no necessity of a fusion for raw matte-an operation which has no object but to remove the gangue. Whether there ought to be a fusion for concentration depends upon the richness of the ore and its adaptability to concentration by machinery. A mixture of rich "smelting ore" and concentrated tailings, such as is now worked up by the smelters, could be roasted and immediately fused with lead. One more fusion with a fresh quantity of lead, if there were silver enough left in the matte to pay for the work, and cupellation, would complete the process. We should then have a process divided as follows:

1. Concentration of poor ore.

2. Roasting of concentrated and rich ore.

3. Fusion of roasted ore with lead.

4. Roasting of matte.

5. Fusion of matte with lead.

6. Cupellation.

The present imperfect concentration of tailings in Colorado is said to cost $6 a ton. A perfect concentration would cost no more. The other expenses would be—

[blocks in formation]
[ocr errors]

Mr. Hague says the millers expect to get 1 ton of concentrated pyrites

from 6 tons of tailings, which seems to indicate a pretty heavy loss. At that basis, however, the theoretical expense would be

Concentrating 6 tons to 1.....

Smelting 1 ton, 3.10 days' labor, at $3.

Smelting 1 ton, 82.17 bushels charcoal, at 25 cents.
Smelting 1 ton, 0.72 cords wood, at $8..


Mining at $10.

Total cost of treatment, 6 tons...

Cost of one ton....





41 84

60 00

101 84

16 94

The expense of charcoal ought to be somewhat less than this, for in consequence of the small quantity of material treated at Lend, no less than 2.5 bushels per ton of ore are expended in heating the furnace. If we add one-half more for loss in blowing out, we have the very large proportion of 3.7 bushels-a quantity which would be lessened to 1 bushel if 500 tons of ore were smelted in one campaign. Wi.h proper management this could be very much exceeded, so that the expense of charcoal for blowing in and blowing out would be too little per ton to be worth reckoning.

It now remains to consider the adaptability of this process to western ores, and I will take those of Colorado as an example, for the reason that Mr. Hague's report on the mines of that Territory offers the best

data for the calculation. He gives commercial assays of ores from various lodes, which prove their value to be as follows:

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The coin value of the first-class ore is therefore $91.36 for the gold and $21.03 for the silver; total, $112.13. By roasting the ore so as to leave one-third raw matte, and smelting with 180 to 195 pounds of lead to the ton, we ought to extract 90 per cent. of the gold,* or 4.05 ounces, worth $83.71; and 73 per cent. of the silver, or 11.90 ounces, wortli $15.35, or $99.06 in all. The cost of this would be about as follows:

[blocks in formation]

28 63

Total for roasting and smelting..

Total for mining, roasting, and smelting.....

If our ore contains no copper, and the matte will not pay for further treatment, and we proceed at once to cupellation, we have in addition:

Cupellation: 0.24 day's labor, at $3.

0.37 bushels coal, at 25 cents..
0.69 cord wood, at $8.....

9 pounds lead, say at 5 cents..



5 52


6 81

Total for mining, roasting, smelting, and cupellation,.... 35 44

Profit, $99.06-$35.44-$63.62.

We have remaining a matte containing $13.07, and probably a certain amount of copper. Let us see whether this will pay to work by itself. The cost will be:

It will be observed by reference to the table of the third fusion that all the gold was extracted by the operation at Lend in 1866. I have, however, adhered to Dr. Turner's general estimate in making the above calculations.

[blocks in formation]

This would cause a loss; for calculating 4 per cent. loss on gold and 10 per cent. on silver in the original ore, we have only $7.50 which can be extracted from the matte. The loss would therefore be $3.38, and unless the matte were worked for other products, as for copper, it probably could not be utilized at present, though in many cases it would be required as a basic flux in the first fusion. Considering the present state of the West and proportion of copper in the ore, the process would probably consist of three operations-first, roasting the ore; second, fusion; and third, cupellation, the copper matte being sold.

Accepting the Burroughs milling ore as an average of the secondclass ore, we have for this, one ounce gold, worth $20.67, and 4.5 ounces silver, worth $5.81; total, $25.48. The cost of treating it would be:

[blocks in formation]

This would leave a matte containing $1.86 in gold and silver, and perhaps some copper.

The above calculations are of course theoretical, so far as they relate to works which have never yet been established in the Territory. There may be errors in the prices assumed for labor and materials; but there is no reason why the amount of labor and material expended per ton should be more than at Lend; that part of the calculations is not theoretical. Undoubtedly in establishing such works some difficulties would be experienced, but with a railroad to the foot of the mountains, and the improved facilities for communication, the difficulties in the way

* A certain correction has to be applied, because the amount of matte is taken as larger than at Lend. I have assumed it to be 50 per cent. more.

Fine ore requires a more expensive roasting than coarse, for which reason I have added 50 per cent. to the cost. Roasting in furnaces, Mr. Hague says, costs $5 in Colorado.

cannot compare with those which have been overcome in establishing the milling system.

A chief drawback to extracting the precious metals in the Territory, instead of concentrating them in a matte to be exported, is thought to be the lack of lead-ores, since the Georgetown mines have not fulfilled their promise as lead mines. Let us see how much is required for works treating 25 tons of ore a day, a capacity which is considered to be quite respectable for a mill; and it is to be remembered that these 25 tons are concentrated ore representing several times that quantity of ore as it came from the mine. The loss amounts to about 17.7 pounds of lead per ton, or less than one per cent. Of galena-ore yielding, say, 70 per cent. lead, one ton daily suffices for, say, 70 tons pyrites, or 21,000 tons yearly; two tons daily suffice for, say, 140 tons pyrites, or 42,000 tons yearly; five tons daily suffice for, say, 350 tons pyrites, or 105,000 tons yearly. If each ton of smelting ore represents 6 tons of ore from the mine, we have more than 600,000 tons of ore treated with 1,500 tons of galena-ore. Even if the mines of Georgetown and Argenta are unable to supply this amount, it could easily be bought in, and brought from Utah, at rates which would at least pay its own cost. My object, however, is not to urge any process upon the attention of western miners, or prove by full figures its applicability. I offer the Lend process as one which deals with ores precisely similar to those of Colorado, and leave it to those who are interested in the mines of that territory to work out its adaptability.



This chapter constitutes a supplement to the preceding one on economical results in the treatment of gold and silver ores by fusion, and was likewise furnished to me by John A. Church, E. M., of New York. I give the chapter without change or comment; but I do not fully concur in the theory of amalgamation which it presents.

It is commonly supposed that mercury takes up gold by reason of an affinity which causes the union of the metals whenever they are brought in contact, and in the use of amalgamated copper plates for catching the gold, the Americans have trusted the success of their gold-mills this action. In Austria they proceed on a different basis. There they acknowledge the affinity of gold for mercury, but confine it within small limits. The gold which is dissolved by the mercury, and which passes with it through the filter, is that which has a chemical union with the mercury; while that which remains in the filter, and after distillation forms the "retort," is merely particles of gold which have mechanically sunk into the mercury by force of gravity. Their sur faces are attacked by the fluid metal, which acts as a cement to bind them together; but in no sense do they form a definite amalgam. I will not discuss this point thoroughly here, but merely point out some facts in relation to Colorado ores which, on this hypothesis, give a ready explana tion for the poor yield of those ores in the mill.

*The principles on which the separation of gold from its ores is effected by mechanical means are easily explained. If we have a substance composed of two elements, one having a specific gravity of 10 and the other of 5, it is clear that if we can provide a liquid having a density of, say, 7, the former can sink in it, and the latter cannot. To . accomplish the separation of the two we have only to crush the substance to a certain fineness and place it in a bath of the liquid. As soon as each particle of gravity 10 comes in contact with the fluid, it sinks, and we have only to agitate the sand and bring every particle in contact with it to produce perfect separation. We have then the two elements, one at the bottom and the other on the top of the liquid.

This is precisely what takes place in the so-called amalgamation of gold-ores. Gold has a specific gravity of 19.33, and mercury of 13.60. The iron pyrites in which the gold of Colorado is found has a gravity of about 5, and quartz, another constituent of those ores, has a gravity of 2.6. It would appear, then, that in a mixture composed of gold, specific gravity 19.33, and pyrites, specific gravity 5, there should be no difficulty in effecting the separation when the gold in a finely divided state is passed over mercury in which the gold can and the pyrites cannot sink. The Austrian gold-mill was devised to satisfy these conditions, and it works perfectly. In it mechanical contact between the gold and mer cury is effected in the most perfect way, and the mercury lying in a bath 1 to 11⁄2 inches deep, is in a condition to act either by affinity or merely as a fluid of medium density. And yet this apparatus fails to extract the gold from most of its ores, and the tailings are sent to the smelting

*What follows is partly taken from an article by me in the Scientific American of October 7, 1871. In that article an error was made in putting the "normal alloy" at 35 silver and 65 gold. It should have been the reverse, or 35 gold and 65 silver. The error. however, leaves the argument unaffected.

« ForrigeFortsett »