Why do we find diamonds in this corner of Arkansas?

 

By Margi Jenks

 

Many visitors wonder why this odd little park in southwest Arkansas is a place where diamonds have been found and mined for the past 107 years.  The answer is fairly simple—you will only find diamonds within a volcano eruption.  Yes, with the exception of some meteor craters, diamonds are always associated with volcanic rocks.

 

Geologists in recent years have been working on this question, and believe that they have the answers.  First, instead of forming from coal that became buried deep in the Earth, scientists now believe that diamonds are the result of carbon dioxide that was trapped as the Earth was formed.  They also believe that the diamonds formed  between 2.5 and 3.5 billion years ago and are now stable in the upper mantle layer of the Earth’s insides, about 100 miles deep.  That area has high enough pressures and temperatures to force the diamond’s carbon atoms into their unusual arrangement.  So, in order for us to find diamonds on the Earth’s surface, something must have transported them up to that surface.  That something that acted as an elevator, anywhere in the world—in Arkansas, South Africa, Russia, Western Australia or Canada—is always a volcanic eruption.

 

The next visitor question usually is, “So if I go to Mt. St. Helens or Hawaii, will I find diamonds in those volcanoes?”  The answer is “No, not all volcanoes have diamonds”.  The lava in most volcanoes came up to the surface from much shallower depths.  In fact, scientists believe that the depth to the Hawaiian magma chamber may be as shallow as only 2 to 2.5 miles.

 

So, why then does this corner of southwest Arkansas have a weakness in the crust that reached down to the upper mantle, diamond bearing part of the crust?  What would create such a deep weakness?  The answer, geologists believe, is due to plate tectonics—the theory that suggests that the crust of the earth is made up of continental and oceanic “plates”.  These plates have floated in various ways, sometimes crashing together, sometimes being pulled apart.  In the case of southwest Arkansas, about 106 million years ago when the Crater of Diamonds volcano erupted, what are now the North and South American plates were being pulled apart.  This stretching of the crust created the types of deep faults that we associate with present day pull-apart areas like the East African Rift or the Nevada Great Basin.  Previous to this rifting event, those same crustal plates had collided, creating the folded rocks of the Oauchita and Arbuckle Mountains in central Arkansas and Oklahoma.

 

Finally, many of our younger visitors, when they find out that our field is a volcano, want to know if it is going to erupt again.  The answer is “no”.  The serendipitous circumstances that allowed diamond-laden magma to reach the surface are long gone, and will not be happening again.

 

Search area last plowed:  April 23, 2013; Most recent heavy rain:  June 1, 2013—1.4 inches

 

Total diamonds found in 2013: 251

 

Diamonds registered for May 26-June 1, 2012 (100 points = 1 carat): 

 

May 26 - Ron Cudmore, Murfreesboro, AR, 13 pt. white; Kelsi Slowe, Springfield, IL, 10 pt. white

 

May 27 - Tom Gomoll, Curtice, OH, 26 pt. white

 

May 28 - No diamonds were registered

 

May 29 - Brian Carstens, Freemont, NE, 12 pt. white; Axel Dempsey, Council Grove, KS, 4 pt. brown; Nancy Jaynes, Council Grove, KS, 4 pt. white; Cubby, Daytona Beach, FL, 4 pt. brown

 

May 30 and 31, June 1 - No diamonds were registered