Finding a gold deposit has always been the goal for miners and prospectors. In most cases, you are more likely to retrieve gold from a placer deposit at a rather shallow depth. Corporations, on the other hand, set up tunnels to recover gold deep underground.
Placer gold can be found at the surface down to depths of tens or hundreds of feet. Lode gold, which is gold retrieved from crushed rock, is found where the vein in the rock is. The deepest gold mine in the world is more than 2,5 miles deep.
In this article, you will learn more about the factors that affect how deep you can find gold. Let’s get started!
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At What Depth Will You Find Gold? (Two Types of Gold)
There is no specific depth at which gold can be found. Examples of this are the Welcome Stranger – the largest gold nugget ever found – which was retrieved at only 3cm (1.18in) below the surface. Oppositely, gold mining operations today take place at a depth of around 3km (1.8 miles) under the Earth’s surface.
The depth at which you will find gold also depends on whether you are conducting small-scale prospecting operations focused on placer gold or large-scale mining processes.
Let’s look at these two types of gold, and how they are different from one another!
Placer Gold
Placer gold is gold that has broken loose from the host rock through erosion and weathering. Small bits and pieces, including gold nuggets, are then washed away by heavy rains until they sometimes end up in rivers, where they can be carried for incredibly long distances.
Most placer gold found by prospectors resides in the top layer, down to depths of perhaps a couple of feet. The reason is quite obvious, as this is the deepest most gold miners will get without the use of heavier machinery and equipment.
Of course, placer gold can be found at even greater depths than that. In the next section of the article, we’ll look at what determines the depth of placer deposits.
Lode Gold
Lode gold is gold that exists in gold veins in rock, and this is the kind of gold that most commercial mines are going for today. However, it requires heavy investment in machinery as well as expertise, which is why it’s not suitable for most prospectors.
Depth of Gold in Placer Deposits
If you are not about to undertake a large-scale mining operation, you will likely be more interested in knowing at what depth you should prospect for gold. However, even in this case, the depth at which the gold is found depends on several factors.
So, let’s have a look at them!
Type of Deposit
The type of deposit you are dealing with will indicate where you are more likely to find gold. It is essential to understand that the high specific gravity of gold (19.3) will cause particles to drop at a much higher speed than surrounding materials.
Now, before reading on, please have a look at the illustration below, and especially pay attention to the difference between eluvial and alluvial gold.
- Eluvial Gold: Gold that has just broken loose from the lode and lies around on the ground
- Alluvial Gold: Gold that has made it into a river and begun mixing with the rest of the streambed material.
Eluvial Placer Gold
Eluvial placer gold, which basically means gold that has just broken loose from the lode and lies around on the ground, is generally found at quite shallow depths. For instance, in Arizona, which is known for producing a lot of gold nuggets, nuggets are often found in the very top layer using metal detectors.
Alluvial Gold (River Gold)
When it comes to alluvial gold, which is gold that has got into a river and begun to concentrate, things can be a little different.
The high specific gravity of the gold will cause it to drop to the bottom. And as the river constantly removes the lighter sands and pebbles, the gold is likely to sink deeper and deeper into the streambed. This will continue until either:
- The flow becomes so powerful that it manages to lift the heavy gold particles and remix them with the rest of the streambed material. This is especially common in spring when melting snow and ice increases the intensity and volume of many rivers.
- The gold reaches bedrock, or false bedrock, where it can’t fall any deeper. In short, this is an impenetrable layer made out of real bedrock or a clay layer (false bedrock) that keeps the gold from falling farther down. (See illustration below)
Cracks, Crevices, and Other Gold Traps
Another other type of gold deposit is the one you can find in crevices and cracks in rocks. These can be either within a stream or in dry-land locations, depending on the current width of the river.
As the gold is transported by the river, it will reach certain zones where it is more prone to getting stuck or deposit. For example, while gold is likely to slip off smooth surfaces, it will remain trapped in crevices.
Other common gold traps are places where the river slows down just so that the gold, which is one of the heaviest elements in the streambed, falls to the bottom, while most other sands and pebbles continue downstream. In places like these, gold can be found at quite shallow depths as well.
For more information about where to look for these kinds of deposits, please have a look at my extensive guide to reading a river for gold.
Age of deposits
As we have seen above, gold falls at a much higher speed than other particles found in similar locations. Therefore, if a deposit is particularly old, other sediments may have fallen on top of the gold particles. In that case, gold will be found at the bottom of the deposit.
Slope and River Speed
In simple terms, the faster the speed of the river, the less light gravels and sands will remains attached to the streambed. In other words, gold that travels down a fast-flowing river is likely to be closer to the surface than that in a slower river.
One way of quickly assessing the speed of a river during the flood stage is how much exposed bedrock there is. If a river has a lot of exposed bedrock, you can be somewhat more certain that the gold is close to the surface.
Similarly, if the river has a steep downhill slope, it will help remove much of the streambed material and leave the gold closer to the surface.
Ancient Rivers
Ancient rivers are a curious occurrence that has been incredibly beneficial for prospectors who happened to stumble across them. These are rivers and streams that were in existence millions of years ago, but, since then, they have dried.
Since gold particles are likely to deposit at the bottom of a streambed, these geological formations are ideal for prospecting. However, ancient rivers can be found at increased depths, especially if a mulch layer has formed on top, which might require large-scale mining operations.
Others, instead, can be identified by prospectors without the need for mining. Signs that indicate the presence of ancient riverbeds include:
- Rounded rocks
- Presence of alluvial stones or gravel
- Signs of an existing riverbed
- Cottonwood or willow trees
Depth of Large Mining Operations
The depth at which large-scale mining operations are conducted depends on where the vein inside the lode is. Lode mining will require professional equipment and mining experience to be successful, especially as the gold will require much processing to be separated from the host rock.
One of the initial theories regarding the formation of gold veins reported that gold derives from the denser depths of the Earth. Therefore, miners had the idea that the deeper they would mine the more gold they would find.
However, more recent studies about gold formation have shown that this is not always the case. For example, gold veins formed subsequently to volcanic activities that filled the cracks in host rocks – also known as country rocks.
Today’s mining operations conducted at a depth tell us that the gold found at deeper distances contains more copper and other contaminants. Oppositely, the part of the veins relatively closer to the surfaces boast higher quantities of pure gold.
In any case, the depth at which the vein is formed indicates where gold will be found. The deepest gold mine today, the AngloGold Ashanti’s Mponeng, operates at over 3.8km (2.3 miles) below the surface. Others, instead, prefer shallower open-pit operations to retrieve gold closer to the surface.
How to Retrieve Gold (Placer and Lode Gold)
Retrieving gold from underground locations can be challenging, especially if you are not equipped with the tools and machinery that miners might use.
However, most prospectors will need to limit themselves to searching for placer gold. Below are the best strategies for both mining and prospecting placer gold!
Placer Gold Prospecting Techniques
Here are the most common techniques used by prospectors today!
- Gold pans
This is by far the most beginner-friendly technique out there. To get started, all you need is a gold pan, a classifier, a shovel, and a bucket.
However, it’s main two drawbacks are that you need to be close to a water source, and that the amount of material that can be processed is rather limited.
However, the latter issue is easily remedied by investing in a sluice box!
For more information about gold panning, please check out the guides below:
- Metal detectors
When panning or sluicing, you are limited to processing the materials near a body of water. If you wish to scan the soil and sediment at dry, arid places, you might opt to use metal detectors.
However, you should be aware that metal detectors won’t be particularly useful in retrieving fine gold. Additionally, the smaller a gold piece is, the closer to the surface it will need to be for the metal detector to identify it. Learning how to use a metal detector and refining your skills is key to success in this case.
I generally don’t recommend beginners to invest in metal detectors, as gold panning is an easier and less expensive method.
- Suction dredges
Suction dredges are perfect for searching the bottom of rivers and lakes. While this might not be particularly helpful if you are searching on dry land, they can help you find gold at greater depths when underwater. Suction dredges are subjected to limitations in many states, and require good knowledge to be operated effectively.
Lode Mining Techniques
Large-scale mining operations tend to use professional pieces of equipment and refined techniques to extract gold. Depending on the geological characteristics of a location, they will either be open-pit operations or tunnels.
- Open-pit operations
Also called opencast mining, this technique allows miners to extract metals from an open pit on the surface. You can check out what these look like in the video below.
- Tunnels
Tunnels can be either vertical or horizontal and allow miners to extract gold from greater depths when the gold vein requires it. These are sometimes more economical and profitable than open-pit operations.
Conclusion
Understanding at what depth gold is found in nature can indicate where you will find it when prospecting. However, the depth of gold varies greatly depending on where the vein initially was. Moreover, how far the gold sediments have traveled over time can influence their position. Using topographic maps and speaking with local prospectors can give you a better understanding of the location’s specifics.
