Geology, Geology Talk

Celebrating a golden anniversary

This month my wife Pam and I celebrate our 50th wedding anniversary – our golden anniversary. I spent a lot of time trying to think of something gold to give to Pam. Instead, I have decided to take the lead from Your Song, recorded by Elton John in the 1970s. To paraphrase, the lyrics go something like this:

My gift is my [article]
And this one’s for you …
And you can tell everybody this is your [article] …

Let me explain why I have resorted to this simple gift.

Even though gold is relatively scarce in the earth, more than 2700 tonnes (or 3000 US short tons) of gold is mined every year.

Gold is concentrated by geologic processes to form commercial deposits of two principal types: lode deposits and placer deposits. Lode deposits are the targets for the “hard rock” prospector seeking gold at the site of its deposition from mineralising solutions. Placer gold is the stuff people “pan” for. Concentrations of gold eroded from lode deposits are carried downstream as flakes, grains or nuggets, and subsequently are concentrated in pockets containing stream bed sediments, where the current slackens.

Gold can survive being eroded from rock and carried downstream because it is a “noble” metal – it does not oxidise under ordinary conditions. In addition, pure gold is relatively soft and is the most malleable of metals. Because of these special properties, gold does not have to be smelted to be used, and was among the first metals to be mined and turned into useful objects.

More than 5000 years ago, artisans in Egypt lavishly decorated tombs and temples with gold and golden objects. In ancient America, gold had both symbolic and spiritual meaning in Aztec society. This was strange, though, because the word for gold in Aztec dialect is teocuitlatl, which means “excrement of the gods”!

Gold has a variety of applications. In 2015 about 41 per cent of the gold consumed for commercial products was for jewellery. But I would not dare buy jewellery for Pam without her approval, so gold jewellery is out.

About 34 per cent of gold is used in solidstate electronic devices. These devices use very low voltages and currents that are easily interrupted by corrosion at the contact points. Gold is a highly efficient conductor that does not corrode, so it is used to plate the metal contacts on integrated circuits. Pam is quite happy with her flip-phone, so electronics are out.

Ten per cent of gold was used for official coinage. No way would a gold coin make an appropriate anniversary gift.

Three per cent of gold is used in dental and medical applications. Gold alloys are used in dentistry for fillings, crowns and bridges because it is chemically inert and non-allergenic, and because less inert materials might have an adverse effect on long-term health. I doubt a gift certificate to the dentist is what Pam has in mind.

And speaking of health, one of the most ingenious uses of gold is to remedy a condition where a person cannot close their eyes completely. The condition is treated by implanting small amounts of gold in the upper eyelid. Gold is very heavy and weighs down the eyelid, helping it to fully close. Hmmm … nope, I can imagine Pam rolling her eyes right now!

The remaining two per cent of gold is used for things such as making glass red, coating the visors on astronauts’ helmets, gold nanoparticles and so forth. They even put gold on ice cream cones and in champagne. Uhmmmm … nope!

So, Pam can tell everybody this is her article. Happy anniversary, my dear!

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