If you ever have struck a gold nugget while prospecting, you have probably experienced what many would call gold fever. And in your elevated state of mind, you might very well have asked yourself how much of the piece you hold in your hand is made up of real, pure gold. So, are gold nuggets pure gold?
Gold nuggets are not pure gold as they are metal alloys. In simple terms, this means that the gold is mixed with other metals such as silver, copper, palladium, or iron. Most gold nuggets found in the US are 70%-90% pure. Australian nuggets are well-known for their high purity, which can reach upwards of 96% in some cases.
In this article, we’ll look at the various aspects of gold nugget purity. Among other things, you’ll learn:
- How to get an idea of what metals are present in a gold nugget
- How to test gold nuggets for purity
- How purity affects the value of gold nuggets
Let’s Get Started!
Table of Contents
What Are Gold Nuggets Made Up Of: How to Tell
Gold nuggets are never 100% pure gold but are mixed with other metals, effectively becoming different types of metal alloys. A metal alloy simply is when two metals are mixed together.
To the untrained eye, every gold nugget will look quite the same. However, once you gain some experience and read up on how a nugget’s color changes with different metal contents, you will soon be able to determine their composition with at least some accuracy. For instance, a pale nugget is very likely to contain a lot of silver, while a reddish tinge suggests that copper is present.
Here are the most common gold alloys you’ll find in gold nuggets:
Silver
Being the most common metal found in gold nuggets, a gold alloy containing silver even has got its own name. An alloy containing more than 20% silver is called “electrum” and has a pale yellow or yellowish-white color. Over the years, many prospectors have found electrum only to toss it away, mistaking it for other less valuable metals. In some cases, silver and gold alloys could have a somewhat greenish tint as well.
Practically every gold nugget, regardless of purity, contains at least some silver.
Copper
Copper is the second most common metal found as an alloy together with gold. However, it seldom makes up more than 5% of the total weight of the nugget. Still, it will give it a somewhat reddish tinge.
Palladium
Palladium can sometimes be found in gold nuggets, although it’s quite rare. When palladium is alloyed with gold, it’s sometimes referred to as “prophesize” and will be of a slightly red color reminiscent of that found in copper or bronze. When present, palladium typically makes up between 5%-10% of the nugget’s weight.
Mercur
Most of the mercury found in gold nuggets comes from the times when old-timers used it to capture the fine gold in their concentrates, and then lost some of it into the river.
Iron
Iron is a very reactive metal, and will quickly be removed from the surface of most nuggets. However, some nuggets will still contain small traces of the metal.
What Affects the Purity of Gold Nuggets You Find?
So, as we have seen, gold nuggets can contain a variety of different impurities. What we haven’t discussed so far, is what makes some gold nuggets purer than others. Even in the same location, it’s not uncommon to see purity levels fluctuate quite a lot.
So, here are some of the main factors that affect the purity of gold nuggets:
Origin
It’s important to not forget that gold nuggets found in rivers could originate from very different locations along the stretch of the river. And if the purity between those locations varies greatly, so will the gold found downstream.
Size
Smaller nuggets are generally somewhat purer than bigger nuggets since there is less opportunity for other metals and impurities to continue to stay clung on to the gold. Simply put, there is a larger surface relative to the weight of the nugget that can be refined as it tumbles downstream and gets exposed to water and gravels.
However, there are many exceptions to this rule, so don’t rely too much on it!
Time in river
Gold that has been present in a river for a long period of time is generally purer than gold that has just recently broken off a gold-bearing vein. The reason is that the water manages to remove at least some of the reactive metals present in the gold. For example, it has been demonstrated that the surface of a nugget has the highest purity, while impurities increase towards its midpoint.
The exact spot
Less pure placer gold will be lighter and therefore deposit at slightly different locations than heavier gold of higher purity. For more information about how gold deposits in rivers, check out my guide to reading a river.
How To Test Gold Nuggets for Purity
There are several options available when it comes to determining the purity of a gold piece. Some could be as simple as just assessing the color of the nugget, while others are more advance and might include acids or even melting the gold down.
It’s important to note that it’s impossible to get a completely accurate number unless you smelt the nugget and remove all purities in the process. Even if you would perform a test with some of the most exclusive gold testing equipment out there, it would have a hard time giving you the right numbers. Unlike a piece of jewelry where the gold is mostly evenly distributed, the gold content of a nugget might vary depending on whether you’re testing the skin layer or its core.
Regardless, you wouldn’t want to smelt a gold nugget, as it would be less worth in its melted form. So how can you test a nugget for purity while still keeping it intact?
The easiest way of testing a gold nugget for purity is to observe its color. The richer and brighter the gold color, the higher the gold content is likely to be.
Obviously, this an approach that would require you have seen at least a couple of gold nuggets in the past, in order to be able to make a decent guess. However, there is a more scientific approach that can be carried out in the comfort of your own home.
Using a gold testing kit to test gold nuggets
The easiest way of testing gold purity yourself is to buy a cheap gold testing kit. They come with a couple of acids that are capable of dissolving gold of varying purities. You first scratch the nugget gently against the tile that comes in the package and put dots of acid onto the tiny gold streak that was left on the tile. By observing which acid was able to dissolve the gold, you can now get a good estimation of the purity of your gold.
Gold testing kits are really cheap and will last for a long time. Here is one I recommend.
Are Pure Gold Nuggets Worth More?
You might expect that a purer gold nugget will be worth more than a less pure one. Well, in some cases that’s completely right, but more often, the exact purity of a gold nugget is quite low on the priority list of an eventual buyer.
Most gold nuggets buyers are more concerned with the shape, weight, and rarity of a piece than its purity, as long as it’s within the normal range.
Of course, very pure nuggets are likely to be more attractive and be valued higher, which has to do not only with the higher gold content but also with the richer color and shinier appearance.
Locations Known For Their Pure Gold Nuggets
The purity of gold obviously varies a lot depending on where it was formed. And although this might give us some hint about what to expect in certain locations, there are significant variations present even within the same location.
This means that it’s hard to say that some states have much purer gold than others, even though it might be the case. The purity depends more on the exact geological processes that formed the gold, than the location. Just to name one example, gold that formed closer to the surface tends to be purer, as the lower temperatures made it harder for impurities to get into the gold.
Local Variations
To exemplify and show you how big the difference in purity could be within a region, I just wanted 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 scattered across six regions.
The study found that the purity of the examined gold in one district 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%.
Australian Gold Nuggets Are Really Pure!
Australia is well-known for its big and pure gold nuggets that often reach purities upwards of 96 percent. Especially the Victoria District is famous in that regard and has yielded many of the world’s biggest nuggets!
The biggest nugget in the world, the welcome stranger nugget, weighed in at 2,5020 troy and was retrieved by Richard Oates and John Deason in 1869 in Moliagul, Victoria.
Conclusion
- Even the purest gold nuggets are not pure gold but are made up of different types of natural metal alloys. The most common metals alloyed with gold are silver, copper, and palladium, which will all alter the color of the gold to some extent. For example, gold nuggets that contain silver tend to have a duller, whitish color, whereas copper will give it a slightly reddish tone.
- To get a general idea of the purity of a gold nugget, you can observe its color. A richer and shiner appearance generally means high purity. You may also use a gold testing kit.
- It’s hard to give a definitive answer as to what locations have the purest gold nuggets. However, although local variations can be significant, Australia is well-known for its big and pure nuggets.
Happy Prospecting!
