SULPHIDE COPPER ORES. The prin cipal sulphide copper ores of the United States are chalcocite or copper glance (Cu,S), con taining 79.8 per cent of metallic copper ; enargite (CuaAsS,), 48.3 per cent; covellite (CuS), 66.4 per cent; chalcopyrite or copper pyrites (CuFeS,), 34.5 per cent; bornite or peacock ore (CtuFeS4), 50 to 70 per cent. Other sul phide copper ores of less commercial importance because in small quantity are: tetrahedrite (4Cu2S.Sb,S,), 25 to 40 per cent metallic cop per; tennantite (4CusS.As,S,), 57.5 per cent; chalcanthite (CuSO4-1- 5H,0), 25.4 per cent; chalmersite (CuFe,S,); cubanite (CuFe,S4) ; and the rare carrollite (CuCo,S4). As all these minerals show evidences of recent formation they are regarded as probably concentrations from pyrite beds. Chalcopyrite and bornite seem to have been the primary deposits from which the others have been derived. In most localities the ores are of such low grade that water concentration is necessary before smelt ing. Nevertheless the sulphide ores must be regarded as the most important of all ores of copper as they supply much the larger part of the metal sold in the world's markets.
The most important sulphide mining dis tricts are Butte, Mont.; Bisbee, Ariz.; Bingham Canyon, Utah; Ely, Nev.; Ducktown, Tenn., and Shasta County, Cal. In the Butte district of Montana, the greatest copper producing terri tory in the world, the ores are mainly secondary sulphides in fissure veins. More than half are chalcocite and considerably less than half enargite, although the proportion of the latter is increasing with the depth. With these are bornite, covellite and cupriferous pyrite. The primary ores of this region were chalcopyrite and pyrite. At deep levels (2,800 feet) are found masses of primary chalcocite, far below the zone of secondary enrichment. In Arizona three-fourths of the copper ores sulphides. At Bisbee occur large masses of primary ore, but in the other districts the replacement of the original chalcopyrite and pyrite with chalcocite has been practically complete. In the Globe district the primary ores — pyrite and chalco pyrite — occur in commercial quantities, but the largest output is from the secondary de posits of chalcocite on deeper sulphides. In the Jerome district the important ore is primary chalcopyrite. At Bingham, Utah, there are large replacement deposits of pyrite, chalcopy rite, sphalerite and chalcocite, with some bornite and primary enargite. In some places covel lite and tetrahedrite are found with chalcopy rite. At Ety, Nev., there are extensive replace ments of chalcopyrite by chalcocite, and also bodies of chalcopyrite enriched with chalco cite. At Ducktown, Tenn., the primary ores are pyrite, chalcopyrite and bronite. The paying ore bodies are secondary chalcocite, with second ary chalcopyrite at a lower level — with some covellite, bornite and chalcanthite. In the Shasta copper belt of California large bodies of massive sulphides are found along the bor ders and within the areas of eruptive rocks, chiefly pyrite and chalcopyrite, with chalcocite below; and some bornite and tetrahedrite.
Examples of replacement of pyrite by chal cocite are found in every important district producing sulphides. The pyrite first becomes coated with a black stain; later the chalcocite penetrates it along cracks and fissures, and finally the whole becomes a mass of sooty black chalcocite.
At some of the sulphide mines all of the ore goes directly to the roasting furnace. At other mines where the ore is of lower grade it is first concentrated by mechanical means— screening, crushing and separating on jigging tables. The flotation process (q.v.) is particu larly adapted to the concentration of sulphide ores, which are difficult to wet, and hence have a greater tendency to float, a tendency which is largely increased by treating them with oil. At other mines the ore is crushed to a diameter of one-fourth of an inch and leached with a solution of sulphuric acid, made on the spot by the burning of pyrite.
Treatment of These are usually roasted in mechanical roasters, the most approved type being the improved McDougal furnace. The chemical action is the change from the sulphide condition to the oxide. The iron sulphide present also becomes the pro toxide and then the sesquioxide. After roast ing to, say, 7V2 per cent sulphur content, the product is fused in reverberatory furnaces to form matte running usually 40 per cent to 50 per cent copper, and slag running 0.30 per cent to 067 per cent copper, which is usually thrown away as valueless. The matte is, as a rule, converted without being allowed to cool be tween reverberatories and converters, Treatment of Lump Ore, Ores are treated in blast furnaces, using coke as fuel in greater or less amounts, according to the smaller or larger content of pyrite in the ore. The smelting generally practised in the United States is known as the °semi-pyritic" and it takes advantage of the fuel value of the sul phides in the ore, as far as possible.
The fines are briquetted before charging them into the blast furnace, wherever suitable bonding material is obtainable, at low cost;— for example, slimes from the water concentra tion of the copper ores. In some localities the fines are sintered and in others nodulized to prepare them for blast furnace treatment. The resulting matte and slag are treated in ways similar to those obtaining in reverberatory smelting.
The most common type of converter is the °trough" converter, with rows of tuyeres along the back, entering the charge a few inches above the bottom. The linings are usually made of magnesite brick. The prod ucts of the converter are sulphurous gases which escape through the flues and stacks ; slag which is returned to the blast, or reverberatory fur naces; and °blister* or converter copper, which is either cast in pigs or anodes for electrolytic refining and the extraction of gold and silver values. For refining, see ELECTROCHEMICAL