The Northstar Mine Powerhouse & Pelton Wheel Museum [map it]

An exhibit of hundreds of mining artifacts, including a working Stamp Mill and Cornish Pump, the largest Pelton Wheel ever constructed

A Guided Tour Through The Mining Museum
Compiled from notes by Glenn Jones.

No county in the Gold Country is more intimately connected with all aspects of gold mining than Nevada County. Here some of the earliest placer mining took place, here much of the hydraulic mining was practiced, and here deep quartz mining was started. Today, the placers are all but worked out, hydraulic mining was virtually forbidden in 1884 and the last of the deep quartz mines closed down in 1959. With gold advancing from $34 per ounce to over $400 per ounce, a number of small mines are now in operation. The equipment of the mines was sold or vanished in other ways. But for the efforts of some far-seeing citizens, such as Arthur Dowdell, former assayer of the Empire mine, only the foundations of former buildings from the mines or the immense chasms, left by the hydraulic operations, would remind one of the former great industries of Nevada County.

Arthur Dowdell collected a large number of objects relating to gold mining, which he presented to the Nevada County Historical Society in 1968. These objects formed the nucleus of the first Nevada County Mining Museum, which was opened on Mill Street, Grass Valley in that year.


10933 Allison Ranch Road,
Grass Valley CA 95945
located at the south end of Mill Street,
Grass Valley, California
Open Wed-Sat 11-5, Sun 12-4 (May 1-Oct 31)
Winter: closed (Nov 1-Apr 30)


Pelton Wheel
In 1959, one of the most important relics from mining days, the 30 feet diameter Pelton wheel, which formerly supplied air used for power to the North Star mine, was rescued from the scrap heap through the efforts of Mrs. Phebe Cartwright, who conducted a vigorous campaign to "save the wheel." The wheel was presented to the Historical Society by Mrs. Cartwright's committee and an acre of land, including the remains of the old North Star mine power house, were donated by the New Verde Mining Company.

Formerly, there were three Pelton wheels in the power house. The first of these was 18 feet in diameter and was used to provide power for the Stockbridge mine, which was located very near the power house.

When it was found that the power developed here was more than adequate for the Stockbridge, it was decided to provide power for the North S tar in the same manner. Some of the early Pelton wheels were made of wood with metal buckets. An example of such a wheel, originally from the Davis mine, is shown in the museum. Such wheels were not very satisfactory; it was very difficult to keep the buckets tight on the wheel since large forces were at work.

In 1970, the collection of mining artifacts was transferred from the Mill Street museum to the power house: the beginning of the present museum. At that time, the Pelton wheel was not enclosed; many photographs show the museum in this state. At a later time, the building was completely enclosed to protect the wheel and the other artifacts from the weather.

The Grass Valley Mining Museum is the most complete one, illustrating hard rock mining, in the Gold Country. This eminence was made possible by the generosity of Mr. Dowdell and many others who donated artifacts. But of equal importance are the many hours of hard work, donated by its director and his helpers, without their work, the museum could never have become what you see now.

In this article, some of the museum's exhibits will be pictured and described. Some others already have been described in former Bulletins of the Historical Society, and will therefore be only mentioned in this text. Still available issues of the Bulletin of the Nevada County Historical Society, which are of mining interest, are: Oct. 1956 and Sept. 1964 (Hydraulic mining); April 1961 (The Pelton waterwheel), to be seen in the museum; May 1961 and May 1963 (The Empire Mine); Nov. 1963 (The North Star Power plant), the present building of the museum; Oct. 1968 (The Mining Museum at Mill Street); April 1979 (The Cornish pump outside the building)


Pelton Wheel


Underground, there was an entire world. One entered through a shaft, which was either inclined or vertical. From the shaft sprung horizontal tunnels, or drifts, if they went up and did not surface, araise. Various levels in the mine were connected by non-surfacing shafts, called winzes. The shafts and the drifts were fairly narrow, but at some places, where the actual ore was recovered, there were larger areas, called stopes.
Shafts were made by blasting and removing the debris by hand. Around the middle thirties, the engineers at the Idaho Maryland decided to produce a shaft by boring. A shaft, made this way would have many advantages, among them smooth walls. They constructed a cylindrical drill, 5 feet in diameter, and successfully bored a shaft, 1125 feet deep. Inside this cylindrical drill, a core was formed, which was removed piece by piece. A part of this core can be seen outside the museum. Although it was claimed that this experiment was successful, the method was apparently not widely adopted. A discussion of this experiment will be found in the NCHS Bulletin for February 1962.


Man Skips
The miners descended into the mine in a man skip, one of which is seen outside the museum. At the right of the museum entrance is a picture of miners, entering the No. 1 shaft of the Idaho Maryland mine in this skip. This shaft entered the mine at an angle of 72 degrees and had a depth of 1500 feet; the descent took about two minutes. The men were sitting on removable seats, putting their legs over the shoulders of the man below. The seats were removable so that the skip could be used for timber or other supplies for the mine.
The man skips and ore cars moved in the mines on rails. These rails extended outside the mine on a huge frame, the head frame. Behind the large Pelton wheel, there is a model of such a head frame, on which the rails are arranged in such a way that the ore cars automatically dump when they arrive at the top. The museum also has a large drawing of the head frame of the North Star Mine.
All movement in the mine was controlled by a man in the hoist house on the surface. He was signaled by bells to lower or raise the ore cars. Signals were standard in all California mines.
Under the head frame were the ore bins in which the good ore was stored. Waste material which did not contain gold was rejected at this point as much as possible.


Cornish Pump
One of the biggest problems in mines was the removal of water. This problem limited the depth of the early mines for a long time, until the Cornish pump was introduced. This was actually a pumping system; a way to drive numerous pumps inside the mine. The surface part of the Cornish pump at the Sneath Clay mine is now installed outside the museum and is the largest, operational Cornish Pump in the United States. A discussion of the Cornish pump is found in the NCHS Bulletin for April 1979.
The Cornish pumps were driven by steam engines or by Pelton wheels. The Pelton wheel, patented in 1880, became an important power source when wood, needed for stoking the boilers of the steam engines, became scarce. The invention of the Pelton wheel is described in the NCHS Bulletin for April 1961. Back of the museum, one can see two surface pumps which came from the Golden Center mine. They are plunger pumps, each with three cylinders.We will now follow the miners underground. The first tunnel display shows two miners, drilling holes in which black powder for blasting will be inserted. The exhibit shows single and double jack drills, picks and shovels used at the site. Light was provided by candles, held by candle picks stuck in the wall. Later carbide lamps were used. The miner who is kneeling wears a Cornish miner's cap; it served mainly to keep his head clean.
While drilling, the hole filled with debris which had to be taken out at regular intervals to keep the drill from jamming. This was done by means of the long rods, called spoons, of which a number are shown.
The next tunnel display shows a Leyner drill in action. This was an air operated drill which replaced the hand operated drills we saw in the previous display. The drill was served by two hoses, one to provide compressed air for power, the other to provide water to wash the debris out of the hole and incidentally keep the dust down which was always troublesome in the mines.
The third tunnel contains a stoper, a device to drill upwards. It worked very much like the Leyner drill. The people who loaded the ore in the cars were called muckers.
The stoper is called by various names, depending on which part of the country one comes from. In this area it was called a "wiggle tailed stoper." In Montana it was called a "buzzy" and in Arizona a "widow maker." Hence, one could tell where a miner came from by the name he gave to the drill.
The last tunnel display shows an area ready for blasting. The hole pattern shown was drilled for tunneling, for blasting straight ahead.
Occasionally, a former miner will remark that there are too many holes in this wall. However, this display was designed with Empire mine in mind. In this mine, the rock was so hard that additional holes were needed.
The dynamite boxes were opened with wooden mallets and wedges, which are also shown. The poles were used to push the dynamite into the hole. Two kinds of fuses, used to explode the dynamite are also shown.
The rock which had been mined was first sorted underground and again at the head frame. There the valuable ore was dumped over grizzly bars, iron bars spaced at about six inches. Rock which could not pass through the grizzly bars was crushed and dumped on the grizzlies again. From the grizzly, the rock passed into the bins at the head frame.


Stamp Mill
From these bins, the ore was transported to the stamp mills. A bank of stamp mills was a unit of five stamps. Stamp mills were usually built in units of ten stamps. Most mills had an even number of stamps, for example, 80 at the Empire, 40 at the North Star, which were later increased to 60 and 20 each at the Idaho, Brunswick, Golden Center and Pennsylvania mines.
The individual stamps varied in weight, they were usually 850 to 1600 pounds when new; they lost about 100 pounds as the shoes wore down. The stamps at the Empire mine were larger; they weighed 1780 pounds when new. The Empire battery of 80 stamps could crush 400 tons of ore per day.
At another location in the museum there is a working model of a stamp mill.
From these bins, the ore was transported to the stamp mill and fed into the Hendy feeder, from which it was admitted to the mortar box of the stamp mill. The mortar box is the trough in which the stamps operated. The gradual feeding of the ore was controlled by the center stamp.
Inside the mortar box there was a curved piece of silver plated copper which was called a chuck block. Water and mercury were introduced into the mortar box. As each stamp dropped 90 times per minute, there was considerable movement of the water and the mercury. The mercury picked up the gold as it broke loose from the rock, forming an amalgam which attached itself to the chuck block. The amalgam was removed from the mortar box at regular intervals. The amalgam is actually a solution of gold in mercury, similar to the solution of sugar or salt in water.
At the other side of the mortar box there was a screen. The ore was milled in the stamp mill until it had the size of fine sand, fine enough to wash through the screen. The mixture of finely milled ore and water flowed from the screen onto the amalgamation tables. These were covered with silver plated copper sheets which had been treated with mercury by rubbing it into the silver. As the pulp flowed over the table, free gold was picked up by the mercury. The person supervising this process could tell by watching or feeling the amalgam when more mercury should be added to the tables or to the mortar box. The more gold the amalgam absorbs, the firmer it gets. It should have the consistency of putty. If too little mercury was added, the amalgam turned hard and could not be scraped off. In this case it was necessary to burn the plates off and re-silver them, an expensive operation. The trick was to keep the amalgam pliable.
At regular intervals, the plates were scraped with rubber squeegees. The recovered amalgam was brought to the Bullion Room.
Another way to remove the gold from the ore was to pass the pulp over a shaker table. This table had wooden riffles, from which the gold was recovered, just like in a Sluice Box.
Especially rich ore and concentrates were ground in a Berdan pan. This Berdan pan was driven by a 24 inch diameter Pelton wheel, operating at 192 RPM through action of water under a 30 foot head. The pan itself rotated at 20 RPM. The iron balls which performed the grinding weighed 100 pounds each. This pan ground much finer than the stamp mills. The mixture of water and finely ground ore washed over the rim of the pan to be treated at another place in the mine.
The amalgam, collected at various places was put into chamois skins and squeezed until all free mercury had been forced out. The amalgam was then placed in amalgamation boats, which were placed in heavy retorts. Two of such boats, one made of iron and the other made of graphite, can be seen in the museum. A pipe, which led to a condenser, emerged from the lids of these retorts. The amalgam which is after all nothing but a solution of gold in mercury was heated to 700 degrees F. or more. This caused the mercury to vaporize and pass to the condenser where it was condensed to liquid mercury again. This mercury could be used again in the recovery of gold.
The gold left in the retorts was put into a large graphite crucible. Many such crucibles can be seen in the museum. After a flux was added, the crucibles were placed in a furnace and heated to about 2,000 degrees F.


Bullion Room
The gold melted and the impurities with the flux to form a slag which floated on top of the molten gold. In front of the retort was pouring block, on top of which the mold for the gold was placed. One of these can be seen in the museum. The crucibles were removed from the furnace by use of a block and tackle and emptied into the mold. The slag, which floated on top of the liquid gold, overflowed on the pouring block; the gold solidified in the mold as it cooled. The molds came in various sizes, usually 450 or 1000 ounces of gold. After cleaning, the gold bars were ready to be shipped to the mint. Most gold shipped from Grass Valley was 850 to 950 fine.
Untilthe time for shipping, the gold bars were kept in a safe. The bullion safe seen in the museum has two time locks in its door. The gold was shipped to the mint in San Francisco by the Railway Express Office.
Bullion from the Idaho Maryland Mine was shipped to San Francisco by airplane. The Lockheed Electra used for this purpose was the property of Errol Mac Boyle, the owner of the mine. The propeller and a picture of this airplane can be seen in the museum.
The miners were not the only people who worked underground. The mines had to be surveyed; surveying instruments and a large three dimensional model of the Pennsylvania mine, presented to the museum by Newmont Mining, remind us of this. The model clearly shows the gold veins, dipping at an angle of between 30 to 50 degrees. All mines had models picturing their underground world.
Another frequent visitor to the subterranean world was the superintendent. He not only checked the operations, but also collected samples of the ore to have their gold content established. This was done at the assay office.
The assay office exhibit contains most of the equipment used there. An actual assay office however was considerably larger than the area shown here; it contained two or three rooms: one room for grinding, one for melting the ore and one inside room for weighing. The latter room was kept free of air currents as much as possible since the movement of air influenced the accuracy of the scales. Even after someone entered this room, a short time was allowed in order to let the air,
set in motion by the movement of his body, come to rest.
Performing a proper assay required about 20 pounds of rock. After a blast had dislodged a large body of ore, the specimen boss came in to collect samples. He had a special bag to transport them, about 15 inches long and about 6 inches in diameter.
The samples were brought to the assay office and broken up in a grinder to pea size pieces. These pieces were passed through a Jones splitter. This was a series of slots of which one half went in one direction and the other half in another direction. This way, the sample was cut in half. `This was done several times, until the sample was reduced to about one quarter of a pound. The purpose of this was to obtain a sample which represented the average of the original sample as much as possible.
The reduced sample was ground until it had the consistency of com starch; it had to pass a 100 mesh screen. The final grinding was done by hand, either in a mortar and pestle or by using the muller and bucking board. These items can be seen in the exhibit. The muller was a heavy, curved piece of iron with an ax handle, the bucking board a piece of heavy sheet iron.
About one ounce and a half of this finely ground material was accurately weighed out on the pulp balance and put in a crucible. A flux was added. The kind of flux depended on the type of ore to be assayed; it usually contained potash, borax, lead and salt.
The crucibles were put in the furnace and kept there for about one half hour at 2000 degrees F. This way, all the material in the crucible was molten. Subsequently, the crucible tongs and their contents were poured into iron pouring molds. Such a mold consisted of an iron bar or pan, with conical depressions.
In these molds, the lead and gold, the heaviest materials, settled at the bottom and the slag floated on top. When the material had been cooled, the slag was removed with a hammer. The slag was quartz silica; it resembled a poor grade of glass, green in color. The lead-gold cone which was left at the bottom was pounded into a cube with rounded corners so that it did not have sharp corners.
This cube was placed in a bone-ash cupel, a little cup. These cupels were made at the mine. Bone-ash arrived at the mine in barrels. It was mixed with water and forced into molds which had the cupel shape. They were dried for a long time before they could be used. These cupels were placed in a muffle oven where the lead volatized off or was absorbed by the bone-ash, while a small gold bead remained behind. This bead was cleaned and weighed on the assay balance.


Subsequently,the bead was placed in a ceramic parting cup and nitric acid was added. At this point, the bead still contained silver; this silver was dissolved by the nitric acid. The gold was left as a black, spongy mass. This material was washed with distilled water, dried very carefully and heated again. This way, it regained the appearance of normal gold. The resulting bead was weighed and, comparing this weight with the weight of the original bead, it could be determined how much gold and silver there was in the original sample. This again allowed determining how much gold there was in one ton of ore; this was usually expressed as ounces per ton or the dollar value of gold per ton.


In addition to mining equipment, displays, and artifacts, there are displayed articles used by miners
and their families in their homes.
This story by no means mentions everything to see in the museum. We have tried to give an overall picture on the mining operations and of these, the main features are covered. We are happy to have had an opportunity to guide you around and we hope you will come back soon.

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