You found an ounce of placer gold! Congratulations! How pure is your natural placer gold? Maybe less than you think.
At $2,300 per troy ounce that gold could be worth as high as $2,1855 or could be as low as $1150. It all depends on the purity of the gold. Gold is the pure metal but since no nuggets or placer are pure, gold found in nature is actually an alloy of gold, silver, and/or copper with gold being the majority metal. That’s why gold looks so different from different areas! The color is affected by the amount of copper and silver that’s mixed in.
Here’s a simple color spectrum chart that explains why your gold looks the way it does.
When gold is mixed with too much silver or too much copper, it stops being gold and becomes something else. It can even sometimes form an alloy naturally with its friend silver.
Electrum: The Natural Gold-Silver Alloy
Electrum is the official name for any naturally-occurring alloy of gold and silver that’s 20-80% gold and 20-80% silver. Only silver can alloy, or intermix with gold naturally in sufficient quantities where you can find specimens that are half silver and half gold. Copper, while almost always found in naturally occurring gold, is only present in small amounts.
Even at 20% silver the alloy becomes so unrecognizable from gold, that often prospectors don’t know what they’re looking at and toss it away. Electrum is incredibly rare, and is mostly found in the gold mining regions of Turkey or the state of Nevada in the U.S.
Rose Gold: Manmade Gold-Copper Alloy
Rose gold is the most common name for the alloy of gold and copper to achieve a golden look with a reddish hue. Rose gold is entirely manmade and does not occur naturally! It is used quite often in jewellery.
Bound Silver-Copper Nuggets
In the Upper Peninsula of Michigan, around old copper mines, you can find natural nuggets that are a mix of copper and silver. For some apparent reason the locals call these “half-breed nuggets.” Silver and copper adheres together strongly, but doesn’t alloy the same way gold and silver does.
100% pure gold actually doesn’t exist
The purest gold in the world is 99.99999% pure. That’s what you find stamped on gold bullion.
That level of purity is achieved through the refining process. Currently, there isn’t a viable method to produce 100% pure gold due to the fact that it would cost more than the gold’s value to remove those last impurities on a molecular level.
Defining purity: Karats and Fineness
The best known methods for defining the purity of gold is by Karat and Fineness. Karat is used when referring to gold. It is the amount of gold alloy out of 24 parts. Meaning 22k gold is 92% pure gold with 8% being a combination of other alloys or impurities mixed into the gold, such as silver or copper.
The fineness of gold represents the weight of gold, in proportion to the total weight which includes any other base metals and impurities, in parts per 1000.
Placer gold is more pure than lode gold
Lode gold is gold that is found in veins in rocks. This is the type of gold that most inland commercial mines are after these days. There are various types of lode deposits that require specialized methods to extract and mine but at its simplest form, lode gold is the veins of gold found in rocks that are the source of placer gold.
Placer gold is gold that has eroded or broken off from the main lode vein and traveled down mountains, in waterways, with the heavy gold settling on the bottom of streams, lakes, rivers or the sea floor. This is the type of gold most miners are familiar with, the stuff you can find with a gold pan.
As it travels impurities and corrosive metals such as copper, quartz or silver are eroded away, making placer gold on average much purer than lode gold. However, due to the soft nature of gold, other impurities work their way into the gold under the surface area, which means it’s never 100% pure.
Natural gold purity ranges are extremely broad
The percentage of pure gold in a placer deposit is a tricky thing to pin down as it can fluctuate dramatically within a small area. It can be as low as 50% pure or as high as 95% pure. Most gold is somewhere between those extremes. U.S. natural gold purity is typically cited between 70% and 85%.
How can I test the purity of my gold?
First thing you can do is look at it. The deeper the yellow-orange color, the more pure your gold is. Compare it to gold bullion if you have any lying around. A more reddish color means it has more copper and a whitish color means it has more silver.
Another option is to perform an “acid test” on your gold. You scratch your gold on a dark slate and use acids to see if it dissolves. The stronger the acid required to dissolve your gold, the higher the purity. It’s cheap and simple, but it’s a bit of a process and doesn’t give you much precision if that’s what you want. The other problem with acid tests is that you may damage the natural state of the nugget or gold and actually de-value it.
Get an Assay Done by a Refining Company
The acid test has limits. For one it just gives you an estimation within a couple of karats. Another is that it just tests the outside of a piece of gold. A gold nugget could have larger chunks of impurities hidden inside.
Know if you send and sell gold to a refiner they’re going to take a % of the metal or cash as a payment for their services, so it can be a lot more expensive than a simple at-home acid test. But if you want a truly accurate read, especially if you have a lot of gold, it’s a favorable option.
DO NOT melt down your gold nugget to remove impurities!
Maybe you have a gold nugget and you want to determine the purity. If this is something you feel compelled to do, the acid test is your best bet. You won’t get a perfectly accurate read on impurities in the nugget, but you don’t want to melt it down either because you’re losing the value and the beauty of the nugget!