Dredge under construction
Apr 20, 2009 12:42:14 GMT 12
Post by RKC on Apr 20, 2009 12:42:14 GMT 12
G'day Roscoe,
The river on the left in the photo above is the Clutha, which usually ran reasonably clear. The river on the right is the Kawarau river which is fed from the famous Shotover river. And the Shotover has historically always carried a very high sediment load ... with most of the sediment originating from natural sources such as the soft schist bedrock which is continually being eroded and fed into the flowing river as fine particles. And some sediment comes from the old hydraulic sluicing mines in the Shotover catchment img.photobucket.com/albums/v172/Coochee/NZGOLD/NewImage41.jpg?t=1240184515. Additionally ... at the time the photo was taken there were two trommel plants operating in the Shotover that were introducing more sediment than usual straight into the river.
The junction where these two rivers meet is now still water
img.photobucket.com/albums/v172/Coochee/NZGOLD/JUNE2005016.jpg?t=1240184735
because of a dam built downstream and its now always cloudy. The mines in the photo are now under water, as is the bridge pictured ... also now buried under water is the 600 ounce patch!
The Kawarau river
img.photobucket.com/albums/v172/Coochee/NZGOLD/Richly%20Auriferous%20rivers%20X/feb22_2005034.jpg?t=1240185263
has always been a difficult dredging proposition for modern day dredgers because it runs cloudy most of the time and it has the additional disadvantage of running very fast in most sections (this river has claimed the life of more than one modern day dredger). There have only been a few times when modern dredgers, who use suction dredges, could get in there. One time was in the winter of 1992, when there was an extremely severe winter and there was a freeze up in the high country. Dredgers were then able to get in with a reasonable chance of getting gold only because it ran reasonably clear and ran at a low level reducing the velocity of the water. And some dredgers did well with others getting little. What was particularly interesting that the dredgers learnt during that winter, was that it was found that the best gold was in crevices just below the water line with little gold out toward the center of the river. What the dredgers had found by having their heads underwater in clear water was that the bucket dredges had gone down the center of the river (as you would expect), but because they were such clumsy machines that were difficult to maneuver, they could not turn at an angle to get into the steep crevices at the side of the river. Modern diver-controlled suction dredges are obviously highly manoeuvrable and had no problem getting into these crevices that the bucket dredges could not mine. And the hand miners that preceded the bucket dredges had also been unable to get into these crevices as they were in water too deep for them to venture into and were at too steep an angle for wing dams to be constructed.
Regards,
Rob (RKC)
The river on the left in the photo above is the Clutha, which usually ran reasonably clear. The river on the right is the Kawarau river which is fed from the famous Shotover river. And the Shotover has historically always carried a very high sediment load ... with most of the sediment originating from natural sources such as the soft schist bedrock which is continually being eroded and fed into the flowing river as fine particles. And some sediment comes from the old hydraulic sluicing mines in the Shotover catchment img.photobucket.com/albums/v172/Coochee/NZGOLD/NewImage41.jpg?t=1240184515. Additionally ... at the time the photo was taken there were two trommel plants operating in the Shotover that were introducing more sediment than usual straight into the river.
The junction where these two rivers meet is now still water
img.photobucket.com/albums/v172/Coochee/NZGOLD/JUNE2005016.jpg?t=1240184735
because of a dam built downstream and its now always cloudy. The mines in the photo are now under water, as is the bridge pictured ... also now buried under water is the 600 ounce patch!
The Kawarau river
img.photobucket.com/albums/v172/Coochee/NZGOLD/Richly%20Auriferous%20rivers%20X/feb22_2005034.jpg?t=1240185263
has always been a difficult dredging proposition for modern day dredgers because it runs cloudy most of the time and it has the additional disadvantage of running very fast in most sections (this river has claimed the life of more than one modern day dredger). There have only been a few times when modern dredgers, who use suction dredges, could get in there. One time was in the winter of 1992, when there was an extremely severe winter and there was a freeze up in the high country. Dredgers were then able to get in with a reasonable chance of getting gold only because it ran reasonably clear and ran at a low level reducing the velocity of the water. And some dredgers did well with others getting little. What was particularly interesting that the dredgers learnt during that winter, was that it was found that the best gold was in crevices just below the water line with little gold out toward the center of the river. What the dredgers had found by having their heads underwater in clear water was that the bucket dredges had gone down the center of the river (as you would expect), but because they were such clumsy machines that were difficult to maneuver, they could not turn at an angle to get into the steep crevices at the side of the river. Modern diver-controlled suction dredges are obviously highly manoeuvrable and had no problem getting into these crevices that the bucket dredges could not mine. And the hand miners that preceded the bucket dredges had also been unable to get into these crevices as they were in water too deep for them to venture into and were at too steep an angle for wing dams to be constructed.
Regards,
Rob (RKC)