I
have been informed that the mine will be expanding and the viewing
area at the coordinates will be closed sometime soon. I have
permission from the mine to move the Earthcache to the visitor
center when the area is closed. I will accept a visit to either
location. See the waypoint for the guard shack to enter the
mine and get directions to the current loction of visitor center.
Their visitor center is closed during certain times of the year,
usually winter, so call to be sure they are open. A donation is
required.
The earthcache brings you to an overlook of the Bingham Canyon
Copper Mine. This is the largest open pit mine in North America and
the largest deposit of copper and gold on the continent. It
produces copper, molybdenum, gold, and silver.
The formation of this ore deposit began with the pulling apart
of the North American continent during the Eocene to form what is
known now as the Basin and Range Province. This time, fractures
developed in the continental crust throughout the region to
accommodate the stretching. At one of these fractures magma pushed
its way to the surface to form the Bingham stratovolcano at Bingham
Canyon. A stratovolcano is a volcano made up of alternating layers
of volcanic ash and lava. Mount Pinatubo is a modern day
example.
Between 38.8 to 39.8 million years ago (late Eocene) two large
stocks (reservoirs) of magma pushed their way through the
surrounding sedimentary rock to form what are now the Last Chance
and Bingham Stocks, two related igneous rock bodies.
At the end of the formation of these stocks, more magma intruded
through the Bingham Stock from 39.7 to 37.7 million years ago. This
intrusion created fractures for hydrothermal groundwater. Later the
magma cooled to form the Bingham Canyon porphyry. A porphyry is an
igneous rock that contains large crystals within a fine-grained
matrix.
The copper and other metals contained in the magmas
were then dissolved in hydrothermal groundwater. Over time, the
groundwater moved through the fractures surrounding the Bingham
Canyon porphyry concentrating the metals around it. As a result,
the porphyry became the major ore body of the canyon.
Image Source: Bingham stratovolcano Source:
Hattori, 2001
In the millions of years since, the Bingham stratovolcano has
been eroded away leaving only the core.
Like the Bingham stratovolcano, Mount Pinatubo has similar
deposits. Even though it is an active volcano, there are mines on
its sides producing copper from its porphyrys.
Note: This discussion is an extreme generalization. Additional
detail regarding additional geologic events, geologic chemistry,
and hydrologic chemistry can be found in the references.
Logging requirements:
Send me a note with :
- The text "GCZ5ZF Stratovolcano to Huge Hole in the Ground" on
the first line
- The number of people in your group.
- Describe the direction the mine is digging.
- Give me your explanation as to why they are digging in that
direction.
The above information was compiled from the
following sources:
- Briggs, David F. Bingham Canyon
- Sec. 25-27, 34-36 T.3S. R.3W. Mining Operations Report, Version
2004, Last Entry 6/23/2005
- Hattori, Keiko, Jeffrey D. Keith, 2001,
Contribution of mafic melt to porphyry copper mineralization:
evidence from Mount Pinatubo, Philippines, and Bingham Canyon,
Utah, USA, Mineralium Deposita( 2001) 36: 799-806
- USGS, America's Volcanic Past - Utah,
http://vulcan.wr.usgs.gov/LivingWith/VolcanicPast/Places/volcanic_past_utah.html
