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Suction dredging over old bucket dredging ground

After some advice about whether or not it is worth suction dredging where the old bucket dredges have worked?
How shallow could the buckets work, did the bother working where the bedrock was close to the surface ?
Did the buckets dig up the bedrock much or just the gravels?
Was the bedrock gold left behind?
Any info on the topic much appreciated, I know the Clutha was packed full of bucket dredges at one point.

Cheers

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Good luck…

In June 1896, the Earnscleugh No. 1 dredge started on a 95 acres area, which had been granted to Charles Weaver, James Kelman, and engineer Alexander Black. The dredge was designed by E. Roberts, built in part by Black’s company, Cossens and Black from Dunedin. The dredge was 27.4 metres long, with 0.76 capacity buckets, and could dredge down to 11.6 metres. H.G. Downie was dredgemaster.

The operation was highly successful in finding gold, and in 1898 the Earnscleugh No. 2 dredge started, with the largest bucket capacity of any dredge in New Zealand at that time. The dredge was 29.8 metres long, with an elevator 21.9 metres long, again in part built by Cossens and Black. It would burn 6 tonnes of coal in a 24 hour period.

The Earnscleugh No. 3 Dredging Company held a neighbouring lease, also with Weaver and Kelman as principal shareholders. The Earnscleugh No. 3 dredge started in 1902. It was 40.2 metres long, with a 36.9 metre long elevator, and could dredge down to 15.2 metres. This company was liquidated, and absorbed by the main Earnscleugh Gold Dredging Company Limited in 1901.

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Dredges we very successful because you could work a huge area with them. With lots, or very little water. You just made a dam big enough to fill in an area, and off you went. In the Yukon they were used 3x over on the same creek and still made money. It would take time. But a large valley with a tiny little creek can still make a huge lake when a dam is made.
You could still make money in some spots. But don’t bother looking to hit bedrock. If they didn’t get it already. Its deeper then you could dredge.

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some dredges only took up gravel and others had a few buckets removed with big hook like rippers attached to break open bedrock.
its all dependant on the deposit as not all gold is on bedrock, many deposits are in layers of ancient gravels ontop of many older barron layers.
the old bucket dredges were nowhere near as efficient as modern technology but had the advantage of cheap running costs and high processing capacity.
the earnscluegh tailings are impressive, l&m were mining adjacent and going down 20+meters to hit the pay layer.

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When I was younger I used to camp down the Roxburgh gorge, met up with old Mr Sanders who owned the orchard at the conflux between the manuherikia and Clutha rivers opposite Alex, back then the manuherikia was a lot lower due to the lack of gravel from tailings upriver. There were rock cliffs at the confluence where when he was young used to hear the banging of the buckets from a dredge digging into it. Seems a bit strange, but I guess they knew what they were doing.

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Great stuff, thank you! Yes makes sense about the depth, I always assumed they needed a fair amount of water, so that’s good to know.
Do you know how they got on in fast flowing water or if there was certain terrain they couldn’t get into?
Cheers

Wow imagine that rock getting ripped. I get the feeling that it could be worthwhile trying a suction dredge in an area that’s been bucket dredged and you could hit bedrock. All the agitation of the gravels would work like a pan and anything missed would work its way down and what was left in the bedrock still there… perhaps.
Amazing, 20 metres, any idea how shallow they would go? 1-2 metres? Wouldn’t seem worth it?
Cheers

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On some of the bigger rivers you can dredge right beside the dredge tailings and get good gold. But deeper then 2 meters and your wasting time. The high flow keeps new gravels moving. And with it comes fine gold. Enough you wouldnt want to waste time digging a deep hole.

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Good old Roxburgh, my Dad owned the bottom pub there many moons ago. Sounds like they ripped up a lot of rock with those beasts, that’s good to know. I was actually wondering about how much higher the Kawerau and the Clutha rose when they filled up Lake Dunstan. It would have had a similar effect to tailings?
Cheers

I remember dredging with another forum member a few years ago , we were working side x side and working a shallow layer one of us decided to go a little deeper to see what was down there , only a foot or so deeper it was discovered we were actually directly ontop of old mullock piles or tailings the rocks all stacked up under us , didn’t even have any sediment amongst it , gold on top was worth dredging.

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Wow yeah that’s really interesting. I suppose it would be pretty clean. Flood gold on the top was it? Thanks :+1:

Be interesting to know if the old bucket dredges hit the bottom at earnscleugh ,i was involved in the last project there which was pretty cool to be involved in,at one point when they went through McPherson road they would have had to have been 30m depth at least,you could see the different layers of heavy gravels in the pit walls.5-7m of wash and they needed at least 20 ounces a day just to cover costs.

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There is some info on dredging in NZ in the following book that may be of interest to you https://www.dropbox.com/s/lbeovd6xy7zqw19/Gold%20Dredging%201908%20-%20Longridge.pdf?dl=0

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@Julian thanks for the share. That’s some old skool dredging, though still relevant to the like of Tony Beets!

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Awesome, yeah I bet that was an experience! Makes you wonder how much has been left behind that they couldn’t reach…

Thanks mate, will have a look at that!