Around the planet, there are more than 1300 active volcanoes, of which approximately 50
are erupting.
These volcanoes are arranged into a variety of shapes and sizes, and each produce distinctive
lavas.
However, among these numerous volcanoes is a single unique example which is the world's
most valuable.
In the last 10,000 years, it has deposited approximately 10 billion dollars worth of
rare earth elements through its unusual solid black lava which cools as a white color.
The volcano I am referring to is Ol Doinyo Lengai, which is located in northern Tanzania.
Looking back further in Earth's geologic history, similar rare earth element enriched lavas
can also be found at locations such as Mountain Pass in California, and Homa Mountain in Kenya.
These deposits, although rare, represent some of the world's most valuable ancient volcanic
eruptions and magmatic intrusions.
So, how do they form?
Should Ol Doinyo Lengai be mined?
This video will answer these two questions and discuss a highly unusual type of volcanic
rock.
All of these deposits including the active Ol Doinyo Lengai volcano contain a highly
unusual rock type known as carbonatite.
Carbonatite is a very unusual type of volcanic rock defined by more than half its weight
being carbonate minerals, which are typically a white color.
This is unusual as around the planet, the main component of lava at every other volcano
is silica, aka silicon dioxide.
While the typical stratovolcano contains 60% by weight silica, carbonatite lava contains
less than 3% silica.
This unusually low silica content causes erupted lava at Ol Doinyo Lengai to have a viscosity
lower than water, causing it to move at unusually high speeds.
You might look at Ol Doinyo Lengai and ask, but wait, how can a volcano with steep slopes
be formed from lavas which move very quickly, like would be expected on a shield volcano?
The answer is that at Ol Doinyo Lengai, the appearance of carbonatite lava occurred very
recently, and began erupting only in the last 15,000 years.
There are several classes of carbonatite volcanic rocks, but the most common such as what is
present at Ol Doinyo Lengai seems to originate from highly alkaline magmas, generally with
a composition known as phonolite.
Over time, pockets of phonolite composition magma in the crust can get so enriched in
alkali elements and carbon dioxide that a threshold is reached.
This causes two different composition liquids to separate from one another in a manner similar
to adding vinegar to oil.
This unique magma then eventually travels up to the surface and erupts, or intrudes
into the crust, depositing large quantities of rare earth elements.
Although carbonatite lavas can be found around the planet, they tend to occur in large continental
rift zones where the crust is spreading apart such as near Lake Baikal in Russia or the
East Africa Rift Zone in Tanzania and Kenya.
While Ol Doinyo Lengai is the most recent example of such, an older volcano in the region
called Homa Mountain in Kenya produced carbonatite lavas around 5 million years ago.
Theoretically, dozens of other rare earth element enriched deposits should be located
in the region, just waiting to be discovered.
For clarification, so called "rare earth elements" are not necessarily rare as each element in
this group is more common in the crust than silver but less common than copper.
The issue lies that rare earth elements are very uniformly distributed in the crust.
Very few areas exist in the world where rare earth elements exist in high enough concentrations
to mine them for a profit.
This is why makes them "rare".
Does this mean we should mine Ol Doinyo Lengai, as it contains more than 10 billion US dollars
in rare earth elements?
The short answer is no, as the value I just provided is misleading.
It is similar to saying "I can make $100 via baking brownies" but you aren't accounting
for the cost of ingredients, equipment, the oven, or your time.
Thus, even if all of the environmental and philosophical objections were to be ignored,
mining Ol Doinyo Lengai would only be negligibly profitable at best.
A better example of a profitable carbonatite lava sequence can be found in California at
the Mountain Pass Mine.
There, several million tons of 1.3 billion year old carbonatite lavas contain an average
grade of 8.5% rare earth elements.
This mine has been intermittently in operation since 1952 and will continue to be in operation
for many years to come.
As the demand for rare earth elements in green energy technologies, defense, and electronics
continues to grow, so will the need for new discoveries.
I recommend that more attention be brought to the following regions of the world which
likely have undiscovered rare earth element deposits; the Northern Cordilleran Volcanic
Province stretching from British Columbia to far eastern Alaska, the Rio Grande Rift
in New Mexico, and the ancient Midcontinental Rift Zone adjacent to parts of Michigan and
Minnesota.
I hope that you enjoyed this video!
If you would like to request a specific topic, please leave a comment below!
Additionally, I would like to thank my new patron Cameron who requested this video's
topic.