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Subsurface Gold Dredge At Mills Creek, Alaska


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Jim I have a four inch Sub Surface dredge and surface dredge. I use both annually.

What I can say is if you are in a area with fine gold and little to no chunky or nugget type stuff and your goal is to maximize the gold weight take home at the end of the day then you need to run a surface dredge. I figure the loss on fine gold is about fifty percent give or take.

Running the two side by side all day I notice the surface dredge is netting a solid 1/4 oz. and the Subbie 1/8 oz. What I see missing from the Sub Surface dredge is the fine gold, there is some but noticeable less, but usually a similar amount of chunky gold.

I have tried to modify the box with classification and grizzly bars but it didn't help and may have been worse off as the box packed up and could not clean out.

One thing I did that worked  is I used the Subbie to move the over burden and a two inch dredge to clean the bedrock cracks. That worked really well. On the days that I did that I found I ended up with more than a 1/4 oz. As odd as it may sound I feel the two inch dredge has the best gold recovery of any size dredge. My two inch is a single stage and the four and six are the triple type. Go figure that one?

The real reason to use a Sub Surface dredge is portability! For a one man dredge operation getting In remote locations or sampling work they just can't be beat by a smaller dredge and a larger size is weight prohibitive.

Also the cost to assemble a four inch Subbie is a lot less than the surface dredge.

I'm curious to hear from the others.

 

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I agree, subbie is good for testing and working where the gold is coarse. My 4" subbie likes to blast out flat flakes 1/16 to 1/8, trust my other 4" much more. A couple things I do is to slow the pump a bit when I see color on bedrock, and empty the box into a bucket about every half hour assuming that helps.

Once running the subbie I apparently sucked up many small flakes without knowing it and when I went to empty the tray I saw a lot of gold in the end of the box and the normal coarse gold in the front. That bothered me so I grabbed a pan, scooped up some tailings and recovered 30 or so flakes in a single pan. I backed up and ran probably no more then a yard of my tailings through the same dredge and found almost an ounce.

What I like my subbie to look like

oP80200052.jpg

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The basic trade is recovery versus portability, but possibly made up for by volume. A subsurface can weigh far less and cost less to build, and employ a smaller motor burning less fuel than the equivalent surface dredge. So for short in and out trips to hard to reach locations they can be great. The longer term the operation, the less sense a subsurface makes.

The volume trick is this. I can use a 6hp pump to make a good 4" surface dredge, or a 5" subsurface about the same size and weight, same fuel consumption. The 4" gets a better recovery per yard, but the 5" can move twice the yards. That means recovery can suffer quite a bit and you still have more gold. If you have the time, get all the gold out of every yard you can. But if you have two weeks a year you might get more gold for your time spent by going for volume, depending on the nature of the deposit. Obviously the coarser the gold the better for a subsurface. If the gold is fine or flat/flaky enough a subsurface could basically just lose all of it - not good.

No real right or wrong here, just different approaches for different situations. I have used subbies a lot and been very happy overall with what I was doing with them. More in depth discussion here.

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I've never really seen one in person. Looks cool. Can u submerge the sluice completely, how's the recovery. I would guess more of a nugget trap.

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