Descriptive Mineralogy of Pugh Quarry, Northwestern Ohio: Marcasite and Pyrite1
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DESCRIPTIVE MINERALOGY OF PUGH QUARRY, NORTHWESTERN OHIO: MARCASITE AND PYRITE1 DAVID F. PARR2 and LUKE L. Y. CHANG, Department of Geology, Miami University, Oxford, OH 4505G Abstract. Minerals from solution cavities and associated collapse breccias in the Middle Devonian dolostone at Pugh Quarry, Wood County, Ohio were collected and identified. Two types of marcasite were recognized: banded encrustations and euhedral crystals. The banded marcasite is widespread in the mineral zone, especially in the northeastern section of the Quarry, and showed 3 distinct habits: subhedral, globular, and columnar. On freshly exposed surfaces, the colors were greenish gray or a mix- ture of pale yellow and gray. A characteristic of the banded marcasite is the presence of extensive intergrowth twinning. The euhedral marcasite was found in rocks in all parts of the Quarry, both inside and. outside the mineral zone. On freshly broken surfaces, the euhedral crystals were gray-white with a greenish cast. Prismatic and tabular habits were observed. Many of the crystals showed hopper development. Pyrite is not a common mineral in Pugh Quarry. Generally, crystals were small, less than 1 mm in size, greenish brown to yellowish brown in color, and highly lustrous. OHIO J. SCI. 77(5): 213, 1977 Museums and private mineral collec- MINERAL OCCURRENCE tions throughout the U.S. and other The stratigraphy at Pugh Quarry is countries display crystal specimens of shown in figure 1. Wisconsin age till and carbonate, sulfate, and sulfide minerals lacustrian sands form the overburden at from quarries in the Paleozoic carbonate Pugh Quarry. Glacial grooves and stria- rocks in the mid-western United States. tions were exposed on the bedrock around Occurrence of these minerals has been the quarry rim where the overburden had previously reported (Kraus 1905; Ford been stripped back. Stylolites occurred and Pogue 1909; Morrison 1935; Howard in the strata exposed at Pugh Quarry. 1951), but little work has been done on Petroliferous black shale seams approxi- their descriptive mineralogy. It is the mately 6 mm thick separated the rocks purpose of this study to provide a de- above and below stylolites, and brec- tailed investigation of the mineral as- ciation was common. semblages in the carbonate rocks at Pugh Marcasite, pyrite, and 6 other minerals Quarry, which is located in the SW]^, occurred in rocks at Pugh Quarry (table SWM, Sec. 6, T.4N., R.9E. in Milton 1). The minerals were generally re- Township, Wood Co., Ohio. In this re- stricted to a zone (referred to hereafter port, marcasite and pyrite are described. as the mineral zone) consisting of nearly Methods used for investigation in this continuous bands of cavities about 9 cm study included megascopic identification, thick located in the upper 18 to 24 cm microscopic examination of thin sections of the Anderson Formation of the De- and polished sections, reflecting gonio- troit River Group (see fig. 1). Breccia- metric measurement, and x-ray powder tion in this mineral zone locally resembled diffraction studies. collapse phenomena associated with areas of cavern development. It was similar to Manuscript received June 24, 1976 and in final the brecciation described by Jackson and revised form May 3, 1977 (#76-54). Beales (1967) in ore zones of the Okla- 2Present Address: Department of Geology, Wisconsin State University, Superior, Wis- home-Kansas-Missouri Tri-State Mining District. The breccias in both cases 213 214 D. F. PARR AND L. L. Y. CHANG Vol. 77 Janssens, 1970 Forsyth, p. 2,22 p. 20 15' Overburden A Dolomite —light gray to dork brownish groy, sugary A texture, petroliferous, fossiliferous zones, and chert nodules in upper Dundee Dundee Dolomite-light 8 medium brown part. Limestone to very light brownish gray, Limestone sandy, bedded to massive, finely sucrosic with good intercrystalline porosity. Nodular fossiliferous chert Unit 8 28' in upper portion of unit. Dolomite —brown, very A dense, thin-bedded, locally conglomeratic. Contains large calcite Anderdon crystals and small 15 Dolomite crystals of fluorite, celestite, pyrite, and disconformity V Dolomite- very Iight gray very light marcasite. and light brown dolomicnte grading into dolosiltite, stromatolitic Unit 7 laminations in lower half. Stromatolitic doiomicrite-dolosiitite, A Unit 6 3-6' brecciated mineralized zone. Dolomite-light brownish gray dolosiltite with interbedded dolo- P Unit 5 J micrite, massive with poor vugqy porosity. Unit 4 2-5' Dolomite-stromatolitic dolosiltite A Dolomite-light grayish brown to •7.5' dark brown dolosiltite. GROU Unit 3 Dolomite— brown to dark R brown, fine groined, Lucas relatively thick bedded. Dolomite A 50 RIVE T Dolomite-light 8 medium brown dolosiltite with interbedded dolomicnte, stromatolitic Unit 2 28 structures, and vuggy porosity. DETROI V Amherstberg Dolomite Sylvania A Sandstone-fine to medium quartz Sandstone-fine grained rounded quartz grains Sandstone sand with rounded 8 frosted groins. relatively thin and t Unit I even bedded. Sylvania I i10 Sandstone FIGURE 1. Columnar section of rocks exposed at Pugh Quarry after Forsyth (1966) and Janssens (1970). Ohio J. Sci. MARCASITE AND PYRITE FROM PUGH QUARRY 215 FIGURE 2. Bio-laminar dolostone. The highly porous character of the rock and the wavy laminations are interpreted as stromatolitic in origin. X 0.4 FIGURE 3. Bio-laminar dolostone. The structure may be the remains of a coral organism. Note the areas of marcasite replacement. Actual size. FIGURE 4. Polished section, one nicol, marcasite (light) and dolomite (dark). Sharp rhombs of dolomite are enclosed in the pore space filling marcasite. X 74 FIGURE 5. Thin section, one nicol, marcasite (dark) and dolomite (light). Sharp rhombs of dolomite are enclosed in pore space filling marcasite. X 60 216 D. F. PARR AND L. L. Y. CHANG Vol. 77 were cemented by accessory minerals. Polished section and thin section ex- The specimens used in this study were aminations showed that marcasite pore deposited in the Department of Geology, filling was prevalent in all of the rocks Miami University, Oxford, Ohio. where marcasite had a banded habit. Euhedral dolomite crystals were enclosed TABLE 1 totally or in part by marcasite. There Minerals Identified from Pugh Quarry, Listed by Chemical was no indication that the development Group of the marcasite in any way interfered with the recrystallization of the dolomite, Chemical Group Minerals indicating an antecedent relationship of the dolomite to the marasite (fig. 4 and 5). Sulfides Marcasite Several specimens had oolite structures Pyrite associated with thick banded marcasite. Sphalerite Carbonates Calcite The oolite structures were most distinct Dolomite along the marcasite-dolostone interfaces, Halide Fluorite which were characterized by marcasite Sulfates Barite filling of spaces between oolite (fig. 6). Celestite MARCASITE Marcasite was a common mineral in the carbonate rocks at Pugh Quarry. Two types were recognized: euhedral crystals and banded encrustations. In this study the term euhedral was used for any crystal which was bounded by crystal surfaces except, perhaps, for the point of attachment to the carbonate rock. Mar- casite consisting of solid coatings of in- tergrown aggregates of radiating or columnar crystals was considered to be banded marcasite. BANDED MARCASITE Banded marcasite was widespread in the mineral zone, especially in the north- eastern section of the quarry. Single bands as much as 5 mm thick were found in this area, particularly in portions of the mineral zone showing strong brec- FIGURE 6. Polished section, one nicol, mar- ciation. In places, marcasite served as casite (white) replacing schalenblende the cementing agent between clasts in sphalerite (light gray) on recrystallized breccias. dolomite oolites (dark gray). X 32 Relation to Host Rock: Dolostones on which the banded marcasite occurred Color: The surface of most banded were oolite, structureless rocks with uni- marcasite from Pugh Quarry was dis- form sized crystals, or bio-laminar (Bio- colored to a reddish brown due to oxida- laminar is a general term for those whose tion. Freshly exposed surfaces were structures represent algal stromatolites, greenish gray or a mixture of pale yellow stromatoproids, or corals). The dolo- and gray. Irridescent colors, dominantly stones were recrystallized; individual blues and blue-greens, were characteristic crystals were 0.5 mm or less in maximum of the natural fracture surfaces of the dimension (fig. 2 and 3). banded marcasite. Ohio J. Sci. MARCASITE AND PYRITE FROM PUGH QUARRY 217 Habit: The banded marcasite showed 3 reasons. A characteristic of the banded distinct habits: subhedral, globular, and habit of marcasite was the presence of columnar. The columnar and globular extensive intergrowth twinning. This, habits were dominant in the very thick combined with the brittle nature of the massive occurrences of the marcasite crystal, made the separation of individual bands at Pugh Quarry. The subhedral terminated crystal very difficult. Sev- habit, generally in bands less than 5 mm eral terminated fragments were separated thick, was made up of elongated indi- from the band and mounted on the gonio- vidual crystals which were intergrown meter. When attempts were made to and formed a solid band of marcasite measure <£ and p angles, it was found that (fig. 7). The globular habit was char- the crystal faces lacked the smoothness acterized by thick encrusting bands of and reflectivity necessory to produce an marcasite composed of intergrown