Finding your own natural gold is the most exciting part of gold prospecting and mining. After a long day of hard work, just a small amount of gold will make it all worth it in the end. With that said, one of the most common questions new miners ask is how much of their natural gold is made up of real gold, and how much consists of impurities.
So, how pure is natural placer gold? Nearly all natural placer gold has a purity somewhere between 60% up to slightly above 95%. Mostgold found in the US is 70%-85% pure. Australia is especially known for its pure natural gold, which can reach purities of 95% or more.
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Vocabulary: Natural gold is referred to as placer gold in this article, which by and large is the same thing. If you want to know more, my guide to placer gold explains it all in much greater detail
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While some regions are known to have purer gold than others, there will inevitably be significant local variations depending on where you are mining.
In addition, to some extent, the size of the gold can affect purity as well. As a rule of thumb, finer gold tends to be purer than bigger gold pieces.
Due to the above reasons, it’s impossible to know with 100% certainty how pure the placer gold of your area will be before you’ve actually tested it yourself.
So, this article will look closer at everything that has to do with the purity of gold, including how to ascertain the purity of a gold piece using two different methods.
Table of Contents
What Affects The Purity of Natural Placer Gold?
The purity of natural placer gold can vary quite a lot, even within the same region. The exact purity depends on a variety of factors, such as:
- The exact spot: Less pure placer gold will be lighter, and therefore deposit at slightly different locations than heavier gold of higher purity.
- The origin of the gold: Rivers stretch for incredibly long distances, and will pick up gold from many different locations. All of these are likely to have gold of varying purity.
- The size of the gold: As mentioned in the introduction, smaller gold is generally purer, since there is less opportunity for other metals and impurities to continue to stay clung on to the gold. However, there are many exceptions to this rule, so don’t rely too much on it!
- Time in the river: The longer time gold has spent in a river, the purer it tends to get. The reason is that water constantly acts on the gold and manages to remove much of the more reactive metals that can make up a large percentage of the impurities. When it comes to larger gold pieces such as nuggets, the surface skin which is subjected to the forces of the stream will have the highest purity, while the impurities increase toward its midpoint.
How Much Gold Purity Could Vary Within a Region: (Study)
To just give you an idea of how big the differences in gold purity could be within a region, I thought it would be a good idea to bring up a study conducted by the University of Alaska. The study was carried out back in 1981 and includes over 41 mining districts spread scattered across six regions.
The study found that the purity of the examined gold ranged from 56,7% up to 99,5%. However, while the lowest individual sample marked the floor of that range, the mean value for the same district was 78.9%.
In other words, there can be great variations within a location that typically yields pretty normal gold. In the example above, the average purity was just under 80%, but despite this, some of the gold wasn’t even 60% pure!
Where Does the Purest Placer Gold Come From?
It’s impossible to say where the purest placer gold comes from. As we have covered so far, the local variations are significant. Stating that gold from one specific area will be of a certain purity will prove to be false in a lot of cases.
However, Australia is well-known for its rich placers that can reach purities of 96% or even higher, often in the form of gold nuggets. In fact, the biggest gold nugget in the world, popularly named “Welcome Stranger”, was found in Australia and weighs in at 2,520 troy ounces (78 kg; 173 lb).
How to Test the Purity of Natural Gold
If you just want to get a general idea of the purity of a gold piece, you could just look at its color. Simply put, the deeper the yellow/orange color, the higher the gold content.
However, this method is not that reliable, since the color of the gold not only varies depending on purity, but also depending on what types of impurities it contains.
For instance, silver will give the gold a more whitish appearance, while even small percentages of copper will add a reddish tinge.
If you want to get a more accurate figure there are many other ways to test gold. These range from big and expensive $40,000 machines, down to cheaper methods such as the “scratch test”, which can be performed easily and for a cheap price in the comfort of your own home!
Let’s look closer at the last option!
Scratch Test: How To Test Gold at Home
To test gold using this method, you must first get a gold test kit. This will include:
- A black tile
- Several bottles of acids, each capable of dissolving gold of a specific purity
Gold testing kits are really cheap, and will last for a long time. Here is one I recommend.
To carry out the test, you scratch your gold piece against the tile, which will leave a tiny streak of gold. You then put dots of acid onto the gold streak to see which one dissolves the gold.
By watching which acid was able to dissolve the gold, you will be able to ascertain its purity. Clever, isn’t it?
What Are Gold Impurities Made Up Of?
Since placer gold isn’t made up entirely of pure gold, you might wonder what those other elements are.
Most of them are other metals that form natural alloys together with gold. In simpler terms, you could say that they blend with the gold, meaning that they also impact properties such as weight and appearance.
Let’s have a closer look at the most common impurities!
Silver
The most common impurity found in placer gold is silver. In fact, it’s so common that an alloy containing at least 20% silver is called “electrum”. Due to the high silver content, electrum often has a pale yellow or yellowish-white color, which has deceived many beginning prospectors into tossing it away! In some cases, the gold could even have a greenish tint.
Electrum is commonly found in the state of Nevada.
Copper
The second most common type of impurity is copper, which adds a reddish tinge to the gold, even though it rarely reaches really high percentages. Copper seldom makes up more than 5% of the total gold weight.
Other Impurities
Here are a couple of other impurities :
- Iron: Since iron is such a reactive metal, it will not last for long in a river before it rusts away. In other words, gold that contains iron only usually do so in very small quantities.
- Palladium: Palladium laden gold nuggets are quite uncommon, and are known as “porpezite”. Porpetize usually contains between 5 -10% palladium, sometimes together with some silver as well. Its color is often described as bronze-like.
- Lead: In some places, such as in the Mother Lode of California, lead is commonly found in free gold.
How Does Purity Affect Price?
The price you will be able to charge for your gold is dependent not that much on the actual purity, but on to whom you sell the gold, and its size and shape.
The only time when purity becomes a critical factor is when it’s unusually low or high, or when you are selling to a refinery, which usually only pays you for the scrap metal value.
In most other cases, buyers are not that concerned with the actual purity. For instance, a local dealer won’t have the gold tested, but just offers 80% of the market spot price, if that’s his rate.
In the same way, a collector or jeweler will be paying for beautiful gold pieces, and won’t care if the purity is 70% or 80%.
if you want to learn more about selling gold and how much you can charge for your placer gold, I recommend my complete guide to selling placer gold and nuggets.
Conclusion
- The purity of placer gold depends on factors such as location, how long it has been worked by a river, and its origin.
- The most common impurities are silver and copper, which form natural alloys together with the gold.
- Gold purity can be ascertained easily with a gold testing kit and doesn’t cost many dollars.
- The purity of your gold doesn’t affect price that much, unless you are selling to a refinery.
Happy Prospecting!
