The A B C of Mining: A Handbook for Prospectors

Although but three American states have supplied this metal, this country has held rank as second producer. Of these California is by far the most important. Oregon and Utah having never had any but a small and spasmodic output. Judging by Californian experience, the prospector is most likely to find cinnabar, the ore from which the quicksilver of commerce is derived, in metamorphic rocks. Mercury is always sold in flasks of 76½ pounds. The production of mercury by the United States (California) was 28,879 flasks in 1899, which were valued at $1,155,160.

The following table shows the rock in which the most famous Californian quicksilver mines are:

A study of the foregoing shows that serpentine is almost as intimately connected with quicksilver as is quartz with gold, or granite with tin. These are the things that prospectors should make a note of. With the great increase of gold mining and the limited store of cinnabar that is available that ore seems certain to rise in value before long.

Mica. The value of Indian mica varies from 90¢ a pound for sheets 4 in. × 1 in. to $13 a pound for sheets 10 in. × 8 in. The white mica in large sheets is valuable. The amber-colored, and spotted, are used for insulating purposes in electric plants, while the coarser sorts are ground and used as lubricants, or in fire-proof paint manufacture.

Nickel. This ore is never found in metallic form, but always in combination. Pyrrhotite, or magnetic pyrites, is the source of about all the nickel of commerce. This ore has been already noticed under iron. Rare but valuable ores of nickel are millerite, nickelite, glance, and nickel bloom.

Some of the nickel of commerce is derived from nickelliferous pyrrhotite.

Petroleum. Crude petroleum is never found in metamorphic or igneous rocks. The stratified rocks of the Devonian, Carboniferous and Cretaceous ages are most likely to hold it. The crude oil is almost black, and consists of about 85 per cent. of carbon, and 15 per cent. of hydrogen. A long iron-shod stick is all the prospector requires to take with him in his search for surface indications of oil. The warmer the day the easier the search, as the oil rises to the surface of the streams, and is found in greater quantities than on cold days.

Oil existing in the lower rocks ascends through them until it accumulates under some layer that will not let it pass through. In this condition deep boring finds it, the rod usually tapping gas first. Petroleum may be noticed oozing out of gravel banks, or floating as a scum on the surface, whenever abundant. It has been found in rocks of widely different age, from extremely ancient formations to some that did not precede man by so very long, geologically speaking.

Platinum. This metal is only found native. Its gravity is very high, from 16 to 22. Hardness, 4 to 4.5. Luster, metallic. Opaque. Whitish-gray. Smooth. Ductile. Cleavage, none. Fracture, hackly. Texture, granular, fine. Platinum is unaffected by acids, but if alloyed with 10 per cent. of silver it dissolves in nitric acid. Almost infusible. Platinum occurs with placer gold in the beds of streams. Usually it is in small grains, but one or two large nuggets are on record from Brazil and Siberia. Serpentine rocks are believed to have originally held the platinum found in the beds of rivers, but none has been found in veins. The entire product of the United States was 300 ounces in 1898; valued at $3,837. In 1899 there was none produced.

Silver. Silver is generally found in serpentine, trap, sandstone, limestone, shale, or porphyry rocks, the gangue being quartz, calc, fluor, or heavy spar. All silver ores are heavy, and many of them are sectile, i.e., may be cut with the knife. Western men test for silver by heating the ore and dipping it into water. Some metal comes to the surface in a greasy scum, should silver be present. Native silver is found occasionally. Owing to the fall in value of this metal its future is not assured. It has fallen, during the past year, once to forty-nine cents an ounce, and this has had a most disastrous effect upon many silver mines, forcing them to suspend operations. Should the fall continue, as seems likely, and the price of silver go down to forty cents an ounce, little will be produced except as a by-product in the treatment of argentiferous lead ores.

As silver enters into chemical combination with sulphur easily, as is seen by the black film that forms on silver articles in a room where gas is burnt, most silver ores are sulphides. The very abundance of silver has caused its great fall in value, and it does not appear that it is ever likely to remain for long at a price exceeding fifty cents an ounce, owing to the ease with which it may be produced, and the large quantities that must find their way to market through it being a by-product in lead smelting. From 1859 to 1891 the Comstock lode in Nevada produced $325,000,000. This lode is a belt of quartz, 10,000 feet long and several hundred wide, and is a contact vein between diorite and diabase. In America galena is the principal source of silver; the chlorides and oxides rank next; while, lastly, some silver is parted from gold when it reaches the mint, as gold always contains more or less of that metal. No precise statement as to the manner of its occurrence may be made since it is found in many different positions, and is associated with all sorts of minerals. It is never found in placer deposits, as it breaks up under the influence of water, air, etc. Its original source is doubtless the igneous rocks, where it occurs in association with augite, hornblende and mica. Silver may be expected in mountainous regions of recent origin. Between 1875 and 1891 the world's product rose from $82,000,000 to $185,599,600. Three quarters of this came from the western hemisphere.

The commercial ores of silver are:

The Anaconda mine in Butte is the largest producer of silver in the country. In 1896 its output was 5,000,000 ounces. The Anaconda is also the heaviest copper producer in the United States, its yield of copper being 125,350,693 pounds.

Sulphur. Brimstone is found native in the neighborhood of volcanoes, extinct or active. It is also derived from iron pyrites. Color, yellow. Hardness, 2. Specific gravity, 2. Luster, resinous. Smooth. Sectile. Texture, crystalline.

Talc. The scientific name of this mineral is steatite. It contains silica and magnesia. Its green color, pearly luster, and greasy feel, are very characteristic. It is not attacked by boiling sulphuric acid. Useful in the arts, but of no great value.

Tin. The composition of cassiterite, the commercial ore of tin, is SnO₂; equal to 78.67 per cent. of metallic tin. Cassiterite or tin stone is a heavy ore which occurs in alluvial deposits or in the beds of streams. It will be one of the latest ores the young prospector will find himself able to name with certainty. Granite, with white mica as one of its constituents, has so far always been associated with tin. The American continent yields little tin, and it is not likely the prospector in either the western states or in Canada will stumble upon it, though a good deposit of stream tin would enrich him in a short time, for the metal is in great demand. The streak, when the metal is scratched with a knife point, is whitey-gray and very distinctive.

Tin may some day be found in the northern Rockies, as there is plenty of granite, which is favorable to this metal. It is worth about thirteen cents a pound, and a vein must yield more than five per cent. of metal to pay the cost of mining and dressing. Cassiterite, the principal tin ore, would have to be roasted. Most of the European tin mines were first worked for the copper they contained. The copper was found in the capping, but as they gained in depth they became more and more valuable for their tin. Some of the Cornish mines are three-quarters of a mile in depth. Very lately tin has been discovered and mined in vast quantities in the Straits Settlements, India. As it is found in the streams the expense of mining is very light, and it is killing the European mines. The Cornish miners put their tin ore on a shovel when they wish to test it. The sample is first crushed fine and a few skillful shakes get rid of all the gangue, leaving behind the tin and wolfram. This wolfram is always associated, in Cornwall, with the tin and it is got rid of by roasting. Australasia and Cornwall produce most of the tin used in commerce. Tin is not found native. Specific gravity of cassiterite is 6.5 to 7. Hardness, 6.5 to 7. Luster, vitreous to adamantine. Translucent to opaque. Brown, black, gray, red or yellow. Harsh. Brittle. Massive. The appearance of this metal is so variable that nothing but a test with reagents determines it with certainty. Granite is frequently the country rock in which tin is found.

Zinc. This is another ore that never occurs native. Calamine or silicate of zinc is the great producing ore. Composition: Zinc oxide, 67 per cent; silicate, 25 per cent; water, 8 per cent. Specific gravity, 3 to 3.7. Hardness, 4.6 to 5. Luster, vitreous. Translucent. White. Harsh. Brittle. Cleavage, perfect. Fracture, uneven. Texture, granular crystalline. Calamine is a difficult mineral to detect without experience, as when impure it does not look in the least like a metallic ore. It would be taken for clay or shale. This ore results from the decomposition of zinc blende. Blende contains 67 per cent. zinc and 33 per cent. sulphur. It is often dark brown or black from iron, otherwise it may be red, green or bluish. It is a troublesome impurity in silver ores. Smithsonite is a carbonate much resembling, and often found with, calamine. Other zinc ores are merely curiosities and do not affect the commercial value of the metal.

In the New Jersey mines the zinc ores are the oxides zincite and willemite, and the zinc-iron oxide franklinite. In the Missouri region, on the other hand, sphalerite and blende are the typical ores. Blende generally associates with the lead sulphide, galena. The Joplin district in southwestern Missouri and the adjoining region in Kansas are now mainly supplying the markets of the country, though the New Jersey deposits are very valuable.

Joplin ore assaying 58 to 62 per cent. has varied greatly in price during the past four years. The lowest quotation was $20 a ton, the highest $51.50.

Zinc is derived mainly from the following half dozen ores:

  CHAPTER V.

MINING.

Although the scope of this work does not include the very complex problem involved in the working of a great mine, prospecting and the simpler mining operations are so intimately connected that it would not be desirable to make mention of the one and ignore the other, because the prospector must perforce become a miner as soon as he discovers mineral, even though his operations should not go beyond a shallow trial shaft.

The simplest method of hoisting dirt or rock out of a shaft, after it has become too deep for the sinker to throw the stuff out with a spade, is by a bucket and windlass, which may be either single or double, according to the power required. In northwestern Canada, where the present gold excitement has attracted so many thousand pioneers, the miners have hitherto been content with a windlass. For their purpose it answers well, as they sink through gravel and not more than thirty feet at the most before reaching the bed rock. The alluvial flats in which the coarse gold of the upper Yukon has been discovered, are composed of gravel that is invariably frozen, summer as well as winter, and which requires to be thawed out before it can be worked with a pick. Strangely enough, dynamite cannot be used, as the ground is so elastic under the frost that the tamping simply blows out and the required effect is not produced. This peculiar condition has led the men, who are mining in that part of the continent, to adopt methods very similar to those used in Siberia, where, also, the ground is permanently frozen to a great depth. After scratching the surface of the soil, and removing the deep moss that invariably covers it, they light large fires over night and in the morning remove the few inches of thawed soil underneath the ashes. By this painfully slow method they eventually sink to the richer gravel, fifteen or twenty, or even thirty, feet below the surface, though there are few shafts of this depth on the Klondike and the other gold-bearing creeks about which we have heard so much. When the bed rock is reached and the few inches of decayed surface removed, the miner builds his fire against the side of the shaft, placing some inclined logs over it as a roof, and goes to bed. When he awakes next day several feet of the soil have fallen down over the logs, and this he has to hoist. It is at this stage that the windlass worked by his companion, or partner, demonstrates its value. In a very short time all the gravel that the fire has thawed out is hoisted to the surface, and added to the dump, where it must remain until the warmth of summer shall have thawed the streams and permitted sluicing.

A sluice is really nothing more nor less than a trough, open at the top, in which the gold is sorted from the lighter gravel and dirt by running water. The grade varies according to the coarseness of the gold. Very fine gold would be carried away by too swift a current, while coarse gold will resist almost a torrent. The sluice is built in joints, usually a dozen feet in length; the sides may be six inches or a foot deep, and the width varies from one to two feet. There is no rule in this matter, but owing to the extravagant price of lumber—as much as a hundred and fifty dollars a thousand feet, board measure—the tendency is to make the sluices very small and very short, thereby saving nothing but the very coarsest gold. A properly constructed sluice should be several hundred feet in length, and the inclination should not be more than one foot in twelve, while it may, in a case of fine gold, be advisable to diminish this inclination by at least a fourth. Riffles, or cross-pieces, are placed across the sluice at intervals of a few feet, and slats are placed lengthwise, filling up the intervals between the riffles. Into the crevices and interstices of these obstructions the heavy gold sinks by its own weight, and every few days, or weeks, as the case may warrant, the miner shuts off the water by closing the gate at the head of the sluice, removes the slats and riffles, beginning at the joint nearest the head and working towards the tail of the sluiceway, and collects all the gold that has accumulated.

This is a very simple form of mining, but it is not the simplest. Much gold has been recovered from the gravel in which nature has placed it by the aid of the pan, a sheet iron dish modeled on the housewife's bread pan.

Next to the pan the cradle is as little complicated as anything used in the winning of gold.

After this comes the long tom, a considerable improvement upon the cradle, but it necessitates more water and more men.

The horse whim is used in developing many a western prospect. The windlass does not work well below forty feet, and where fuel and water are to be had any sensible man will use steam power for deep mining, but there is a gap between the windlass and the steam hoist which the horse whim fills acceptably. To a depth of 300 feet a horse whim can usually handle the rock and water. It is inexpensive, in the first outlay, and costs but little to run. You can bring your bucket from a shaft a hundred and fifty feet deep in two and a half minutes, and with a seven hundred pound capacity in the bucket, in forty-five trips you could raise fifteen tons a day. A shaft three hundred feet deep would require four hours' steady work to bring to surface the same amount. A fair speed with a one-horse whim from a three hundred foot shaft is one hundred buckets per shift of ten hours, but the prospector rarely has to figure on shafts of that depth. If the mine turns out well it is likely to be in the hands of a powerful company (of which he should be the principal shareholder) before the three hundred foot level is reached. The weight of the horse whim is about eight hundred pounds. It can be taken to pieces and packed anywhere that a mule can travel; the heaviest piece will not weigh more than a hundred pounds.

A small stamp mill, run by horse power, is a very favorite machine with western men, where the ore is free milling. The mortar in which the stamps work has copper plates amalgamated with mercury inside, and copper tables with amalgamated plates over which the pulp passes after oozing through a fine screen in front of the mortar. These little mills are so constructed that they can be taken apart or put together in an hour or two. They require but one horse power and will do good clean work up to their capacity. The following are the specifications of a good one:

A diamond drill is a most useful adjunct to exploration of a mine or deposit. It is, essentially, a hollow drill which may be lengthened at will, rotating rapidly and carrying a crown of "bort" or black diamonds at its extremity, that eats into the strata very quickly. Holes 3,000 feet deep have been driven by the diamond drill, but such extensive investigations of the earth's crust are tremendously costly, and may only be undertaken by governments or rich companies. For a depth of 700 feet, however, the expense need not exceed $2,100. The cost of the plant for drilling would be $3,500 more. Water is pumped down the hollow center of the drill, to keep it cool. The great advantage of the diamond over the percussion drill is that it permits the saving of a core, so that the character of the rocks and minerals passed through may be known. The diamond drill does better work in hard strata than it does in soft. The rate, in limestone, may be about two feet an hour, down to a depth of 200 feet.

A complete outfit for boring with the diamond drill includes a steam engine and boiler, diamond crown, lining tubes, rods, and various minor accessories.

Hydraulic mining is the cheapest known method of recovering gold. In four years the North Bloomfield Mining Company of California worked 325,000,000 cubic yards, which yielded only 2.9 cents of gold per cubic yard, and realized some profit. Very poor gravel will pay when the conditions are good. Cheap water, grades of four inches in a hundred, ample dumping room, big banks of light gravel, large areas of deposits, labor at a dollar a day, and a clever superintendent, make a combination that will yield a profit out of three-cent gravel.

Miners speak of "surface" and "deep" placers; of "hill claims;" of "bench claims" on the old river terraces; of "gulch diggings;" of "bar claims" on the sand bars of existing rivers; of "beach sands" or those that in a few favored localities border the ocean. A "sluice" is a long boxway to catch the gold; a "drift" is a tunnel into the gold-bearing gravel; and hydraulic diggings are those in which water under pressure is used to disintegrate the gravel.

A ground-sluice is a trench cut through the bed rock. The roughness of the natural floor serves for riffles. Booming is a process requiring a large accumulation of water in a reservoir, which may be discharged at once, and carry all the material that has collected below the pass, with one full tide, into the sluices. This practice is extremely ancient; Pliny mentions it in his Natural History.

Deep mining may be divided into drifting and hydraulic mining. In the former the metal is won by means of tunnels and drifts or horizontal passageways along the length of the deposit. It is usually resorted to in districts where a flow of lava has covered the gold-bearing gravel, and made hydraulic mining impossible. It is followed in Alaska for another reason, viz., because the constantly frozen ground will not permit of the more remunerative method. The gravel is carried to the mouth of the tunnel and there dumped to be washed in the sluices. When "cemented" it must be broken up by stamps.

Rich deep placers may be worked by drifting, but whenever practicable hydraulicing is to be preferred as giving better results. It yields from four to six times the amount of gold that drifting does. Thorough exploration should precede the expenditure of large sums in a hydraulic plant. Even should the explorations result in finding barren gravels the money will have been well spent in saving the cost of an unproductive plant.

Black sand (magnetic iron) almost always accompanies gold, but this alone is no sign that gold is present, as black sand may usually be obtained by grinding and washing crystalline rocks.

Ditches and flumes of wood or metal are used to bring the water for hydraulic mining from the region where it was impounded in a catch basin, often a distance of many miles. It is said $100,000,000 have been invested in ditches and flumes, mining and agricultural, in the western states, and new flumes are being planned every month. Some of them consist of wrought iron pipe carried over ravines by trestles 250 feet high.

In planning a ditch the miner must see to it that his water supply is at a sufficient elevation to command the ground. The more pressure the water works under the better. The supply should be continuous, or at least be available during the whole working season. Ditches in regions of deep snow should have a southern exposure. All streams crossed by the ditch should be diverted into it, to counteract leakage and other loss. Waste gates must be provided every half mile. Ditches are better than flumes. Narrow, deep, and steep ditches are to be preferred in mountainous regions, and the reverse in valleys with soft soil. Some Californian ditches with a capacity of 80 cubic feet per second and grades of 16 to 20 feet per mile have been built.

Sometimes the face of the country requires flumes; they may even be hung along the face of a cliff. In shattered ground and where water is scarce flumes are better than ditches. The grade for a flume is usually 25 to 35 feet per mile and its capacity is smaller than that of a ditch. Pine planking 2½ inches by 12 to 24 inches, and 12 feet long, is the dimension stuff generally preferred. A flume 2 feet 6 inches square requires posts, caps, and sills of 3×4 inch; stringers 4×6 inch. Great care is needed at curves to avoid slack water and splashing. The boxes must be shortened and the outer side wedged up until the water flows as evenly as in the straight stretches. Should anchor ice form the water must be shut off at once. The life of a flume seldom exceeds a dozen years, whereas at the end of a similar period a ditch would be carrying 10 per cent more water than at first, owing to the sides and bottom having become consolidated.

Wrought iron pipes are employed largely in California to replace ditches and flumes. When the pipe crosses a ravine it is known as an inverted siphon. Piping is also used to convey water from the "pressure box" to the "gates" and "nozzle." Wrought iron pipes have to stand pressure varying from 34 pounds to 800 pounds to the square inch. Air valves or blow-offs must be provided at intervals to allow the escape of air from the pipe while filling, and to prevent a collapse of the pipe after a break. A covering of coal-tar should be given the pipe both inside and out. Cost varies from one dollar to two dollars a running foot.

The pressure box ends the ditch and from it the water passes into the supply pipe. The head of water is measured from this point. A box to catch sand and gravel, with a side opening and sunk below the level of the ditch, is called the "sand box."

One and a half inch plank is generally the material out of which the pressure box is made. The depth of water in it is such that the mouth of the pipe is always under water. A grating in front of the pipe catches all rubbish. As no air must be allowed to get into the pipe the water must be kept quiet and deep at the pipe-head; this is insured by dividing the box into compartments, the first receiving the water and discharging it through suitable openings into the second. The water supply and the discharge should be equal. The water passes down the feed pipe, iron gates distributing it to the discharge pipes. Water must be turned on gradually, and the air valves must be open. The piping terminates in a nozzle with knuckle-joint and lateral movement. Nothing but the most secure bolting to heavy timber and the heavy weighting of the last length of pipe should be relied upon to keep the hydraulic giant in its place. Should it once begin bucking every man within reach of the powerful column of water is in imminent danger. The nozzle is directed by means of a larger deflecting nozzle, which receives the impact of the water and causes the main nozzle to swing right or left, up or down, as the case may demand.

A derrick capable of moving heavy boulders, and driven by water power, is a necessity in all hydraulic mining. Masts 100 feet high and booms 90 feet long are sometimes used, the motive power coming from a "hurdy gurdy" direct impact wheel. Experiments have shown that the bucket has much to do with the power of the wheel. For instance, when the water impinged against a flat bucket the efficiency of the wheel was less than 45 per cent. of what it should have been in theory, whereas, with the Pelton bucket, it rose to 82.6 per cent.

There is a great amount of so-called cement, or in other words consolidated gravel, in all the northern placers, and in many California deposits, as well. In the old Cariboo diggings on the upper Frazer, strong companies are now pulverizing the ancient cements that resisted all the efforts of the 59 miners with powder and stamp mill, and are deriving large profits therefrom.

Black powder gives even better results than dynamite in gravel. The usual allowance of powder is 20 pounds in weight for every 1,000 cubic feet of ground to be moved. Make drifts T-shaped, and tamp the main drift almost to the junction with the arms, which should be parallel to the face it is required to dislodge.

Sluices have their maximum discharge when set straight. Increased grade may be given below any unavoidable curves with advantage, and the outer side of the sluice must always be raised. Steps or "drops" in the sluices help in the recovery of the gold. In general, a grade of 6-6½ inches to the 12-foot box is found best; this is equal to a 4-4½ per cent. grade. Exceptional instances are on record, however, where grades ran from 1½ per cent. to 8 per cent. In a 4 to 7 per cent. grade the water in the sluice should be 10 inches deep at least. The following table gives useful details:

"The longer the better," is the sluice-builder's motto. The best "riffles" are made of blocks of pine 8 to 13 inches deep, wedged into the bottom of the sluices. They are laid in rows separated by a space of an inch or an inch and a half. Riffle strips keep them in position, these latter being laid crosswise on the bottom. When worn down to five inches, the blocks should be replaced. This amount of wear will probably require six months. Stone and longitudinal riffles running lengthwise of the box are often preferred.

An undercurrent is a broad sluice set at a heavy grade below the level of the main sluice. The fine stuff drops through a grating, while the coarse gravel continues on down the sluice.

Refuse material from quartz, hydraulic or other mines is known as tailings. Tailings are deposited on a dump, which in the case of a hydraulic claim must be sufficiently spacious to receive the thousands of yards of debris deposited on it each day. When available a narrow, deep canyon, or a tunnel, may take the places of dumps.

Quicksilver is used in the sluices, 14 to 18 flasks being used every fortnight in a long sluice. It is not placed in the last 300 or 400 feet.

In working, keep the face of the bank "square." Washing should be carried on continuously. Watches must be set over the sluices, or gold is likely to be missed. As an extra precaution, the sluices should be run full of gravel before shutting off the water. There is no fixed custom regulating "clean ups." Some managers do so every 20 days, others run two or three months, others again clean up but once in a season. In large operations, the first 2,000 feet of sluice are cleaned up every fortnight; the remaining boxes once a year.

Sluices are cleaned from the head downward, the blocks being taken up for that purpose. The amalgam of gold and quicksilver is collected in sheet iron buckets. The final step is reached when the amalgam is retorted and melted in a graphite crucible.

The principle of which the hydraulic miner takes advantage is the great specific gravity of gold as compared with water and rock. To illustrate this quality it may be noted that on a smooth surface inclined at an angle of 1 in 48, subjected to a heavy stream of water, 95 per cent. of the fine gold in gravel does not travel three feet.

The loss of quicksilver fed into sluices will vary, even under good management, from 11 per cent. to 25 per cent. of the amount fed to the boxes.

Hydraulic mines under favorable conditions are very paying investments. Gravel yielding 10 cents a cubic yard has been worked for 6 cents a cubic yard, at the rate of a million cubic yards a year. On another large claim 600,000 cubic yards were worked for 6 cents a cubic yard, yielding 13 cents a cubic yard.

River dredging is another form of gold winning that has been brought to a great state of perfection in New Zealand. Although the dredge has not yet acquired the importance in America that was expected, it is successful on one or two western rivers, and as the subject becomes better understood it is conceivable that American mining engineers will be as successful in devising improved dredges as they have been in all other branches of their profession.

In New Zealand the bucket dredge has proved more satisfactory than the suction dredge, although a hasty conclusion would probably give the latter the palm. At Bannack, Mont., the Bucyrus Company has several dredges in successful operation. One is 102 feet long, 36 feet wide, and draws 36 inches of water. It is very substantially made, and weighs nearly 700,000 pounds. Before such a dredge is launched, a dam is built across the gulch to impound sufficient water. As the gravel is dredged and washed, it is dumped astern of the dredge, which, in the case of a shallow creek, moves up to the excavation made by the buckets. The boilers of this dredge are double, and together have 250 H.P. There are 36 buckets, and each one has a horizontal drag of eight feet, a capacity of five cubic feet, and travels at the rate of fourteen feet a minute. After treatment by trommels, or revolving screens, coppers, and sluices, and finally by a centrifugal pump, the now almost valueless gravel goes overboard again, leaving behind 98 per cent. of the gold it once held.

The traction dredge is really a land-mining machine, as it is adapted for work on land nearly flat, where but little water is obtainable. The machine travels on bogie tracks. A 50-H.P. boiler supplies the water. A boom, 40 feet long, carries a shovel of 1.5 cubic yards' capacity, and moves 70 cubic yards each hour.

Mr. John W. Gray, one of the best authorities, has recently written to the Mining and Scientific Press of San Francisco a most interesting description of the progress made in saving the gold from the streams in New Zealand. He says, in part:

"After great effort, numerous trials, many failures and some large losses, this system of gaining gold has been evolved from crude beginnings into a systematic and satisfactory method of mining. Dredging for gold is now attracting attention and bids fair to become an established form of mining for that metal. In New Zealand, where more work of this nature has been done than elsewhere, the evolution of the industry has been the work of years. The rivers upon which dredging operations are carried on are swift-flowing streams, subject to frequent floods, having a considerable depth of gravel, with boulders and runs of pay dirt interstratified. The conditions are, therefore, not the best for economical and successful work, and it is not surprising that many failures have occurred. The runs of gold are, however, often extensive and rich, and operations carried on upon such reaches have in a number of cases given satisfactory results.

"The improved form of dredge is a double pontoon, with ladder and chain-bucket arrangement between. Screens separate the coarse from the fine material. Wide sluicing tables catch the gold, centrifugal pumps supply the water, and waste material is handled by elevators. The power is usually steam, although electricity is used in a few instances, where conditions are favorable. The dredges vary in size and capacity, but are now built of large size and great strength. Twenty thousand dollars is the cost of a large dredge with all the latest contrivances. Under favorable conditions, material has been handled without loss that only yielded a grain of gold to the cubic yard. The real cost in actual continued working is believed to be very much in excess of that figure where average conditions exist.

"One dredge on the Clyde side of the Shotover, working to a depth of twenty feet below water level, lifted 40 tons per hour when operating. The profit on eleven dredges for the four weeks ending July 24, 1897, was an average of $2,686 for each dredge.

"So far in this country (United States), with a few exceptions, dredging operations for gold have not been financially successful. From crude beginnings, however, the machines have been rapidly improved and perfected, until now, in some localities, dredges believed to be the most complete yet constructed are being put in operation, and results are promised, not yet attained, in the way of economical working and high percentage of saving. During the last few years, a number of dredges have been operated in California, British Columbia, Idaho, Montana and Colorado, but with poor success. Very few prove themselves capable of paying their way. Some of the machines were faulty within themselves, others were entirely unable to cope with the swift currents and large boulders of the streams upon which they were operated. This latter is said to have notably proved the case with the dredges tried upon the Frazer and Ouesenelle rivers.

"Dredging operations on Grasshopper Creek, near Bannack, Mont., are now carried on successfully upon a large scale. The upper Sacramento river, in this state, has a dredge doing profitable work, and, in a small way, dredging is successful upon the Kzamath. A dredge upon that river, composed of two flat boats with a large steel scoop between, is able to cut and hoist the gravel and soft bed rock, and to handle boulders of from four to six tons' weight. The dredge is run day and night, has a 25-H.P. engine, and requires three men for each shift. In gravel 10 to 25 feet deep, 400 cubic yards can be handled every twenty-four hours. Cost of dredge, $8,000.

"A large dredge of the chain-bucket variety is operating in Northern Mexico, in a dry country, where there is little water. The actual capacities of these machines are 60, 100 and 150 yards per hour.

"Perhaps the most interesting dredge yet brought to the notice of the public is one lately built by the Risdon Iron Works, San Francisco, and now operating upon the Yuba river, near Smartsville, Cal. It is of the elevator, or chain-bucket, type, 96 feet long, composed of two pontoons, separated by a space five feet in width, in which is operated the ladder carrying the buckets. One man controls the dredge by means of a power winch with six drums. Four drums carry lines from the corners of the dredge to anchorages on shore—one a head-line and one the ladder line. The machine is to dredge to a depth of 45 feet, and is said to have a gross capacity of 93 cubic yards per hour. The material discharges from the buckets into a revolving and perforated screen. This segregates the large material, which is then conveyed away by the tailings elevator. Water (3,000 gallons per minute) is supplied to the revolving screen for washing and sluicing purposes by a centrifugal pump, and the fine stuff falls through the holes in the screen into a distributing box, from which it passes to a set of gold-saving tables and thence to a flume. The tables are covered with cocoa matting and expanded metal. The top tumbler of bucket-chain is operated by a vertical compound condensing engine indicating 35 H.P., which also operates the pump. It is claimed for this dredge that in any ground not deeper than 60 feet below water level or more than 20 feet above, and which contains boulders of not more than one ton weight, the material can be handled at from 3 to 5 cents per cubic yard. If the capacity of the machine is given without deduction for water raised, imperfect filling and general delays, and the increase in volume of the gravel when broken up in filling the buckets, the actual working capacity would be less, and from these causes and the losses from wear and tear, breakages and repairs, the cost of operating would be increased. The cost of the dredge complete upon the river is said to have been $25,000.

"In the evolution of the dredge into the elevator or chain-bucket machine, now the popular form, the various kinds of dredges were given trials. The dipper dredge is not adapted to dredging for gold, and some of the gold is lost. With agitation of the gravel the gold soon settles and is not recovered. It is also very difficult, if not impossible, to construct a dipper dredge that is water-tight. Another objection is that the material is supplied intermittently, thus making necessary certain undesirable arrangements for supplying the material in a continuous flow to the gold-saving tables. The same objections apply with greater force to the clam-shell form of dredge. It is by no means water-tight, and loses most of the gold in the act of dredging and bringing up the gravel. The objections would seem not to have the same force if applied to hard cemented gravel or to gravel with sufficient clay or other binding material to make it consistent. It is well to remember that these forms of dredges are, in many positions, economical of operation.

"The hydraulic dredge has had fair trials and proved a failure. Large storms greatly lessen the efficiency of this form of dredge, and numerous boulders hamper the pumping work. The suction force, being intense near the pipe and decreasing rapidly a short distance away, causes the sand and gravel to be carried off, leaving the gold behind. A centrifugal pump is therefore of little use to catch coarse gold, or to clear a hard, uneven bottom. Cutters do not remove the trouble, since the gravel is dispersed by the cutting, and the gold is separated therefrom.

"These objections would not obtain under certain conditions, and it would seem quite possible that conditions might be found existing where the suction dredges might be arranged to do good work. A dredging company is now constructing, at Seattle, two dredges of the suction type to operate upon the Yukon river. This would indicate that there are those who believe that deposits occur in and along that river which can be successfully worked in this way.

"The chain-bucket machine, the popular form for operating under average conditions, is a combination of the following elements: An excavating apparatus which clears the bottom and handles the material with little agitation and slowly and continuously delivers a regular quantity of gravel to the gold-saving appliances; revolving screen to receive and wash the material and separate the coarse from the fine; an elevator or contrivance for carrying off the coarse gravel and stones; gold-saving arrangements, or tables, over which the fine material passes and upon which the gold is caught; a pumping apparatus to supply water for washing and sluicing.

"The proper capacity of a machine seems to be regulated by the capacity of the gold-saving appliances. The tables should be as wide as possible, with frequent drops, and the fine material should be distributed over the tables in a thin film. The tables are covered with plush or cocoa matting, and sufficient water supplied to keep the material clear. The material should be supplied evenly, continuously, and regularly to the tables. Care and attention are required to catch the fine gold. A disregard of the foregoing directions results in great loss, more particularly in the fine gold. Mechanical skill is required to properly design and construct a dredge, and the care of a competent mechanic is necessary to see that the machine is kept in order and economically operated. The saving of the gold, however, is what makes dredging operations a commercial success. A man skilled in these matters should be in charge of running operations. Dredges should be built of determined capacities, and should be designed to suit the conditions under which they are to operate. Careful examination and investigation of the ground to be worked should be made beforehand, and the surrounding conditions studied, and it goes without saying that these matters require engineering skill and experience.

"The field for dredging for gold seems large. Where the proper conditions exist, it is a system which commends itself, and which gives promise, in competent hands, of being an economical method of mining. There is probably a very large extent of country where dredging for gold will be carried on profitably. The ground need not be in a river, if there is seepage water sufficient to float the dredge and supply clear water for the saving of the gold. Dredging requires little water as compared with that required for sluicing and elevating, and this water can, in many dry localities, be supplied at small expense, where a supply for hydraulic work or elevating would cost a very large sum, or be impossible at any cost. Any power suitable for driving the prime motors can be utilized to run the dredge. Indeed, it would seem as if a system of mining was about to be perfected which may make possible the profitable working of many deposits not easy to be worked by other methods, and which may, in many instances, solve problems regarding the successful working of deposits which hitherto have seemed most perplexing and even impossible of solution. Some doubt exists as to possible economical dredging operations under the water of torrential streams. The strong currents, the frequent floods, and many large boulders found in the channels of such streams make the working of the machines difficult and costly. This would not be so much the case in the long stretches of less current, nor would it be so at all in the valley-like reaches in the lower portions of rich streams, nor in the wide, flat portions of country where the streams enter the plains."

Very few gold-bearing lodes contain nothing but free gold; on the contrary, they carry the bulk of their values in the form of sulphurets, having more or less gold incorporated, and even when the gold is native and free-milling at the surface, it is generally changed into sulphurets as depth is gained. So the miner has to consider methods of recovery more complicated and expensive than simple amalgamation with mercury, for upon gold included in pyrites mercury has no effect. Titanic iron, hematite, and tungstate of iron often hold gold, or soft clay ores carry it in their midst, and such combinations tax all the skill of the mining engineer merely to save a respectable percentage of the assay value. Sometimes chlorination and sometimes cyanization are the measures tried, but supposing the preliminary treatment to have been by stamps in the battery, concentrating is one of the main reliances of the mill man. The blanket table is undoubtedly the oldest type of concentrating machine, but it is very inferior to modern inventions. Percussion tables often do good work. In this system a sharp and frequently repeated blow is given the table, in such fashion as to make the heavy material separate from the light. "Shaking" and "rocking" tables are favored in some mills, and they give better results on fine gold than any of the previously mentioned devices. But the best machine so far invented is the Frue Vanner—an endless rubber band drawn over an inclined table, having both revolving and side motions. The lighter particles are carried off by water, and the heavier collected in a trough.