Copper Ores and Copper Bearing Minerals

Copper-bearing minerals are not only numerous, but widely though irregularly distributed. More than this, copper is found associated with many different metals and under varied conditions. Nevertheless but few copper-bearing minerals are important in the ores of this metal, and the number of important producing districts is comparatively small. Most of the copper ores now worked are of low grade, but can be profitably treated because of the extent of the operations and possibility of concentration. Occasionally low-grade ores are found which are self-fluxing, as those of the Boundary District of western Canada. The introduction of pyritic smelting has permitted the profitable treatment of low-grade pyritic-copper ores, even if they carry no gold or silver. Complex ores of copper, lead, and zinc sulfides are more costly to treat, but this expense may be more than made up for by their gold and silver contents. Sulfide ores of copper are almost invariably leached near the surface, except where the former surface material has been removed by rapid erosion or glaciation. Many copper ores, however, contain other metals that are not so easily leached as copper. As a result, many valuable deposits of copper sulfide ore have been discovered by downward exploitation of oxidized gold and silver ores. In regions where copper ores abound areas richly stained with iron are generally considered worthy of exploration in a search for copper. On the other hand, deposits of copper have been found below outcrops that show very little iron oxide. These outcrops, however, are generally silicified and kaolinized. Most of the large copper sulfide deposits in the United States show three zones a leached zone near the surface, an enriched zone below the leached zone, and a zone of lower-grade primary ore below the enriched zone. In the unaltered primary portion of the ore body the copper compounds are mainly sulfides, but arsenides and antimonides are also known. In the leached goethite gossan zone the copper occurs as carbonates, sulfates, silicates, oxides, native, and more rarely as phosphates, arsenates, antimonates and vanadates.

Native copper:  

This is man's first copper ore. Native copper is often alloyed with gold, silver, lead and mercury. Copper is widely distributed in nature. The metal is easily oxidizable and also easily reduced. It therefore occurs both as native copper and in its numerous compounds. Native copper is commonly, if not always, of secondary origin, either deposited from solution or formed by the reduction of some solid compound. Pseudomorphs of copper after cuprite are well known. W. S. Yeats has described pseudomorphs of copper after azurite from Grant County, New Mexico. W. Lindgren states that the vein of metallic copper at Clifton, Arizona, appear to have been derived from Chalcocite. The greatest known deposits of metallic copper are found in the Lake Superior region.

F. W. Clarke states its original home was, perhaps as sulfide, in the unaltered igneous rocks, but its concentrates are now found in the sandstones, conglomerates, and amygdaloids. In the sandstones and conglomerates it acts as a cement. Frequently native copper has been reported as holding enclosed nodules of native silver. The largest single mass of native copper ever found was discovered in the Minnesota mine, Michigan, in February, 1857. It was 45 ft. long, 22 ft. wide and 8 ft. thick. It weighed 420 tons. It was 90 per cent, pure copper and contained an appreciable amount of silver.

 

 

Malachite

The green carbonate. Commonly occurs massive, encrusting, stalactitic, or stalagmitic, and with a smooth, mammilla or botryoidal surface. The internal structure is often divergently fibrous and compact. Also occurs granular and earthy. The color is a bright green; different shades of the color following a concentrically banded arrangement. Malachite is found in the zone of weathering or gossan of copper lodes. Localities are Cornwall, Cumberland, Chessy (France), Spain, Siberia, Burra Burra Mine (South Australia), Chili, Pennsylvania, etc. The color-banding marks the successive deposits of the mineral, which has, in most cases, resulted from the percolation of water through copper-bearing rocks, and the subsequent deposition of the dissolved carbonate in fissures or cavities, the solution having apparently dripped in slowly, and the water evaporated, thus forming a series of layers in the same way that stalactites and stalagmites of calcite are formed by percolation of water through limestone. Malachite is valuable as an ore of copper. It is also, when cut and polished, used for ornamental purposes.

Azurite copper pocket:

This dark blue colored high grade pocket is mostly azurite, a copper carbonate ore. It also features malachite (green) and chrysocolla (light blue). This rich pocket was mined at Bisbee in Arizona.

 

This ore from Nevada features the green copper carbonate Malachite. The rich copper minerals  boost the copper content of this bonanza grade ore.

Azurite: 

The blue carbonate. It has a deep azure blue color, whence the name. The two basic carbonates of copper, malachite and azurite, are common copper ores of secondary origin. They are formed in the upper portion of ore bodies by the action of carbonated waters upon copper compounds or by the reactions between cuprous solutions and limestone. At Corinth, Vermont, the author has found fine specimens of both malachite and azurite formed from chalcopyrite by the action of carbonated waters. Azurite is distinguished from malachite by its azure-blue color (while Malachite is green). It is found associated with other copper ores in the zone of weathering or gossan of copper lodes, and when occurring in sufficient quantity, is a valuable source of copper.

 

Bornite   

Known as horseflesh ore by some miners, because of its fleshy pink color on fresh unoxidized surfaces. These surfaces quickly oxidize to multicolored iridescent colors - this leads to the name of peacock copper ore. Bornite and chalcocite are next in importance at least among the sulfides. These three minerals have been repeatedly indentified as of magmatic differentiation. They are doubtless the primary compounds from which the other ores in most cases were derived. B. Lotti has reported chalcopyrite, bornite and chalcocite in some ores.

 

Chalcopyrite

Chalcopyrite is the most important ore of copper. Copper pyrites is the principal commercial source of copper. The mode of deposition of chalcopyrite in a certain number of deposits like those formed in limestone or at its contact with other rocks leads to this conclusion. The same authors state that the solutions may have come from above or below. The solutions were transported in the form of sulfates, either due to the oxidation of pyrite in the neighboring rocks, or in the form of aqueous emanations from an igneous magma during the later stages of its cooling. They also state that the metasomatic chalcopyrite deposits are due to ascending or descending solutions of sulfides carrying hydrogen sulfide and alkaline sulfides.The most important mode of occurrence of the mineral is in hydatogenetic veins associated with quartz, pyrites, etc. Some localities are Wallaroo (South Australia), Great Cobar and Broken Hill (New South Wales), Mount Morgan (Queensland), Shasta County (California), Sonora (Mexico), Bisbee (Arizona), Alaska, Chili, Monte Catini (Italy), Urals, and Rhodesia.

 

 

Chalcocite 

A gray sulfide, also known as copper glance. Cupric solutions formed in the upper part of copper bearing ore bodies reacting upon pyrite precipitate chalcocite. Copper glance is a very valuable ore, but does not occur in very great abundance. Occurs in veins and beds associated with other copper ores, as in Cornwall, Siberia, Saxony, Kongsberg (Norway), Monte Catini (Italy), Mexico, Peru, Bolivia, Chili, etc.

 

 

Cuprite

This is the red oxide of copper. The two oxides, cuprite and tenorite, are always of secondary origin. They may be formed by the oxidation and reduction of other copper minerals. Cuprite is by far the more important species. It has been observed as an incrustation upon ancient objects of copper or bronze.

 

Tetrahedrite:

Known as gray copper, it is often argentiferous. Sulfide of copper and antimony,. Part of the copper is often replaced by iron, zinc, silver, or mercury. Part of the antimony is often replaced by arsenic, seldom by bismuth. It sometimes contains 30 per cent, silver in place of part of the copper, and is then called argentiferous grey copper ore, or silver fahlerz. Occurs associated with other ores of copper, and with pyrites, galena, sphalerite, etc. Localities are Levant (Cornwall), Andreasberg (Harz), Freiberg (Saxony), Przibram (Bohemia), Chili, Bolivia, and Arkansas and Colorado (U.S.A.).

Covellite  

This is an indigo blue sulfide that is a minor ore of copper. Covellite may be precipitated from copper sulfate solutions by the reaction of chalcocite. It is typically found in secondary enrichment zones in copper deposits.

 

Chrysocolla:

Of the two silicates of copper, dioptase and chrysocolla, the first is rare but the second becomes an important copper ore in certain localities. According to F. W. Clarke, chrysocolla is formed by the action of silica-bearing waters upon soluble compounds of copper. Also that the mineral may possibly be produced during the processes of secondary enrichment. Occurs in the zone of weathering or gossan of copper lodes, and when found in sufficient quantity, constitutes a copper ore of some value, and is easily reduced when mixed with limestone. It seldom, from its impurities, yields more than 10 per cent, copper.

 

 

Chrysocolla:

This mineral is a common one and occurs in the secondary zone of many copper ore bodies. Notable localities are Cornwall, Saxony, Bavaria, Siberia, South Australia, Chili, and the United States. It is sometimes considered to contain a variable amount of free silica, and some specimens are sufficiently hard to scratch glass and to be cut and polished for jewelry.

 

 

 

 

Dioptase:

Emerald green crystals, combinations of prism and rhombohedron ; sometimes found in a massive form. Found in the zone of weathering or gossan of copper lodes, as at Chili, Nassau, Siberia. While it forms beautiful crystals, Dioptase is, because of its rarity, not a very important ore of copper.

 

Turquoise:

This mineral is a hydrous phosphate of aluminium, with a small percentage of copper oxide. Turquoise occurs in patchy deposits and seams in a trachyte in Persia, Nevada, Arizona and New Mexico. A few copper ore bodies have some turquoise as a minor ore mineral. Uses: Turquoise is much used in jewelry.

 

Azurite Copper Ore, Nevada:

This beautiful specimen of copper ore comes from Nevada. The dark blue colored mineral is azurite, while the orange and gold colored material is limonite. The combination makes for a beautiful specimen.

 

More About Standard Types of Copper Ores:
In some deposits the oxidized ores and in some the primary sulfide ores are rich enough to work. Yet in other deposits, only the enriched ores of the secondary sulfide zone are profitable. In the oxidized zones of sulfide deposits the mineral waters are sulfuric acid and ferric sulfate solutions. Such solutions dissolve copper readily, and in contact with copper compounds such a system will contain also copper sulfate. The copper sulfate in solution reacts with carbonates or with acid carbonate in solution, precipitating copper carbonates like azurite or malachite. The sulfates chalcanthite and brochantite also may be precipitated. The silicates of copper like chrysocolla are probably formed by copper-bearing solutions reacting with silicic acid, which is commonly present in mine waters. If phosphate ions are present, turquoise may form. Native copper, cuprite, and tenorite are formed by the reduction or oxidation of various copper compounds. All these minerals are formed in the main in the oxidized zone, and in sulfide ore deposits their occurrence below this zone is exceptional. Below the oxidized zone, where air is excluded, copper is precipitated as sulfides: chalcocite, covellite, bornite, chalcopyrite, and possibly some of the more complex antimony and arsenic compounds are formed by these processes. Precipitation may be brought about by chemical interchange with pyrite, chalcopyrite, pyrrhotite, sphalerite, and galena, the process being mainly replacement. The copper sulfides are precipitated also by hydrogen sulfide, which is generated by attack of acid solutions on several of these sulfides. In a reducing environment the copper sulfides are highly stable. In pyrrhotite ores chalcocite enrichment is shallow. In deposits of sphalerite copper ores without pyrrhotite the chalcocite zone may be moderately extensive vertically. The most extensive chalcocite zones are in  arid regions with chalcopyrite deposits that do not contain pyrrhotite. Carbonates react with acid solutions and tend to delay the downward migration of copper. If there is much lime carbonate in the gangue of the ore or in the wall rock, the downward migration of metallic sulfates may be checked. Native copper is a common alteration product of copper sulfide ores.

Check this link for information on The major Copper Ore Deposits of the USA

Copper and Our Modern Culture:
Copper, is a copper red to reddish-brown, soft, ductile and malleable metal. Its color as copper red is best seen by reflected light. It is extremely tough, therefore, capable of being drawn out into exceedingly fine wires or hammered out into thin leaves. Its ductility and malleability are greatly diminished by the presence of impurities. As an electrical conductor it is second only to silver. The metal slowly tarnishes in dry air but in a moist atmosphere it is readily coated with a basic green carbonate. It is readily soluble in the mineral acids. Its specific gravity is 8.9. It melting point is 1083 C. Since prehistoric times copper has been important to mankind. Alloyed with tin has been used in various parts of the world for the manufacture of bronze. Thus it was used for this purpose in Homeric times, and it is found in the lake dwellings of Switzerland. The bronze found in Troy contains a very little tin, and since this metal is not found in the excavations in the West, it seems probable that the bronze was made in Asia, perhaps in China or India, by some secret process, and imported to the western countries. By an alloy of copper and tin, although both metals are soft, a comparatively hard metal is produced. The properties of this alloy, bronze, vary greatly according to the proportions of the two metallic constituents, and these vary with the use for which the alloy is intended. United States ordnance is 90 per cent copper and 10 per cent tin, while ordinary bell metal is about 80 per cent copper, though the percentage varies with the tone required. Statuary bronze is generally an alloy of copper, tin, and zinc; and, in these various bronzes, the color varies from copper-red to tin-white, passing through an orange-yellow.

In the new world copper was also put to various uses. The pre-Columbian tribes of South America alloyed copper with gold to reduce the amount of gold required to cast an object.  Since ancient times copper has been alloyed with both gold and silver. Another alloy is brass, produced when zinc is added to copper, it has found of so much value for small articles used in building and for ornamental purposes in machinery. Copper is has also used in roofing and plumbing since ancient times. In our modern world, large supplies of this metal are made into copper wire, and this is the most important present use of copper is in electricity, for which its high conductivity especially fits it for the transmission of electric currents. Our high tech modern society would simply not be possible without the use of copper and copper alloys.

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