The El Oro Mining & Milling Co. has issued a pamphlet dealing with its property and proposals for ore treatment. The Company owns 60 acres and has an option on 50 acres in the district. According to the report of R. L. Riggs, the best claims are on the north slope of Battle Mountain, and numerous veins and dikes cross them, as proved by surface work.
About ten years ago the 500-ft. shaft was sunk and the adits were driven fifteen years ago. About $1,000,000 worth of ore has been shipped from the property. There is now 500,000 tons of ore opened to 200 ft. which should be mined and milled at a profit of $1 per ton. Tests on the ore show that, by simply crushing to 8 mesh and cyaniding, 85% recovery should be made.
A 200-ton plant is recommended, to be erected on the hillside. A report by Linderfelt & Stewart practically confirms these figures.
Recent development has opened 100,000 tons of ore. Tests on this ore showed the assay value to be $12, and the tailing to be 20c. per ton after a 72-hr. leach on a 12-mesh product in a 3-lb. cyanide solution.
The ore slimes readily, and will require classification, treating the slime independently of the sand. This will increase the extraction with little if any additional cost of treatment.
The following description of the proposed El Oro mill is given by the Cripple Creek Times:
It is favorably situated on the side of Battle and Squaw mountains in Eclipse gulch. Ores from the mines of the Company will be trammed to a storage-bin above the rock-crusher, and from this passes through a trommel, where a certain per-centage of waste is rejected.
The oversize from the trommel will be sent to the coarse-crushing rolls, and the fine rolls get that which passes the trommel. All ore is to be carried by a belt-conveyor to the main plant, where it is sampled and then run into storage-bins behind the Chilean mills.
From one of these storage-bins that portion of the oxidized ores amenable to direct cyanide treatment will be conveyed to a series of sand tanks where the usual leaching process for extracting the gold will be used.
From the storage-bins containing the sulphide ores, the material is fed uniformly by plunger feeders into the Chilean mills, along with weak cyanide solution. After being crushed, the ore flows to a distributing barrel, and then to concentrating tables. The product from these will be shipped to smelters.
The pulp next is lifted by a belt and bucket elevator to classifiers, which make two products, sand and slime.
Part of the former is reground in tube-mills, the balance being leached in vats. The reground pulp is elevated to a height sufficient to return it to the classifiers which separate from it and return to the tube-mills any sand that may have escaped being crushed fine enough in going through the mills the first time, while the slime classification flows to cone classifiers.
The underflow of these goes back to sliming tables, the overflow to the dewatering tanks. The overflow solution separated from the pulp during the pulp-thickening process is pumped back to the mill service tanks for re-use in the Chilean mills and general mill service.
The underflow of the heavier pulp particles separating from the charge passes to a series of Pachuca tanks. The pulp from these is finally filtered by a revolving machine, and gold is precipitated by either zinc dust or shaving.
The tonnage of the local mills will be increased soon by the completion of the El Oro mill.