Alaska flagCore logging project - Fortymile district, Alaska

Kurt Friehauf - 2011

xOne 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.

xThe 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." 

drill coreThis 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.

minimum-impact drill siteThe 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.

water pump for drillThis 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

drillThe 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. 

friendly driller's helperI'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. 

helicopter arrives to move coreThe 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.

core yardThe 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 moving drill coreDan 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? 

core shedWe 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. 

Ken, Melania, and Dan logging coreLogging 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. 

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