Copper Ores - Chemistry and Origin
THE ORES OF COPPER
There are nearly 200 distinct copper ores, but the principal copper ores of
commercial importance may be divided into seven classes, as follows:
- Native copper (Cu) existing alone as pure copper
or practically so, as in the Lake Superior district, Bolivia,
and elsewhere, and occurring in the oxidized zone of copper mines
in almost every mineral field.
- Oxide ores, a combination of oxygen
and copper, of which Cuprite and Melaconite are good examples.
- Carbonic
ores, a combination of carbon and copper, as Malachite and
Azurite. These two ores are largely used as semiprecious gems,
when pieces of sufficient hardness are found.
- Sulphide ores,
a combination of sulphur and copper, of which Chalcocite, Bornite
and Chateopyrite are the most important.
- Sulphate of copper,
a combination of sulphur and copper, as Chalcanthite, which
occurs as an alteration product in many rich sulphide mines,
and which is the source of the copper secured by precipitation
from cupriferous mine water.
- The Arsenides, a combination of
arsenic and copper, of which Enargite is the most important.
- The Chlorides, a combination of chlorine acid copper, of which
Atacimite is a good example.
In commercial importance, the sulphide group is
easily in the lead, about three-quarters of the world's copper
supply coming from ores of this class. Of this group Chalcocite
alone produces nearly one-half of the world's supply of copper.
Next in importance commercially is native copper, which is mined extensively
in the Lake Superior district.
Third in importance are the carbonates, Azurite
and Malachite being the only ones found in large quantities. Malachite
is the most important, as it is rich in copper and is easily smelted.
Most copper deposits carry both gold and silver, usually in small quantities,
but frequently in amounts sufficient to add materially to the value of
the mine. Lead and zinc are found very commonly in connection with copper
ore, the three sulphide ores of copper, lead, and zinc being closely affiliated.
Iron, while very rarely a commercial product of copper mines, is found
in varying quantities in the great majority of copper mines.
Many mines have been opened for gold that really
contained immensely greater values in copper at depth. There are
frequent instances of gold mines turning into copper mines, the
most recent example of importance of this change in metallic values
being afforded by the Mount Morgan mine of Queensland, Australia,
which for many' years was one of the largest gold producers of
the world. and which is now a copper mine of great value.
Examples of silver, lead, or zinc mines changing
into copper mines at depth are numerous in Utah, Mexico, and elsewhere,
the best examples being furnished by the mines in the Bingham district
of Utah. The zinc ores of the mines at Leadville, Colorado, are
replaced at depth by copper ores.
The Red Jacket shaft of the Calumet and Hecla mine
in Michigan is the deepest copper shaft in the world, 4,920 feet.
The principal ores
of copper with the approximate
percentage of copper found in each is as follows:
- Cuprite, (Cu2O) a copper oxide which contains 89
per cent of copper. This is the ore that is richest in copper,
frequently shading to crystals of native copper.
- Chalcocite, (Cn2S) or copper glance, a copper sulphide containing
80 per cent of copper. This is the richest commercial ore of
copper, and it yields more than one-half of the world's entire
copper supply. It is found in all copper districts.
- Chalcopyrite, (CuF eS2) often called copper pyrites, or yellow
copper ore, a copper and iron sulphide which contains 35 per
cent of copper and 30 per cent of iron. This is the primary ore
of copper, all other ores of copper being derived from it. It
is found in all the copper fields of the world, and is second
to Chalcocite in importance as a commercial ore of copper.
- Enargite, (3Cu2AsS5) a copper sulphoarsenite bearing 48 percent
of copper. This is the most common and valuable ore at the largest copper
producing district in the world, Butte, Montaua.
- Bornite, (3CuSFe2S3,) a peacock ore, a copper and iron sulphide
bearing 56 per cent copper, 16 per cent iron, 28 per cent sulphur,
is another of the important commercial ores.
- Azurite, (2CuC03Cu(0H)2) sometimes called Chessytite or blue
carbonate of copper, a copper carbonate with 55 per cent of copper.
This is an ore of a most beautiful dark blue color, and is very
largely used as semi-precious jewel.
- Malachite, (CuCO3Cu(0H)2) a copper carbonate containing 58
percent of copper. In
only a few districts is it fomed in large enough quantities to be of
value as a commercial ore. It is dark green in color and the compact
pieces are valved as semi-precious stones.
- Adgadonite, (Cu6As) a copper arsenide found in Chili and the
Lake Superior district, bearing 85 per cent of copper.
- Horsfordite, (Cu6Sb) a copper antimonide with 76 per cent
of copper, found in Asia Minor.
- Covellite, (CnS) a copper sulphide bearing 66 per cent of
copper. This is a valuable commercial ore, found in Utah, Wyoming,
and a few other localities.
- Chrysocolla, (3Cu02Si036H0) a hydrous copper silicate with
36 per cent of copper. This ore is valuable as a commercial ore
and also as a semi-precious stone for mounting in jewelry.
- Stannite (Cu2SSn2S2Fe2S3)
a copper, tin and iron sulphide, with 30 per cent copper, 13
per cent iron, and 27 per cunt of tin. It is found in Ireland
and England.
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