Test # 97
High Velocity – Medium to Low Turbulence, Black Beach Sands Gold Extraction
1- Pre-test outline.
2- Video of the actual test and clean ups.
3- Some of Doc's notes from post test.
Problem / Question/ Objective
One of the most difficult materials to extract gold from is black beach sand
deposits. Gold LOSSES for most prospectors / miners can range from 30 –
with most sluice / equipment setups. Our goal is to run bare mats and get
recovery rates into the 80 - 90% range. However, we want to accomplish this
recovery rate at a higher sediment rate / feed rate without any manual
Thanks to Mike Pung from the
Cube for sharing some of their loss rate
testing results on a variety of equipment.
Current Observations and Hypothesis
Black sand deposits on waterways and beaches are created due to the SD
(specific density / weight) of the black sand in comparison to the lighter
quartz sands. Water and wind easily move the quartz sands, ranging in the
2-3 SD (specific density) range, while the black sand often ranges in the
4.5 – 6 SD Range. This leaves a concentration of “heavies” containing
mostly fine gold. (In the 50 – 200 mesh range.)
When water and the BS (Black Sands) material are mixed,
it becomes a slurry and enters the sluice. However our observations have
indicated that this slurry quickly transitions from a sediment / suspended
load, into a bed load. As soon as the slurry starts to travel down the
sluice, settling rates are very high for all (most) of the material
contained within and the majority of the material enters into a bed load
stage. This bed load stage puts / forces most of the material into the
lower 20% of the water depth or in other words, it is all riding / moving
along the bottom.
(One additional known trait is that most of the "black
sand", as well as the gold, is very fine as well.)
This bottom / bed load overload overfills and overloads
the capture zones of riffles, matting grooves, expanded metal, and other
“capture zones” / exchange zones that would normal be very active and
exchanging. Because the gold is very fine, most miners tend to fear creating
turbulence and are afraid of too much velocity (water speed). This fear of
losing gold more than likely creates a reduced processing time within the
incremental processing patterns down the sluice.
This reduced incremental processing pattern and reduced
exchange activity keeps the “gold holding zones” loaded with heavy bed load
deposits and allows both gold and other heavies to ride down the sluice
unprocessed / never captured.
Our Objectives / Testing Patterns...
We believe that through a series of gentle lifting and falling patterns, we
can keep the capture zones more open, have the gold fall first, and keep
these exchange areas more actively exchanging, and retain capture rates
above 80% on FIRST RUN material with no screen less than 1/2".
Again... a KEY factor of this test is high sediment /
feed rates. 2.5 gallons per 30 seconds is our approximate target goal. This
will represent / replicate one person shoveling non-stop and equal about 2
tons per hour.
At different points in the sluice water speed will vary. Water near the top
will have less energy and be slower. It typically increases throughout the
sluice run and we will be noting changes in this variance during the run.
This is usually a VERY positive aspect of running a longer sluice.
Type of gold...
Many areas that have black beach sands also have what we call "seismic or
pressured" flat gold. This gold is very flat due to exposure to extreme
pressures, movements, glacial and seismic activity. This "flat gold" has a
low settling velocity and is prone to "flip" down a sluice. the material we
will be using has this gold in it, plus we will be adding a large amount of
gold, about 1/2 of which is this "flat gold".
Notes for set up and running:
1-We will be running a Viper highbanker.
2-Mat pattern will be Scrubber / Razorback / Riverhog and this
will be repeated throughout the sluice.
3-Riverhog main riffle will be removed / cut down and almost
level with the lifting ramp.
4-Pitch will be set at 7.5 degrees and may be adjusted in the
field based on visual inspection.
5-GPH on the 12” sluice will be approximately 6000 GPH
6-Feed rate will set at approximately between 70 – 100 lbs per
minute or roughly 2.5 tons per hour.
7-Black sand from the west coast will be used.
8-Approximately 6 grams of gold will be seeded into the sand.
All this gold ranges between 50 mesh and 200 mesh.
9-Known amount of seeded gold is irrelevant to the results as
the base test material already contains some gold. Also losses due
to shoveling, spilling, etc. will skew any know measurements taken.
The results will be based on weight of the gold captured in the
sluice vs. gold found in the tailings.
11- All the tailings will be captured and run through the gold
Working up the testing material.
New mat being made at the shop for Doc's unit.
Gold being screened through 50 mesh.
We pulled about 6 grams of the 21 you see here.
Post test notes from Doc...
-I wouldn't mind trying a bit of UR and Bedrock
as the last two mats near the end. Water speed was good and they
might do well there.
-Natural gold was present in the dirt we received
as well as the seeded gold. I was happy to see the unit pulled that
gold as well. Found a bunch of gold in the 150-200 range.
-New side flaps on the Viper were just awesome. No
water off the sides. Permanent change to the unit for production.
-Pitch on the unit was about 7.5 degrees. I think
that was about right. No need for adjustment. Water flow was pretty
-Most of the gold was in the first 40% of the
sluice. However, incremental exchange rate was definitely slower
with the black sand.
-Gold Cube did a great job, but we did run very
slow. When we ran the Viper cons through, about one quart, we did
see some losses. However, they were minimal. the Vortex mat did
struggle a bit with exchanging fine black sand. I think the Cube
would run better at 1500 gph (vs. the 1100 stock pump) on black
sands to reduce the bed load drag on exchange. I would like to see a
line of almost pure gold at the top, followed by black sand and
gold. I'll run that test next month.
-New punch plate at the top, under reverse riffle,
did GREAT. calmed down the water. I am recommending we make that
change to production.
-Losses by weight... about 3/4 of a grain was in
the losses. approx 110 grains in the mats. I did NOT finish panning
out the Viper cons, just too much time. Probably another 5-10 grains
still in the cons easy.
-Losses by count... We easily caught 40,000 pieces
of visible gold. Estimated loss count was around 150 pieces.