(71) Stamp Mill "Dry" Stamping

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