NOTE WELL: Even though
this is a very minor road, it is a public road, and you should be
alert for traffic. Also, the fencing in the area carries
a significant electrical charge, and you should stay well away from
any fences. Please do not go down into the creek area
itself.
"Streams have a way of seeking out major
junctions in the earth's surface, picking out old weaknesses."
Richard
Fortey
You are on Old Mine Road, standing at the edge of a bridge over
Little Buffalo Creek near the village of Gold Hill. If you
look both north and south from the bridge, you might notice
something odd about this little creek. Unlike most such
rivulets that meander all around, exploiting the softest rocks
available, this stream seems to go almost in a straight line to the
northeast and southwest. In fact, if you were a bird, and
flew southwest over the creek, you'd see Buffalo Creek, Adams Creek
and Rocky River all coming from the northwest, into what started
out as Little Buffalo, and turning almost 90º to the southwest
to flow in the same direction as the creek you're
observing. You can draw a straight line from where you
are standing to the far southern border of Stanly County, and that
straight line will almost exactly trace the course of the
creek/river.
Adding to the weirdness, if you could fly a short distance
northeast to Abbotts Creek, you'd find the same phenomenon in
reverse: It goes straight to the northeast, along the same
trend line that Little Buffalo follows to the southwest.
In 1910, Francis Baker Laney wrote a 137-page Bulletin for the
North Carolina Geological Survey entitled "The Gold Hill Mining
District". Dr. Laney didn't have the benefit of a helicopter or
airplane to fly over this area, nor did he have many of the tools
and techniques available to the field geologist today, but he did
have two very important tools: He was smart and he was
observant. He recognized that Abbotts Creek, Reedy Branch,
Little Buffalo Creek, Buffalo Creek and Rocky River flowed in
basically a straight line for "at least 75 miles".
Geologists preceding Dr. Laney had suggested that there must be
a fault in the Gold Hill area, and he offered the following
evidence:
1. Pretty much following the line of the streams, the
rocks to the west were different from those to the east. To the
west were granites and medium grade metamorphic rocks, while the
eastern rocks were mostly sedimentary and low grade metamorphic in
nature.
2. There were numerous springs along the "line of
contact" between the two types of rock, but few to the east or west
beyond it.
3. Numerous minor joints and faults were seen, and
they were generally parallel to the line of contact.
4. Numerous granite dikes intruded the rocks to the west,
but did not exist in the eastern rocks.
5. There were ore bodies and mines along the area of the
line of contact, a few or none to the east and west.
Modern geologists are as intrigued by this fault as was Dr.
Laney. In fact, it turns out that there are two actual
faults, the Gold Hill on the west and Silver Hill fault on the
east. They are parallel to each other, and the distance
between them is generally a few miles. The area between these
faults is important, and that area today is referred to as the Gold
Hill Fault zone (GHFz). Today, researchers led by Dr.
Jim Hibbard of North Carolina State University believe that the
GHFz is a very important clue to the ancient history of today's
Piedmont. The rocks west of the zone have been
radioactively dated to have formed some 613 million years ago (Ma),
while those to the east date back only to about 540 Ma.
The Time Line*
To help understand what happened to create such different rocks,
the Gold Hill Fault zone, and the interaction between them, it's
helpful to see the time line of several important events.
Please understand that there is plenty of controversy over
some of these dates and events, but they represent the results of a
considerable body of research.
~630-610
Ma. As an ancient ocean seafloor dove under
(subducted) under another ancient seafloor, molten rock (magma) was
created. A chain of volcanic islands was formed, spewing out
billions of tons of volcanic debris. Eventually, the source
of magma dried up, the volcanos became extinct, and the island
chain sank under the ocean.
~579-554
Ma. The volcanic island arc (and all of its
volcanic sediments) collided with either another volcanic island
arc or a continent (geologists really don't know which), resulting
in deformed rock layers of the island arc. The layers were
arched up and down in miles-long structures, and the rocks within
were lightly changed (metamorphosed).
~550-530
Ma. Another period of volcanism began on top of
the old volcanic island arc deposits. Evidence of this volcanism is
today very visible in the rocks and old mountains of the Uwharrie
Mountains, from Asheville to just south of Morrow Mountain State
Park.
~450 Ma. The
"new" volcanic island arc (with the old one underneath) collided
with the ancient North American proto-continent.
For those standing at Little Buffalo Creek, this last event
holds the key to the straightness of the creek. Once again,
the layers of rock were arched up and down in miles-long
structures, and there was more light metamorphism. The
shove from the southeast and the resistance to the northwest
created an "irresistable force vs. immovable object" situation, and
something had to give. The Gold Hill Fault zone formed
and thrust the older rocks (the 613 Ma ones) up over the basement
rocks of the proto-continent, and out from under and next to the
540 Ma rocks.
A terrane is a region of the earth's crust,
bounded by faults, that is clearly unrelated to the rocks around
it, indicating that it has moved as a unit from
elsewhere. The region west of the GHFz is referred to as
the Charlotte Terrane; those rocks east of the zone comprise the
Carolina Terrane. The fault zone is the boundary between
them, and must have been the scene of intense heat, pressure, and
shearing/breaking of rocks. So... Where's the fault?
There is no visible "crack in the earth" like the San Andreas
Fault in California, nor is there a dramatic, obvious change in
topography like that of the Teton Range's Teton Fault in Wyoming.
Like Dr. Laney, we must rely on our brains and powers of
observation to figure out that there really was a major, active
fault here, and that the rocks within the GHFz were extensively
broken, stretched and fractured. Those streams, the springs, and
the gold ore all still point to the presence of a fault zone.
So, why is the Gold Hill Fault zone a "good fault?" The
defining characteristic of virtually any type of fault is that it
creates a chaotic place for rocks. They get broken, ground up,
boiled, squeezed, etc, etc, all of which make easy routes of escape
for hot liquids (called volatiles) from the heat and pressure in
the zone. Liquid water is a different critter within an
active fault zone than what we're familiar with at the surface.
Super-heated water dissolves and carries lots of minerals with it,
including abundant quartz, plus some other minerals and elements,
including some gold and copper (depending on the chemistry of the
rocks in the zone). As the volatiles reach cooler areas under
reduced pressures, the quartz and other minerals begin to
precipitate out. Without the mineral-concentrating
activity of the fault zone hundreds of millions of years ago, there
would be little or no gold here, and no village of Gold Hill
today.
"For wherever the earth moves, metals are
concentrated"
Richard
Fortey
Note: For other EarthCaches in the Gold Hill mining district, go
here.
Logging Requirements:
To log this EarthCache, send me an e-mail (Not part of
your log entry!) with the following:
1. Make the first line of your e-mail: "Gold
Hill: A Good Fault"
2. Tell me how many are in your party.
3. Send me answers to the following questions:
a. The GHFz has been
described as "extinct", but some scientists think it was
reactivated when South America/Africa slammed into North America,
about 300 Ma. This is a toughie, but try to answer it
for me, and remember the straight creek/river, and the quote at the
top of the write-up: Describe a scenario whereby the fault zone
might once again become active.
b. You are a geologist in
the field, and you have noticed that the rocks east of the fault
zone and west of the fault zone are different from each other.
Between the two faults (that is, in the fault zone itself),
would those rocks be different or the same as either those to the
east or west? Why?
4. Please post a photo with your party on the bridge
(watch for traffic).
Bibliography:
*The author thanks Phil Bradley, Senior Geologist, North
Carolina Geological Survey, for his valuable corrections, additions
and suggestions relative to this write-up. Any mistakes
herein, however, are solely the responsibility of the author.
The author thanks Vivian Hopkins, Vice President, The Historic
Gold Hill and Mines Foundation, Inc., and Chair of the Foundation's
History Committee. She has been a tour guide, source of
knowledge, and careful fact checker for the author.
Fortey, Richard. Earth, An Intimate History. Alfred A.
Knopf, New York. 2004
Hibbard, J., et al. "The Heart of
Carolinia: Stratigraphic and Tectonic Studies of the
Carolina Terrane of Central North Carolina", Geological
Society of America, Southeastern Section Field Trip Guide,
2008.
Laney, F. B. The Gold Hill Mining
District. Bulletin 21, North Carolina Geological and
Economic Survey, Raleigh. 1910.
Meldahl, K. H. Hard Road
West. University of Chicago Press, 2007.
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