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Post by aucn on Nov 30, 2009 23:08:40 GMT 12
Has any one got any photos of hydraulic riffles on a suction dredge
are they placed under the classifying screen on an over under setup. ?
looking at the possibility of incorporating them on the dredge i am building..
ken
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Post by RKC on Dec 1, 2009 12:48:32 GMT 12
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Post by aucn on Dec 1, 2009 16:40:36 GMT 12
thanks rob this will be for a 6 inch dredge weight will not be much of a factor,
looking for some thing to help in black sand,
can use up to 26 hp for the dredge so should be able to run second pump
we have a bit of black sand on our permit area and I intend to use hydraulic riffles .just after some clues from other dredgers who have tried them..ie
best to have them under a classifier screen
or at the end of the sluice ..etc.
number of riffles etc..
looking at 25X 25 mm stainless and 25mm flat on top as straight riffle..
ken..
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Post by RKC on Dec 1, 2009 19:11:03 GMT 12
G'day Ken; A 6 inch dredge would lend itself well to the use of hydraulic riffles. In fact the dredger I referred to in my previous post had a 6 inch dredge on which he employed hydraulic riffles. I had another go at trying to get the search feature on this forum to work and I think I've found out what I was previously doing wrong. I found a number of my previous posts that mention hydraulic riffles and a copy 'n' past of the posts follow: In my opinion the key to solving the black sand problem is simply to use Hydraulic riffles. And as we all know, just about all of the South Island trommel plants use hydraulic riffles, so its an already well proven method of fine gold recovery (in effect industry best practice).
img.photobucket.com/albums/v521/NZGOLD/Excavators%20and%20trommels/P1010052.jpg?t=1247625391
smg.photobucket.com/albums/v521/NZGOLD/Excavators%20and%20trommels/?action=view¤t=083457.flv
smg.photobucket.com/albums/v521/NZGOLD/Excavators%20and%20trommels/?action=view¤t=083457.
Where the innovation comes in with hydraulic riffles that is of interest to us, would be their use on Production (eductor) dredges. The accumulation of the heavy black sands (which are more abundant in the South Island gold fields than in any other gold field anywhere in the world) in sluice box's is what makes fine gold recovery the major problem it is in New Zealand. And hydraulic riffles are particularly effective in ensuring the fine gold is trapped in a sluice box and do not run over the top of hard packed black sand to go out the end of the sluice box ... but hydraulic riffles do need to be used in conjunction with processes for treating the sluice box concentrates such as removing the magnetic black sand
(such as with one of these
img.photobucket.com/albums/v172/Coochee/magneticseperator.jpg?t=1247626680 )
before running the concentrates through something like a Gemini table
img.photobucket.com/albums/v172/Coochee/table2.jpg?t=124762658
or
img.photobucket.com/albums/v172/Coochee/table.jpg?t=1247626644
Pause Hydraulic riffles
img.photobucket.com/albums/v172/Coochee/blksand.jpg?t=1247626828
Hydraulic riffles
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/P1010GreyX138.jpg?t=1247629834
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/P101011gold5.jpg?t=1247629889
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/goldgold005.jpg?t=1247629928
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/goldgoldZZS011.jpg?t=1247629955
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/d58c893f.jpg?t=1247630011
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/4715dc6b.jpg?t=1247630035
Hydraulic riffles on a production dredge
img.photobucket.com/albums/v521/NZGOLD/NZ%20Hydraulic%20riffles/d80276d0.jpg?t=1247630062
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Attaching the motor to the dredge frame will only help with the problem of the black sand packing between the riffles and will not solve the problem completely. Only you can make the decision whether it is something worth doing and forgoing the advantage of having your motor on the riverbank. Hammy used to always place his motor on the river bank when he was in the small streams of Otago. And in such small streams it can be a considerable advantage to do this.
Hydraulic riffles have only previously been used on the larger production dredges (such as 8") and to employ hydraulic riffles you would need significant upgrading of dredge components such as pumps. And, in my opinion, you are already underpowered.
I would strongly suggest that you just work with what you have ... for now. The season is upon us and its time to get in the water. The best classroom is in the river, doing it. There are bound to be some mechanical problems arise with your dredge and you need to be doing some dredging for the problems to become aparent so they can be fixed.
Put it this way ... with the dredge you have you will get more fines than you would if you were using a Suitcase dredge, but would be getting less than if you were using a big dredge with hydraulic riffles installed. And using a bigger dredge would introduce other problems such as a lack of portability ... swings and roundabouts.
The dredge I used in the Arrow when I got the 50 ounces, I also lost a lot of the fines ... but I still got reasonable gold. In fact I had a reminder of the amount of fines I was losing when I went back to where I had dredged the Arrow in the previous season, and while I was dredging to try and find where I had finished up the previous season, I dredged into my old tailings. And on getting to bedrock I could see fine gold sprinkled around on bedrock glittering like a Christmas tree back at me. It was all gold that had gone through my dredge and the spring floods had then sieved the gold through the lose tailings until all those small specks stopped moving when they got to bedrock. If I had not dredged up the gold I saw, the gold would have been moved again by following floods to move further downstream where it would have collected and concentrated in traps such as bedrock crevices. (Actually, what I found when dredging the Arrow is that chunky gold collected in spots on bedrock that were clay like. The clay held the gold like glue. This was in areas that had not been dredged previously and what would happen is that I could dredge for hours and not see anything, and then come across a patch of bedrock that was clay. And in an area of only say a foot or so square there would be about a quarter ounce or more of visible chunky pieces of gold nuggets ... not necessarly in a crevice but just in a patch of bedrock that was clay. Something else worth noting is that in the Arrow a rusty red wash is always worth investigating. The rusty red wash has something to do with how the miners of the 1800s hand worked the ground.)
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You have come across the most significant impediment that presents itself to Kiwi dredgers which makes fine gold recovery extremely difficult from South Island rivers.
Its great that you have recognized the problem first time out. Most Kiwi dredgers of the past have not even acknowledged the problem as significant because their experience has been limited to dredging in New Zealand and they have had nothing to compare the black sands they have seen, with. But those of us who have dredged in other countries knew of the problem from the very first time we dredged a New Zealand river. My educated guess would be that the heavy black sands that are found in such massive quantities in the South Island rivers are in much greater quantity than in any other country ... anywhere! Because of this problem a very different approach needs to be taken to dredging in New Zealand's South Island (I'm referring to production dredging, recreational dredging is a different proposition as some gold loss is generally more acceptable to a hobbyist).
The solution is to use Hydraulic riffles in a sluice box. But ... hydraulic riffles are not all that practical for installing on a small portable dredge. A dredge can easily be built with hydraulic riffles installed, but it would then be a large dredge (essentially a production dredge).
tinyurl.com/4tenwu
If you increase the angle of your sluice box you will start to lose more of the fines. The problem is the packing of the black sand between the riffles that do not allow the fines to go to bottom and much of the fine gold will sail down the sluice box over the black sand and back into the river.
Its worth mentioning here that because of the abundant black sands in New Zealand South Island rivers, subsurface dredges are even more useless in New Zealand than they are in other countries. Otago rivers that have been dredged by Suitcase dredges (probably even the river you are to dredge) have a great deal of fine gold remaining. The remaining gold has gone straight through the Suitcase dredges and has sat in the rivers waiting for someone to come along with a surface dredge. One spot I dredged on the Arrow river, I got over 50 ounces from, and all but about 10 or 11 ounces of chunky gold that came from one small area, was fine gold that had gone straight through Suitcase dredges.
There have been some previous references to the black sand problem on the GDF and following are some references I have found from previous posts.
From:Re: Constructing a dredge hot water system
« Result #3 on Nov 14, 2008, 9:05am »
When designing a sluice box for use in Otago you need to be aware that the massive quantities of black sand in all Otago rivers (and to only a slightly lesser extent in other auriferous rivers of the South Island) necessitates an innovative approach to sluice box design if the intention is to aim to capture fine gold in 'payable' quantities from a 'production' dredge.
A conventional sluice box with standard Hungarian riffles will clog with black sand in minutes when dredging in any Otago river (these examples
img.photobucket.com/albums/v172/Coochee/Hot%20linked/728b398a.jpg
img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/nzgoldB_013.jpg?t=1229728756
are from the Arrow river) and pack solid. Much of the fine gold then travels straight down the sluice box and back into the river. (This example
img.photobucket.com/albums/v172/Coochee/Hot%20linked/3672fa87.jpg
is from a Nth Queensland river and dramatically shows the difference between a river with just some black sand -- which is most auriferous rivers throughout the world -- and a river with massive amounts of the stuff.)
Re: Dredge under construction
« Result #5 on Nov 12, 2008, 1:03pm »
It’s a significant advantage to have the sluice box vibrate, as vibration aids gold recovery.
Having a sluice box vibrate is probably not as important to a dredger who intends to dredge rivers with little black sand as it would be to any New Zealand dredgers who dredge the South Island rivers that carry massive amounts of the heavy black sands which clog a sluice box.
The heavy black sands found in New Zealand ’s South Island rivers will fill the space between each riffle and prevent the riffles working as intended. However, the vibration from the motor agitates the black sand to allow gold to sink down into the carpet under the riffles (what occurs is similar, but not quiet as efficient, as using hydraulic riffles in a dredge sluice box). Without the vibration, the black sand would tend to pack solid and much of the gold would jump riffles until it reaches the end of the sluice box and is returned to the river.
Its important that any dredges with conventional riffles, that are to be used in New Zealand ’s South Island rivers, have the motor directly bolted to the dredge frame without any damping added. If a motor and pump is separated from the dredge (as it is on the NZ Suitcase dredge) the problem of the dredge riffles packing solid will result, and gold recovery would be significantly impaired.
Please note: I'm not saying that there is no vibration if the dredge motor is not attached directly to the frame, I'm just saying that vibration is reduced.
Re: Building a small dredge
« Result #1 on Nov 15, 2008, 9:12am »
Achieving an acceptable 90% fine gold recovery with a dredge that's designed to be portable, is difficult ... especially if the dredge is used in Otago where the abundant heavy black sands
img.photobucket.com/albums/v172/C....pg?t=1224453122
will clog a sluice box with conventional Hungarian riffles. However for the sake of portability some loss of gold would probably be acceptable to most beginner dredgers. The inclusion of hydraulic riffles on a dredge is the main way known to professional Kiwi dredgers to dramatically improve fine gold recovery when dredging in areas of abundant heavy black sands. However hydraulic riffles are not a practical option to use on a portable dredge as the design would be complicated and the whole dredge would have to be much bigger and heavier. Hydraulic riffles are therefore only for use on Production dredges.
The usual way for a beginner to get a bad start in dredging is to purchase a dredge thats a dog. And most beginners do start with a dredge that is useless or near useless ... I did, as my first dredge was the 4-inch Goldstriker subsurface dredge. The main problem that results from buying a dredge that's a dog is that it then puts most beginners off dredging altogether ... which is unfortunate as when a well designed dredge is used nothing beats dredging as a profitable and interesting means of getting gold (especially in New Zealand which has an abundance of rich auriferous waterways).
A portable 5-inch dredge such as I have described above would inevitably be priced more than what has been offered to beginner dredgers in New Zealand previously, however the difference would be that such a dredge would actually do the job. Also, there would not be a market among experienced dredgers for such a dredge, because experienced dredgers nearly always make their own dredges. And the inexperienced would probably think the dredge is overpriced and far too large as they would be comparing it with other dredges they have seen advertised. So ... it probably won't happen, and beginners will continue to throw their money away, and give up on dredging. When using a dog of a dredge beginners spend most of their time, when they should be learning how to dredge, fighting the dredge. The answer might be for someone to import quality dredge parts, such as dredge pumps, which would then allow people to put their own dredge together.
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Achieving an acceptable 90% fine gold recovery with a dredge that's designed to be portable, is difficult ... especially if the dredge is used in Otago where the abundant heavy black sands
img.photobucket.com/albums/v172/C....pg?t=1224453122
will clog a sluice box with conventional hungarian riffles. However for the sake of portability some loss of gold would probably be acceptable to most beginner dredgers. The inclusion of hydraulic riffles on a dredge is the main way known to professional Kiwi dredgers to dramatically improve fine gold recovery when dredging in areas of abundant heavy black sands. However hydraulic riffles are not a practical option to use on a portable dredge as the design would be complicated and the whole dredge would have to be much bigger and heavier. Hydraulic riffles are therefore only for use on Production dredges.
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The trend in New Zealand for some time now has been away from triples to using a single sluice box. There are however still a few Kiwi dredgers who prefer triples, and there is an Otago miner presently constructing a 7” triple. The design he is utilizing is fairly conventional, with the only innovative feature the use of hydraulic riffles in the sluice boxes. I’ve been advising him on the construction of the hydraulic riffles and when he has it finished I’ll try to get some photos to post in my Photobucket album in the Hydraulic riffles folder. (We had some discussion whether it was worth using hydraulic riffles in the side boxes as well as the center box, and my suggestion was to use convention riffles in the side boxes. But, he is going to try both).
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So, a single sluice box with either a diffuser feeding the box, or a precisely designed header box, is a better overall choice for a Production dredge. And in New Zealand, particularly Otago, where heavy black sands are in abundance (more so than anywhere else in the world) the replacement of standard riffles with hydraulic riffles can dramatically improve fine gold recovery (I'm not sure an over-under box would be suitable in New Zealand as my guess would be that it would quickly clog with the ever present heavy black sands).
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The heavy black sands found in New Zealand ’s South Island rivers will fill the space between each riffle and prevent the riffles working as intended. However, the vibration from the motor agitates the black sand to allow gold to sink down into the carpet under the riffles (what occurs is similar, but not quiet as efficient, as using hydraulic riffles in a dredge sluice box). Without the vibration, the black sand would tend to pack solid and much of the gold would jump riffles until it reaches the end of the sluice box and is returned to the river.
Its important that any dredges with conventional riffles, that are to be used in New Zealand ’s South Island rivers, have the motor directly bolted to the dredge frame without any damping added. If a motor and pump is separated from the dredge (as it is on the NZ Suitcase dredge) the problem of the dredge riffles packing solid will result, and gold recovery would be significantly impaired.
Please note: I'm not saying that there is no vibration if the dredge motor is not attached directly to the frame, I'm just saying that vibration is reduced.
--------------------------------------------------------------------------------------------------------Regards, Rob (RKC) |
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Post by aucn on Dec 1, 2009 22:02:41 GMT 12
Thanks rob i will definitely be incorporating
them in the dredge i am building
have a p355s keene pump for the jet and got 6 roper floats from indac for a good price i hope they should be enough to float everything
if not will add few more ;D
cheers ken
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Post by RKC on Dec 2, 2009 8:28:19 GMT 12
G'day Ken,
I would be interested to know how you go with the Roper floats. My experence with Indac floats is limited to the pontoon floats (which are an excellent product) exclusively and I would particularly like to know if the Roper floats are a good substitution for the pontoon floats.
Correction: I just remember this morning that the Kiwi dredge I refered to above that used hydraulic riffles was an 8 inch not a 6 inch as I first thought.
Regards,
Rob (RKC)
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Post by dgr on Dec 2, 2009 19:15:21 GMT 12
Ken / Rob
The Keene 355s is a mighty pump and you will need some Hp to get over top of it, should drive a 6 and some riffles on its ear.
Im just about to float my new dredge but was wondering if anyone new what pressure to run Hydraulics at.. ive gone with 1.5mm holes but recommend running a inline filter to screen out larger particles as once they are in a Hyd Riffle system they are hard to get out..
Any suggestions would be appreciated
Cheers
Vaughan
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Post by RKC on Dec 2, 2009 19:55:27 GMT 12
G'day Vaughan,
In Lindsay Herron's patent there is no mention of what pressure to run the riffles at and my guess would be that its not all that critical. If you find there is too much pressure maybe you could put a valve between the pump and the riffles to control the flow to the riffles (and thus reduce the pressure). There is a 6 inch dredge presently working an Otago river that has hydraulic riffles and I'll attempt to find out how well its proving to be and if he has had any problems. Hopefully I will be able to get him to send me some photos.
Great idea to run a filter!
Regards,
Rob (RKC)
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Post by boaraxa on Dec 2, 2009 20:30:35 GMT 12
hi aucn i was reading how your useing roper floats how are you going to attach them to your frame?
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Post by aucn on Dec 2, 2009 21:15:41 GMT 12
boaraxa , 50mm stainless strap with threaded stainless rod on the end,
will wrap around the floats recesses in place, on top 50mm aluminum
angle across the top and a length box section down each side of the floats 4.2 meters..
3 floats each side 2 straps per float. hope this explains..
ken
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Post by aucn on Dec 2, 2009 21:33:27 GMT 12
remember reading something about 4psi
this would depend a lot on your sand size
will be putting a pressure gauge on mine,
a filter is a must,
will have a dredge through some stuff i have and see if i can find it,
would love to look at your dredge dgr be over in six weeks,
think Alaskan mines dept have some test work on the riffles..
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Post by RKC on Dec 3, 2009 11:12:41 GMT 12
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Post by dgr on Dec 3, 2009 12:56:43 GMT 12
Ken
Your more than welcome to have a look at the dredge , will be having sea trials end of next week hopefully.
What part ofe the country you planning on operating your dredge.
Will post some photos shortly, just finishing off the trailer.
Cheers
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Post by aucn on Dec 3, 2009 16:33:49 GMT 12
dgr have pm
rob think that might have been the report , see they had 10 psi setting
so it looks like pressure is reasonable low for the riffles
bit of trail and error i would say,
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Deleted
Deleted Member
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Post by Deleted on Dec 4, 2009 15:22:07 GMT 12
Wouldnt the pressure be dependent on the size,shape and quantity of blacksands and the same with the gold. I know having worked both the Buller and the Lower Clutha that both are different the Buller gold being extremely flat and the Clutha blacksands being very fine. I would have a gauge and be experimenting. I still put a lot of faith in the new style of keenes 3in 1 box. We stole the idea and the gold retrieved was far far finer than we ever got with any triple no matter how big/wide/ riffle system. Heres to a season of yellow boxes whatever the type. Cheers Mark
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