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About Subsurface Gold Dredges - 6/24/99
Water conditions are now
at peak spring melt levels, as warming temperatures melt snowfields and
glaciers at higher elevations. There is certainly dredging to be had, but
I prefer to just play around this time of year, and wait for the water to
settle. It is a good time for moving equipment around, and to prospect and
metal detect. It is also a good time to do those household chores!
The drive from Anchorage to
Crow Creek Mine on the Seward Highway is a spectacular one. On one side
of the road is Turnagain Arm, a glacial fjord. On the other side, cliffs
rise into the Chugach Mountains. There area is rich in wildlife; beluga
whales and even a rare orca (killer whale) are seen in the Arm. Eagles are
common, and the mountains are dotted with Dall Sheep, mountain goats, and
bears. So it was that on this drive I had a chance to stop and take pictures
of a Dall Sheep next to the road, with a lamb perched on the cliff above.
Dall Sheep and lamb in Chugach Mountains
I've been packing my 6"
dredge out of Crow Creek Mine, where it has resided for the last couple
of years. I've decided to sell the 6", and downsize to a 5" dredge.
The 6" has been a very good unit for me, but recent regulatory changes
in Alaska have made me decide to go to a smaller dredge. All dredges in
Alaska must have an EPA permit. Dredges with a 4" nozzle opening and
smaller require a free permit with a simple set of requirements. A more
stringent permit, with reporting requirements, has been required of dredges
with a nozzle opening larger than 4". Keep in mind that a typical 5"
dredge, so designated by the manufacturers because of the hose size, usually
has a nozzle opening of 4" to prevent clogs, and so would be designated
a 4" dredge under these permits.
As if it was not bad enough that larger
dredges had a more stringent permit requirement, the EPA permit for dredges
with a larger than 4" nozzle opening (the Medium Dredge permit) has
expired as of June 30, 1999. This General Permit has not been replaced,
and so now anyone wishing to use a dredge with a larger than 4" nozzle
opening is in for a major permitting process. An Alaska Placer Mining Application
(APMA) must be applied for. There is a $100 permit fee. This permit is reviewed
by ALL applicable State and Federal agencies and is subject to public review
and comment. It is advisable to file this permit no less than 6 months in
advance; a year is even better. You must provide a detailed Plan of Operations,
and you can expect the agencies to add additional requirements to whatever
plan you submit. 2012 Update: Dredges with a less than
a 6" nozzle opening are now considered "small dredges" and
fall under a general permit with no special cost or reporting requirements.
But as always, check for the latest rules.
A process of this sort
may be appropriate for a full-time, large scale dredging operation. It certainly
is not for casual, weekend miners such as myself. The worst part of it is
that if you wish to move to a new site, you must go through the whole process
all over again. I've avoided the issue by restricting my nozzle on my 6"
dredge to 4", which has made it a wonderfully non-clogging dredge,
and allows me to operate under the EPA Small Dredge permit. Ultimately,
however, I am carrying more equipment than I need, as a 5" dredge with
a 4" nozzle will move nearly as much as a 6" dredge with a 4"
nozzle, as long as care is taken to not clog the hose. I plan to use a 5"
subsurface dredge. My dual 5.5HP engine 6" weighs about 400 pounds.
A single 5.5HP powered 5" subsurface will only weigh about 150 pounds
and will burn one-half the gas as the 6". I'll move about the same
yardage, but at a higher percentage of gold loss per yard. In the areas
I work, however, I feel the loss will be acceptable, when I consider packing
250 lbs. less equipment into remote sites. Add to that a reduction of 50%
in fuel, and I'll save my back a lot of work!
5" Subsurface dredge on inflatable pontoons
The pictures above are of a unit I built and
used last fall on my claims on Mills Creek. It uses a 5.5HP Honda pump,
running into a 5" suction nozzle that pushes the material back through
15' of 5" hose to the underwater sluice box. I liked the light weight
of the inflatable pontoons floats, but I am worried about them abrading
against rocks and sinking, so I plan to go to marlex floatation this year.
The recovery system/sluice box on a subsurface dredge is underwater, with
a riffle area about 8" wide by 24" long. The fact that you are
not lifting the material above the surface of the water is what keeps the
horsepower requirement small, which cuts the weight and expense of the dredge
considerably. I have used these units often in the past, and am very happy
with subsurface units in general. I plan to use the 5" subsurface on
Crow Creek in the future. I have another, even smaller 4" subsurface
that I plan on using at Mills Creek this year.
Subsurface dredges have a higher gold loss than most surface units, but
are MUCH lighter. A 5" subsurface dredge can be built that is as light
as a 3" surface dredge and with the same pump. While it may have a
higher percentage of gold loss per yard moved than the 3", the 5"
will move 2-3 times as much material. The final result is that you will
normally get more gold by the end of the day with a 5" subsurface than
a 3" surface dredge. In areas with fine gold, and higher loss rates,
the difference will not be as dramatic. In fact, in areas with extremely
fine gold, the 5" may even get less gold even though more material
is moved, as the loss rate can be very high on extremely fine, flaky gold.
In areas with coarse gold, the 5" subsurface will get 2-3 times more
gold as the 3" surface unit, as the loss rate on coarser gold is negligible.
I frequent areas with coarser gold, and that tend to require a lot of backpacking,
so the subsurface dredge is a great way to go for me.
I spent part the day packing more equipment out of the canyon. I'm doing
it a few loads at a time, and then spending the rest of the day playing.
I wandered up the creek metal detecting and hit the area that I had found
on my last trip up to the mine. No dramatic new results, just more small
nuggets. A couple of hours detecting netted me 19 little nuggets, totaling
exactly one pennyweight (1/20th troy ounce). At some point I will have to
hit this area hard for a full days work to see what I can get. For now,
however, it is simply a nice way to work in the morning packing equipment,
and still get a little gold by the end of the day.
19 Little gold nuggets!