Hydraulic Riffles ?

[Deleted]

Vaughan

Hope to be up your way next week. Ok if we pop in and take a look at the new beast. Cheers Mark

[aucn]

RKC Had a good trip back home
cannot say enough about the westcoast miners very helpful in showing there gear and all vouch for hydraulic riffles,liked the idea of a boil box at the start of the riffles,
my dredge is getting fabricated and should be ready this coming summer had a lend of a 6 inch keene dredge for a few days from a friend from naseby, worked well but still had some issues with black sand,
could not get hold of dgr to see his dredge next trip maybe?

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[RKC]

G'day aucn,

Good to know your trip went well. No doubt about it, The Coast is great and the Coasters are one of the main reasons that makes The Coast so special. I'm living on The Coast permanently now and I could not think of anywhere else in the world better to live. For example, today I road my motorbike up the coast road from Greymouth to Westport, and a better more enjoyable scenic drive would be hard to find anywhere.

Nice photo of the boil box. Boilboxs have long been used on trommel plants in New Zealand and they are very common here (therefore they must work) . They are also used in many other countries but probably not to the extent they are in the New Zealand mining industry.

smg.photobucket.com/albums/v521/NZGOLD/Excavators%20and%20trommels/NZGOLDnzgold041.jpg

There will always be "issues" with black sand (on a production dredge) in New Zealand's South Island rivers if a dredge has only conventional riffles. In particular, if using a production dredge to dredge a widely dispersed deposit of fine gold from the overburden, then its well worth while going to the trouble of ripping out conventional riffles and replacing them with hydraulic riffles.

Regards,
Rob (RKC)

[aucn]

had great weather ,here is a few photos will put a few on photobucket (aucn) later this week, bit wet here at moment..
cheers ken

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[RKC]

Hydraulic riffles – 1980s research in New Zealand and Canada

www.mine.mn/Robin_Grayson_gold_recovery_method40.pdf

Regards,
Rob (RKC)

[aucn]

rob thanks for that .
at present welding up a set of stainless hydraulic riffles
will be back in oct to fit the dredge out etc..

ken

[Dredger89]

I remember around 20 years ago, perhaps 1989? Seeing an add for a Queensland built clean up Jig, it had a sump that was filled with lead shot, attached to a sump was a spray bar system, like Hydraulic riffles, the water inlet was set to 10PSI. Concentrates were then fed through system, i think it was a 2 pass system first pass pulled out black sands & Gold, second clean gold. I also think 2 different size lead shots were used. I think the unit cost around $1500 or so? I was contemplating building a 4" subsurface dredge using the principle at the time, more of an experiment. Does anyone recall seeing these units?

Rod

[aucn]

have put a few videos of a sluice on photobucket.
i like the double box idea and after using a keene triple
i did not like the idea of restricting the flow to the underbox by cutting down your classification area.
initially set up the sluice to check what size gap is required to restrict the flow to the bottom box
all material pass 5mm sieve except couple flattened buckshot balls

box 150mm wide 1000mm long
60mm in 900mm slope.
underbox is 50mm overall height
restriction gap 13mm and 150mm long
water flows are total 250 l/m
underbox 90 l/m

the interesting one is the ones with just two riffles and how there is a strong backflow up the sluice
any way has given me a few ideas for the sluice set up,
hope it helps someone..
open to constructive criticism
.. if it does not work it is easy to change back to the standard idea..

s446.photobucket.com/albums/qq186/aucn/Building%20the%20Dredge/sluice%20testing/

cheers ken

[RKC]

G'day aucn,

When I first read your post in the hydraulic riffles thread that "(I) have put a few videos of a sluice on photobucket" I thought I would be seeing some videos of hydraulic riffles :-)


I'm not sure how your test sluice box in the videos is configured. But judging from what is visible, it appears to me as if your experimental set-up might be a triple sluice box, or similar, with one of the side box's shown ... with the side box having clear perspex so the reaction of the water flow over the riffles is easily viewable (not sure what you mean by a “double box”). And it appears as if angle iron is used as a type of Hungarian riffles.

In all the videos there is severe boiling occurring between the riffles that would throw any fine gold quickly over each riffle and not allow anything but maybe a few large heavy pieces of gold, to settle. There appears to be far too great a volume of flowing water, and the velocity of the water is way too fast. The aim of diverting the fines into a side box (such as in a conventional triple sluice dredge) is so the fines will be more easily caught because of a reduced velocity and volume of water in a side box, compared to the center box. And it appears as if reversing the direction of the angle iron only makes the problem of the occurring boiling action, much worse. I don't like the idea of using angle iron at all (bent at an angle of 90 degrees), in a dredge sluice box. And you won't see angle iron used in modern dredge sluice box's. The riffles I favour, and the riffles of choice for most dredge builders (when using conventional riffles as opposed to hydraulic riffles), have a slight lip at the top and would be placed at an angle in the box ... with the angle in the direction of the flow of the water (for example: img.photobucket.com/albums/v172/Coochee/OKheaderBoxCCCC1kkkk.jpg?t=1280892976 ). (angle iron in a sluice box img.photobucket.com/albums/v172/Coochee/OKheaderBoxCCCC-1.jpg ). Your aim should be to reduce the volume and velocity of the water flow in a side box as much as possible, with just enough water velocity to keep the rubbish moving through the box so it returns to the river without overloading the box and clogging the riffles. In an experimental set-up the volume of water is easily controlled and does not bear much relation to what will occur when a dredge is working in a river. So, the way to be sure riffles are working is ‘only’ after they have been used in a dredge during a dredging operation where river wash is run through the dredge.


A commonly used method to establish if conventional riffles are working is to look at the box after river gravel has been run through the box in a dredging situation. Upon turning the dredge off, the riffles should show a strip above each riffle with some bare carpet visible (somewhat like this img.photobucket.com/albums/v172/Coochee/Hot%20linked/3672fa87.jpg ). However, because of the massive amounts of heavy black sands found in the auriferous New Zealand South Island waterways, black sand will pack in between each riffle and no carpet will usually be visible ( tinyurl.com/26htmp5 ). The amount of black sand in the South Island waterways make it difficult to easily know if sluice box riffles are working, as it would in a country such as Australia.

I used to experiment with riffles whenever I've built dredges in the past, and when deciding on the space between each riffle I came to the conclusion that I should put the riffles quiet close to each other. The distance I spaced each riffle was much closer than is conventional practice among all dredge builders. But I liked the result after running dredges for some time with close spaced riffles ... just a personal preference that evolved. The riffles on the side box's of this dredge I built ( tinyurl.com/297jkkt ) show the close spaced riffles I prefer. On first sight this dredge would probably appear to be overkill to most dredge builders, and it probably is in the context of building a gold dredge. However, this particular dredge was built for dredging tin, as well as gold. When I did use it for gold there were massive amounts of concentrates to get the gold from ... which was a problem that I could have done without.

When I was recently looking at photos of a dredge manufactured by one of the new dredge manufactures that have appeared in the last few years to cash in on the gold boom, the riffles used in the sluice box were just flat steel strip placed at an angle ( img.photobucket.com/albums/v172/Coochee/sluiceboxflatriffles.jpg )
which is probably an easy riffle for the builder to fabricate, but is not the optimum design and would not catch the fines anywhere near as well as riffles designed the conventional way. Obviously, the reason a design comes to be utilized by the majority of commercial dredge builders is that the design works!

Regards,
Rob (RKC)

[aucn]

thanks rob for a good reply
initially i was only trying to find out what size gap i would need to restrict the flow of water to the bottom box screening to 5mm
i got down to 13mm but thought any smaller could cause blockages
the riffle etc were just an after thought to try
an under and over system with hydraulic riffles at the start are what i am going to try first , riffles will be as you say
just had aluminum angle in the shed..
thanks for the input

ken

[2dredge]

Interesting video of the angle iron riffles. In the past, early 80’s working next to a dredge with angle iron riffles (not modified) it never appeared to retain as much fine gold as conventional riffled dredges.
So Earlier on this year I have been doing some retesting with a side by side testing of three types of recovery systems to see which preformed the best; one of them was based on the angle iron riffles simular to yours. Getting the feed flow, angle, spacing and the height of the riffles including the slope of the ‘box were all very critical for good recovery and clearance (riffles not loading up). The riffles with a backward slope of aprox 15 degrees was about the best so far with a ‘box slope 12 to 15 degrees.
Looking at yours I would say try increasing the slope of the sluice box a lot more so the riffles are just about vertical, repeat Vertical, Backward sloping angle iron riffles are high energy riffles and work best with a fast flow and a steeper slope to make them effective. Probably better in a static plant than a dredge. So far I have been getting some interesting results that need to be followed up from the different riffle systems. So it is back to more testing when I get some time so sorry no results yet. Dr.edger

[aucn]

Hi 2dredge
good to see you sharing bit of info ..always ways to improve
recovery....just hard to get info which is shame a lot of reinventing the wheel then happens...
i initially wanted to just test the size of restriction that i would need to regulate the flow to the bottom box, as with the keene sluice the sliding plate restricts the flow but also decreases the classification area, hence you still get a fair % of fines retained in the top box ..
got down to 13mm where i stopped as if the material was screened to 5mm and was flaggy any smaller and you could get blockages..i was able to regulate the input water to a steady state and the 13mm gap 150mm wide passed 90litres a min
with the pump running normal i got 90litres bottom and 160litres top box.... combined 250litres minute
the picture will show the concept i mean i was more interested in water flow to do away with the restrictor plate as in the keene,
but the shots of the just 2 riffles i found the most important with the backflow running up the sluice for 6 inches, lot of variables to test but most i will test on the full size dredge this summer
and compare with the standard keene dredge..




ken

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[aucn]

finally got some fine weather, over here starting to assemble dredge
here is few photos, hope to have motor ,pump, compressor mounted in next couple weeks if weather is kind to us

cheers ken

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[aucn]

finally got the dredge in the water in jan this year, had problems with the hydraulic riffle setup pump and underbox...went back to a normal sluice .
pleased with the dredge and gold recovered just the river was not helpful this year.. to much water . ... still some modifications and changes to be done for next season .. installing a heat exchanger for hot water..winch..etc and to get on top of hydraulic riffles etc..

posted few photos on photo bucket

s446.photobucket.com/albums/qq186/aucn/?action=view¤t=P1020479.mp4

[RKC]

G'day aucn,

Thanks for posting! Great to see it in action. Your Otago river looks perfect for dredging.

Regards,
Rob (RKC)