The lead production of Utah is chiefly from the Park City, Bingham Canyon, and Tintic districts. The ores, composed of galena, tetrahedrite and pyrite, and in places sphalerite, with their oxidized derivatives, occur in lodes cutting limestones, sandstones and shales, chiefly of Carboniferous age, and also as bedded deposits in limestone. Both types are frequently associated with porphyry and form irregular ore bodies in contact-metamorphosed limestone. In many mines copper is an important constituent of the ores and the silver content is always important.
The production of Colorado in 1917 comprised 33,995 short tons of lead, of which 9,293 short tons came from the Leadville district in Lake County, 10,412 short tons from the San Juan district in San Juan, San Miguel and Ouray counties, and 6,816 tons from the Aspen district in Pitkin County. The Leadville deposits are in the Mosquito range. The chief producing companies are the Iron Silver Mining Co., the Yak Mining, Milling & Tunnel Co. and its subsidiary, the Leadville Exploration & Mining Co.; the Western Mining Co.; the Downtown Mines Co.; the Ibex Mining Co.; and the United States Smelting, Refining & Mining Co. The Yak Mining, Milling & Tunnel Co., and the Western Mining Co. are subsidiaries of the American Smelting & Refining Co. In the San Juan district, the principal producers are the Liberty Bell; Smuggler-Union; Tomboy; Black Bear; Iowa-Gold Tiger; Dives; Shenandoah; and Silver Lake mines. The veins penetrate all the clastic and igneous rocks of this region, and the ores are exceedingly complex. In Pitkin County, the Smuggler Leasing Co. operates most of the producing mines at Aspen. The ores are peculiarly free from other metals than lead, antimony, and silver.
Australia.
—The lead resources of the Commonwealth of Australia are chiefly in New South Wales, Western Australia, Tasmania, and Queensland. New South Wales has been the chief producer in the past, but the Tasmanian deposits are now being rapidly developed and equipped for production.
The most important source of ore in New South Wales is the great Broken Hill lode, situated in the arid Barrier Ranges at an elevation of about 1,000 feet above sea level. The lode ranges in width from a few inches to 400 feet and has been worked over a distance of three miles. Mining began in 1884 and now is conducted by several mining companies which, in the order of the importance of their production and ore reserves, are: Broken Hill South Silver Mining Co.; Broken Hill North Mining Co.; Zinc Corporation; Sulphide Corporation; British Broken Hill Proprietary Co.; Broken Hill Proprietary Co.; Broken Hill Proprietary Co., Block 10; and Broken Hill Proprietary Co., Block 14.
Although the deepest workings are 1,815 feet deep, the ore still continues downward. For many years the estimated ore reserves of all the mines have approximated 12,000,000 tons. The upper part of the lode consisted of a gossan 20 to 100 feet wide of siliceous and manganiferous limonite, hematite, and kaolin. Below the gossan were great masses of cerussite, anglesite, cuprite, and malachite, with abundant cerargyrite, embolite, and iodyrite. Between the oxidized and primary sulphide ores was a thin zone of secondary sulphides. The early operations in the district were conducted for the purpose of obtaining lead ores, and immense dumps were accumulated of zinc-bearing ores sorted out or zinc-bearing tailings left after concentration of the lead ores. In 1903 these dumps were estimated at 5,687,400 tons, carrying 18.6 per cent. zinc. With the development of a demand for zinc sulphide ores and of oil-flotation methods of separation and concentration, these dumps have been important sources of zinc. There are two classes of sulphide ores, distinguished as silicate gangue ore, and calcite gangue ore. The sulphide ores are a close mixture of galena and zinc blende, carrying silver. The silicate gangue ore bodies carry rhodonite, garnet, and quartz; and are richer in zinc and silver than those with calcite gangue.
The Broken Hill South Silver Mining Co. has ore reserves estimated at 3,350,000 tons and is the largest ore producer in the field. Broken Hill North, Broken Hill South, Amalgamated Zinc (De Bavay), Zinc Corporation, and Barrier South, Ltd., are controlled by the Hoover-Govett-Bailliau group of British and Australian capitalists.
The Amalgamated Zinc Co. in 1913 treated 498,289 tons of tailings containing 17.1 per cent. zinc, 3.7 per cent. lead, and 4.4 ounces silver, obtaining 140,098 tons zinc concentrates carrying zinc, 48.9 per cent., lead 5.9 per cent., and silver 8.5 ounces per ton. The Zinc Corporation, a company formed by Bewick, Moreing & Co., has ore reserves estimated at 1,504,211 tons, averaging 14.8 per cent. lead, 9.2 per cent. zinc, and 2.5 ounces of silver per ton.
The largest lead-producing district of Tasmania is on the West Coast, where the largest producers, the Hercules of the Dundas group and the Primrose and Tasmanian copper mines of the Rosebery company group, are now controlled by the Mount Read-Rosebery Co., affiliated with the Mount Lyell Mining & Railway Co., Ltd. The deposits contain complex sulphide ores, the reserves being estimated by the state geological staff at 1,272,500 tons, averaging 29.79 per cent. zinc, 8.89 per cent. lead, 12.16 ounces of silver, and 0.17 ounces gold per ton. This estimate has since been revised and made more conservative.
In 1913 Western Australia produced 26,589 long tons of lead ore and 125 tons of silver-lead ore, almost wholly from the Northampton district on the West Coast. The only company working on a large scale is the Fremantle Trading & Smelting Co., operating the Baddera and Narra Tarra mines and, formerly, a smelter at Fremantle. The Chillagoe district is the largest producer in Queensland, its output amounting to 2,550 long tons of pig lead in 1913, chiefly from the Girofla mine of the Mungana company, but in part from lead-copper concentrates. The Chillagoe operated a small smelter. The total pig lead production of Queensland was 3,603 long tons in 1913.