Mineral Commodities

Silver


Silver (Ag) is a metallic element with brilliant white lustre and a melting point of 962°C. It has the highest electrical and thermal conductivities of all metals and, although tarnished by sulphur, is relatively corrosion-resistant. Silver is second to gold in malleability and ductility, being easily rolled or beaten into foil or drawn into fine wire. Its use for ornaments and utensils predates recorded history. Silver has been an important medium of exchange since very early times. Mines in the eastern Mediterranean and Spain were early sources, but the centre of production had moved to the western hemisphere by the 16th century.

Important producing countries now are Argentina, Mexico, Peru, the Commonwealth of Independent States, the US, Canada, Australia, Chile, Poland and China. Photographic films and papers account for about 25% of the demand for silver. Industrial use, jewelry and silverware represent about 70% of fabrication demand. Industrial use includes electrical and electronic, eletrodeposition, mirrors and coatings, batteries, catalyst and water purification systems. Silver use in silverware is mostly in jewelry and works of art, as sterling silver (92.5% silver, 7.5% copper) and for silver plating. The use of silver in coinage is now largely confined to numismatic coins and medallions, although Mexico began to use silver in the production of 10, 20 and 50 peso coins for general circulation in 1993.

Silver is recovered from mined ores and recycled materials such as film, electronic devices, industrial wastes, silverware and jewelry. Approximately 20% of the silver produced annually is from recycled materials. Some silver is recovered from ores mined principally for the silver content, e.g., around Coeur d'Alene, Idaho, and Mexico. However, about 85% of mine supply is a by-product of treating lead-zinc-copper and gold ores.

Gold


Gold (Au) is a bright, shiny, yellow metal, notable for its high density (19.3 times the weight of an equal volume of water) and valued for its extreme ductility, strong resistance to corrosion, lustrous beauty and scarcity. Pyrite, or fool's gold as it is sometimes known, can be distinguished from real gold by its brittleness and hardness as well as the fact that it appears black in powder form.

As it is the least chemically active of all metals, gold usually occurs in a free or uncombined state. It is found as nuggets, flakes or dust in gravel and sand deposits along creeks and rivers, but more often gold is recovered from veins (called lodes) in bedrock. Gold is also produced as a by-product of base-metal mines; about one-fifth of Canada's gold production comes from this source.

There are various ways to separate and recover gold, depending upon the nature of the ore. When gold occurs in a relatively coarse, free state, it can be recovered by mechanical means such as gravity traps and shaking tables, where the gold separates out because of its high specific gravity. Cyanidation is a chemical process used to recover gold that is very finely distributed in the ore. The process is complex; it involves adding a cyanide solution to finely ground ore and then agitating it in the presence of air to dissolve the gold. After a variety of treatment steps, the solution containing the gold is clarified and the gold is precipitated by the addition of zinc dust to the solution. The carbon-in-pulp stage of this process uses activated carbon to collect the gold without having to filter the ground ore slurry. The activated carbon is stripped of its gold in an acid bath and then recycled.

Once the gold is separated from the ore and is in the form of an impure precipitate, it is placed, along with a fluxing agent, into a high-temperature furnace. A chemical reaction takes place, in which the flux and the impurities combine to form a slag and the molten gold sinks to the bottom of the furnace where it is drawn off and poured into moulds to form doré bars, which contain the gold and any silver that may have been present in the original ore.

World industrial demand for gold includes jewelry (86%), electronics (6%) and official coins (2.5%). Gold has been a symbol of wealth from the earliest civilizations to the present. Even though it is too soft for weapons or tools, people have treasured gold for its decorative and monetary value. Since it is chemically inert, it has long been popular in dentistry for crowns and caps. Resistance to corrosion, along with electrical conductivity, makes it useful in precision electronic equipment. When a thin film of gold is applied to window glass, a building's thermal properties are improved dramatically, reducing the amount of heat gain in the summer and heat loss in the winter, e.g., the ROYAL BANK building in Toronto.

Zinc


Zinc (Zn) is a bluish-white metal of low to intermediate hardness that melts at 419°C and is estimated to comprise about 0.013% of the earth's crust. Zinc is an essential element for human health; over 200 enzymes in the body require zinc for proper functioning. Zinc usually occurs as the mineral sphalerite. Geologically, zinc generally occurs concomitantly with copper or lead or both, which are recovered as co-products. Important minor by-products such as gold, silver and cadmium are often recovered as well. Ore bodies are mined using either open pit mining or underground mining, depending on the depth of the vein.

Brass, produced by coloring copper with the zinc mineral calamine, was in use 3000 years ago. Zinc was recognized as a metal in the late 14th century in India. It was identified as a separate metal in Europe in 1546. Zinc was introduced to China from India in the 17th century. European production began in 1743 at Bristol, England. Production in Canada began in 1916 at Trail, BC, when Cominco Ltd (now Teck Cominco) opened a small electrolytic plant, using ore from the Sullivan Mine. Production was hampered because the complex lead-zinc-iron ore was difficult to treat. In 1920 the differential flotation method was successfully used to separate out lead and zinc concentrates, marking the beginning of substantial zinc production in Canada.

All primary zinc metal production in Canada is carried out by the electrolytic process, which yields a product that is more than 99% pure. Solution purification, electrowinning and casting are preceded by either conventional roasting and leaching or by the zinc pressure leach hydrometallurgical.

Canada is the world's largest zinc producer. Preliminary estimates for production in 2001 indicate that Canada produced 1 009 571 tonnes of zinc, worth an estimated $1.4 billion. About 90% of production is exported as refined metal or concentrates; major customers are the US and Taiwan for metal, and Belgium, Germany, Spain, Italy and the Republic of Korea for concentrates. Zinc is used principally to galvanize steel as a protection against corrosion. The next most important use is in the creation of alloys such as brass and bronze, followed by use in die-cast products, e.g., small electrical appliances, tools, toys, automobile door and window handles and carburetors. Rolled zinc metal is used in dry-cell batteries and for roofing; zinc oxide is used in paints and as a catalyst in rubber manufacture. Zinc is also the primary ingredient in sunscreen.

Lead


Lead (Pb) is a silver-grey metal commonly found with zinc and copper sulphides as the mineral galena. Properties such as a low melting point (327.4°C), high density and malleability, corrosion resistance and a good ability to attenuate gamma radiation and sound vibration have led to a wide variety of uses. Lead oxide was used for pottery glazing as early as 7000 to 5000 BC, and lead was one of the earliest smelted metals. It was used for coinage in China and Greece, and about 100 BC the Romans began using it for plumbing and solder. Roofing and ammunition applications developed during the Middle Ages. Lead-acid batteries, which account for the largest use of lead today, were introduced in 1911. More recent applications capitalize on lead's ability to block gamma radiation and dampen sound vibration. Lead is used for electronic equipment, chemicals, alloys and cable sheathing, and as a protective barrier against nuclear radiation or X-rays from televisions, computer monitors and medical-dental equipment.

Lead is extracted from mined ores containing zinc, silver and minor amounts of copper. It is also recovered from recycled materials; more than 50% of world metal production comes from recycling, making lead one of the most recycled metals in the world. Canada mines approximately 149 000 tonnes of lead annually, refines about 285 000 tonnes and recycles about 126 000 tonnes.

Indium


Indium is a soft, gray metallic element with a bright luster and a very low melting point. It is relatively rare and ranks 61st in crustal abundance. It is about three times as abundant as silver.

Indium's current primary application is to form transparent electrodes from indium tin oxide in liquid crystal displays and touchscreens, and this use largely determines its global mining production. It is widely used in thin-films to form lubricated layers (during World War II it was widely used to coat bearings in high-performance aircraft). It is also used for making particularly low melting point alloys, and is a component in some lead-free solders.

Indium is not known to be used by any organism. In a similar way to aluminum salts, indium (III) ions can be toxic to the kidney when given by injection, but oral indium compounds do not have the chronic toxicity of salts of heavy metals, probably due to poor absorption in basic conditions. Radioactive indium-111 (in very small amounts on a chemical basis) is used in nuclear medicine tests, as a radiotracer to follow the movement of labeled proteins and white blood cells in the body.

A small amount of indium is used to make every liquid crystal display screen. This is the primary use of indium today and accounts for over 50% of consumption. These LCDs are key components in laptop computers, flat panel monitors and flat panel televisions. They are also in cell phones, PDAs, digital cameras, clocks, watches, GPS receivers, answering machines and other electronic devices. Many of these are in very high demand and LCDs are being incorporated into an increasing number of devices.

The United States does not produce any domestic indium and relies on imports from China, Canada, Japan, Russia and other countries. China controls over 60% of the world's refined indium production.

On the demand side the growth of LCD products is increasing and this will support the price of indium. On the supply side the association of indium with zinc production from sphalerite causes the commercial availability of new indium stocks to be 100% dependent upon the mining of sphalerite. This makes it very hard to increase the production of indium when demand for zinc is low. Fortunately, the current demand for zinc is strong and that should support a steady indium supply.

Source: www.thecanadianencyclopedia.com, http://en.wikipedia.org/wiki/Main_Page