Mine geologists — whether they work at open-pit or underground mines — eventually end up supervising drill machines and sometimes the work can be dangerous.
My first job as a naïve geologist in my early twenties was working underground in the deep mines of South Africa’s Transvaal, now known as Gauteng province.
I had a three-year contract and couldn’t believe my luck. Not only had I managed to avoid the North Sea oil rigs, but I was being paid to travel around southern Africa and hang out with a bunch of like-minded geologists from the United Kingdom. We worked hard and played hard.
Late in my tenure at the Vaal Reefs mine, I had seven underground drill machines running in different parts of the No. 2 shaft. That’s a lot of drilling. It was exhausting and I was stressed. Scheduling holes for so many machines became a 24-hour-a-day obsession. Planning the holes, getting crews to move the machines, logging and sampling the core, plotting the results, approving the invoices and then making sure the drilling company wasn’t screwing you over by billing for meters it hadn’t drilled. We tried to plan three or four weeks ahead so that we were never paying for an idle machine and crew.
Most holes were routine production holes. These get drilled for lots of different reasons but are a vital part of the day-to-day production effort. We would drill regularly spaced holes above access tunnels to determine the geometry of the ore body (the Reef), so that the survey department could properly plan the mining faces that would exploit the gold-bearing horizon. Other holes might target the lowest point in a particular block of ore, which is where the engineers preferred to aim the ore passes (known as box holes) so that ore could be easily pulled downslope and loaded into the haulage trains. And then there were the structural geology holes drilled to outline the dip, strike and throw of some of the myriad faults that disrupt the rocks of the Witwatersrand basin.
If a main access haulage was heading into a new part of the mine, we might be tasked by the engineers with drilling very small diameter holes — called cover holes — up to 100 to 200 metres ahead of the face to check for possible dangers like methane pockets, broken ground or pressurised pockets of water; all potentially lethal to a drilling and blasting crew.
Other holes were for pure exploration and those were the most fun. We’d drill long holes to explore the blank spaces on our geology maps, looking for unknown blocks of ore. This took careful thought and interpretation and was the one time an underground geologist could have a really good think about the geology.
But underground drilling isn’t without its risks. One of my drill machines once accidentally cut into the water-filled hole left by an old surface exploration core hole. We were mining 2,500 metres below surface so the old hole, which had cut the water table, had a 2,500 metre head of water in it.
When we knew that a tunnel was approaching one of the old surface holes we would issue a danger notice. The old drill hole surveying techniques were pretty inaccurate, so we could only estimate the hole’s position roughly to somewhere in a circle with a radius of about 100 metres. The drill/blast crews would take extra safety precautions as they got closer. This time, when the crew hit the hole, the enormous water pressure spat the steel drill rods out of the hole, and the 85 kilogram drill machine went with them, about 50-60 metres down the tunnel. Luckily no one was hurt but there was lot of mangled steel.
On another occasion the drill crew wasn’t so lucky and it was the only time in my career that I experienced the visceral shock of a fatal accident.
One afternoon, after wrapping up my routine work in the office, the phone rang. It was the production manager at Vaal Reefs #2 shaft where I was the responsible mine geologist. He muttered something about an accident with one of my drill machines and told me to get over to the shaft PDQ. I jumped in my 1976 Volkswagen Bug and drove to the shaft as fast as I could.
I got there just as the main lift arrived at surface from 7,500 feet (2,286 metres) down. A rescue crew was bringing out a stretcher with a man strapped to it. One of the rescue team was holding a saline drip plugged into the man’s arm. The man was looking around himself, conscious but obviously in shock. As I watched he was loaded onto an ambulance and driven away to the mine hospital. He died on the way there.
The victim was part of one of my underground production drilling crews. They’d been drilling a hole, about 70 metres upwards at an angle of about 15 degrees off vertical. The type of drill machine we were using had a hollow diamond-encrusted bit that cut 3.5-centimeter-thick core samples for the geologist to examine. It was a robust, simple machine but they did tend to break down from time to time.
The machine had suffered a minor mechanical failure, so the drillers shut it off and pulled the drill rods out of the hole to allow them to repair the machine. The crew started to repair the machine immediately beneath the hole that they’d been drilling. What the crew didn’t know (and could not have known) was that a 1 metre length of core was left hanging at the top of the hole when the drill rods were removed. As the men worked to repair the machine, the core broke free and barreled down the 200 foot (61 metre) long hole. The rock was hard, glassy quartzite and it had broken off at a very shallow angle to the drillhole axis, creating a knife-like point on the end of the piece of core.
One man was working directly under the hole. He was bending over the dismantled drill machine when the core shot out of the hole. It went completely through his upper back and out through his chest, fatally injuring him.
I was 23 years old when the accident happened and loved mining. I still do. The smells, the sounds, being surrounded by fresh rock, all of it.
But as I approached my third year working underground, I was seeing more and more close shaves; incidents that served only to reinforce that if I stayed working there long enough, something nasty would happen to me eventually.
It was about that time when I made the incredibly sensible decision to leave the mine at the end of my contract and go back to university to study for a post-graduate degree.
I’ve never regretted it.