Monday, July 21, 2014


As a CSMS and Western Dakota Gem and Mineral Society delegate, I recently attended the combined American Federation of Mineralogical Societies—Rocky Mountain Federation of Mineralogical Societies meetings in Tulsa, Oklahoma.  The host society was the Tulsa Rock and Mineral Society and members did a fantastic job.  I am uncertain of attendance; however, members came from across the U.S.

As a native Kansan, I have traveled I-35 and I-70 hundreds of times; therefore, whenever possible I like to ramble around on the two-lane state highways taking in the different scenery and stopping to examine a few outcrops---as I did on my trip to and from Tulsa.  In addition to mind numbing, travelers who stay on the interstates often miss observing some really interesting landforms.  Oklahoma is one of those states with a diverse geology and physiography that travelers often miss.  In fact, the geology is actually quite complex with the folded and thrust faulted Ouachita Mountains in the southeast, the Wichita Mountains with an interesting granitic core in the south, salt plains and gypsum caves in the northwest, former zinc and lead mines in the northeast, and lots of land in-between.  In addition, there is a plethora of fossil collecting localities with an abundance of Paleozoic specimens. Therefore, this blog and two others that follow will attempt to entice travelers to visit some of the really great sites in the state. 

Geologic map of Oklahoma (from Oklahoma Geological Survey).  The Ozarks are in the northeast corner east of Tulsa, the Ouachita Mountains are the arcuate areas in the southeast, the Coastal Plain is represented by the green Cretaceous rocks in the far southeast.  The Arkansas River cuts east between the Ozarks and Ouachitas.
Of the eight physiographic divisions in the lower 48, Oklahoma contains three: Interior Plains, Interior Highlands, and Atlantic Plain. The Interior Plains dominate the western and central portions of Oklahoma while the Interior Highlands form high hills and mountains in eastern Oklahoma.  Lastly, in a surprise to many people the Atlantic Coastal Plain occupies extreme southeast Oklahoma. 

Physiographic regions of Oklahoma (Oklahoma Geological Survey).  OZ the Ozark Plateau, O the Ouachita Mountains, CP the Coastal Plain.  Compare with map above.
Perhaps the most interesting area in Oklahoma is the Interior Highlands composed of the Ozark Plateaus, the Arkansas River Valley, and the Ouachita Mountains.  As a school kid growing up in Kansas we were “told by the teacher” that some of the Ozark Mountains were present in the southeastern part of our state.  Now, that “fact” was of great interest to me---mountains in Kansas.  Wow.  I was living out in the prairies of central Kansas and thought that mountains were always of the high, snow-covered, peak variety!  Later in life, as a geology student, I learned that about 50 sq. miles of Mississippian rocks cropped out in extreme southeastern Kansas and those rocks were actually part of the Ozark Plateau---no snow-covered peaks. When teaching geology, I informed my students that the only surface “mountains” in Kansas were the large piles of “chat"—overburden and tailings from the lead-zinc mines in the Ozark section. 

However, I can’t really blame my grade school teacher for any misinformation since she (always a “she”) had to simultaneously take care of two grades.  It wasn’t exactly a one-room school (my mother taught in those) but a four room school with two grades in each room.  That situation continued in high school where freshmen and sophomores took classes together as did juniors and seniors.  Kindergarten and Junior High---didn’t know they even existed.  It was six man football and 47 total students in high school.  But, life was good in a small town.
Map (public domain) showing location of the Ozark Plateau.  Note: ~50 sq. mi. extend into southeastern Kansas; the core of the Mountains are the volcanic and igneous rocks of the St. Francois Mountains in Eastern Missouri; the Boston Mountains are known as the Crookston Hills in Oklahoma. 
Most of the Ozark Plateaus (or Mountains in the vernacular) are located in the southern one-half of Missouri, and northern Arkansas east of the Mississippi River Embayment.  They are a large domed plateau where the relief (elevation gain and loss) is caused by stream erosion rather than strong vertical uplift (as in the Rocky Mountains) or large-scale folds and thrust faults with differential erosion (as in the Appalachian Mountains).  However, the Plateau was slightly domed upward as a result of the Ouachita Orogeny during the Pennsylvanian (~323-299 Ma).  This action, however slight, caused the outcrops to get progressively younger away from the geological core of the Plateau (the igneous and volcanic St. Francois Mountains in southeastern Missouri).  The Ozarks of Northeast Oklahoma are on the southwest flank of the Plateau and most outcrops are gently dipping sedimentary rocks of Mississippian and Pennsylvanian age (see geological map).

Map (courtesy of Kansas Geological Survey) of Tri-state Mining District with major mining districts shown in dark blue.
The Springfield Plateau section of the Ozarks (see maps above) has well-exposed Mississippian (~359-323 Ma) limestones and the surface topography is one of gently rolling hills. Perhaps the most interesting aspect of this province is the presence of the Tri-state Mining District (Missouri—Kansas—Oklahoma), a past producer of lead and zinc.  The initial discovery of lead and zinc ore seemed to have been in Missouri sometime in the 1830’s-40’s and production of lead, mostly it seems from surface cobbing, was important during the Civil War.  Kansas followed with production in the early 1870’s while Oklahoma, then “Indian Territory” (became a state in 1907), did not begin commercial recovery until the early 1890’s.  Initially, the Oklahoma ore was shipped by rail or wagon to smelters in Joplin, Missouri, or to southeastern Kansas (Weir City and Pittsburgh).  By the 1920’s several plants in Oklahoma were smelting the ore. Production of lead and zinc in the Tri-state district lasted nearly a century and the last mines finally closed in the 1970’s.  Peak production seemed to be about from World War I until the beginning of World War II.  In 1926, the Oklahoma County of Ottawa was the world’s largest source of lead and zinc, and during World War I it produced about 50 percent of the zinc and 45 percent of the lead needed in the War (Oklahoma Historical Society, 2007).
Mickey Mantle, the Commerce Comet, was a 1953 All-star.  Photo public domain.
One of Oklahoma’s favorite sons is Mickey Mantle, my boyhood hero. The “Mick” grew up in Commerce, near the mining center of Picher, where his father worked in the lead and zinc mines.  I suspect that most “gentlemen” of my age wish they still had their 1961 Topps baseball card of the Mick!  I cherish my baseball (locked in the vault, sigh) signed by the 1962 Yankees including Berra, Mantle and Maris.

The primary ores of the Tri-state district were the sulfides: galena (PbS) and sphalerite (ZnS). The genesis of the ore is of great interest to geologists but is still not fully understood.  What researchers do know is that cherty limestones were deposited in Mississippian marine waters and indicate a time of crustal stability.  However, the early part of the Pennsylvanian was a time of crustal instability as South America bumped into southeastern North America (these are current configurations and terms) and begin to shove previously deposited basin sediments on to the continent.  Today we know this tectonic event as the Ouachita Orogeny.  Probably related to this collisional and plate-destructive event was the uplift of mountains in Colorado, New Mexico and Utah that geologists term the Ancestral Rockies.  In Oklahoma, shoving and bumping produced the Wichita and Arbuckle Mountains to the west of the Ouachitas.  In the Tri-state area the uplift related to Ouachita tectonics was more subtle; however, the previously deposited cherty limestones were subjected to subaerial erosion.  During this erosional period the soluble limestone created voids, cavities and even caves but left behind the sturdy chert.  Later in the Pennsylvanian, shallow marine waters again returned to the Tri-state and “mud” was deposited that today geologists know as shales of the Cherokee Group. 
A Cartoon showing configuration of continents at the end of the Paleozoic Era. Note how Africa and South America collided with North America and produced the Appalachian and Ouachita Mountains. Public Domain map.
The Kansas Geological Survey (2001) believed that metal-bearing hydrothermal solutions originated deep within the earth’s crust and journeyed upwards along faults and fractures.  As the solution reached the cherty limestone, at least what was left of it, the metals were deposited in the voids, as cement between grains, and as finely disseminated grains. The Cherokee shales essentially served as a cap and hot solutions could not proceed further.  These Tri-state ores, and all of the Ozark ores, are termed Mississippi Valley Type as the ore fluids were expelled from the Arkoma Basin and Reelfoot Rift along the previously mentioned faults and fractures (Cosatt, 2009).

I have written about the Reelfoot Basin before so interested readers should consult the November 21, 2013 Blog. The Arkoma Basin is actually a subsurface basin (Foreland Basin in geology-speak) that received thousands of feet of sediments shed off the rising Ouachita Mountains (~20,000 feet of Pennsylvanian rocks).  Today the Arkoma Basin is an important area for petroleum production and exploration and is generally located between the Ozarks and the Ouachitas.

Weathered cubes of galena, Picher, Oklahoma. Specimen width ~6.7 cm.

Specimen from Picher, Oklahoma with quartz crystals (Q) and sphalerite (S) attached to a bed of chert (C). Width ~6.0 cm.

Chalcopyrite crystals on dolomite, Picher, Oklahoma. Width ~10.5 cm.

Large boulder of smithsonite from Morning Star Mine, Oklahoma. Note security guard in Field Museum, Chicago, 1906. Public Domain photo.
 For the rockhound, the Tri-state District has been a wonderful place to acquire crystals of galena, sphalerite, chalcopyrite, dolomite, marcasite, and a variety of others including a huge bolder of smithsonite.   If you notice, I used a past tense in the previous sentence since most of the old mines are closed and many have been reclaimed and/or flooded.  After the termination of active mining in the early 1970’s, the Tri-state district was an environmental disaster and in the 1980’s the U.S. Bureau of Mines and later the Environmental Protection Agency, along with various state agencies, begin the slow process of mine and land restoration.  The old underground mines, no longer supported by pillars, begin to subside and the sinkholes filled with water that in turn was contaminated by some nasty metallic sulfides that ended up leaching out into the ground water.  I have already mentioned the huge “chat” piles (piles of overburden) that dominated the landscape.  Again, some nasty sort of metals leached into the ground water, and in addition, the piles provided fine particles that were moved to new areas by the wind.  In many localities these chat piles were a cheap source of road aggregate and material was spread on county and township roads.  In turn, the traffic created dust-size particles that were blown on agriculture fields containing “feed” for cattle.  The livestock ate the feed and some of the metals, such as lead, were absorbed into milk which in turn was consumed by residents, especially children.  The good news is that great progress has been made in the environmental restoration.

The highest “mountains” in Kansas---although these chat piles are located near Picher, Oklahoma.  Note water leaching out some nasty stuff.
I was “lucky enough” (read old enough) to have participated in some collecting forays into the Tri-state district and came out with some pretty nice specimens.  Today collectors are on the lookout for “old specimens” brought out in the “lunchbox” by miners (to quote Bob Jones).  A couple of my specimens from Kansas are of that variety, others were self-collected.

The southern or southwestern section of the Ozark Plateau is known as the Boston Mountains and across the state line in Arkansas they are the highest and most rugged section of the Ozark Mountains.  The dissected Boston plateau has capping rocks of Pennsylvanian age with the oldest rocks representing stream deposits flowing off the Ouachita Mountains into an ocean while the younger rocks are mostly deltaic.  In Oklahoma these Pennsylvanian sandstones and shales (the Boston Mountains in Arkansas) are generally referred to as the Crookson Hills.  The Hills have granted to the state a fantastic bit of scenery for they are heavily forested with trees such as hickory and their streams/lakes are famous for providing fishing opportunities and boating.  On one geology field trip a long time ago, I was able to collect numerous pieces of tree ferns (a group not really related to modern deciduous trees); however, over the years the specimens sort of migrated to museum and laboratory collections.

South of the Ozark Plateau the mighty Arkansas River turns east (entering Oklahoma flowing south from Kansas) and slices a large valley through Pennsylvanian sandstones and shales (see geology map). This valley continues into Arkansas all the way east to the master stream, the Mississippi River.  The river valley separates the Ozarks from the Ouachita Mountains to the south.  This valley is at the location of the subsurface Arkoma Basin discussed above. 

South of the Arkansas River Valley are the Ouachita Mountains, an area of folded ridges and valleys that is a geologist’s (and sightseer’s) paradise.  Clastic Paleozoic rocks predominant, (deposition in a shallow marine environment, the continental shelf), as opposed to limey rocks in the Ozark Mountains.  During most of the Paleozoic, in what is now the Ouachitas, a deep offshore abyssal plain, perhaps more than 3000 feet below sea level, existed (Arkansas Geological Survey, 2012).  But then the “big bump” came along as South America was pushed “north” and collided with Laurentia.

Google Earth© image of folded Ouachita rocks in McCurtain County, Oklahoma. Broken Bow lake is partially visible at extreme right (east).
So, these folded Ouachita Mountains have an interesting geological history--with deposition in a deep water basin during the Ordovician and Devonian, but a wild change in the Mississippian and Pennsylvanian.  During this later Paleozoic “action” what is now South America collided with Laurentia (the geological name for what is now the North American continent).  The rocks and sediments in the marine basin were thrust up on the continent at this convergent and destructive plate boundary.  This collision compressed and folded the rocks as they were thrust northward.  Perhaps as much as 50,000 feet of Paleozoic rocks, much of it back shale, quartzitic sandstone, or bedded chert rocks are present. 
The Ouachitas are a western continuation of, and closely related to, the Appalachian Mountains.  The major difference is that the Oklahoma-Arkansas Mountains are the result of South America bumping into Laurentia while the Appalachians are related to the collision of Africa with Laurentia. The result of all of these collisions is the formation, at the end of the Paleozoic, of a vast supercontinent called Pangaea. 

I have not really collected much (mostly just studying the stratigraphy) in the Oklahoma Ouachita Mountains except for exploring a few road cuts on a field trip to Broken Bow in the southeastern part of the state. The group collected small quartz crystals with included “green stuff”—chlorite, from what I believe is Ordovician sandstone.
Quartz crystal with chlorite inclusions. Height ~2.1 cm.
South of the Ouachita Mountains are outcrops of poorly consolidated, gently dipping, off-lapping rocks of Cretaceous age.  These unconsolidated sands, gravels, clays and limestone of mostly shallow marine origin are part of the proto-Gulf of Mexico; they are generally featureless and belong to the Gulf Coastal Plain, a part of the Atlantic Coastal Plain.


Brosius, L. and R.S. Sawin, 2001, Leas and Zinc Mining in Kansas: Kansas geological Survey, Public Information Circular 17.

Cosatt, M., 2009, Geophysical Evidence for the Origin of the lead-Zinc deposits in the Tri-state Mining District, KS, MO, and KS.: Geological Society of America Abstracts with Programs No. 31-1. 

Johnson, K.S. (compiler), 2008, Geological History of Oklahoma: Geological Survey of Wyoming Educational Publication 9.