A quick disclaimer.
I am being paid to make this video by the European Union and NS Kožare as part of a
series meant to share several wonderful geologic features within the nation of Slovakia.
Today, gold is actively being mined at a location adjacent to Slovakia's town of Banská Štiavnica,
much like it has been since approximately 1,000 years ago.
The ore in question contains thick sulfide mineralization, but the golden colored mineralization
you are looking at is not gold but rather the copper ore mineral chalcopyrite.
Instead, the gold occurs as numerous less than 3 millimeter diameter crystals scattered
throughout the host rock, resulting in an average grade of 8 grams of gold per metric
ton of ore.
While more than 255,000 troy ounces of gold have been produced from this mine, the reason
it exists is quite unusual.
As, this rich mineralization formed due to volcanism related to an ancient supervolcano.
This supervolcano is known as Stiavnica, which once was an absolutely stunning glacier topped
stratovolcano that rose to an impressive height of 4,000 meters or slightly more than 13,100
feet.
However, this volcano would subsequently produce a catastrophic eruption, as 13.85 million
years ago so much volcanic rock was ejected in a mere 72 hour timespan that a site 15
kilometers distant was coated in a whopping 100 meters thick of material at these GPS
coordinates.
Alongside ejecting hundreds of cubic kilometers of volcanic rock, the eruption caused the
4,000 meter high stratovolcano to collapse into a massive caldera that measured 22 kilometers
long and 18 kilometers wide.
The story of the Štiavnica supervolcano began approximately 15 million years ago during
a time when this section of south central Slovakia was actually beachfront property.
As, to the south, a massive inland sea existed known as the Pannonian Sea, which was approximately
half the area of the modern Black Sea.
In this ancient sea, at its very northern edge sprung up a series of volcanic islands
along a chain of activity.
As andesitic magma from Štiavnica erupted through the shallow seafloor, it created a
series of white and black colored explosions, eventually creating a small plateau out of
ash.
As additional eruptions continued, a dark gray colored volcanic cone interwoven with
layers of lighter gray ash climbed more than 100 meters above the sea surface.
Fast forward ten thousand years, and repeated moderate volume explosive eruptions had expanded
this volcano to make it no longer an island but rather a peninsula.
While Štiavnica's summit climbed to more than 1,000 meters above sea level, some magmatic
intrusions failed and did not reach the surface, which as they cooled created the aforementioned
gold ore alongside laccoliths, and sills.
Some batches of localized magma around 14.5 million years ago became more silica rich,
allowing for more viscous dacite domes to form on the stratovolcano's slopes.
Finally reaching a height of 4,000 meters, Štiavnica now had a diameter of 50 to 60
kilometers, encompassing 4.8% of modern Slovakia's landmass.
Glaciers then developed, a large 1,000 meter wide crater was visible on its summit, and
a secondary volcanic cone 4 kilometers to the west-southwest grew.
Yet, at depth, an unusually large magma chamber was building, totalling more than 100 cubic
kilometers of material.
Additionally, several smaller magma bodies were experiencing fractional crystallization,
causing their composition to change from andesite to dacite and then rhyolite.
Finally, a portion of the andesitic magma intruded into the small rhyolitic magma chamber.
This caused a chain reaction to occur, sending large volumes of both magma chambers to the
surface.
All at once, several vents oriented along an east-northeast trending fissure explosively
erupted, sending a plume of ash 50 kilometers into the atmosphere.
Dense parts of this eruption column then fell back to the ground, going on to race across
the surrounding landscape at speeds exceeding 200 kilometers per hour, eventually reaching
as far away as 60 kilometers distant.
As a firestorm swept much of the surrounding landscape, thick piles of ash and pyroclastic
flow deposits piled up.
Then, due to the thick amount of erupted material, which likely totaled approximately 385 cubic
kilometers of rock, Štiavnica's underlying magma chamber was now significantly drained.
This caused a 22 kilometer wide stretch of ground to collapse downwards like a sinkhole
and fill this empty space, forming a vast caldera which was more than 500 meters deep.
This catastrophic eruption would be assigned a 7 on the volcanic explovitiy index, being
more voluminous than the largest of the Campi Flegrei supervolcano's eruptions.
In the remains of this largely destroyed volcano, volcanism would not occur for another 400,000
years.
However, activity would eventually resume, where numerous andesite lava flows filled
much of the existing caldera over a 600,000 year period.
While this volcano's underlying magma chamber was slowly refilling, the at depth material
pushed up the center of the volcano, forming what is known as a resurgent dome until 11.4
million years ago.
Some large cracks allowed rhyolite to erupt onto the surface during this timespan, forming
more than a dozen rhyolite lava domes.
After this, eruptive activity completely ceased, and the remnants of this now permanently extinct
volcano were significantly eroded over millions of years to create its modern appearance.