Ohio Copper Company Leaching

From the beginning and for the period from 1923 to 1931 this leaching operation was very successful with a production of about 40,000,000 pounds of copper and enabled the Ohio Company to pay off its debts and simplify the company structure by retiring a bond issue and acquiring the Mascotte tunnel from a separate company, the Bingham Central Railway Company.

Subsequent to 1931 the leaching of the fills and caved areas was employed periodically in order to allow for oxidation of the copper minerals during the rest periods. However this procedure was uneconomical and was finally discontinued.

With the funds derived from the leaching operation expended the Ohio Company sold the Ohio property (in 1937) from surface down to a horizontal plane 50 feet above the Mascotte Tunnel level to the Kennecott Corporation. This block of ground was necessary for the expansion of the Utah Copper pit in order to make available a large portion of the Utah Copper ore body at depth by the pit system of mining.

(From AIME Transactions, Volume 73, 1926, pages 31-57)

In August, 1922, pumping was started, distributing 250 gal. per min. of water from Bingham Canyon Creek upon the surface of a large fill of broken rock overlying a portion of the caved zone. The solution reaching the Mascotte tunnel contained 0.45 per cent copper, demonstrating that recovery of the copper values would be commercially feasible; the following January, the pumping capacity was increased to 400 gal. per min. At that time, the copper was precipitated in a row of boxes, using "country scrap" or whatever iron was available locally. These faciiities were inadequate and insufficient, but results were soon sufficient, financially, to permit of a widening of the Mascotte tunnel and the installation therein of two rows of launders of improved design, one on each side of the haulage track; a larger and more efficient precipitation was promptly realized with improved profits. In the spring of 1923, with the installation of a larger pump, the water was increased to 600 gal. per min. In November, 1923, water from the Bingham Mines became available, which, with a reuse of a portion of the tailing solution, gives a supply of 1200-1400 gal, per min. at the surface, delivered by a relay system of pumps.

The leachings reach the Mascotte tunnel through some one or other of the old ore chutes, depending on where it is applied at the surface, and is laundered to the precipitation boxes. In the earlier operations, leakage losses were serious; these losses were stopped by guniting the precipitation launders.

Production in January, 1923, was 120,000 lb,; in October of that year it had reached 351,801 lb., the recovery having increased from 41.9 to 99.2 per cent. For 1924, the production was 11,496,530 lb, of copper, a recovery of 97.3 per cent, and the copper content of the product shipped from Lark averaging 88.99 per cent.

Early in the operations, it was recognized that the "country scrap" was an inefficient precipitant. Since June 1923, a detinned scrap iron prepared by the Metal & Thermit Corpn, in California has been used; this has proved highly efficient, more than justifying the greater initial cost.

The precipitation plant is located in the Mascotte tunnel about 2 miles from the portal at Lark. It is arranged in two rows of launders on either side of the haulage track, each row aggregating 1600 ft. in length, or 3200 ft. in all. The rows are subdivided into sections of 320 ft. with a siphon at the end of each section to bypass the pregnant solution to the opposite row during washing or loading operations. The individual units arc 16 ft. long with a cross section 32 by 32 in. They are gunited to prevent leakage.

The scrap, or detinned iron, is received in compressed bales weighing about 75 lb. each. The Metal & Thermit Corpn., from whom it is obtained, remove the tin by treatment with caustic soda, leaving a metal with a surface very well adapted to copper precipitation. Usually it reaches the launders in excellent condition, but sometimes there is a little adherent caustic and rust. The bales are torn apart at the launders and the loosened scrap heaped upon the false botton; it is the duty of the plant operatives to keep a full supply in the launders always.

The Mascotte tunnel and all offsets where men are employed are well lighted by electricity. Extra and ample lighting is provided in the precipitation plant. An electric tram provides adequate haulage facilities and the ventilation in the plant is good. At intervals, 2-in. piping with hose attachments are provided for washing the copper and keeping the equipment clean. The equipment is first class and adequate, and the operations well done, due, in great measure, to the small labor turnover. Three shifts of fifteen men each are employed in the plant operations.

The pregnant solutions reaching the head of the launders vary somewhat in volume, from 1200 to 1500 gal. per min.

Utah State Historical Society; MSS B 292; 16.75 lin. ft. (29 boxes)

Ohio Copper began to shift its efforts to recover copper from low-grade porphyry ore in 1919, but the decline in the price of copper led Ohio Copper to defer the project until 1923, when the company used leaching methods to retrieve the copper. The venture proved successful, saving Ohio Copper financially. In addition, Ohio Copper broke the world record for low-cost copper production.

Ohio Copper continued its leaching operations until 1937, as its profitability began to decline.

After selling the ground above the mascotte tunnel to Utah Copper, the Ohio Copper company turned its attention to developing a leaching process that could be applied to the tailings at its Lark mill. The company operated a mill and plant to re-treat tailings from earlier milling endeavors. When the company exhausted ores in the area by 1947, it ceased operations. United States Smelting, Refining and Mining Company bought Ohio Copper's leases in 1950 (May 1951).