Across wide swaths of the deep ocean floor is a strange geologic oddity.
There, millions of rounded rocks, which are essentially solid geodes called nodules, are
spread across the ocean floor, seemingly with no apparent pattern.
In some areas, they cover 70% of the ocean floor, while in other places they are nonexistent.
These mysterious masses of rock are referred to as manganese nodules, and are incredibly
valuable.
Why?
They contain economic concentrations of several industrial metals such as copper and cobalt.
As a result, these unique features have long been a target of underwater mining operations
in an attempt to facilitate an easy profit.
So, how did these unusual manganese nodules form?
Why do they only exist in very specific stretches of the ocean floor?
This video will answer these two questions and discuss this geologic oddity.
Although manganese nodules are found around the planet, even in shallow seas such as the
Baltic Sea, they tend to be found in the deep ocean.
Specifically, they are most frequently found at between 4,000 and 6,000 meters depth, with
one example location with widespread nodules being the Peru Basin offshore of Peru.
With this being said, the vast majority of the ocean floor does not contain manganese
nodules, indicating a unique geologic environment which is required to form them.
On average, manganese nodules tend to be between 2 and 6 centimeters wide, although they can
range from the size of a pea to 25 centimeters in length.
These nodules contain onion like layers which formed on top of one another, with a distinct
core and outer shell.
So, how did these nodules form?
In the oceans, various factors have led to numerous ions and compounds distributed throughout
the water, the most common of which are chlorine, sodium, and magnesium.
However, there are also particles of various elements called colloids which are insoluble
and are dispersed throughout the ocean such as manganese.
Sometimes, particles of suspended manganese reach the ocean floor in areas with low rates
of sedimentation.
If the rate of sedimentation is high, nodules cannot form as the particles would be buried
by sands and clays.
Due to a series of chemical reactions, trace elements such as copper and nickel which are
found in the remnants of dead plankton sink to the ocean floor, where they are attracted
to the manganese nodules.
Over time, a core begins to grow around the manganese nodule, and is further expanded
by additional manganese in seawater which largely originated from eroded basalt.
These nodules take a very long time to grow, as each growth ring only expands by about
15 millimeters every 1 million years.
Eventually, the composition changes, forming a crust, and the reaction stops.
While some nodules purely form from ion precipatiton which are called hydrogenous nodules, others
form when they are buried in layers of metal rich sediments, called diagenetic nodules.
The main component of interest in these nodules is manganese, which makes up 30% by weight
of a nodule.
Nodules also contain economic concentrations of nickel, cobalt, copper, and molybdenum.
Since they are scattered across large swaths of the ocean floor, they have long been a
target of mining operations.
To explain why they are so attractive to geologists, let me explain how much it typically costs
to mine a ton of ore.
At a typical open pit or underground mine, it generally costs between $40 and $160 per
metric ton of ore to mine.
Thus, if the ore is worth more than that figure, you can make a profit.
Breaking down nodules into their individual components, they are worth $1,747 US Dollars
per ton of ore, a figure which is insanely high and unmatched at the majority of active
mines.
The issue lies in the following.
While manganese nodules are insanely valuable, vehicles which attempt to extract them are
insanely expensive, requiring the expenditure of tens of millions of dollars per day.
No large scale system which can extract nodules at a depth of 4 kilometers has yet been found,
which means that a profit cannot be generated.
Also, these nodules are the source of a unique deep ocean ecosystem, where crabs and other
fauna live, so mining them could pose an environmental hazard.
Although it may one day be economic to mine the many billions of tons worth of manganese
nodules, I never expect a way to extract them which allows for a profit.
I hope that you enjoyed this video!
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