Copper - the red metal

Peter Russell and Kelly Snyder

Native copper vein in shale, White Pine Mine, Michigan

Copper, a soft red-coloured metal, was one of the first metals to be used in the ancient world. It has been exploited for at least 7000 years. The name comes from the Greek, Kyprios, the name of the island of Cyprus in the Mediterranian Sea where copper occurs. The Latin, cuprum, (Cu) also means "metal of Cyprus," as the Romans had large copper mines on the island.

Copper is an excellent conductor of heat and electricity and is found in most of the flexible cables used in the world. Its softness also makes it suitable for tubing for water pipes and central heating systems because it can be easily bent to fit around corners. Above all, it can be mixed with other metals to make extremely useful alloys such as brass and bronze.
Copper is a metal that has been deposited from hot sulphur solutions, created in volcanic regions. The hot solutions concentrated the copper up to a thousand times more than would normally be found in rocks. The resultant enriched rocks are called copper ores.

About nine-tenths of the world's reserves of copper are found in just four areas: the Great Basin of the western United States, central Canada, the Andes regions of Peru, Chile and Zambia. In each case, the extraction of copper is of crucial importance to the country. The amount of copper in the ground is relatively small and most of it occurs in low-grade ores that have to be processed twice to extract the copper. This is why it is important to reuse as much copper as possible, and why about one-third of copper consumed in most industrial countries is recycled from scrap.
Copper is found as the pure metal and in combination with other elements. There are over 166 known copper minerals. Copper minerals are divided into five groups based on their chemistry.

Native copper

Sulphides - copper in combination with sulphur.
Oxides - copper in combination with oxygen.
Carbonates - copper in combination with carbon and oxygen.
Complex copper minerals - copper in combination with: iron, nickel, cobalt, lead, zinc or silver and other elements.

Volcanogenic massive sulphide deposits

Volcanogenic massive sulphide deposits are a major source of copper, zinc, lead, silver and gold. These deposits have been found actively forming at a temperature of 350ºC. Hydrothermal vents on spreading ocean bottom ridges, such as those found in the eastern Pacific Ocean, are actively precipitating metal sulphides. These deposits are formed by the discharge of solutions into the seafloor. 

Porphyry copper deposits

A Porphyry Copper Deposit derives its name from a porphyritic stock located at the center of the mineral deposit. A stock results from a cylindrical mass of magma, which moves up through the Earth's crust underneath a strato-volcano and cools. In a porphyritic rock, some of the minerals are very large crystals (up to 10 cm in length) and the rest are microscopic. Generally we find that the upper parts of the strato-volcano have been eroded away. The surrounding country rock, which has been intruded by the stock, is often metamorphosed by heat and pressure. During this metamorphism sulphide minerals form in the rocks surrounding the stock. Heat and pressure causes preexisting rocks to be altered into a new type of rock. An enriched mineral blanket or oxidized zone will then form near the surface of these deposits.

The porphyritic stock at the center of the system may not contain enough of the copper minerals to be an ore deposit. The rock that surrounds the stock however may be rich in copper mineralization. 
The porphyritic stock is the engine that allows the development of the minerals. The ore minerals are found in a series of zones radiating outwards from the stock. Each of these zones contains a specific suite of minerals. These minerals include azurite, malachite, gold, silver, chalcocite, and chalcopyrite.

The largest porphyry copper deposit of the Canadian Cordillera is approximately one billion tonnes with grades just under 0.5% copper; most are much smaller. At the present time, approximately half the world's copper reserves, 60% of Canadian copper resources, and 90% of British Columbia's reserves are contained in porphyry deposits.

(Left) Pouring molten copper into ingot molds, Calumet - Hekla Mines, Calumet, Michigan.

Oxidized zone minerals

Copper generally starts as chalcopyrite, a sulphide, which is then oxidized and enriched by interaction with the atmosphere, naturally acidic rainwater and nearby rocks and minerals. The top of an enriched copper deposit is a spongy mass of iron oxides left behind when iron sulphate and sulphuric acid are removed from sulphide minerals. The liquid generated then converts the copper sulphides into copper sulphate, starting a chain reaction. As the copper sulphate solution trickles down through the unsaturated zone of the deposit (where air and water are available) the reaction continues. If the solution contacts limestone or other rock containing calcium, the copper sulphate will react to form malachite and azurite which are copper carbonates. It can also react with copper sulphide (chalcopyrite) to form bornite and chalcocite.

Oxidized zones reach considerable depths in arid regions. The bottom limit of the oxidized zone is always at the water table (where the saturated zone begins). Oxidation stops here and without oxygen the reaction cannot continue. Other reactions take place as the copper sulphate reacts with the copper sulphides. The copper sulphides are enriched from 34% copper in chalcopyrite to 66% in covellite, one of the minerals formed in this enriched zone. By this process, copper is taken from the upper parts of an ore body and deposited at the water table. Below the enriched zone, the sulphides may not be concentrated enough to carry the cost of deep mining. Oxidized zones are found in arid regions of the United States, Mexico, Peru, Chile and Africa. Many attractive and colourful minerals are found in oxidized zones of copper deposits.

Uses for copper

Copper is second only to silver in its ability to conduct electricity (and is far cheaper and more abundant).

Bacteria will not grow on copper. Copper is essential to human beings as a micronutrient in our diets. It is used by the body to form bone cartilage, tendons and the sheathing around nerves. It is also a critical element in the manufacture of hemoglobin in the blood of higher animals.
About nine million tonnes of copper are used every year in a wide variety of ways. About half of all copper is used in the electrical industry.

In North America:
40% of copper produced is used in construction
24% for electrical and electronic products
13% Transportation equipment.
12% Industrial machinery
10% Consumer and general products.

Copper ingot, made from Pewabic Mine ore, Keweenaw Peninsula, Michigan. This ngot was recovered in 1974 from the Pewabic steamer which was lost in 55 metres of water off Alpine, Michigan, in 1865.

Famous copper deposits

Keweenawan Copper is associated with lava flows and conglomerates in the Keweenaw Peninsula of Michigan. This deposit is also seen at Mamainse Point, north of Sault Ste Marie. The copper was deposited mainly in conglomerates and flows of basalt, especially near the tops of the flows where the rock has gas bubble holes (vesicles). Hot water, containing sulphur and copper, migrated upwards through the basalt flows and moved across the top of the lava flows where it was sealed by the impermeable barrier of the overlying flow. Hematite (iron oxide) in the lava oxidized the sulphur, depositing copper. The iron and sulphur were carried away as iron sulphate. 

Sometimes the copper was deposited in fractures in the rocks. Some masses formed in fractures are of unusual size. The largest of these was a mass found in the Minnesota vein on the Keweenaw Peninsula in 1880. The mass weighed 500 tonnes and was 14 metres long, 5.7 metres wide and 2.6 metres thick. These large masses were difficult to mine profitably, so they are still underground!

Copper pebbles and boulders from the Keweenaw Peninsula were moved south by glaciers during the ice age. Copper was used by the native people to make tools. They hammered copper into the desired shape. This hammering made the copper harder just as a blacksmith tempers steel. When tempered in this way, knives could be made which were much better than the stone or bone knives used before.
Copper was used as early as 15,000 years ago. The metal was found as lumps of native copper and could be easily fashioned into jewellery, tools, or cooking and storage containers. The use of copper increased about 5,500 years ago with the discovery that it could be easily mixed or alloyed with other metals such as tin, zinc or lead. These alloys produced bronze and brass with with a variety of useful properties.

Mamainse point

In Ontario, native copper was first mined nearly 5,000 years ago along the eastern shore of Lake Superior. In the 1600s, Jesuit missionaries noted the widespread use of copper for fashioning jewelry and cooking utensils. These reports noted that pieces of copper were being cut from a large boulder of native copper on Michipicoten Island, near Wawa. Ontario's first copper mine was opened at Mamainse Point, north of Sault Ste Marie in 1770. Sparce ore reserves and a cave in, which caused the first mining fatalities in Ontario, closed the mine shortly after it opened. 

Bruce mines

The first successful copper mine in Ontario opened in 1847 at Bruce Mines on the north shore of Lake Huron, east of Sault Ste. Marie. Chalcopyrite ore was produced from this mine for 50 years. Deposits in the area were extensive and supported several mines, including the Pater Mine which opened in 1954. The Pater mine produced over 36,393 kilotons of copper prior to closing in 1970. 

Sudbury

The nickel deposits of the Sudbury area were originally worked for copper. The abundant nickel sulphides in the ore were considered a contaminant and made the extraction of copper difficult. A method for separating the two metals was discovered in 1891, a market for nickel was found and copper was replaced as the primary metal mined in Sudbury. 

Manitouwadge

Ontario's next discovery of copper ore was the rich deposits of the Manitouwadge area, north of Lake Superior. James Thompson, a geologist with the Ontario Department of Mines, located several areas of rusty weathering rock called gossan. Gossan, a spongy mass of iron oxides, forms by the weathering of sulphide minerals. Thompson's map and report sparked interest among the prospectors, though most were only interested in the gold potential. Finally prospectors realized the potential for copper in the area and staked what became the Geco and Wilroy Mines (Wilroy Mine is named for two of the prospectors - William Dawidowich and Roy Barker). The Geco Mine, owned by Noranda, is still in operation and has produced nearly 2 billion dollars worth of metals including copper, zinc and gold.

Timmins

Kidd Creek Mine in Timmins was found in 1959 by an airborne electromagnetic survey. Drilling, started in 1963, outlined what was the largest base metal mine in the world. Falconbridge's Kidd Creek Mine continues to produce most of Ontario's silver, zinc and a large percentage of the province's copper. Other products include indium and sulphuric acid. 

Copper alloys

Brass

Brass is one of the most widely used alloys. It is mainly copper, alloyed with between 5 and 40 per cent zinc. Brass is often used for corrosion-resistant decorative purposes such as door handles, locks and knockers. It is much harder and stronger than copper and it will machine well.
A form of brass can be made that changes its shape above a certain temperature and returns to its original shape when it cools down. This "memory" brass can be used to operate safety devices and other applications. It is used, for example, in the automatic switching devices in many electric jugs and kettles.

Uses for Brass:

Bronze

Bronze is an alloy of copper that is significantly different from
brass. Bronze is a copper alloy with tin as its major secondary constituent.

Bronze has been used since ancient times for decorative metal objects and also for coins. It was one of the earliest metal alloys used, giving rise to the first metal-working age, known as the Bronze Age, over 3000 years ago. Bronze Age people, however, did not know about alloying (mixing) metals, but used copper ores that naturally contained tin impurities.

There is a wide range of specialized bronzes, each one having its own distinctive properties. The brittleness of bell-making bronze makes bells liable to crack. However, this disadvantage is outweighed by the particulary sonorous tones made by the metal.

Uses for Bronze:

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