For several years past Colorado metallurgists have been attempting to solve the metallurgical puzzle presented by the low-grade ores of Cripple Creek. Millions of tons of ore running from $3 to $10 per ton have lain on the great dumps for years, while other millions were exposed in hundreds of miles of underground workings.
The Portland company alone had enough low-grade ore in its forty odd miles of workings to materially increase the Cripple Creek gold production provided a method of profitable treatment could be devised.
Shipping the ore to the Colorado Springs reduction plant of the company cost $1 per ton, roasting the ore cost $.76 per ton, and the other milling expenses ate up the small margin of profit.
Thus, for some years previous to 1907, the issues were clearly presented, first, to eliminate roasting the ores if possible, and, second, to eliminate freight charges by building mills at the mines.
It will, of course, be understood that until a way of eliminating the roasting of the tellurium ores was discovered, it would be useless to erect mills at the Cripple Creek mines where roasting costs even more than at Colorado Springs.
The first great plant to be erected at the mines was that of the Stratton Independence Co. nearly two years ago. Little information is available concerning this, except that the method of treatment followed was fine grinding of ore followed by cyaniding.
Owing to the low grade of this company's dump ores the mill has not so readily proved successful up to the present time as it might had it treated the dumps of other mines.
In the meantime, the great Golden Cycle plant at Colorado City has been completed and successfully operated by roasting the ores and then cyaniding. During the year 1908 this plant is said to have produced roughly $6,000,000 in gold.
Owing to the fact, it is commonly believed, that the cyaniding of low-grade ores at this plant gave a chance for little or no profit, the company has lately decided to erect a plant at its Cripple Creek mine.Ground has been broken for the erection of this plant and construction work is progressing rapidly.
Contrary to the conclusions of the Stratton Independence and Portland companies' metallurgists, those of the Golden Cycle are to the effect that concentration of the low-grade ores before shipment to the Colorado Springs mills will solve the problem.
According to Manager McGarry, the exhaustive tests carried on at the company's experimental plant at Colorado City have resulted in a saving of 65 per cent. of the gross value of these low-grade ores. It is, therefore, planned to treat those ores which will not stand transportation charges by a system of dry concentration at a ratio of 6 tons crude ore into 1 of concentrates.
These concentrates will then be shipped to Colorado City for treatment at the company's cyanide plant. The mill in the course of construction on Bull Hill, near the Golden Cycle's main shaft, is to have the initial capacity of 80 tons of concentrates per 24 hours.
During the two years in which the Stratton Independence and Golden Cycle metallurgists have been evolving their plants, those of the Portland company have also been most active.
It is now common knowledge that the widely advertised Moore-Clancy process was given an extended trial at the experimental mill of the company but was evidently found unsuitable. The great amount of experimental work, however, did result in the evolution of what is known as the "Portland process," whose details are as yet unavailable.
It has been thoroughly tried out at the company's Cripple Creek 10-stamp experimental plant, however, with such success that a large mill is soon to be built close to the mines.
The annual report of the company recently issued says that from many tests the company is convinced that the problem of treating the low-grade dump ores has been solved.
The directors have decided to back up their judgment by the expenditure of at least $100,000 for a 300-ton mill, erected near the mine on Battle Mountain, to treat the great company dumps. These contain enough ore to run the mill for many years at an estimated net profit of from $1 to $2.50 per ton.
The building of these new mills is expected to have a regenerating effect on the entire camp of Cripple Creek, which combined with the events expected to follow close upon the completion of the Roosevelt drainage tunnel, is likely to prolong the life of the great camp for many years.