One of the projects we worked on involved developing an
objective approach to analyzing drill core. The company with whom
we worked had several drill holes that targeted zinc ore. The
host rock was monotonous schist - a type of rock that hides some of its
secrets well. One company geologist suggested the drill holes
were just short of hitting ore, and another argued they weren't.
We wanted to objectively assess the core.
Here, Ken, Melania, and Dan very carefully analyze drilled rock cores.
The core can be pretty broken up and oxidized near the
top of the hole. That's because rainwater contains dissolved
oxygen that the drops pick up as they fall through the sky. That
oxygen-bearing water seeps into the ground and "rusts" iron and
sulfur-bearing minerals in the rock. The rock tends to break up
more after this because iron-sulfur minerals like pyrite sometimes
serve to hold the rock together and oxidation "dissolves" the pyrite
"glue."
This rock core was drilled from deep beneath the zone of
oxidation. There's still plenty of pyrite in veins holding the
rock together (see the little dark lines that cut across the
core?) These boxes are one meter (39") long.
The group we worked with have a strong commitment to
minimum environmental impact. the entire drill site is about the
size of a shipping container. When they're done drilling, the
company removes every bit of machinery and every plank of wood from the
site using a helicopter (so there are no new roads, either). It
is difficult to visit old drill sites from previous years work because
there's nothing left to see.
This is the water pump used to flush ground up rock dust
out of the drill hole. It's fresh water pumped from a local
creek. Waste water is first impounded in a sediment settling
trough before being returned to
hydrologic
cycle.
The pipes in the foreground are the hollow steel tubes
that are spun into the ground by the powerful engine. At the end
of the "drill steel" is a diamond-encrusted drill bit that grinds the
rock by abrasion. The drill bit has a hole in the middle like a
super, industrial-strength cookie cutter, so the bit cuts around a
circle of rock that feeds up into the hollow steel, forming a
core.
Drill holes do not need to be vertical. Shallow exploration holes
like this can enter the ground at any angle. Deep holes drilled
in the oil industry are
really amazing
because
drillers
can bend and snake the drill hole in
curves,
branches,
or
other weird directions using specialized directional
drilling technology.
Drilling requires three people: the driller, the driller's
helper, and the fifth man. The driller is a highly trained person
who knows precisely how to operate the drill and how to "read and feel"
the rock as the bit cuts down. The driller's helper does a lot of
the heavy lifting and inserts new drill steel into the hole as
needed. The fifth man (presumably called that because drilling
used to require more people) helps with odd jobs around the site,
including making sure water gets to the drill station.
I've liked a lot of the drillers I've worked with.
They're a
mixed bag, like any group - some good people, and some
not-so-good. This crew was great. They were friendly,
professional, and conscientious.
The project used a helicopter to bring the core back to
camp for analysis. Helicopters were used for all movement of the
drill, too, in order to minimize environmental impact. Using
helicopters, for example, meant there was no need for a bulldozer to
cut a road into the forest.
This is a
Hughes/MD
500E - one of my favorite helicopters. The thing has a
turboshaft engine - basically a jet engine, but the power is used for
turning the rotor instead of thrust. The engine and drive shaft
are mounted at an obtuse angle relative to the rotor shaft, so there's
much more mechanical advantage giving the helicopter power than one
finds in machines that have a 90º transfer.
The core is store in secure wooden boxes at camp.
It's all organized like a library, so a geologist can revisit rock
drilled from any place in the region by simply walking down the
isles. Rock core is, of course, a whole lot heavier than books,
but the idea's the same. The nice thing about rock core is that
is is the raw data - the story as originally written by nature, rather
than some interpretation by human minds (i.e., no
eisegesis
with raw drill core!).
Dan and Melania stop to smile at the fact that, while
they're working hard to lug heavy boxes of drill core to the inspection
tables, their professor is gallivanting around with a camera taking
their picture. I guess good help is hard to find, eh?
We logged some of the core in a big tent when it was
raining. The lighting was good and hung at the optimum height to
illuminate the rocks.
Ken is using a household spray bottle to wet rock, which helps reveal
subtle textures in the sample.
Dan is scratching a sample to determine its hardness - one of the
tricks geologists use for identifying minerals.
Logging on a sunny day is nice because the air is fresh,
the sun is warm, and the work is interesting.
The no-smoking sign in the background warns people that they're near
the fuel tank for the electric generator.