Gold is such a unique metal, displaying properties unlike any other metal, even fellow precious metals.
We can all glimpse gold jewelry as we pass stores and other adorned citizens each day, but how exactly is gold made into, well, gold?
Here’s the part most of us never contemplate－how dull, lumpy rocks of ore are refined into that most desirable of metals.
Gold is extracted from the earth, and although bygone eras saw miners panning for gold in streams and rivers, they were merely skimming off the limited quantities of gold exposed by our planetary weather over millions of years.
The modern commercial search for gold means digging and digging deep.
The gold mined today is dug out of the soil in intensive, expansive operations that are highly mechanized.
Gold deposits are identified by geologists, and valuable quantities are then mined out of the planet’s crust as a gold-containing rock.
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From rock to glittering metal
Unfortunately, pure gold bars aren’t found simply buried beneath the soil on this planet.
Instead, gold-containing rock is chipped, blasted, and shoveled out of deep shafts purposefully dug to follow gold seams.
It’s dangerous and heavy work, and a lot of energy needs to be expended to bring the fragmented rock or gold ore to the surface for processing.
Four broad approaches are taken to mine gold.
The placer method is popular with amateur gold hounds, as it involves using available water and gravity to separate gold out of the substrate, usually river and stream beds.
Commercial operations practice more sophisticated bulk extraction, and hard rock (digging shafts into rock containing gold seams), ore (chemically liquidizing traces of gold from ore), or by-product mining (mining for gravel or rock and generating gold as a by-product) are practices common to every country, no matter the prevalence of any one methodology.
That said, gold ore processing involves using cyanide and other potentially hazardous chemicals and processes, and then often in pursuit of limited quantities of gold (making it expensive), hence it’s the least favored method of today.
So much for mining and bringing gold to the surface－now it needs to be separated out from the carrier rock.
That starts by crushing the rock into sand grain-sized particles, where after a chemical treatment called “leaching” primes the gold to separate from the rock in the next step.
A tremendously high heat (around 1600° Celsius!) smelts the processed mixture, allowing the gold to sink and be separated out from the waste slag.
Finally, gold emerges
Refining the gold we employ in coins and jewelry involves further eliminating the impurities in the gold residue obtained from the smelting process.
Here, further intense heat is applied, along with chemicals and pressure, in a process that results in a very pure gold residue.
Modern electrical processes enable the removal of all impurities from the gold, and it’s fair to say that modern gold is “cleaner” than the gold of bygone eras.
Electro-refining (as the process is called) sees electricity coursing through a solution of the chemical gold chloride in which the gold is immersed, finally resulting in the pure metal being cast as coins or bars.
Apart from this electrolysis methodology, another process called pyrometallurgical chlorination is also employed.
In this process, chlorine gas gets pumped into the molten gold, which sees impurities evaporate as chlorides, or form on the surface as a final slag layer.
When purple fumes from the chloride gas appear, that’s a sign of the gold’s purity sitting at the (internationally agreed minimum) of 99.5 to 99.7 percent gold purity.
The finally refined gold is then typically assayed in a laboratory, and although the aim is for 99.9 percent purity in gold (and silver), a 99.5 percent purity is the internationally accepted minimum.
As 24 karat gold melts at just below 2000°, the process of pouring bars and minting coins is still labor, but from now on manufacturers are working with pure gold.
The molten gold is typically poured as long strips which are then annealed and pressed into the gold bars we’re familiar with.
As you can see, a heavy industrial process that involves giant machinery and huge smelting furnaces of intense heat is needed to produce the gold metal that we encounter as jewelry and gold coins.
The intensity (and cost) of the process that finally produces pure gold from the soil, goes some way to explain why all of us aren’t digging for nuggets in our backyard!
Also Read: How Much Gold is There in the World?