Michele - It is a structural geologist's dream, to stand in the middle of a fault zone. I've stood on many outcrops of faults and I've stood next to many cliff exposures of faults before. What I'm talking about here is the ultimate 3D experience not matched in any cinema show with uncomfortable glasses; standing inside a fault zone with fresh exposures under you, to both sides and above your head. How lucky can a girl get to have such an opportunity?
Through Tom Blenkinsop's wonderful connections and Steve Micklethwaite's willingness to give a talk to the Mt Isa Mines (MIM) exploration geologists, Steve and I got an underground tour from Brad Miller, an amazing underground geologist at MIM. Until about 8 am you can descend to the mine in a cage that holds 92 people. Because we had to go through training and get suited up we missed this and drove a spiralled network of roads down to 1.8 km below the surface. The drive to the ore body took 1 hour. But I'm getting ahead of myself.
Training: We had to watch two induction videos and pass a safety test. As you can imagine mine safety is huge priority. We would be under Brad's watchful eye but we also needed to know some basics before they would let us underground.
Equipment: The red suit indicates that I am a visitor. On right side of my waist belt is the battery to my head lamp. I never asked how long those batteries last between chargings but judging from the weight, I'm going to say 4.3 years. On the left side of my hip is the "self-rescuer". If needed you pop open the lid and strap a plastic bag to your face for breathing. The disk in the bag produces oxygen that should last ~1 hour as long as you breathe normally. Yeah right, breathe normally... I'm also holding eye protection, which I wore the whole time. On my feet I'm wearing standard issue steeltoed boots.
The trip: We rode in an extended cab diesel pickup through the active lead-zinc pit to the portal to the deeper copper mine. My first thought through the portal was "Ooo cool, rock bolts!". I've always had a fascination with rock bolts - but if you know me you are not surprised by this. I didn't realize in those first moment that I would get to see thousands and thousands of rock bolts in the next few hours. Forget being impressed by bolted roadsides along the Mass Pike west of Springfield, at MIM I was in the land of rock bolts. I rode in the back seat, which meant that I couldn't lipread Steve and Brad but it also meant that I was free to gawk like a kid at the surroundings without them mocking me. Although the mine tunnel snakes around, the host rock for the ore is a west-dipping shale so you can use the rock dip to get your bearings... well kind of. It was still pretty disorienting.
After an hour of driving we got out of the truck to see a faulted exposure at 1.6 km below the surface. Getting out of the truck, my first impression was "Jeesh this equipment is heavy" and my second impression was "They weren't kidding about that geothermal gradient.". I tell my GEO101 students that due to radioactive decay and residual heat of our planet's formation, the temperature increases ~25 degrees C for every km into the Earth. Sure, it makes sense but it is WAY more convincing to experience this first hand than to just talk about it. At 1.8 km, the deepest we went that day, the temperature of the rocks was probably about 45 C or 115 F. We sweated through our overalls and we kept drinking water regularly.
Because of the drilling and the passing vehicles a lot of the walls of the mine get dust covered. When the mine geologists map parts of the mine they pipe water so that they can clean off the walls. This mine is dry (no ground water) but in the active parts of the mine there is water everywhere from the drilling operations. We trudged though several pools that we nearly as deep as my boots and drove through many more pools. Near the drill it was noisy so I took out my hearing aids. The combination of dust, heat and humidity would be a perfect conditions for corrosion. I can imagine my audiologist cleaning out my hearing aids and saying "What did you do with them?!" She probably wouldn't believe the answer.
We drove around to exposures revealing a wide range of fault textures and conditions. Some of the faults were amazingly well-exposed on the walls and ceiling. I saw lots of veins in various states of deformation. We also got to visit regions of high ore grade. I picked up very warm samples of graphite, talc, quartz and chalopyrite, from which the copper is smelted. The rocks were amazingly fresh. No weathering on these rocks!
After several hours of amazing rocks, we drove the spiraled path back to the surface. At one point underground our truck died (dead battery) and I was really wanting to be back on the surface. However, once I was back in the sunlight, I appreciated how wonderful the inside of the Earth looks and wanted to go back. I may not get the chance to go underground again, but if I do, I will certainly say yes.