Uses:

Gold is the most malleable and ductile of all metals. A single troy ounce of gold can be beaten into a flat sheet measuring roughly 5 meters on a side. Thin sheets of gold, known as gold leaf, can be as thin as 0.000127 millimeters, or about 400 times thinner than a human hair.

Pure gold is soft and is usually alloyed with other metals, such as silver, copper, platinum or palladium, to increase its strength. Gold alloys are used to make jewelry, decorative items, dental fillings and coins. Gold is a good conductor of heat and electricity and does not tarnish when it is exposed to the air, so it can be used to make electrical connectors and printed circuit boards. Gold is also a good reflector of infrared radiation and can be used to help shield spacecraft and skyscrapers from the sun's heat. Gold coated mirrors can be used to make telescopes that are sensitive to infrared light.

Measurements

Commonly used measurements often used when dealing with gold are carat and troy ounce.

The amount of gold in an alloy is measured with a unit called a carat.
One carat is equal to one part in twenty-four, so an 18 carat gold ring contains 18 parts pure gold and 6 parts alloy material.

Precious metals like gold are measured in troy ounces and troy pounds. The troy ounce is approximately 10% heavier than a typical grocery store (avoirdupois) ounce. A troy pound weighs approximately 17% less than a grocery store pound.

20 pennyweights = 1 troy ounce = 31.10 grams

12 troy ounces = 1 troy pound = 373.2 grams

History:

An attractive and highly valued metal, gold has been known for at least 5500 years. Gold is sometimes found free in nature but it is usually found in conjunction with silver, quartz, calcite, lead, tellurium, zinc or copper. 

It occurs in either veins or alluvial deposits and is recovered by hard rock or placer mining. The gold deposits of the Klondike region were placer deposits.  This meant the gold could easily be extracted by panning or sluicing and didn't require the need for heavy earth moving equipment or blasting. 

It has been estimated that all of the gold that has currently been refined could be placed in a cube measuring 20 meters on a side.