__________________________________________ Introduction _____________________________________ Purpose of the investigation____________________ Location and geographic setting__________________ Field work.____________________________________ Acknowledgments. ______________________________ Regional geology and stratigraphicrelations_____ ________ Structure ______________________________________ Regional stratigraphic summary __________________ Stratigraphic principles._________________________ Stratigraphic problems. _________________________ Platteville-Decorah boundary _ _______________ Beloit dolomite.____________________________ Unnamed limestone member, Decorah formation. _ Subdivisions of Galena dolomite ______________ Origin and application of the names.______________ Madison sandstone-________________________ Pecatonica dolomite member.________________ McGregor limestone member_________________ Quimbys Mill member _______________________ Stratigraphy of the mining district.___________________ Pre-Platteville rocks_ ___________________________ Pre-Cambrian rocks_________________________ Cambrian rocks_ ___________________________ Ordovician rocks____________________________ Prairie du Chien group __________________ St. Peter sandstone_ ____________________ Platteville formation____________________________ General features____________________________ Glenwood shale member.____________________ Lithologic description and stratigraphic relations _______________________________ Distribution.. __________________________ Fauna and correlation.__________________ Economic products______________________ Pecatonica dolomite member.________________ Lithologic description and stratigraphic re-lations_ ______________________________ Distribution, ___________________________ Fauna and correlation.__________________ Economic products______________________ McGregor limestone member.________________ Lithologic description and stratigraphic relations. ______________________________ Distribution. _ __________________________ Fauna and correlation.__________________ Economic products._____________________
The U. S. Geological Survey in cooperation with the Wisconsin Geological and Natural History Survey explored the Prairie du Chien group in the main productive area of the Wisconsin zinc-lead district during 1949-50. Eight properties-Crow Branch diggings, Leix, Harris, Spitzbarth, Kennedy, James, Raisbeck and Vinegar Hill Roaster were explored using both diamond and churn drills. Twenty holes were drilled that totaled 8,582 feet in depth. The objectives of the exploration were to determine if the Prairie du Chien and other formations below the principal ore-bearing strata (Galena, Decorah, and Platteville formations) of the district are favorable for ore deposits, and to determine the type of ore deposits, if present. Lean deposits of sphalerite, marcasite, and pyrite were found in the Prairie du Chien on five properties Crow Branch, Leix, Harris, Spitzbarth, and Vinegar Hill Roaster and also in the Franconia sandstone on the Leix property. In the drilled area the sulfides in the Prairie du Chien group occur in certain more brittle or soluble dolomite beds that contain cavities formed by brecciation or solution. Objectives of project The objectives of the exploratory program of diamond drilling and churn drilling, by the U. S. Geological Survey in cooperation with the Wisconsin Geological and Natural History Survey, were to
OF T23 WSCOKSI1T L3AB-ZINC 12 STRICT.' , Alien P. Agnew and Alien Vj: Heyl, .Jr. '. . .'^"^ " ' ' , t Sae Mifflin-Cokerville area is in the-north-central part of the Wisconsin lead-zinc district, about-lU. miles-north of Plattevilie, Ifis, The lead deposits jji t this area, particularly those .in the .vicnity of Mifflin, were-among the-' largest gjjd most extensively worked in the district, and the old Penitentiary mine was among the first-from which zinc was recovered in quantity. Prom about 1900 to. 1928 the Mifflin-Cokerville area v/as one of the most active in Wisconsin, ''and the Cokerville group of mines included some of the largest zinc mines in the State. ^ present only-three-mines the Mew Dale Rundell, the Defense, and the Okay are being worked, and the operations are on a small-scale, A large flotation joill is being-erected by the Defense Plant Corporation to rework the Coker Kb. 1 and Ho. 2 jig tailing piles. Churn drilling, moreover, has revealed large reserves of zinc ore near by, and recent investigations by geologists of the Geological Survey, U.1 S, Department of the Interior, indicate strongly that further prospecting1 'for zinc ore is justified. 3!his brief preliminary paper deals chiefly the zinc deposits, the lead ores being touched upon only incidentally. Soth the zinc ores and the lead ore occur in the Galena dolomite and Platte-. tille limestone, both of Ordovician age. .-. She Galena consists in general of cherty dolomite, but it becomes less chert^. nod more calcareous near its base. Elsewhere in this district it has an average total-thickness of 235 feet; because of erosion, however, the uppermost member of this unit is not exposed in the Mifflin-Cokerviile area. 33ie for&ation may be divided into 'the' following lithologic members, the popular terms for.. which are given in quotation marks beloi?: .
Since 1942 the U. S. Geological Survey has been studying the geology of the zinc-lead district and has been mapping the structure, stratigraphy, and the occurrences of ore bodies. The program here described was centered in two areas at the margin of the district. Twenty-five holes that totalled 7,466 feet were drilled in 1950-51. In the Tete des Morts area, Iowa, the drilling showed lithology, structure, and evidences of mineralization that are favorable indications of the possible existence of pitch-type lower-run ore bodies; it showed a lateral extension of the potentially productive part of the district. In the Highland area, Wisconsin, lithology and evidences of mineralization found in strata of the Prairie du Chien group indicate that this unit might warrant further investigation as a potential source of ore at a lower stratigraphic position than that now being prospected in the main part of the zinc-lead district, farther south. Drilling in beds of the Prairie du Chien showed a vertical extension of the potentially productive part of the district. C. W. Tandy, Jr., aided by surveying during the preliminary geologic investigations of the two areas.
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