Minerals are frequently found in vugs or cavities of the Springhill Limestone. There is a quarry where this limestone is being mined in Anderson County, Kansas, and the variety of minerals found in these vugs is the topic of this webpage. Commonly, vugs that are hollow will be lined with calcite, dolomite and chalcopyrite crystals. Also, sphalerite is found in vugs, which are filled completely with a massive mineral habit. When hunting for minerals in this rock quarry, smithsonite may be found among the broken pieces of rock on the quarry floor; however, smithsonite is not found within the vugs of the limestone. Marcasite nodules frequently occur in the Vilas Shale, which is stratigraphically above the Springhill Limestone. The geologic formation of these minerals may be Mississippi Valley-type deposits, a hydrothermal derivative.
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The Springhill formation is a thick limestone bed ranging from seven to 23 feet in outcrops in the north, and zero to 88 feet thick in southern Kansas outcrops (Zeller, 1968, p. 33). At the Anderson county quarry site, the Springhill limestone is approximately 25 feet thick. This limestone is fine-grained and gray in color, as well as fossiliferous with wavy-bedding planes. At this quarry, the upper portion of the bed that is mined is calcarenite (p. 33). Within a thick bedding plane, voids occur and are filled primarily with calcite, but with other mineral crystals as well. This occurrence is not unique to the Springhill though, as other limestones in eastern Kansas contain crystal-lined voids including the Hartford Limestone and the Deer Creek Limestone (Paul Johnston, personal communication).
Overlying the Springhill Limestone, is a gray to black, well-bedded formation called the Vilas Shale. It is one to 35 feet thick in Anderson County and northward, and in southern Kansas it is five to 120 feet thick (Zeller, 1968, p. 33). This layer contains many marcasite nodules interbedded in the shale. One interesting observation can be made on sunny days following a rainstorm, in that it is possible to smell the marcasite, which has the odor of burned matches. This odor is the result of the sulphur in the marcasite. Both the Springhill Limestone and the Vilas Shale were deposited during the Pennsylvanian Period.
Many of the vugs contain calcite crystals are covered with a brown iridescent coating. According to Larry Skelton (personal communications), who works at the Kansas Geological Survey, this is probably a thin coating of sphalerite. Other calcite crystals are without the sphalerite coating and are translucent to clear. The chalcopyrite appears to be crystals sprinkled over the dolomite and calcite crystals or found alone in small voids in the limestone. Dolomite lines some of the cavities and these crystals will be mixed with the calcite and the chalcopyrite crystals. The marcasite nodules occur interbedded in the shale and are easily recognized by the oval or round shapes created in the shales. Samples of the calcite, dolomite, and the chalcopyrite crystals and marcasite nodules are in the photographs below. These samples were collected from the Springhill Limestone and the Vilas Shale in Anderson County.
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A Photo Gallery of Minerals Found in Sedimentary Rocks |
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Fig. 1. Sample of Springhill Limestone. |
Fig. 2. Calcite crystals in a vug from |
Fig. 3. Chalcopyrite on dolomite. |
Fig. 4. Calcite crystals typically found |
Fig. 5. Calcite crystals. |
Fig. 6. Marcasite from Vilas Shale. |
Fig. 7. Irregular opening containing |
Fig. 8. Sphalerite found in Springhill |
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In the late Paleozoic, there were four types of calcite deposits occurring in limestone according to Harbaugh (1961, p. 93). They were: 1) grain growth calcite, 2) blade calcite, 3) encrusting calcite, and 4) void filling calcite and these are classified by these characteristics (p. 93). Grain growth calcite and blade calcite are formed through a recrystallization, while the other two types are formed from precipitation (p. 93). Vugs at the quarry in Anderson County contain void filling calcite accompanied by dolomite and chalcopyrite. The vugs or voids in the Springhill Limestone are round or irregular openings and do not appear to be created by fractures occurring after lithification of the rock. It is possible to find fossil brachiopods and straight cephalopods, both with the interior portion of the shells encrusted with calcite or chalcopyrite crystals.
The presence of void filling calcite is common in limestone (Harbaugh, 1961, p. 107). Calcite crystals form by precipitation of minerals in water filled voids. This precipitation is presumed to be controlled by inorganic factors since evidence of precipitation influenced by organisms is not found (p. 108). There is a connection in the solubility of calcium carbonate and the relationship to organic processes such as photosynthesis of green plants and algae; where limestone forms, organic processes influence the precipitation of calcium carbonate in water-filled voids indirectly (p. 109). According to Harbaugh (1961), the voids in the sediment can be created in many ways, and in the late Paleozoic limestones there were seven principles have been proposed (p. 109). Those seven principle modes are: 1) leaf like algae or skeletal material form an umbrella and voids form beneath these, 2) calcarenites and oolites are cemented, 3) breccia has filling between the fragments, 4) irregular openings are filled, 5) the hollows of shells and leaf like algae are filled, 6) filling around transported intraclasts, and 7) filling of fractures that occur after the lithification of sediments (p. 111-18).
One proposal was that voids in sedimentary rock may have been created under umbrellas of leaf-like algae or skeletal remains as the organic remains prevented sediment infilling (Harbaugh, 1961, p. 111). These voids would have begun filling with minerals soon after the umbrellas were laid down and continued to fill as deposition of sediments occurred around the voids and after this consolidation as well (p. 111). Harbaugh (1961) called these irregular openings stromatactis, a term originally given to crystalline calcite masses from Devonian limestone in the Ardennes, Belgium, believed to be representative of reef building stromatoporoids (p. 118). Harbaugh went on to write that geologists use this name as a sedimentary structure term and is not related to the name of an organism (p. 118).
Another explanation for voids was that the irregular openings occurred because of pre-lithification cracks, which could be filled with calcite (Harbaugh, 1961, p. 118). While another scenario could be that the decomposition of the animal’s soft tissues in the interior of the shells provided a space for minerals to accumulate. The voids found in the Springhill limestone are likely the result of some combination of Harbaugh's speculations.
The method of transport of the minerals infilling the Springhill Limestone voids could be connected with the Alleghenian/Ouachita Orogeny in Pennsylvanian geologic time and the Mississippi Valley-type (MVT) deposits. When the supercontinent Pangaea was forming, land masses were being joined together and present day continents enlarging land surfaces and creating mountain ranges. The Ouachita Mountains were folded along a tectonically active belt at this time (Bethke and Marshak, p. 287). Saline brines of warm groundwater migrated across the craton of North American, crossing several hundred kilometers (p. 287). These regional hydrothermal systems occurred flowed through parts of Kansas, Oklahoma, Missouri, Arkansas and Iowa in connection with the Ouachita-Arkoma Belt (p. 287). The highly saline brines carried dissolved ions which created minerals including: galena, zinc, calcite, dolomite, chalcopyrite, and marcasite.
The proposed causes of fluid migration include: 1) flow driven by gravity, and 2) flow driven by compaction (Misra, 2000, p. 597). In the compaction driven model, the fluids move from depth, flowing horizontally across great distances through permeable aquifers that dip and are shallow; sediment porosity decreases with depth and because of this compaction, a large amount of fluid can be released (p. 597). However, the MVT deposits of the Tri-State area of Kansas, Oklahoma, and Missouri have been considered to possibly be gravity driven flows (p.598). To have gravity driven flows, uplift must occur along a distal portion of a basin to produce the regional gradient needed to create a fluid flow (p. 598).
The zinc and lead deposits of the interior of the North American continent occurred at temperatures between 75º C and 150º C (Bethke and Marshak, p. 290). These high temperatures probably came from mineralized brines, as there is no evidence of igneous intrusions in the ore districts, according to Bethke and Marshak (p. 290). These temperatures likely covered the entire Mid-Continent, not just the ore bearing districts. Temperatures this high in the region would be known as a thermal anomaly (p. 290).
To determine the age of the brine migration of the MVT deposits, paleomagnetic analysis and radiometric dating were used (Bethke and Marshak, p. 299). The paleomagnetic studies determined the brine migrations depositing the minerals of the MVT deposits probably occurred during the Alleghenian/Ouachita orogeny (p. 303). However, radiometric dating was problematic in that there was not much data to study. While the potassium bearing minerals are used in radiometric dating, the K-feldspar overgrowths are used to determine age (p. 303). Bethke and Marshak used the K-feldspar overgrowth data to confirm the age of mineral deposition from brine migrations in the Mid-Continent was during the Pennsylvanian and early Permian Periods (p. 303). This dating was consistent with the Alleghenian/Ouachita orogeny.
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Harbaugh, John W. Relative Ages of Visibly Crystalline Calcite in Late Paleozoic Limestones. State Geological Survey of Kansas, Bulletin 152, Part 4, University of Kansas Publications, Lawrence, 1961.
Misra, Kula C. Understanding Mineral Deposits. Kluwer Academic Publishers, Dordrecht, 2000.
Zeller, Doris E. The Stratigraphic Succession in Kansas. State Geological Survey of Kansas Bulletin 189, University of Kansas Publications, Lawrence, 1968.
Johnston, Dr. Paul. Professor Emeritus, Emporia State University. Personal communication, October, 2005.
Skelton, Lawrence. Kansas Geological Survey. Personal communication, November 8, 2005.
Bethke, Craig M. and Stephen Marshak. Brine Migrations across North America---The Plate Tectonics of Ground Water. Annual Review Earth Planet Science. 1990, 18: 287-315. University of Illinois at Urbana-Champaign http://www.geology.uiuc.edu/~bethke/pdf/AnnualReviews1990.pdf Date accessed 25 Nov. 2005.
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Return to the GO336 Mineralogy student webpage index, www.emporia.edu/earthsci/amber/go336/webpages.htm.
Created 29 November, 2005, from the Earth Science Department, Emporia State University: http://www.emporia.edu/earthsci/, at Emporia State University, Emporia, KS http://www.emporia.edu/.