Geological Destination - The Bingham Canyon Mine

Identified as the largest open pit mine in the world, the Bingham Canyon Mine, also known as the Kennecott Copper Mine, is a local attraction here in Salt Lake City. The mine sits within the Oquirrh Mountains, on the opposite side from where I live. I had the frequent hopes of grabbing a good photo of the mine taking off from the Salt Lake airport and that time finally arrived when flying down to Las Vegas a couple of years ago. 

View of the Bingham Canyon Mine facing west

In the photo above you can see the mine nestled within the Oquirrh Mountains. The mountains in the background are the Stansbury Mountains with the Tooele Valley (where I live) located in between. 

View of the Oquirrh Mountains facing the western side of the mountains

Above is a view of the Oquirrh Mountains from the western side of the mountains (facing east). The Bingham Canyon Mine is located on the other side of the mountains towards the right (southern) edge of the picture. 

Another shot of the pit a little further along in the flight path.

Per the Utah Geological Survey, the Bingham Canyon Mine:

"...  is one of the largest and most efficient mines in the world. It has produced more copper than any other district in the U.S., accounting for over 16% of total U.S. copper production. In addition to copper, the mine produces gold, molybdenum, and silver. KUC’s combined annual value of these metals peaked in 2011 at $2.9 billion."

Currently the Bingham Copper Mine is the 2nd most active copper producing mine in the US and one of the top gold producers in the US as well. 

Geology

The rocks within the Oquirrh Mountains were deposited a long time ago during the Paleozoic (250 to 540 million years ago). Much of these rocks were deposited in marine environments as Utah represented the edge of the North American continent. Eventually the land started to be raised up and dried off and then around 100 million years ago the Farallon Plate started to subduct beneath the North American Plate.

Diagram of the Farallon Plate subduction zone along the western United States. Image courtesy of the NPS. 

The pressure of the Farallon Plate pushing on the North American Plate did two things. First, it compressed the North American Plate, creating a "wrinkle" in the surface producing mountains along the western part of the US. Second, as the Farallon Plate was subducting, it then started to melt. That melted rock eventually rose up and created a line of volcanoes. Around 30 to 40 million years ago, that line of volcanoes was located within Utah. Magma was slowly injected into the Oquirrh Mountains, predominantly into the 300 to 350 million years old rock formation known as the Oquirrh Group. These rocks, laid down in the Carboniferous (i.e. the Pennsylvanian and the Mississippian), are composed mostly of quartzites and limestone beds. This magma body slowly cooled to form what is known as the Bingham Stock, an igneous body identified as a monzonite porphyry. In addition to the magma body itself, is that the hot magma produces a lot of hydrothermal fluids within proximity of the magma body. These hydrothermal fluids move the heavy metals (such as gold, copper, silver, etc.) from within the magma and redeposit them within the surrounding landscape. 

Model for the magma-hydrothermal mineral deposits. From Groves and Santosh, 2015.

Cross Section of the Bingham Canyon Mine from Kennecott, 1991. Image courtesy of the Society of Economic Geologists. 

Stratigraphic column of the Bingham Pit Mine from Kennecott, 1991. Image courtesy of the Society of Economic Geologists.

So what you are left with is an isolated region that has a high concentration of metallic ore deposits. Many of the more prolific ore deposits across the globe have formed in a similar way (hydrothermal fluids surrounding a magma body) and therefore understanding how the Bingham Canyon mine formed helps us to understand where other ore deposits originated from.