Part 5

Before 1875 the supply of water was obtained from creeks on the eastern slope of the mountains lying east of Lake Tahoe, but in the year named, the water company pushed their main supply flumes through to Marlette Lake, which lies inside of the Tahoe basin. To do this it was necessary to run a tunnel 3,000 feet in length through the dividing ridge, or rim, of the Tahoe basin. The sheet of water known as Marlette Lake is almost entirely artificial, and owes its existence to a big dam—is in reality a large reservoir. The water covers an area of over 300 acres, and in the middle is about 40 feet deep. The reservoir holds 16,000,000,000 gallons of water.

The second pipe was laid under the supervision of Capt. J. B. Overton, Superintendent of the works of the water company, who also extended the flumes, constructed the tunnel through the mountain ridge, and made all the other improvements. In 1887 a third iron pipe of twelve inches inside diameter was laid across the valley alongside the first two. It was also a welded pipe and delivers much more water than either of the others. The inlet pressure has been raised on all three pipes, and they now deliver a total flow of about 10,000,000 gallons in twenty-four hours. In 1887, also, a branch flume was run to the northward (Marlette Lake lying to the southward) a distance of nine miles, which taps a number of creeks tributary to Lake Tahoe on the east and northeast sides. In the same year a reservoir capable of holding 20,000,000 gallons was constructed on Hobart Creek, on the east side of the dividing ridge. In and near the city are reservoirs holding from 3,000,000 to 10,000,000 gallons, and a number of tanks along the side of Mount Davidson of from 60,000 to 80,000 gallons, capacity. The water is brought a distance of from twenty-five to thirty-seven miles, and the supply (aided by the several storage reservoirs) is ample for all present uses. The total cost of the works of the company has been about $2,500,000. Each of the three pipes has its separate inlet and outlet, from two flumes and into two flumes. Between the outlet and the city the water passes through a large storage reservoir.

The Sutro Tunnel.

While there was a scarcity of water on the surface at Virginia City, there was a superabundance of it, both hot and cold, under-ground in all the mines. Levels were flooded so suddenly that oftentimes the miners narrowly escaped being drowned by the vast subterranean reservoirs that were unexpectedly tapped. Great delays in mining were caused by these floods, and to pump out the water that filled the lower levels cost immense amounts of money. Several tunnels from 1,000 to 5,000 feet in length were run into the mountain, but they were of only temporary utility, as the shafts of the mines were soon below their level. In order to overcome these water troubles, Adolph Sutro early conceived the idea of running an immense drain tunnel under the Comstock Lode from the lowest possible point. A survey was made by Mr. H. Schussler, and work was commenced on the great drain tunnel (since known as the Sutro Tunnel) October 19, 1869. It starts at the edge of the valley of the Carson River, at a point nearly east of Virginia City, and has a length of 20,145 feet—nearly 4 miles. It taps the central parts of the Comstock Lode at a depth of about 1,650 feet. The tunnel is 16 feet wide and 12 feet high. Drain flumes are sunk in the floor and over these are two tracks for horse-cars. It required nearly eight years to construct the tunnel, and the total cost was about $4,500,000. Although the leading mines had their shafts down nearly 3,000 feet before the tunnel was finished, yet it was of great use, as it saved 1,600 feet of pumping.

From the main tunnel branches were run north and south along the east side of the vein for a distance of over two miles, with which the several companies connected by drain drifts from their mines. The flow of water through the tunnel has at times been over 10,000,000 gallons in twenty-four hours. Between the mouth of the tunnel and the Carson River there are 155 feet of fall, but it has never been utilized for driving reduction works. New connections are still being made with the tunnel for drainage. Though it never paid anything near what was anticipated by Mr. Sutro, the tunnel still brings in a snug sum annually. Last year (the fiscal year that ended February 29, 1888) the receipts for royalties amounted to $237,258.33. It costs a considerable amount annually to keep the main tunnel and branches in repair. This great drain at a depth of 1,600 feet below the surface allows of Pelton water wheels being set up in the shafts of the several mines and worked under immense pressure, there being a free discharge from the wheels. At the C and C shaft of the Consolidated California and Virginia, such wheels have been put in every 500 feet from the surface down to the Sutro Tunnel level. The water used on the first wheel on the surface, in the stamp-mill, is caught up, led to the shaft, and used on the second 500 feet below, and so on down to the tunnel level, the power being brought from wheel to wheel to the surface by means of a system of steel wire cables. Thus is transmitted to the surface the power developed by the whole series of wheels.

The Reduction Works of the Early Days.

In the early days the building of quartz-mills kept pace with the building up of the towns. As early as October, 1859, Logan & Holmes had a four-stamp horse-power mill in operation at Dayton, and Hastings & Woodworth had two water-power arastras at work, which reduced six tons of ore a day. This ore was not worked as silver ore. It was from the surface of the Comstock Lode, at Gold Hill, and was worked for gold only. In the spring of 1860 many mills for working silver ore began to be erected.

The First Silver Mill.

The first silver-mill that went into operation was the “Pioneer,” erected by Almarin B. Paul, on Gold Canyon, at the north end of Silver City, just below the Devil’s Gate. It was a steam mill and contained twenty-four Howland rotary stamps and twenty-four amalgamating pans. The work of erecting the mill was commenced May 24, 1860, and it began work August 13, the same year. Some others have claimed the honor of starting the first quartz-mill in Nevada, but this was undoubtedly the first silver-mill. In it were operated the first silver amalgamating pans ever seen anywhere. The iron amalgamating pans were the result of experiments made by Almarin B. Paul before he began the erection of his mill. He thought the German barrel process and Mexican patio too slow, and began to make experiments with some small iron pans that had been in use at some of the quartz-mills in California for grinding and working the sulphurets saved by concentrating machines in working the quartz of the gold mines. The best of these was found to be the “Knox Improved Pan,” in which was a false bottom that formed beneath the pan a steam-tight heating chamber. By the use of this kind of pan, and by treating the heated pulp with certain quantities of salt, sulphate of copper, and some other chemicals, before adding quicksilver, it was found that a charge (whatever amount of crushed silver ore the pan would hold) could be amalgamated in about three hours. The results obtained with Knox’s Improved Pan were so satisfactory that Mr. Paul placed pans of that pattern in his new mill. Soon after a score of pans of different styles were invented, and to this day pans of new patterns are still being invented and patented.

The Coover & Harris Mill, Gold Hill, was the first mill in the country to start up with steam. It blew its steam whistle a day before that of Paul’s “Pioneer” was heard, but it could not then be called a silver-mill as it was working gold quartz, the same as was worked, in October the year before, at Dayton, by Logan & Holmes and Hastings & Woodworth. The mill had a fifteen horse-power engine that drove an eight-stamp Howland rotary battery and crushed six tons of ore a day. At first it was a dry crusher, but soon Paul’s Concentrators and Knox’ pans were used. The Harris of the firm was Dr. E. B. Harris, now a resident of Virginia City.

The Many Mills of the Early Days.

Very soon after these first mills went into operation several others started up. By the spring of 1862 no fewer than eighty-one quartz-mills were at work, the majority of them on ore from mines situated on the Comstock Lode. These mills were located in Virginia City, on Six and Seven-mile Canyons, at Gold Hill, Silver City, Dayton, at Empire City, and all along the Carson River below that town; two or three near Carson City (on Clear Creek and Mill Creek), and a dozen or more about Washoe Valley and down toward Steamboat Valley. Many of these mills were of small capacity, having only from two to ten stamps, but there were already a few first-class reduction works, as regards capacity, though their methods and processes were defective. The reduction works of the Ophir Company, in Washoe Valley, cost $500,000, contained thirty-six stamps, were driven by an engine of 100 horse-power, and was capable of working 100 tons of ore a day. The Gould & Curry Mill then building on Six-mile Canyon was of still greater capacity, and the Land, Bassett, Winfield, Empire State, Central, Marysville, Trench, Swansea, Phœnix, Succor, Rock Point, Merrimac, Vivian, and several other mills, contained from fifteen to twenty-five stamps each. After the completion of the Virginia and Truckee Railroad the majority of the outside mills (mills to which it was necessary to transport ore, wood, and other supplies by wagon) were pulled down and removed to new mining camps in various parts of the State. The greater part of the ores of the Comstock were then reduced in steam mills near the mines or in water mills on the Carson River on the line of the railroad; and this is still the case.

We now have fewer mills than in the early days, but they are of greater average capacity, and are in every respect more effective than were those first erected. More ore is crushed to the stamp, and the time required for the amalgamation of the pulp has been very materially reduced. All the present mills are so constructed that there is very little handling of the ores operated upon, and labor-saving apparatus has been introduced into nearly every department. Even the old oil lamps are being thrown out of the mills and the electric light introduced.

REDUCTION WORKS OF THE PRESENT DAY.

Description of the Process of Working Comstock Silver Ore.

In speaking of the works at present in use for the reduction of silver ore, it will only be necessary to describe the process in use in one mill, as all work after the same system. Being the most recently erected, and quite perfect in all its arrangements, the new mill of the Nevada Mill and Mining Company, commonly called the Chollar Mill (as it stands near the Chollar old shaft), shall furnish the illustration necessary to an understanding of the method of working Comstock ores now generally in use. The mill covers nearly an acre of ground, and the machinery is at present (March, 1889) driven in part by a Pelton water wheel 11 feet in diameter, and in part by power electrically transmitted from the Sutro Tunnel level. The mill building stands in a depression near the head of a small ravine. Such a site was selected in order that from the time the ore enters the mill its course at each stage necessary to its complete reduction, shall be downward—that there shall be no lifting or hoisting of ore or pulp.

The mill stands a little over one hundred yards south of the Chollar shaft. From the shaft the ore is run in the same cars in which it is hoisted from the mine directly into the upper story of the mill. It is there dumped through openings in the floor into the ore bins. Over these ore bins are placed in a slanting position iron bars three inches apart, forming screens called “grizzlies.” Through these screens the fine ore falls into the bins, while the large lumps of rock roll down upon a floor in front of the rock-breaker, an apparatus that works much on the same principle as a lemon-squeezer. Between the jaws of this powerful machine the largest and hardest piece of quartz rock is at once chewed into fragments sufficiently small to be fed into the batteries, where the heavy stamps reduce it to pulp. The ore is delivered into the batteries by self-feeders, which are so regulated as to keep constantly under the stamps the proper quantity of rock to do well the most work. At the Chollar (or Nevada) Mill there are sixty stamps,—twelve batteries of five stamps each. Each stamp weighs about eight hundred pounds. On the end of each stamp is a heavy head or block of iron or steel called a “shoe,” and in the bottom of the mortar (a long iron box in which the stamps of each battery work) is a similar block of iron called a “die,” upon which the shoe of the stamp strikes when it pulls. It is between these two blocks of steel that the quartz is crushed.

A small stream of water flows into each battery, and as the ore is reduced to a powder the water floats it out through the fine screens that are fitted into the face of each mortar. The pulverized ore and water, on passing through the screens, falls into a small trough, or sluice, which carries the muddy mixture down to the settling tanks, on a floor below, in the amalgamating room. In the tanks the crushed ore settles and the water runs off. From the tanks the pulverized ore, which resembles thin mortar, is shoveled out upon the floor alongside the amalgamating pans, into which it is shoveled whenever they are to receive a fresh charge of ore.

The pans are of iron and each holds a “charge” of about 3,000 pounds of the mortar-like pulp. In the bottom of each pan are thick plates of chilled iron or steel called “dies,” while revolving upon these are other heavy pieces of steel, called “shoes” or mullers. In the pans the pulverized ore is ground till it is much finer than when it passed through the screens of the battery.

When a pan has received its charge of pulverized ore (“pulp”) a small amount of water is added to render it sufficiently thin to be readily stirred by the mullers. The pans have tight covers and double bottoms. The double bottoms are steam chambers by means of which the pulp in the pan is kept hot while it is ground and agitated. After a charge has been ground about two hours, some 300 pounds of quicksilver are added (for 3,000 pounds of pulp), also a certain quantity of salt and sulphate of copper; and sometimes soda or caustic potash and other chemicals, if thought necessary, when the agitation in the pan is continued two hours longer. The time of working in the pan varies from three to five hours.

The Chollar Mill has thirty of these pans. On a platform below that on which stand the pans are fifteen settlers. These are about twice the size of the pans. At the end of three or five hours each settler has drawn off into it the contents of two pans. In the settler the pulp, quicksilver, and amalgam are kept in motion for about two hours. During this time water is let in and the pulp made very thin. The quicksilver and amalgam settle to the bottom of the “settler,” and are drawn off through a pipe and pass into a strainer—a strong canvas bag. There is an iron box around each strainer, and this is kept locked.

It is in the pan that amalgamation takes place. There the sulphuret and chloride of silver is changed to the metallic form by the chemical action of the sulphate of copper (bluestone) and salt, and when it takes the metallic form it at once unites with quicksilver. The gold contained in the ore (generally one-third of its whole value) being always in the metallic form, is amalgamated as soon as it is ground out of its inclosing shell of quartz, or pyrites of iron.

The thinned pulp—mere muddy water in appearance—on leaving the settlers passes into large wooden tubs called “agitators,” in which are revolving rakes. In these tubs is caught some valuable material—principally amalgam and quicksilver. From the “agitators” the pulp flows out of the reduction works through a small flume which conducts it to the blanket sluices, fifty yards away in the open air. The blanket sluices are broad, shallow flumes in the bottom of which are placed strips of coarse woolen blanketing. In passing over these blankets the pulp deposits pulverized iron pyrites containing gold, some fine particles of amalgam, and quicksilver; also such silver sulphurets as escaped being amalgamated in the pans. From time to time the blankets are taken out of the sluices and rinsed in a large tank, in which operation is saved whatever of value they may have caught.

The amalgam collected in the strainers standing below the settlers is placed in a press and as much quicksilver as possible pressed out, when it is placed in retorts, which are heated till all the mercury is driven off. There then remains behind the silver and gold, in a dull, rough-looking mass. This “crude bullion” is then broken up and placed in the melting pots, to be made into “bricks” and assayed. The bars or bricks made weigh about 100 pounds each. From the top and bottom of each pot or crucible of molten gold and silver is taken a small quantity of the fluid metals from which assays are made to determine the value of the bars. About thirty per cent of the value of the Comstock bullion bars is in gold, though it has at times run up to fifty per cent in some mines, and as low as ten per cent in others.

Though the Nevada Mill is in part driven by water, half the power used is electrically transmitted from six forty-inch Pelton water wheels set up in a large chamber excavated on the Sutro Tunnel level of the Chollar Mine, 1,630 feet below the surface. These small Pelton wheels drive six Brush dynamos, which generate the current that passes over the copper wires to the electric motors in the mill. The electric apparatus transmits to the main driving shaft of the mill about sixty-five per cent of the power developed by the Pelton wheels. Each Pelton wheel drives a dynamo, and one, two, four or all the dynamos may be run at the same time, just as may be required, each Pelton and dynamo being independent of the others.

After the water is used on the large-surface Pelton wheel in the mill it is caught up and by means of a small flume is conducted to the shaft of the Chollar Mine, near at hand, down which two large iron pipes carry it to the six small Peltons below. By thus twice using the same water a saving of one-half is made. The pressure on the lower Pelton wheels is immense. Never before has any water wheel been operated under a vertical pressure of 1,630 feet.

The Nevada Mill was built to work the ores of the Hale and Norcross, Chollar and Potosi Mines. It is one of the most substantial mills in the country, and no mill in the State is better arranged. It is lighted with electricity, and the grounds in front are illuminated by means of an arc light on a tall mast.

The Two California Mills.

The California stamp and pan-mills in Virginia City reduce the ores of the Consolidated California and Virginia Mine. The stamp-mill is situated immediately east of the C and C shaft of the mine. It contains eighty stamps. The ore crushed in this mill is amalgamated in the pan-mill, which stands about 1,500 feet further east. The crushed ore is conducted from the stamp-mill to the pan-mill through an iron pipe four inches in diameter. The process of amalgamation is much the same as at the Chollar Mill, except that the pulp goes directly into the amalgamating pans instead of being first received in settling tanks. It flows from pan to pan—the outflow of the first pan passing into the second through a pipe, thence into a third, and so on and from settler to settler, being in all about three hours in passing through the series. This is called the Boss Continuous Process. It is in use in no other mill on the Comstock, as yet. In connection with the Rae electrical process of amalgamation (in which a current of electricity is passed through the settlers) it is found to work satisfactorily. The electric current prevents loss of “floured” quicksilver. Both mills are driven by Pelton water wheels. A single Pelton wheel eleven feet in diameter, placed on the surface, drives the eighty stamps of the battery-mill, and also twelve Boss grinding pans. The water used on the surface Pelton is caught up and conducted to the C and C shaft, where it is used on a series of Pelton wheels of the same size. These wheels are placed in chambers made for their reception 500 feet apart from the top of the shaft down to the Sutro Tunnel level (there 1,500 feet), and by means of steel wire cables, used as belts, the power of all the lower wheels is brought to a main driving shaft on the surface. The whole power is then transmitted to the pan-mill (about 1,600 feet) by means of steel wire cables passing over pulleys placed on a series of tall wooden towers. The cables pass over a considerable depression between the top of the C and C shaft and the pan-mill; three high towers are required in the middle portion.

River and Canyon Mills.

The Mexican Mill, on the Carson River, contains forty-four stamps and a corresponding number of pans, settlers, and other amalgamating machinery. The Morgan Mill has forty stamps. It works ore from the Consolidated California and Virginia Mine. The Brunswick Mill contains seventy-six stamps, the Vivian sixteen, Santiago thirty-eight, and Eureka sixty. All these mills are about and below Empire City, and all work Comstock ores. The Eureka Mill is run on ore from the Consolidated California and Virginia. The Rock Point Mill (thirty stamps), at Dayton, and the Douglas Mill (ten stamps), in Lower Gold Hill, also work Comstock ores.

At and about Silver City are two or three small mills that work the ores of mines in that neighborhood, and on the Carson River are the Douglas and Woodworth Mills, which work tailings.

On Six-mile Canyon, below Virginia City to the east, are several small water mills having an aggregate of about thirty stamps. These work ores from the mines on the canyon and in Flowery District. On the canyon are also one or two small mills that work tailings and the concentrations from blanket sluices.

The Alta Mining Company has a ten-stamp mill, with concentrators, immediately adjoining the hoisting works at their mine. The Justice Company have a new ten-stamp mill near their mine.

Owing to the fact that many mines are now at the same time producing large quantities of ore, a lack of milling facilities is being felt. To meet this demand the Nevada Mill has been enlarged one-third, and the capacity of other mills will be increased, and perhaps some new mills will be erected. Processes by means of which low-grade ores may be profitably worked will no doubt yet be invented or discovered, which will cause many new works to be erected either on the Carson River or in the neighborhood of the mines producing large quantities of such ores.

THE COMSTOCK LODE.

Hoisting Works, Shafts, and Mining, Past and Present.