Constructing a dredge hot water system
Nov 14, 2008 9:02:26 GMT 12
Post by RKC on Nov 14, 2008 9:02:26 GMT 12
From: RKCNZ Sent: 15/01/2008 2:33 p.m.
G'day,
I also find it difficult to envisage any dredging situation where it would be worth making a dredge so wide that a triple-sluice box could fit between the floats ... with the only aim being to get the box lower to the water level. The resulting 'very wide' dredge would be very difficult to navigate around most rivers and the drag on such a dredge would be significant ... the dredge would always require good securing, especially in fast water, and each move of the dredge would be difficult and time consuming and probably require two or more men.
The Precision dredges (particularly the 10" Precision img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/nzgoldZ_006.jpg dredge, shown on the Kalamath river in California ) are all "large" dredges, and they need to be to accommodate such features as a diffuser that is of optimal size. However, the Precision dredges are nevertheless reasonably simple to move around a river as they are a 'narrow' dredge (and are designed with that particularly in mind). And, even being narrow, they are stable as all the weight is kept low with all parts positioned as close to the water level as possible. Precision dredges are the 'longest' production dredges that have been manufactured, however, in most rivers, the width of a dredge has much more of an impact on maneuverability than length.
There is no doubt the triple-sluices are an excellent design for good recovery of fine gold ... nevertheless, its a design that will probably not be seen on any Production dredges in future (the only exception I can think of might be if stream tin was to be dredged). The major problem that will prevent them being used in future is that 'if' the box is designed to provide the maximum possible fine gold recovery, then the resulting dredge would of necessity be a massive size. An example is the Dave McCracken designed triple img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/promackdredge_002.jpg
that was sold in the ... I think, the 1980s. His dredge must have had excellent fine gold recovery ... but at a price (the "price" being the size of the dredge). Any triples designed to be any more compact would start to have gold loss. And the more comprised the design the more the loss of fine gold would increase. Any design of a triple should have as its main aim to get the fines into the side box's (once any gold gets in a triples side box's its not going anywhere else).
This img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/website_002.jpg was a great 6" triple which had brilliant fine gold recovery. I suspect the defining factor in the design, which gave it such good fine gold recovery, was the use of a diffuser to feed into the box. The diffuser had probably positioning much of the gold on the bottom and as it entered the sluice the gold would have easily gone through the screen, then along the slick plate, and then into the side box's where it would not move any more due to the reduced velocity of water flow.
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).
I'm very much still involved with dredging, and detecting is more of a sideline. Detecting, particularly in New Zealand, is becoming more interesting all the time with the improvements in the technology that are occurring, and are about to occur, and I'm detecting at present (going after float with my Goldquest SS V2).
There are interesting developments about to happen for commercial scale (Production) dredging in Third World countries (unfortunately the same can't be said to be about to happen in New Zealand unless the regulations are significantly changed to better facilitate dredging). And its only now that eductor/suction/eductor dredges are being considered by mining companies and investors as a serious mining method that can produce profits and good returns on investment. Much of the work Lubo has done over the last 20 years in PNG to demonstrate the potential of dredging has been a significant contributor to this change. And the final trigger we have all been expecting for a long time, that is now about to get it all going, is the recent sustained rise in the price of gold!
Regards,
Rob (RKC)
G'day,
I also find it difficult to envisage any dredging situation where it would be worth making a dredge so wide that a triple-sluice box could fit between the floats ... with the only aim being to get the box lower to the water level. The resulting 'very wide' dredge would be very difficult to navigate around most rivers and the drag on such a dredge would be significant ... the dredge would always require good securing, especially in fast water, and each move of the dredge would be difficult and time consuming and probably require two or more men.
The Precision dredges (particularly the 10" Precision img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/nzgoldZ_006.jpg dredge, shown on the Kalamath river in California ) are all "large" dredges, and they need to be to accommodate such features as a diffuser that is of optimal size. However, the Precision dredges are nevertheless reasonably simple to move around a river as they are a 'narrow' dredge (and are designed with that particularly in mind). And, even being narrow, they are stable as all the weight is kept low with all parts positioned as close to the water level as possible. Precision dredges are the 'longest' production dredges that have been manufactured, however, in most rivers, the width of a dredge has much more of an impact on maneuverability than length.
There is no doubt the triple-sluices are an excellent design for good recovery of fine gold ... nevertheless, its a design that will probably not be seen on any Production dredges in future (the only exception I can think of might be if stream tin was to be dredged). The major problem that will prevent them being used in future is that 'if' the box is designed to provide the maximum possible fine gold recovery, then the resulting dredge would of necessity be a massive size. An example is the Dave McCracken designed triple img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/promackdredge_002.jpg
that was sold in the ... I think, the 1980s. His dredge must have had excellent fine gold recovery ... but at a price (the "price" being the size of the dredge). Any triples designed to be any more compact would start to have gold loss. And the more comprised the design the more the loss of fine gold would increase. Any design of a triple should have as its main aim to get the fines into the side box's (once any gold gets in a triples side box's its not going anywhere else).
This img.photobucket.com/albums/v172/Coochee/Eductor%20dredges%20and%20equipment/website_002.jpg was a great 6" triple which had brilliant fine gold recovery. I suspect the defining factor in the design, which gave it such good fine gold recovery, was the use of a diffuser to feed into the box. The diffuser had probably positioning much of the gold on the bottom and as it entered the sluice the gold would have easily gone through the screen, then along the slick plate, and then into the side box's where it would not move any more due to the reduced velocity of water flow.
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).
I'm very much still involved with dredging, and detecting is more of a sideline. Detecting, particularly in New Zealand, is becoming more interesting all the time with the improvements in the technology that are occurring, and are about to occur, and I'm detecting at present (going after float with my Goldquest SS V2).
There are interesting developments about to happen for commercial scale (Production) dredging in Third World countries (unfortunately the same can't be said to be about to happen in New Zealand unless the regulations are significantly changed to better facilitate dredging). And its only now that eductor/suction/eductor dredges are being considered by mining companies and investors as a serious mining method that can produce profits and good returns on investment. Much of the work Lubo has done over the last 20 years in PNG to demonstrate the potential of dredging has been a significant contributor to this change. And the final trigger we have all been expecting for a long time, that is now about to get it all going, is the recent sustained rise in the price of gold!
Regards,
Rob (RKC)