GO 324A Rocks and Minerals
www.emporia.edu/earthsci/amber/go240/field_trip.htm
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Emporia State University |
GO 324A Rocks and Minerals
www.emporia.edu/earthsci/amber/go240/field_trip.htm
|
Emporia State University |
|
Students enrolled in a two-credit petrology course offered through Emporia State University are introduced to rocks and minerals by participating in weekly course work and a field trip excursion. The field trip takes the student to see sedimetary, igneous, and metamorphic rock, all within the state of Kansas. Follow along on the field trip through images and text below. Throughout the webpage, click on any image to see an enlarged version.
The image right shows the fall semester 2008 class. From left to right, students include Joseph, Gayla, Susie, Scott, CeLena, John, and Sam. While many students have taken this field trip, a few additional recent classes are shown below. |
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 Photo © by J.S. Aber, April 2008 |
 Photo © by J.S. Aber, April, 2006 |
Silver City
Rose Dome
Links
References
Upland Chert GravelThis field trip began in Emporia, Lyon County, and made stops in Coffey, Woodson, and Wilson counties located in the eastern one-third of Kansas. The first stop was south of the Neosho River and Burlington, Coffey County, along Hwy. 75 at a high point in the topography. A rock and mineral collection is a required course project and at this location, an abandoned open pit mine for chert gravel, students collected pebble- and cobbled-sized sedimentary rock. These specimens included weathered chert, milky quartz nodules, quartzose-quartzite pebbles, and Permian age fossils, among the local Pennsylvanian age sandstone and shale bedrock. Since gravels are draped over the Pennsylvanian bedrock, one obvious explanation is an abandoned river channel deposit.These gravel deposits date to Neogene (Miocene-Pliocene) or Tertiary in age. Students pondered the question of how river gravel become deposited on a high hill overlooking the modern day Neosho River drainage valley? Also, where did this assortment of rocks originate? Coffey county is located in the Osage Cuestas physiographic province, and to the west is the province known as the Flint Hills, which is made up of Permian age flint or chert-rich limestones interbedded with shales. Chert is a microcrystalline quartz and has a higher resistance to weathering than its limestone host or the shale. So the abundance of chert in the deposit is because it also withstands transportation from the Flint Hills by merely rounding angular edges. However, the quartzose-quartzite pebbles are not common to the Flint Hills and are referred to as exotics. The nearest western source is the High Plains province and the Rocky Mountain beyond, with transport by streams that flowed across the Flint Hills (Aber, 1988). |  County map taken from the Kansas Geologic Survey. |
 Kansas Geologic Timetable segment taken from Kansas Geologic Survey. |
| The chert gravels examined in Coffey County resemble the Leon Gravel, which is a name assigned by J.S. Aber (1992) to chert gravel deposits in Butler and Cowley counties. Leon Gravel is associated with the Olpe or Olpe-Norge soils and found on high terraces and hill tops, about 1-2 m thick and resting on the local bedrock. More information on upland chert gravels of eastern Kansas by J.S. Aber is found in the KGS Open File Report, http://www.kgs.ku.edu/Publications/OFR/1991/OFR91_48/index.html. |
 Photo © by J.S. Aber, 4/2006 |
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The field trip continued south on US Highway 75 to Woodson and Wilson counties. Much of the surficial bedrock in these two counties is Pennsylvanian. For example, the Weston Shale within the Stranger Formation was examined at a roadcut along the highway, as was the Stanton Formation at Wilson County Lake, in the spillway and nearby road cuts (www.kgs.ku.edu/Publications/Bulletins/189/07_penn.html). Students collected the limestones, shales, and siltstone along with calcite and pyrite. In addition to these sedimentary rocks and minerals, the class viewed and collected igneous and metamorphic rock in Woodson County.
Geologic time scale shown left was taken from the Kansas Geologic Survey. Click on the image for clear viewing. |
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Silver CityAs immigrant pioneers moved from east to west across the U.S., many small permanent settlements arose in Kansas as oil and natural gas were discovered. One such community was Buffalo, Woodson County (skyways.lib.ks.us/towns/Buffalo/history.html), which quarried a ready supply of shale and exploited the natural gas to fuel brick making operations for building materials (skyways.lib.ks.us/towns/Buffalo/bricks.html). West of town is a water filled open pit that resulted from quarrying rock of the Pennsylvanian Weston Shale Formation. When the abundant natural gas in the area played out, the brick plant closed. However, another part of the history of Buffalo involves the exploitation of an unusual occurrence of igneous rock that helps to keep this small town in existance today. | |
| The intrusive igneous rock west of Buffalo is known the Hills Pond lamproite and is found in an area referred to as Silver City. Silver City was named for a small mining settlement, which was initially shrouded in a scandal (www.ghosttowns.com/states/ks/silvercity.html). During the 1870s, investors were led to believe they were buying shares in a silver mining operation. Abundant bronze colored phlogopite mica sparkles in the sun and from a distance has the metallic look of silver or gold! |
 Photo © by J.S. Aber, 4/2006 |
 | Today the mining operation is run by the Micro-Lite company, which has a distribution plant on the west edge of Buffalo. The Micro-Lite quarry is located a few miles on to the west and north of Buffalo, where the company quarries the weathered lamproite deposit. This igneous intrusive rock punched up to the surface during the Cretaceous, some 88-91 million years ago, and is famous worldwide for producing diamond. The lamproite magma, originated in the upper mantle, moved through Precambrian and other younger rock to Pennsylvanian age strata, which is the surface today. These Pennsylvanian rocks include layers of sandstone, siltstone, shale, and limestone. |
| The relatively explosive intrusive process folded and faulted the bedrock, and created a sill structure that spread among stratigraphic layers in both uniform layers as well as intrusive fingers among the sedimentary strata. More information about this process and site can be found at an external link from a Kansas Geological Survey field trip, www.kgs.ku.edu/Extension/fieldtrips/guidebooks/SCKS/SCKS3.html. |
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| This KGS website provides a schematic diagram of a carrot-shaped lamproite deposit intruding through the granite basement rock and layers of sedimentary rock. Lamproite beneath the weathered zone is a consolidated rock that is blue to dark green in color. Earth movers and bull dozers are used to unearth and move the highly weathered lamproite or yellow ground to the staging area. |
| The product is gathered and dropped onto a conveyor belts that move the material to a large tank for drying. After drying, it is loaded in dump trucks and hauled to the storage elevators and distribution plant. Here it is packaged and taken by rail or truck to market. |
 Photo © by J.S. Aber, 4/2006. |
 Photo © by J.S. Aber, 11/2008. | Initially, the product was used as a human food additive because of the nutrient-rich mica. In the 1950s, an entrepreneur tried to sell the mica lamproite as insulating material, but the inexpensive price of gas and oil created little interest in making homes and businesses energy efficient. However, a marketable product was created by the 1970s and Micro-Lite has operated the plant since 1982 (www.kgs.ku.edu/Extension/fieldtrips/guidebooks/SCKS/SCKS3.html). |
| Lamproite deposits in Australia and along the Colorado-Wyoming border contain diamonds in sufficient quantities to mine, but this is not the marketable product for Kansas. It may never be publically known if Kansas lamproite and peridotite deposits contain diamond, but Micro-Lite company is mining this weathered mica and marketing it as a mineral supplement for cattle feed because they noted that grazing cattle naturally ate the material and gained weight. The KGS reported in 1996, 70,000 tons of lamproite were removed (www.kgs.ku.edu/Extension/fieldtrips/guidebooks/SCKS/SCKS3.html). |
 Photo © by J.S. Aber, 11/2008. |
 Photo © by J.S. Aber, 4/2006 | While the deposits exist in other areas within Woodson county, the company has not expanded beyond their original quarry site; today the eastern end of the quarry is being worked. The lamproite deposit of interest is on the floor of the mine which is more than 50 feet (15 meters) below the surrounding landscape now. |
| Historically, Wagner (1954) described this deposit as the Hills Pond Peridotite. He remarked that it was medium-grained, olive-gray peridotite when fresh and grayish-yellow when weathered. Zartman, Brock, Heyl, and Thomas (1967) were the first to date the material to Late Cretaceous, 88-91 million years using K-Ar on samples of phlogopite mica. |
 Photo © by J.S. Aber, 4/2006 |
 Photo © by J.S. Aber, 4/2006 | As interest in the deposit grew, so did the research and publications. O'Connor (1968) reported the Hills Pond rocks were in contact with late Pennsylvanian age Lansing and Douglas Group sedimentary rock at the surface (in D.E. Zeller, p. 68). However, Cullers, Bamakrishnan, Berendsen, and Griffin (1985) were the first to argue the so-called peridotite was really lamproite (p. 1383-1402). |
| The lamproite mineral composition is defined by about 25% phlogopite mica and 15% olivine, diopsidic augite, red-brown amphibole, which is all in a serpentinized clay groundmass. The lamproite is up to 60 feet (18 meters) thick in the northern part of the Silver City Dome. Overall, this deposit represents a network of sills that came out from a main lamproite pipe structure and at Siver City, the lamproite is located along a steeply dipping fault in a ring-graben structure. |
 Photo © by J.S. Aber, 4/2006 |
 Photo © by J.S. Aber, 4/2006 | The KGS reported other "sills extend away from the main pipe and have been encountered at depths of about 1,300 feet (396 meters) during core drilling, and drilling for oil and gas, in the area around the dome" (Micro-Lite Quarry/Silver City Dome). These sills created a ring of contact metamorphic rocks, which are shown in these images. These hornfels-grade metamorphics can be horizontally layered or brecciated and folded masses. |
| Intruding hot lamproite magma into the surrounding Pennsylvanian clastic sandstones and shales created a odd assemblage of quartzite, skarn, and slate. Blue and green quartzites can contain pockets of smoky and clear quartz crystals; while, blue, green, mauve, tan, brown skarns may be brecciated, faulted, and folded. |
 Photo © by J.S. Aber, 2/2006 |
 Photo © by J.S. Aber, 4/2006 | The contact metamorphics are primarily exposed on the north and south areas of the quarry. Obvious faults can be seen along the north face and several brecciated and folded skarns are evident on both the north and south sides. In addition to the lamproite deposit and contact metamorphics, limestone xenoliths have been found at Silver City (picture shown left). |
| While the authors of this webpage have been visiting this quarry since 1981, limestone xenoliths were first discovered at the far west end of the pit in 2000 (Aber and Aber, 2001). The unusual specimen shown above contains areas of gray and brown limestone with abundant fossils that are criss-crossed with white and gray quartz veins. In the smaller cobble- and boulder-sized xenoliths, weathered out pockets occur as well, where limestone once was located. |
 Photo © by J.S. Aber, 4/2006 |
 Photo © by J.S. Aber, 4/2006 | The pictures above and to the left, show the position of the xenolith specimens in the quarry, as well as some of the larger xenolith boulders. In determining the source of these limestone xenoliths, Pieter Berendsen (pers. communication) reported drilling a core hole on the southern ridge of the open-pit mine that first, encountered rocks in the Stranger Formation and second, encountered rocks in the Stanton Limestone at a depth of 226 feet (69 meters). |
| After much consideration, Aber and Aber (2001) speculated the likely limestone source for the xenoliths was the Stanton Limestone (p. 126-127). This limestone is thin bedded and brecciated at several levels; there was no chert or obvious dolostone within the xenoliths which rules out the deeper Mississipian age limestones as a source. |
 Photo © by J.S. Aber, 4/2006 |
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No metamorphism, recrystallization, or partial melting of limestone to marble was noted; this leads to the conclusion that transportation of the limestone xenolith was a relatively short distance and that "the limestone may have been uplifted along the fault that marks the southern edge of the sill at this location" (Aber and Aber, 2001, p. 126-127).
Thus, Aber and Aber concluded that the limestone xenoliths were derived from shallow Pennsylvanian sources within the sill complex, and that "genesis of the xenoliths began as quartz veins were precipitated in highly fractures wall rocks. Some fragments of the wall rocks were detached, transported a short distance (10s of meters), and emplaced at the rapidly cooling margin of the sill" (p. 127).
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Rose DomeAlthough the limestone xenoliths were a relatively new discovery, other foreign rock or xenoliths had been known from an area near to Silver City at Rose Dome. This was the final stop on the field trip, and the name Rose Dome came from proximity to the former city of Rose. The site is off Hwy. 75 and in a pasture with a small creek flowing on the north side, which is shown below. | |
 Photo © by J.S. Aber, 11/2008 |
Students were introduced to the Rose Dome granite, the only in-situ granite exposed at the surface in Kansas. The texture is phaneritic to brecciated, and the granite was dated with Rb-Sr to about 1.2 billion years or middle Proterozoic (Bickford et al. 1971).
Through the years, researchers had speculated on how this granite came to be in Kansas, with proposals from Pleistocene glacial erractics to displaced basement rock along a major thrust fault. Others suggested a grantitic intrusion or iceberg rafting from glacial centers in Gondwana in the Pennsylvanian. As late as 1998, Luczaj argued that the granite was the uplifted center of an meteorite impact crater, where the meteorite skipped along the 38 degree lineament crossing through several states. |
| Rose Dome Granite is Kansas basement rock that was brecciated and is composed of 30 percent blue-gray quartz, 45 percent sanidine feldspar, 25 percent albite, and less than one percent biotite (Franks et al. 1971). It is unlike most granite because sanidine is not a typical felsic feldspar. One student collected this specimen of Rose Dome Granite, which had a vug of euhedral amethyst crystals. What an unusual and beautiful find! |
 Photo © by J.S. Aber, 4/2006 |
 Students examining drill hole in Rose Dome Granite. Photo © by J.S. Aber, 11/2008 | |
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If the greater regional structures are considered, evidence points to lamproite intrusions at Silver City and Rose Dome taking place along deep crust, pre-existing fractures. The intrusions are isolated but widespread mid-Cretaceous igneous activity events across the central U.S., which may be related to sea-floor spreading in the Atlantic or rifting of the Mississippi Embayment. Although origins of the intrusions are at least 100 km deep, recurrent crustal movements have led to measurable joints in the sill at Hills Pond/Silver City. Finally, there is absolutely no physical evidence at Rose Dome for meteorite impact origin and the connection between Rose Dome and the 38 degree lineament is only a coincidence. This interpretation is most obvious by basing all speculation on topographic maps and no ground truth. Return to Table of Contents |
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This page originates from the Earth Science department for the use and benefit of students enrolled at Emporia State University. The curriculum is © by the author, 2006-2009. Creation and last update 18 July 2009. For more information contact the course instructor, S. W. Aber, e-mail: saber@emporia.edu
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