Today's trivia is all about the a mine in North Mexico known as the Naica Mina.
This mine was first opened in 1794, though only officially exploited in 1900. The mine is of interest commercially for its deposits of lead, zinc and silver, among other minerals which are still actively being extracted.
Before mining could start the mine has to be drained of water. The water level normally resides at a depth of 110m below sea level. This needed to be drained to a depth of 850m below sea level. A complex pumping system had to be developed to be able to do this and can extract 22,000 gallons of water per minute when turned on.
In the year 2000 another system of three caves were discovered which contain some rather impressive crystals. We'll be talking specifically about the "Giant Crystal Cave", located at 290m below sea level. Some of these selenite crystals are immense. The cave's largest crystal found to date is 12m (39 ft) in length, 4m (13 ft) in diameter and weights 55 tons.
Formation of the Crystals
The Naica mine lies on an ancient fault above an underground magma chamber below the cave.
The magma heats the ground water which was saturated with sulfide ions. Meanwhile cool oxygenated surface water comes into contact with the mineral saturated heated water, but the two did not mix due to the difference in their densities. The oxygen slowly diffused into the heated water and oxidized the sulfides into sulfates.
This creates an environment where hydrated sulfate gypsum can crystallize at an extremely slow rate of over the course of at least 500,000 years forming the enormous crystals found today.
The key to this process is the slow diffusion of oxygen from the cool, low density surface water into the hot, high density ground water.
Conditions in the Cave
Exploring the cave is particularly hazardous for humans. The ambient temperature is 58C (136F), and the humidity is close to 100%.
This represents two significant risks to humans:
- Heat Exhaustion Unprotected from the heat, the human body cannot regulate its temperature quick enough in those sorts of temperatures. You would be sweating profusely if you found yourself stuck down there would ultimately pass out from the lack of water and sodium in your body.
- Breathing The air in this sort of temperature would be incredibly difficult. It would be likely that the in insides of your lungs would be cooler than the outside temperature. The humidity would start to condense inside your lungs leaving only a short time window for exploration.
A lot of infrastructure has been put in place to support exploration of the caves.
Before you can enter the caves you reach a staging area which is at a comfortable 41C. This staging area hosts all the support equipment required to venture into the actual crystal caves. This includes freezers to store the cooling suits, video monitoring equipment and paramedics on standby in the event of a medical emergency.
Camera equipment has to be allowed to come up to temperature before it can be used in the caves, otherwise it would risk fogging up.
Refrigeration Suits
To explore the caves, researchers had to develop specific suits to help protect the wearers from the conditions in the caves.
Ptolomea Suit
The initial suit design created by Giovanni Badinno consisted of multiple layers:
- Insulated layer: protects the wearer from direct skin contact with the icy cooling layer
- Cooling layer: Ice tube covered layer to protect the entire body from the` excessive temperature.
- Outer layer: Rugged overalls to reduce heat transfer by radiation and protect from jagged environment
This suit allows the wearer an hour of effective research time in the caves however it comes at the drawback of being heavy and restricts mobility for the wearer.
View of the inner cooling layer of the suit, total weight 22kg
Lightweight Suit
The researchers were able to optimise the design trading off some exploration time for a more mobile suit design. Instead of complete body coverage in cooling ice tubes, they opted for a cooling layer which just covered the torso in frozen gel packs. This allows more mobility for the arms and legs with an exploration time of around 30 minutes.
The lighter suit system weighs 8kg in total
Breathing System
Breathing in the cave is difficult without breathing apparatus. For this they developed a backpack based system. Replaceable frozen metal bottles are stored in the backpack with a fan which blows warm air over the bottles. This is then fed into a face mask which allows the wearer access to cool air to breath.
Fitted facemask
Inside the backpack of the air cooling system, frozen metal bottles act as the cool source
Future of the cave
Once the mining operations in the cave end, it is expected that they will turn off the water pumping system, allowing the thermal water level to rise and once again fill the the entire cave system. The facilities to support exploration of the crystal caves and the caves themselves would become inaccessible and will resume their slow growing process.
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