The Upper Mississippi region comprises deposits in nearly horizontal limestones of Ordovician age. Three-fourths of the output of this district is made by five companies: the Mineral Point Zinc Co., a subsidiary of the New Jersey Zinc Co., with seven mines; the Vinegar Hill Zinc Co., with six mines; the Wisconsin Zinc Co., a subsidiary of the American Zinc, Lead & Smelting Co., with four mines; the Frontier Mining Co., with five producing mines; and the Cleveland Mining Co., with two mines. Other important companies are Burr Mining Co., Block House Mining Co., M. & A. Mining Co., B. M. & B. Mining Co., and Oliver Mining Co., a subsidiary of the U. S. Steel Corporation. All of the mines are equipped with milling plants. The production of the district shows a steady growth.
The zinc deposits of southwest Virginia and northeastern Tennessee occur as disseminated replacement breccia along crushed and faulted zones in folded Cambro-Ordovician limestones, and also as oxidized ores in clays residual from the weathering of the same limestones. The gangue is calcite and dolomite. The American Zinc Co. is the largest operator in Tennessee; it has a milling capacity of 3,000 tons daily and zinc-blende ore reserves greater than 6,000,000 tons averaging between 4 and 5 per cent. zinc, from which 60 per cent. zinc-blende concentrates are made. This company is a subsidiary of the American Zinc, Lead & Smelting Co.
The Western province comprises most of the western states; it extends north into British Columbia and south into Mexico. The chief subprovinces are those of Leadville, Butte, and Coeur d’Alene.
The Leadville deposits are found in strata varying in age from Archean to Cretaceous, which have been intruded by igneous rocks. The ores are mainly replacements of limestone and occur in large masses. This district first became of importance in zinc production upon the recognition of smithsonite and calamine in the large masses of oxidized ores. Of recent years sulphides form an increasing part of the production, now coming largely from deeper levels. The ores carry gold, silver, manganese, copper and sometimes bismuth. The United States Smelting Refining & Mining Co., the Empire Zinc Co., a subsidiary of the New Jersey Zinc Co.; the Western Mining Co., the Downtown Mines Co., the Wellington Mines Co., at Breckenridge; and the Mary Murphy mine, at Chalk Creek, are the largest operators in this region.
The Butte ores occur as veins in igneous rocks. The area in which zinc ores predominate surrounds that of important copper veins on three sides. On the border of the two areas, zinc-silver ores predominate in the upper levels and copper in the deeper workings. Many of the present zinc mines were formerly worked for silver. These complex zinc ores have been made available by the successful application of oil flotation and electrolytic deposition. The Black Rock mine of the Butte & Superior Mining Co., the Elm Orlu of W. A. Clark & Son, the Alice, and several other mines of the Anaconda Copper Mining Co., and the North Butte Mining Co. are among the most important producers. The twelve mines yielding zinc in 1915 together have immense reserves. The ores all carry lead and silver and some pyrite, and many contain copper and gold.
The Coeur d’Alene subprovince comprises a number of mining districts in Idaho, at least five being zinc producers. The Interstate-Callahan, in the Beaver district, is the largest zinc mine in the state. The ore is remarkable for the small percentage of minerals other than sphalerite, averaging 28 per cent. zinc.
The Northeastern province comprises important deposits at Franklin, New Jersey, and in the Adirondack Mountains in New York, and others of minor importance in the New England states. It is characterized by deposits of igneous metamorphic origin in Pre-Cambrian limestone. The Franklin deposits, in New Jersey, consist chiefly of franklinite, willemite and zincite in a gangue of calcite, rhodonite, garnet, pyroxene, magnetite and hornblende. Willemite is separated magnetically from these ores and used to produce a very high-grade spelter free from lead and cadmium and therefore in great demand for certain purposes. The other classes of ore are smelted for the production of zinc white and spiegeleisen. These mines, owned and operated by the New Jersey Zinc Co., have produced more than 1,500,000 tons of zinc in the form of spelter and zinc oxide. The Edwards-Balmat district, in St. Lawrence County, New York, comprises an area two to three miles wide and fifteen miles long, of Pre-Cambrian limestone. The ore occurs in lenses and is a mixture of sphalerite, pyrite and a little galena with a gangue of dolomite. Separation is effected by magnetic tables. The typical ore contains: sphalerite, 25.5 per cent.; galena, 1.43 per cent.; pyrite, 12.4 per cent.; barite, 3.9 per cent. The ore reserves of the Northern Ore Co., the largest operator, are known to exceed one million tons.
Germany.
—Imperial Germany comprised most of one metallographic province of major importance, Silesia, and other districts ranking as follows: Upper Silesia; Rhenish Prussia; Westphalia; Saxony; Hanover; and Nassau.
The major part of the mineral province of Upper Silesia lay within the boundaries of Germany in 1914. Once it was part of the Kingdom of Poland, except for portions included in the old empires of Russia and Austria. The pre-war production of zinc ores from Russian Poland was entirely from this metallographic province. The deposits, which contain lead and zinc together, occur in Triassic formation overlying Carboniferous rocks that carry important seams of coal. This juxtaposition of ore and fuel has furnished an ideal basis for the great smelting industry that has been developed, and facilitates the smelting of low-grade ores. The ores are said to average 17 per cent. zinc and 5 per cent. lead. They come from two ore horizons. The lower is characterized by blende, with a little galena and marcasite; the upper or lead horizon comprises a very persistent sheet of galena 0.05 to 0.30 meters thick, which generally is underlain by red calamine. The blende deposits are extensive and will be productive for a long time.