FAIRBURN AGATE: WYOMING

I have written a couple of other blogs about Fairburn Agates in South Dakota and one about Teepee Canyon Agates.  Since I have long been interested in these agates, I report on another specimen.  But readers should be aware that I really lack any expertise either in their discovery, formation, or distribution.  I saw my first Fairburn back in the mid-1960’s and decided “they were pretty neat” and my interest has remained.  The initial Fairburn that I collected still sticks out in my mind---I had found a Rapid City (I suppose) AM radio station that played “rock & roll” that I could receive out on the plains east of the Hills.  I had cranked up the radio and decided to look at some gravel exposures to see what was there---Tommy James’ My Baby Does The Hanky Panky was playing when I looked down and there it was.  Now, my mind has a penchant for being able to remember trivial factoids from decades ago but is unable to recall where I left the car keys.  But, life is good.

At any rate, South Dakota Fairburn Agates are “plains’ agates” mostly to the south and east of the Black Hills and mostly associated with terrace gravels along streams and/or conglomerate beds and lag deposits on top of the Eocene-Oligocene White River Group (Chadron Formation or perhaps the underlying Eocene Chamberlain Pass Formation).  However, Fairburns or Fairburn-type agates have been located in the adjacent states of Wyoming and Nebraska.  Buena Vista Gem Works (2013) noted that in Nebraska the area of collecting is north of US 20 from Chadron to the Wyoming state line, generally following outcrops of the Chadron.  Major collecting localities in Wyoming include Lance Creek and Hat Creek (southwest and reasonably close to the Hills) and Glendo and Guernsey (further to the south).  Gemworks (2013) also reported “stray finds” of Fairburn-type agates from the Yellowstone River in Montana, near New Raymer, Colorado, (northeast Colorado) and along the Yampa River in northwest Colorado.  The Chadron crops out near New Raymer but is absent from the Yellowstone and Yampa River localities. Pabian and Cook (1976) reported Fairburn-type agates at localities along the east-flowing Platte River in Nebraska.

Most agate hunters describe Fairburns as fortification agates with a holly leaf banding. They have sort some of red to orange banding due to iron oxides with the black banding ascribed to manganese.  The “type area” for Fairburns is near (east) of the small village of Fairburn along French Creek (see blog postings on 6-12-12and 8-19-12).  It seems well established that the agates out on the South Dakota plains originated in the Minnelusa Formation of  Pennsylvanian-Permian age and were transported away from outcrops in the Black Hills by Cenozoic streams.  Perhaps the best-know site for observing in situ Fairburn agates is at Teepee Canyon west of Custer (see blog posting 8-18-12).

Map showing location of Hartville Uplift in eastern Wyoming.  The topographic expression of the Uplift is limited to the notation “Hartville Uplift” while a subsurface structural high (arch) extends northeast to the Black Hills.  Map from Dickinson and others, 1988.

I find it interesting that Fairburn-type agates found at the Glendo and Guernsey locations in southeastern Wyoming most likely came from rocks similar to the Minnelusa Formation (Hartville Formation) exposed around the perimeter of the Hartville Uplift (Sutherland, 1990).  This uplift is a Laramide structure, not unlike the Black Hills with which it connects on the north, but much more topographically and structurally subdued.  It separates the Powder River Basin (northwest) from the Denver Basin.  The Uplift does have a core of Precambrian rocks with a surrounding ring of Paleozoic and Mesozoic rocks; most of the uplift is now covered by Cenozoic rocks.  I have written about the Hartville Uplift in a previous blog (12-22-12) and noted: “The Precambrian exposures are of interest to Coloradans since the rocks contain large deposits of iron, both banded iron formations and specular hematite.  Iron was first produced from the Sunrise mine, and later the Chicago, Central, and Good Fortune mines, near the towns of Hartville and Sunrise in the late 1800’s.  These mines then shipped this hematite ore to the Colorado Fuel and Iron Corporation open-hearth furnaces in Pueblo, Colorado. (Sims and Day, 1999). At the time when mining ceased at the Sunrise mine in 1980, the Hartville district had produced about 45 million tons of iron ore (Hausel, 1989).”

It appears, then, that the Hartville Formation (Hartville Uplift) is stratigraphically equivalent to the Minnelusa Formation (Black Hills); both produce similar fortification agates. I also find it interesting that Pabian and Cook (1976) believed the "fortification agates [Fairburn-type] found in Nebraska originated chiefly in sedimentary rocks…of Pennsylvanian age in the Hartville Uplift and the Front range of Wyoming.  Some may have originated in the Black Hills but this appears to be a minor source."  It appears that Pabian and Cook (1976) expressed this belief because of statements in a 1955 paper by Shultz and Stout noting that “no physiographic evidence exists to show a major north-south drainage from the Black Hills to Nebraska.”  I don’t know enough about recent stratigraphic studies on the White River Group to speculate on the accuracy of this statement.  So, perhaps Nebraska Fairburn-type agates came from the Black Hills and/or from the Hartville or Front Range Uplifts?  Perhaps some reader knows the answer to this question?

Fairburn agate collected near Douglas, Wyoming.  Length ~7 cm.

My Wyoming Fairburn was collected near Douglas, Wyoming, from lag gravels associated with rocks of the White River Formation.  That is I presume a Fairburn, or is it a Fairburn-type?  Did it originate in the Black Hills or from the Hartville Uplift?

As I remember my first Fairburn (the real thing) the music floats through my mind::

I saw her walking on down the line
You know I saw her for the very first time
A pretty little girl standing all alone
Hey, pretty baby, can I take you home…

My baby does the hanky panky

REFERENCES CITED

Buena Vista Gem Works: www.buenavistagemworks.com/agates/fairburn.htm

Dickinson, W.R., M.A Klute, M.J. Hayes, S.U. Janecke, E.R.Lundin, M.A. McKittrick and M.D. Olivares, 1988, Paleographic and Paleotectonic Setting of Laramide Sedimentary Basins in the Central Rocky Mountain Regions: Geological Society of America Bulletin, v. 100. 

Hausel, W.D., 1989, The Geology of Wyoming’s Precious Metal Lode and Placer Deposits: Geological Survey of Wyoming Bulletin 68.

Pabian, R.K. and Allan Cook,1976, Minerals and Gemstones of Nebraska: A Handbook for Students and Collectors: Nebraska geological Survey Educational Circular no. 2.

Sims, P. K. and W. C. Day (compliers), 1999, Geologic Map of Precambrian Rocks of the Hartville Uplift, Southeastern Wyoming with a section on Mineral Deposits in the Hartville Uplift by Terry Klein: U. S. Geological Survey  Map I-2661.

Sutherland, W.M., 1990, Gemstones, Lapidary Materials, and Geologic Collectables of Wyoming: Geological Survey of Wyoming Open File Report 90-9.