Stamp Mill
Dry Stamping
The
process of “dry” stamp milling was used back in the day with some different applications.
I first heard of this while working with the folks in Philipsburg, Montana on
their 5-stamp mill. They mentioned that some of the mines in the area used a
system called “dry stamping”. They said that with this process they did not add
water to the ore when it was put through the stamp mill. At the time I thought
that the process was hard to visualize, since without water there would be a large
amount of dust produced and how did they get the crusher ore out of the mortar
box?
I
forgot about this until just recently and it came to mind again. I talked with
the folks at the World Mining Museum and Montana Tech, in Butte, Montana. They
did not know much about the process. I called the stamp mill crew at
Philipsburg and one individuals said that he had some information on the
process. This was about silver mining in Virginia City, NV and the Bonanza
King. There is also a book that talked about the process called Taggert
Handbook of mining devices that has information on dry milling. All of the
above contacts and information did not help me to better understand the process
I
got with the folks again at Philipsburg and they did some additional research on
the “dry stamping” process. This time I received the following information that
was taken from the government report on the mines, geology and mills of the
Philipsburg Quadrangle by W.H. Emmons and F.C. Caulkins USGA Professional Report #78, dated 1913, on field work completed in 1906 to 1907.
This proved to be more understandable and the following is a synopsis of this
1913 report. This starts with treatment of various silver ores, basic dry
stamping process and the actual process used in some of the mines situated in
the Philipsburg quadrangle.
Treatment of Silver Ores
Stamp Milling Processes
The following was information extracted
from the above document, the first being under the topic of “Treatment of
Silver Ores”. According to the report there were (3) different
processes used to remove silver from the ore. They were Washoe, Reese River and
the Combination Process. The processes were used based on the makeup of the ore
as follows:
Washoe Process This process used wet
stamps, settling reservoirs, silver pans and settlers. This ore had
very little sulphides therefore no need for roasting and the process could be
done wet.
Reese River process This
used a dryer going to dry stamping, chloridizing roasters, cooling floor,
silver pans and settlers. There were high sulphides in this ore therefore the
need for dry roasting and dry stamping.
Combination process This
process used both of the above methods. The ore was of a nature that it could
be separated by passing it through vanners and then going through the roasting
process and the settling process in parallel paths.
We will consider the Reese River process since it was
used at the Granite Mines in the Philipsburg, Montana location. This is the dry
stamping process. This process utilized two locations to complete the silver
removal process. The first location was the Granite Mountain Mine where the ore
was mined and concentrated. The second part of the process was the Bimetallic
Mill where the ore concentrates were stamped, processed and the silver removed
from the ore.
Basic Dry
Stamping Process
Philipsburg Reese River
Process
Before I go into the actual process I think it is worth while to identify the components of the process.
Jaw Crusher Crushing The ore was crushed at the mine by (3)
9” by15” Blake Jaw crushers. The ore was sent to the mill via a tramway that
was about 1 ½ miles from the mine. The material was stored in ore bins.
Salt Addition They added about 10% salt to the mixture
in the bins. This changes the sulfide ore to a chloride ore that will
amalgamate readily with mercury.
Drying Process The ore was passed through (4)
Howell-White dryers using producer gas for fuel.
Stamp Mill Crushing The ore was fed automatically to (20)
5-stamp mill batteries where it was crushed “dry” and passed through 20-mesh
screens and collected in bins along with the dust.
Dust Collection The dry crushing produced a lot of
dust. The dust was collected by a device designed by Louis Bailey that was a
large V-shaped trough closed at the top and running above the batteries the length
of the mill. This would trap the dust particles and blowers would direct it to the bins on
the outlet of the batteries. The lighter materials suspended in air would be
directed to the roaster stack using a rotary exhaust fan.
Ore Roasting The material was transported from the outlet
of the stamp mills via screw conveyors, then raised via bucket elevators to
Stetefeldt roasting furnaces. This furnace is a shaft through which the
powdered ore falls. Heat is supplied by gas flame at the bottom of the shaft.
This is where the chloritizing reactions take place where the stamp mill outlet
and the dust chambers come together.
Amalgamation The pulp is amalgamated (mercury) in
pans for a period of time.
Separation The amalgam and tailings are separated
and the recovered amalgam is then passed through to the retort plant where the
metal was separated from the mercury and melted into bars. This was then sent
to the smelter for refinement and the mercury recycled back into the process.
Granite Mountain Mine
Concentrator
Process
The ore was processed at two sites. It
was sent from the mine to the concentrator where it was processed, removing the
waste rock from the ore so that they could transport less via the tramway to
the stamp mill about 1 ½ miles away. Once they completed
the primary crushing with gyratory and jaw crushers they separated the
concentrates down into course, fine and slimes. The fines went to the Wilfley
tables and the course went to rolls and the Chilean mill and the slimes went to
the setting tanks.
The final concentrates were sent to settling tanks and
then transported to the Bimetallic Mill. The drawing below was taken from the Emmons and F.C. Caulkins Report referenced above.
Bimetallic Dry Stamping Mill
Dry Stamping Process
The processed ore
concentrates was transported 1 ½ miles via a Bleichert two wire tramway to the
stamp mill.
The concentrates were dumped into bins and salt added
to the ore.
The material was then automatically fed into the (20)
stamp mill batteries where it was crushed down to a fine powder.
The ore was then fed into the roasting furnaces, cooled
down and then transported into the settlers.
Finally, the concentrates were placed into retorts and
the mercury boiled off and re-used. The silver was then send to the refinery. The drawing below was taken from the Emmons and F.C. Caulkins Report referenced above.
THE END
