Alaska flagPotential porphyry/epithermal mineralization on Mount Fairplay, Interior Alaska

Kurt Friehauf - 2011

One of our projects was an investigation of Mount Fairplay.
People have looked at Mount Fairplay for its potential as a mineral deposit for hear.
The U.S. Geological Survey did a reconnaissance study back in the mid 1960's (The Geology of Mount Fairplay).
There was also a University of Alaska - Fairbanks master's thesis done on it in the mid 1980's.
Most recently, Dr. Rainer Newberry (a very good and smart guy) and his students did a big study of the ages of mineral deposits in the region in the late 1990's.

Our hosts on the expedition told us they knew nothing about the mineral potential of the mountain.  With the goal of assessing the extents of mineralization on the prospect, we made a geologic map of Mount Fairplay.  I love geologic mapping.

xThere are few good outcrops on Mount Fairplay - which is typical of the Alaskan interior.  Freeze-thaw action breaks rock up into chunks ranging from hand-sized to bathtub size.  The arctic conditions also cause the rocks to work their way down the slopes like very slow-moving rivers and cascades.  Mount Fairplay sheds her skin seasonally like a shaggy caribou shedding its fur.
Nature is full of beautiful things!

xThis is what Mount Fairplay looked like when we were mapping in late May.  The snow drifts were deeper than I am tall, so we worked around them.  That's Dan in the foreground, inspecting a rock.

xThere was a forest fire up near Delta Junction - about 100 miles away.  The wind carried the smoke over to Mount Fairplay one day, dramatically decreasing visibility.  We didn't know where the fire was because we didn't have phones, internet, or long-distance radio.  The smoke wasn't so bad that the smoke irritated our throats and lungs, though, so we continued working as usual.  Later, we ran across some Alaska state forestry guys who told us the fire was way over near Delta.  The wind blew it all away by early afternoon. 

planning a traverseOrienting ourselves for our traverse - one of the keys to efficient mapping is starting by knowing where you are located, and never getting lost after that.

We used GPS to locate ourselves.  When Melania, Dan, and Ken were doing a traverse without me and the GPS broke down, they used their compasses to triangulate their positions

hiking up the mountain
Hiking up the mountain - life without helicopter assistance is a whole lot slower, but the exercise is great!  I'm no fan of running on a treadmill or riding a stationary bike, but wilderness hiking is awe-inspiring and a very palatable means of working out. 

outcrop? or big landslide block?An example of rare, firm outcrop.  This cohesive block of rock could either be solid bedrock, or a large slide block.  The coherent strike and dip of the bedding relative to other outcrops of the same rock type suggested this was not large block slide, but actual outcrop.  

lichen covering some rocks, but not othersOne of the ridge tops had two very distinct kinds of rocks - on that the black lichen liked to grow on, and another that was not conducive to lichen growth.  A good geologist keeps track of the relationships between rock type and plant life.  Each plant requires nutrients in different proportions - some tolerate acidic conditions, others prefer alkaline, and still others need a rich supply of iron or some other element.  Different rock types have different compositions and so are better/worse places for different plants to grow on. 

The tripod in the background is someone's radio repeater - a device used for extending the range of radio transmissions.

nice outcrop of volcanic tuffA very nice outcrop of volcanic tuff on the ridge top.  True outcrop is a very welcome thing after tracking down geologic contacts in loose rock (what geologists term "float").

Melania taking strike and dipMelania uses a Brunton compass to measure the orientation of the volcanic tuff beds.  Geologists measure the direction the bedding plane dives down into the ground (called the dip direction) and the angle of dip (how steeply the bedding plane dives down).  Personally, I usually record the direction the bed dives down using the "strike," which is perpendicular to the dip direction.  Dr. Malcolm Reeves at the University of Saskatchewan has a nice graphic illustrating these measurements here.

volcanic tuff brecciaThe volcanic tuff had some large fragments set in a matrix of fine-grained volcanic ash.  Fragments of volcanic rock are collectively called volcanic tephra.   The fragments here would be classified by size.

volcanic tuffThis is an example of a different volcanic tuff unit.  Note the many different kinds of rock fragments within the tuff, torn from the throat of the volcano as magma and volcanic gas explosively erupt from the volcano. 

talusTalus slopes (also known as scree slopes) like this one are common in places where there is a lot of freeze-thaw action.  Water gets into fine fractures in the rock called joints.  When the water freezes at night, it expands, prying the rock apart into pieces.  During the day, the ice melts, allowing the water to seep deeper into the fracture or to flow into a new fracture, which it will then pry apart, too.  You can see this effect in your home by putting a water bottle in your freezer overnight.  The sides will bulge when the ice forms because ice is less dense than liquid water.  This process is called "frost wedging."  Freeze-thaw action also slowly transports this broken rock down the mountain side.

frost boilFrost boils are places where the permafrost churns rock up to the surface.  The ground here is covered in soil that rests on top of hard bedrock.  The soil is porous, so water can seep in between the grains.  In permafrost, the water between the grains is frozen ice that binds the soil grains together.  That ice swells and shrinks - more in some places, less in others.  The differences probably reflect irregularities in the shape of the bedrock-soil interface, the availability of newly infiltrating water, and groundwater flow in the bedrock.  Frost boils are places where that expanding ice pushes upward like an underground fountain of frozen soil, carrying rocks up to the surface. 

frost boilBecause the soil is constantly churning in frost boils, they are usually only very sparsely vegetated. 

frost boilHere, a frost boil erupts to the surface and the rocks and soil flow downhill (to the right).  This frost boil occurs in a slight gully with bit of a slope.  Groundwater commonly mimics surface water patterns.  Apparently, permafrost does so, too. 

solifluctionThe freeze-thaw action in an arctic environment also forms rivers of rock.  The blocks of rock that form by frost wedging (scree) slowly work their way down the mountainside.  This happens because the ice lifts the rock, then as the ice melts, gravity pulls them down the slope. 

solifluctionThe freeze-thaw action of the arctic not only forms rivers of scree rock, but also causes the soil itself to flow downhill.  When soil oozes down a slope, we call the process solifluction (from the Latin word roots sol = soil, fluction = flow). 

solifluctionWaves of flowing rock and soil dripping off the mountain due to solifluction. 

The high mound on the ridge top is the remnant of a much broader sheet of volcanic tuff. 

solifluction lobe with toeMelania stands near toe of lobe of soliflucting soil and rock.  Look carefully and you will see there's a mound of disturbed soil at the base of the rock flow. 

soil pushed up by flowing rockThe flowing rocks here have pushed up the tundra moss like a bulldozer pushing earth.  All of this slow rock and soil creep mean geologic contacts on our maps are rough approximations.  Geologists must sometimes live with imprecision like this.  That's one of the things that geology an unusual science - working in extremely complex systems with only limited data to try to arrive at the most precise, predictive model possible.  I imagine biology and biochemistry might be similar in nature because there are so many interactions. 

xIn spite of differences in background, experience, ... and, obviously, height,... Melania, Ken, and Dan got along better than any group of students with whom I've done field work.  It was a pleasure working with such positive people. 

The canister on Ken's belt is a can of bear spray.  Bear spray is a very strong type of pepper spray that has been shown to be effective at deterring bear attacks.  Although we carried firearms, those were just for use a last resort.  We were the visitors tromping around in the bear's home

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