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Roger Weller, geology instructor
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Gold, Silver, Copper
Simara Hubble
Physical Geology
Fall 2005


Precious Commodities


Image Courtesy of Stan Celestian
Glendale Community College

Gold

Gold, element Au, has been known to mankind for thousands of years, or as most sources claim, since “ancient times”. Its value has stood the test of time and its uses have progressed from monetary and decorative to industrial and technological.

Where is it found?

Native gold, amounts of the element that are not contained in an ore are very rare. According to Mine-Engineer.com, the Earth’s crust “averages a mere 0.004 grams of gold per ton.” Most gold is found in concentrated miniscule portions, in nugget form in alluvial deposits or in ore. In the case of ore, it is broken down so that the small amount of gold can be separated from the rock.

Quartz with Gold
Image Courtesy of Brooks R. Dillard
YupRocks.com

Gold Ore:
White quartz veins or massive quartz are forms of gold ore. Quartz itself is the most common mineral on our planet. Gold is also found in relation to copper ore.

Alluvial deposits:
Alluvial meaning loose sediment that is carried by a flowing stream or river and is deposited in a mixture of dirt and gravel in riverbeds and mouths, creating deltas and point bars, for example. The deposits along the river are also called placer deposits, which consist of gold nuggets. Gold nuggets are rare and are extracted from an eroding igneous rock. Since gold is dense, the method of “panning” for gold is used to recover the nuggets from the gravel.

Oceans:
There is a considerable amount of gold in seawater. However, there is currently not a cost-effective method for recovering it.

U.S. domestic gold mining production was 353 tons in 2000 and 247 in 2004 (USGS). Dominant gold producing areas in the United States are Nevada, Alaska, California, South Dakota, Colorado and the Sierra Nevadas. Globally dominant gold mining areas are South Africa, China, Russia and Australia.

Economic Uses:

Gold is an excellent conductor of electricity, highly malleable, ductile, sectile, resistant to corrosion and tarnish (it is only dissolvable in aqua regia) and obviously attractive. These factors allow it to be used in jewelry, decoration, and electro, dental and computer technology. Mark Winter of WebElements states that gold is “the most malleable and ductile metal; 1 ounce (28 g) of gold can be beaten out to 300 square feet." Because gold is soft and also rare, pure gold itself is not normally used for the aforementioned tasks, rather, gold alloy is used. In 2004, U.S. domestic gold production was broken down in terms of use as: jewelry and arts, 92%, electrical and electronics, 4%, dental, 3%, and other, 1% (USGS).

Most well known is the use of gold as money, a medium of exchange for the past three thousand years (The Privateer). This use was due in large part to its durability, common appeal, and scarcity, among other factors, all of which are necessary for a material to be used as a medium of exchange as defined by The Privateer. Contrary to what one might assume, gold has not been used as a reserve currency since 1971 (The Privateer). The reason being is that there is simply not enough of it to accommodate the global markets of the world’s industrially advanced economies and less developed economies do not have access to it at all (The Privateer). The concept of paper money can be traced in part to paper “receipts” that goldsmiths would issue in return to commercially storing gold for those who owned it (The Privateer).

The Gold Industry:

“From 1837 to 1934, one U.S. Dollar was fixed at 23.22 grains of Gold” (The Privateer). Gold was used as a reserve currency, that is, gold was the true money, and paper was merely the evidence of possession, until 1971. In fact, early U.S. fifty dollar notes clearly stated that they were redeemable in gold (The Privateer). The common unit of weight for gold is the troy ounce, equal to 31.1034807 grams (Gold Information Network). The price for a troy ounce in the U.S. has varied from twenty U.S. dollars in 1934 to as high as eight hundred and fifty in 1980, due to certain national and global economic situations. One of the significant events that are pointed to in relation to the volatile gold prices is the separation of gold from the value of paper currency and the creation of a floating currency. According to The Privateer, one ounce of gold is currently worth approximately 480 U.S. dollars, 419 Euros, 286 U.K. pounds and 58,568 Japanese Yen. These prices are highly monitored, and highly subject to change.



Image Courtesy of Brooks R. Dillard
YupRocks.com

Copper

Copper, Cu, the second element focused on in this report has been key to the evolutionary progress of mankind since prehistoric times. Pure copper has been used for weapons and decoration, and the discovery of strengthening it by creating alloys has propelled civilizations into new eras.

Where is it found?

Like gold, native copper used to protrude through the surface of the planet. It was visible, with no mining necessary to aid in its discovery. Man’s eventual search for the mineral led to digging for it once it was no longer visible. Unlike gold, placer deposits of copper nuggets are very rare (http://www.unr.edu/sb204/geology/smelt.html) and while native copper is still produced from existing mines, it is now primarily extracted from copper ore (www.unr.edu).

Copper in Basalt
Image Courtesy of Roger Weller
Cochise College

Basaltic Lavas:
Native copper is found as cavities in basaltic lava rocks, such as the Andean Mountains in Chile. (www.desertusa.com).

Copper Ore:
Copper combines with other elements to form many different minerals. Oxidized ores, such as malachite, azurite and cuprite, can be used to produce marketable copper normally through a process by which copper concentrate is extracted (http://www.unr.edu/sb204/geology/smelt.html). Sulfide ores like chalcocite, chalcopyrite, bornite, must first go through a process called “leaching” and then “precipitated” before the produced copper can be smelted and refined (www.unr.edu).

Copper is also recycled; in fact “40% of the world's demand is met by recycled copper” (www.schoolscience.co.uk/).

Bingham Canyon in Utah still produces copper, although it the low grade copper ore discovered there has been mined for over a hundred years (www.unr.edu).

U.S. domestic copper mining production was 1,450 tons in 2000 and 1,160 in 2004 (USGS). Arizona is still the largest copper producer in the United States. Utah, New Mexico, Montana and Nevada contribute to the majority of production as well (www.unr.edu). More dominant than the United States in mining production is Chile, with Peru and Indonesia a close third, then fourth.

Economic Uses:

Less dense than gold and silver, copper has found the most practical uses in society. Like gold, it is also malleable, ductile and sectile. “A copper bar 4 inches thick can be heated, rolled, then drawn into a round wire so thin that it is thinner than a human hair” (www.unr.edu). In ages past, it has been used as weaponry, utensils and decoration. Now it is still primarily used for its electrical conductivity. “60% of copper is used in electrical and electronic goods” (School Science). Copper is also used for motors, appliances, plumbing, utensils, coinage and communications. Bronze and brass are both useful alloys of copper, combined with tin and zinc, respectively. Copper has also been used as money, although it never achieved the value of gold or silver.

The Copper Industry:

The average price per pound of copper in 2004 was $1.32 (domestic producers), and $1.28 (London Metal Exchange) (USGS). In 2000, the average price was 88 cents (domestic producers) and 82 cents (London Metal Exchange) (USGS). Regardless of the continued mining and refining of copper and copper ore, the demand is exceeding the current supply, according to the USGS. Given copper’s individual uses for nearly every aspect of our daily lives, this is not surprising. As developing countries are able to advance industrially, this demand will only increase. Acceptable substitutes for copper are used, such as aluminum, steel and plastic. These materials, however, cannot rival the superior heat and electrical conductivity of copper.



Image Courtesy of Brooks R. Dillard
YupRocks.com

Silver

Silver, element Ag, is the most electrically and thermally conductive metal known. Discovered by mankind not long after copper and gold, it has been used for thousands of years in ornaments and utensils, and has had an important role in the chemical and photographic industries.

Where is it found?

Like the other precious metals discussed, occurrences of native silver are rare in our current age. In fact, according to the Silver Institute, silver is normally found unintentionally as a “plus” while mining for other base metals.

Silver Ore:
Silver is normally found in association with other minerals. It can be found in the oxidized zones of ore deposits, such as prousite, pyrargyrite and galena and also in sulfide ore veins. Silver occurs frequently in nature with lead and/or zinc, gold or copper ore.

For the most part, silver is commonly produced as a by-product in mining. According to the Silver Institute, 32% of world silver production was due to its occurrence in lead and zinc ore. The U.S. produced 1,860 tons of silver and 1,200 in 2004 (USGS). The leading silver producing states are Alaska, Nevada, Arizona and Michigan. Globally, the dominant silver producing areas are Mexico, Peru, Australia, China and Poland (The Silver Institute) for 2004.

Silver
Image Courtesy of Roger Weller
Cochise College

Economic Uses:

Silver serves many uses in industrial technology. Silver coated steel bearings are used in jet engines. Silver is also malleable, ductile and sectile, in fact, it sometimes crystallizes in nature as delicate wires. It is also catalytic, bactericidal, photosensitive (silver halides), highly reflective, non-corrosive (the tarnish associated with silver does not affect its commercial uses for the most part) and the most thermally and electrically conducive metal. Silver halides are photosensitive, and are used on photographic film. The invention of the digital camera however, is lessening the demand for conventional cameras. Silver’s catalytic properties are used to create the chemicals formaldehyde and ethylene oxide used in the beginning stages of plastic production. Silver is also used in jewelry, tableware, mirrors, electrical and electronic products, batteries, dental technology, water purification and coinage.

Silver, while not used as a reserve currency in most countries, is still used as a medium of exchange in the form of coins. In the U.S., we have the silver dollar, more a collector’s items than money and in Africa or the Middle East, silver coins are also used in place of paper money when acceptable. Mexico still uses silver as an official part of its currency. According to The Silver Institute, most countries used silver as money for day-to-day purchases, until the increasing amount of gold available lessened the demand for it.

The Silver Industry:

Silver is also measured in troy ounces, like gold. The average price for a troy ounce of silver in 2004 was $6.46 in comparison to $5.00 in 2000 (USGS). Despite suitable substitutes for silver such as aluminum, rhodium, tantalum and stainless steel, world demand for silver still exceeds the world supply (USGS). As stated before, most silver is found with other precious and base metals ores. According to the USGS, the discovery of silver as a byproduct of demand for silver bearing base metals will be a continuing factor in world production.


It is clear that these precious metals are not merely tools used by our ancestors in their early civilizations. These are not merely ornaments that you wear on your wrists, fingers and ears. They have many applications, uses integral to objects we use without consideration to the inward components. They will continue to be useful to mankind; indeed, the only concern with these metals is in the continuance of their production.


Sources Referenced

Glendale Community College Earth Science Image Archive
Gold – Dr. Stephan Rudolph
The Mineral and Gemstone Kingdom
Mindat.org
The Privateer
The Gold Information Network
About.com – Gold
Mine-Engineer.com
USGS Minerals Information – Mineral Commodity Summaries
schoolscience
WebElements
Amethyst Galleries
Bottega del Rame
Early History of Copper Mining and Use Geology Project Homepage
Copper.Org
DesertUSA
Copper – Dr. Stephan Rudolph
The Mineral and Gemstone Kingdom
Amethyst Galleries
WebElements
Silver – Statistical Compendium
The Silver Institute
Silver Mineral Data
Glendale Community College Earth Science Image Archive
Wikipedia.org – Silver
Silver History
History for Kids