work with those who will benefit. He will also be demonstrating the technique and equipment at the Placer Geoscience Forum on Sunday, November 16th at the Gold Rush Inn and later in the week at the Geoscience Trade Show.

The research was funded by contributions from CanNor's Strategic Investments in Northern Economic Development Program, Economic Development’s Strategic Industries Development Fund, the Cold Climate Innovation of the Yukon Research Centre at Yukon College, and the Klondike Placer Miners’ Association. The KPMA would like to thank the funding agencies and all the miners that participated in the research program.

Background -Yukon Placer Mines
Placer mining has been a cornerstone of the Yukon’s economy and culture since the great Klondike Gold Rush of 1898. Placer mining is responsible for the accelerated early development of northwestern Canada. The industry has been the Yukon’s most reliable generator of economic wealth and has continued unabated through the great depression of the 1930’s and recent economic recessions. In recent years placer mines were the only operating mines in the Yukon.

Currently there are over 100 family based placer mines with a combined gross income in excess of $60 million annually. Spin off benefits to the local economy are in the order of 2.5 times that amount with local labor, purchases of fuel, equipment, parts, groceries and other supplies. Placer mining is especially vital in the Yukon’s rural areas including Dawson, Mayo and Haines Junction. Most of the recent “gold rush” (2010-2012 with total annual exploration at $150 to $300 million) to explore for lode gold mines is based on the presence of placer mining in those areas.

Typical placer mines range from small Mom and Dad operations to those employing a dozen workers and several of the largest available sizes of heavy equipment. Placer mines are heavy equipment intensive resource industries. The next greatest concentration of large scale heavy equipment (D11 bulldozers) would be found several hundreds of kilometers southeast in the Alberta oil sands mega projects.

Background - Placer Gold
Placer gold ranges in size from finer than 74 microns (200 mesh) to coarse nuggets depending on the source of the gold, size and gradient of the stream and many other factors. Sluiceboxes are the primary means of concentrating the low grade alluvial gravels and can provide relatively efficient concentration (in excess of 95% recovery efficiencies) at high ratios of concentration (20,000:1).

These primary sluicebox concentrates must be upgraded to a purer saleable product. Secondary concentration methods generally include long toms (small sluices), hydraulic jigs, hand panning, hand-held magnets and hand sorting. Many of the secondary concentration methods are very labor intensive, arduous and result in some gold losses. Often the tailings from secondary concentrates are stored in buckets for years awaiting time-consuming hand sorting methods. Extended periods of hand sorting of gold concentrates also pose a security risk to placer miners.

In recent years due to the depletion of higher grade reserves and due to higher gold prices, the industry has focused on mining and processing lower grade deposits (side pay), deposits with fine gold and other accessory minerals, and on reprocessing tailings from previous operations.

As mining has progressed in the Klondike, the placer industry in Yukon is faced with lower grade ground and areas with fine gold and with reprocessing tailings to recover gold that was lost in previous mining eras. Many of the sluicebox concentrates contain very fine -74 micron, -200 mesh) flattened particles in a mixture of high density minerals such as galena, hematite, illmenite, magnetite, scheelite, wolframite, cassiterite, pyrites and phyrhotites.

Separation of both the coarser >1 mm and fine <150 micron particles can be tedious and problematic. Generally the coarser gold sizes are hand-picked. Magnetic minerals such as magnetite and tramp iron are removed with hand held magnets. In the Yukon and Alaska, the finer gold particles are processed in small sluices, concentrating tables and gold wheels, often with gold losses.

on my dry blower I found the use of rare earth magnets usefull in minimising some of the magnetite-black sands etc prior to getting caught in the riffle trays.

u need to keep the magnets relatively clean for them to work efficiently.

I usually find 2 rare earth magnets per tray will do the job.

interesting article and hopefully will get to see some pics down the track.

If we can get one of these universities on side to refine the dry blower then a whole new ball game will open up.

regards
oneday

bit of a different way of tackling the problem eh Ray, would need to be a pretty fine sieve to get the flour gold

CONSIDERING WE USE 100 mesh cloth on the dry blowers..the dam stuff would just about float off into thin air..

regards
oneday

Good on Randy Clarkson for coming up with something so simple and so good.

http://yukon-news.com/business/new-gizmo-could-help-placer-miners-snag-lost-gold/



another link here...http://www.whitehorsestar.com/News/tool-could-help-miners-cash-in-coffee-can-gold

Clarkson explains in an interview this week the traditional sluice box will generally turn 20,000 cubic metres of paydirt into one cubic metre of concentrate.

Miners use an array of methods to recover somewhere between 70 and 80 per cent of the gold from that one cubic metre, whether it be a smaller and specialized sluice, a gold wheel, shaking table....

But it’s that 20 or 30 per cent of gold that is too fine to be recovered with conventional methods, even too fine to be captured by traditional hand panning, he says.

Alistair Maitland/Yukon News
p27BIZplacerminer1.jpg
Randy Clarkson, executive director of the Klondike Placer Miners' Association, at his home in Mary Lake. Clarkson invented a prototype rod mill that would allow placer miners to easily separate fine gold particles from waste minerals.


Randy Clarkson doesn’t know how his homemade rod mill wasn’t invented long ago.

But he can predict with certainty it’ll be found at every Yukon placer mine within the next five years.

“It’s too cheap, simple and easy to use,” he said.

An engineer by trade, Clarkson has spent the past two years working on a prototype to allow placer miners to separate fine gold particles from difficult concentrates.

Clarkson, the executive director of the Klondike Placer Miners’ Association, gave a demonstration of his invention at last week’s Geoscience Forum.

He’s been in the field since 1985, working on upgrading sluice box efficiency and conducting research in the Amazonian jungle and elsewhere in South America.

Placer miners may pass many cubic metres of gravel through a sluice box, a process that usually recuperates between 70 to 80 per cent of the gold.

Sluice boxes help separate gold from dirt using barriers called riffles. The riffles catch the heavier gold, while lighter rocks are washed away.

Sluices in the Klondike are often pretty quick, Clarkson said, and can process 50 to 200 cubic metres of gravel per hour.

Once or twice a week, miners clean out the equipment and come up with about a cubic metre of sluice box concentrate, from which they can no longer separate the gold unless they do it by hand - a tedious and time consuming process.

There’s quite a bit of gold in that sluice box concentrate but miners can’t sell it, Clarkson said, because it’s not pure enough.

That’s why placer miners have been storing the concentrate away in coffee pots and peanut butter containers, waiting for the right equipment to come along to be able to separate the gold from it.


Alistair Maitland/Yukon News
p27BIZplacerminer2.jpg
Clarkson’s prototype rod mill is comprised of a cement mixer, pulleys and small steel rods.


Although the gold weighs more than heavy minerals, the particles are flat, making it much harder to separate.

The particles vary in size but can be as fine as 50 microns, or 0.05 millimetres.

That’s where Clarkson’s simple invention comes in, to get the other 20 to 30 per cent of gold that was missed.

This time last year, Clarkson and a colleague at the University of Fairbanks in Alaska were ready to throw in the towel.

“We were at our wit’s end,” Clarkson said.

Then they hit a breakthrough and came up with the idea of using a rod mill, which has been around for hundreds of years.

In this case, the rod mill is a steel tumbler, small enough to be moved on a dolly, that’s partly filled with 20-cm steel rods. Concentrate is put inside, and as the tumbler turns, the rods inside grind any rock into dust and flatten any bits of gold.

Through trial and error, they eventually realized the mill had to contain approximately 1 to 1.5 kilograms of concentrate and rotate at 70 revolutions per minute for it to effectively work.

The minerals and gold are put into the rod mill with a small amount of water, and ground between six and 10 minutes.

“Then you just take this ground up paste and put it through a fine sieve and the gold sits on top.”

After that, it’s easy to recover the gold using a shaking table.

By the end of the process, about 99 per cent of the gold that was missed has been recovered.

The invention was tested over the summer by placer miners around the territory and yielded successful results.

“This technique recovered between five and 10 ounces of gold per day of testing this summer at a profit of $5,000 per day - from concentrates that would normally be left behind,” said Clarkson.






Gold is extremely malleable and can be flattened extensively, Clarkson said, referring to gold-plated ruins in the Middle East.

“They look impressive but there isn’t a heck of a lot of gold because it can be hammered so thin.”

It costs under $2,000 to put together Clarkson’s invention, using a cement mixer, pulleys and small steel rods.

He said he’s been asked to build four of them and is helping other placer miners build their own.

He has no plans to commercialize the design, however.

“You could, but that’s not the idea because all my life I’ve done research for placer mining and I’ve always made it available publicly,” he said.

“Usually there’s been some component of public funding involved so that’s the whole idea - if you spend public money it should be available to the public.”

The rod mill could work separating other minerals such as platinum and lead, Clarkson said, and might also be useful in the developing world where they’ve been using cyanide and mercury to separate gold.

He said he would be publishing a research paper on his findings, which will be published on the Yukon Geological Survey website, among other places.

The next step would be to improve the rod mill and turn it into a continuous, rather than batch, process.

“Someone else can look at that,” he said with a laugh.

Contact Myles Dolphin at

myles@yukon-news.com

now we just gotta get Albo to get the idea to continuously flow..

get yah dancing shoes on young fella, and skip dede do dah..

regards
oneday

doesn't a ball mill do exactly the same--only they use steel balls to pulverise everything then cyanide leach the gold,

maybe a knudson concentrator would do the same?

just throwing it out there.

regards
oneday

i think Clarksons idea is to flatten the partical, like a rolling pin to flatten the pastry. Droppin ball's of steel onto pastry will eventually break the lump/partical into smaller pieces, flatning them with rollers would broaden the surface area makin it easier to be caught in the screen/mesh. no cyanide/c.i.p, no licence, needed.
Think thats the idea anyway. just throwin it back.  
As he said, "When you crush the granular material, it turns to dust. When you crush the gold, it flattens out."

she the type that would like to tag along I reckon..just kidding..

mmm i'll have to have a go with the rolling pin action next time I get some dirt.

with the tub angled at about 25' one would have thought the concentrated dirt would simply go to the bottom and congeal.

maybe have to do some more reading.

regards
oneday

just found some more readin for ya uncle, got pictures too.    It shows how particals are folded and slip threw the mesh when coming from a ball mill,... I think for this way of recovery for ultra fines has Huge potential.
The bucket of rods is operated level, pics explain so read on, haha, now you got somethin else to make.  
Sizeable fraction
flattened, settled on
coarser sieve than
starting size

Grind high density
middling cons just
until gangue
pulverized,
flattening/preserving
gold

Use ductile nature of
gold and brittle
nature of gangue

http://www.geology.gov.yk.ca/pdf/141114_Nov1014_Grinding_for_Gold_Presentation.pdf

thanks Flyin Kiwi for postin subject.