« SebelumnyaLanjutkan »
there are saw-mills at this time, but fuel for the engines and furnaces, and for domestic purposes, cannot be brought so far except at too great expense.
Coal must therefore be found, and it is possible, and even probable, from what I can hear, that it may be found not far north of the mines—in the “valley," as it is termed.
If it cannot be found, then the next step necessary will be to enlist capital for the purpose of securing the construction of a narrow-gauge railroad from Fort Steele, or Rawlins, via Seminole Gap, and thence up the Sweetwater to the gold mines. This would supply coal from the coal-fields at Carbon, or north of Fort Steele, or from valuable veins that exist not far south of Rawlins. It would also give access to the gold and silver mines of the Seminole Monntains, close to this line of road, which in a short time will exhibit sufficient wealth in mineral products, and so attract public attention and confidence as to command the building of a railroad thus far toward the Sweetwater mines. The whole line would require but very little more grading than for a railroad over an Ilinois prairio.
THE SMELTING OF ARGENTIFEROUS LEAD-ORES IN NE
VADA, UTAH, AND MONTANA.
The material for this chapter has been collected in part by my deputy, Mr. Eilers, and myself, by personally visiting the localities and works described. I believe all the works mentioned in the chapter have been visited by one or the other of us; but in urany cases the brevity of the time at our disposal prevented us from as detailed an examination as was desirable. The deficiency was remedied by the courtesy of Mr. 0. H. Hahn, a metallurgist of skill and experience, well known in the West, whom I requested to furnish me with such data as were at his command. This he has kindly done, and I have incorporated in this chapter his very detailed and admirable article, discussing the principles involved, and giving much information with regard to special operations in Utah and Nevada. I can give Mr. Hahn this general acknowledgment only, since the free use I have made of his materials, interpolating, distributing, and altering, to suit my own views, renders it necessary that I accept the responsibility of this chapter, while I would not deprive any colaborer of his due share of credit. The same remark will apply to the contributions of my deputy, Mr. A. Eilers. Perhaps it would be nearest the truth to say that these two gentlemen are primarily the authors of the chapter, but that their work has been edited after a somewhat arbitrary and self-willed fashion, so that they cannot be asked to adopt and acknowledge it as it stands.
I shall speak here only of such works as beneficiate ores directly in the mining districts. And when I say that more than twenty furnaces exist in Utah, about as many in Nevada, five in Montana, and four in Cerro Gordo, Inyo county, California, it is obvious that a business so extended deserves attention. Wide apart as these different works are located, they have nevertheless to deal in nearly every case with the same or very similar circumstances and conditions, so that, with very few exceptions, virtually the same system of smelting is fol. lowed in all these establishments. This is the so-called method of reduction and precipitation in blast-furnaces.
As the principal reasons for the employment of a blast-furnace process, are to be considered: the low percentage of lead in the ores, the high price of the only available fael, charcoal, and the exorbitant rates demanded for labor. The reasons why the reduction and precipi. tation process is preferred to a roasting, reduction and precipitation process are the high prices of labor and materials, and the preponder. ance of oxidized ores over sulphurets, though in some cases the latter are quite abundant.
The weight of these reasons will be better understood when the character of the ores to be treated and the object of the smelting are more minutely stated. The ores are in nearly all cases a preponderating mass of oxidizedlead ores, such as:cerussite, anglesite, and leadbillite, in wbich nests and nodules of undecomposed galena occur. Associated with these are: in Eureka, Nevada, arseniate of iron and arsenical pyrites, hydrated oxide of iron, quartz, and calcareous clay; in Little Cottonwood Cañon and American Fork, Utah, iron oxide, and in some
cases a combination of antimony, the nature of which I have not ascer. tained ; also dolomite and quartz in widely varying proportions; in Bingham Cañon, Utah, only quartz and comparatively little oxide of iron, or iron sulphurets; in Cerro Gordo, California, oxide of iron, iron pyrites, antimonial compounds, copper-oreş and, as gangue, carbonate of lime and quartz. In Argenta, Montana, occur, besides the abovenamed lead-ores, pyromorphite, and molybdate of lead. The preponderating gangue of the Argenta ores is quartz, and there is here a larger proportion of galena than elsewhere in the West. · In most of the localities named, the lead-ores themselves contain sufficient silver to render its separation from the ore the main object of the smelting; but in some of the districts, and especially in Montana, the lead-ores serve only to furnish the extracting-agent for the silver of true quartzose silver-ores, which at the same time contain a sufficient percentage of lead to make amalgamation impracticable. They are tberefore bene. ficiated by smelting, although the lead itself has no market value.
As there is more or less sulphur or arsenic present in all these ores, none of which are submitted to a thorough preparatory roasting, the formation of matte, or speiss, or a mixture of both, is of course unavoidable; and as silver has not only great affinity for lead, but also for sulphur, much of this metal goes with the patte. In most, works the latter is not roasted before adding it to a subse. quent charge, if it is at all treated further; and the extraction of the silver from it is therefore, in this case, only possible after it has passed the furnace quite often, very little of the sulphur being driven off in the upper parts of the blast-furnace at each smelting. In Eureka, a mixture of matte and speiss, the latter predominating, is formed, the contents of silver and gold in which hardly ever surpass $12 to the ton; and this amount is at present not considered worth extraction in that locality. The speiss, or “white iron," as it is there termed, is therefore thrown over the dump.
The marketable product which the smelting.works produce is argentiferous lead, with the exception of the works at Argenta, Montana, which cupel the lead and ship the silver only. As a general rule it pays best in the mining districts to produce argentiferous lead bars or crude bullion, the contents of which in silver and gold vary from $60 to $500 in the different districts. The main reason for not cupelling the lead in the West is found in the increased rates and risk of freightage for bullion ; but the separation of the silver and lead, and the refining of the latter, can also be accomplished at much less cost in the eastern centers of trade than in the mining districts. There are of course ex. ceptions, as, for instance, in Montana, where the smelting-works are located so far from the railroad that the price obtained for the lead would uot even cover the cost of smelting and freight, and where only the silver is therefore shipped, the lead remaining in the furnace-yard in the form of litharge. Part of this is used over again in smelting such silver-ores as are naturally too poor in lead; but the greater portion remains to await cheaper reduction and railroads.
A few remarks in regard to the present tendency of metallurgical ideas as far as smelting is concerned may be here in place.
Formerly the blast-furnaces used for lead-smelting usually bad an oblong rectangular cross-section, the size of the hearth being rarely larger than 20 inches by 24 feet, and frequently they were drawn together at the top. The capacity of such a furnace, with one or some. times two tuyeres, was about six to eight tons per twenty-four hours. But of late years essential improvements have been made, the aim of