DEPARTMENT OF THE INTERIOR MISCELLANEOUS FIELD STUDIES UNITED STATES GEOLOGICAL SURVEY MAP MF-1511-A PAMPHLET MINERAL RESOURCE POTENTIAL OF THE IRISH WILDERNESS ROADLESS AREA, OREGON COUNTY, MISSOURI By Alien V. Heyl, Sarah K. Odland, and C. K. Moss, U.S. Geological Survey and George S. Ryan, U.S. Bureau of Mines STUDIES RELATED TO WILDERNESS Under the provisions of the Wilderness Act (Public Law 88-577, September 3, 1964) and the Joint Conference Report on Senate Bill 4, 88th Congress, the U.S. Geological Survey and the U.S. Bureau of Mines have been conducting mineral surveys of wilderness and primitive areas. Areas officially designated as "wilderness," "wild," or "canoe" when the act was passed were incorporated into the National Wilderness Preservation System, and some of them are presently being studied. The act provided that areas under consideration for wilderness designation should be studied for suitability for incorporation into the Wilderness System. The mineral surveys constitute one aspect of the suitability studies. The act directs that the results of such surveys are to be made available to the public and be submitted to the President and the Congress. This report discusses the results of a mineral survey of the Irish Wilderness Roadless Area (Whites Creek) in the Mark Twain National Forest, Oregon County, Mo. The area was proposed as a wilderness under H.R. 10469, September 24, 1973, and w .us 'ater classified as a further planning area (09221) during the Roadless Area Review and Evaluation (RARE II) by the U.S. Forest Service, January 1979. MINERAL RESOURCE POTENTIAL SUMMARY The U.S. Geological Survey and the U.S. Bureau of Mines made a mineral and geological survey of the Irish Wilderness Roadless Area (hereafter called "study area"), southeast Missouri, in 1975-81. The study area covers 17,322 acres (7,010 hectares) in the Mark Twain National Forest in northeastern Oregon County (fig. 1). The study area is in the southern part of the Salem Plateau region of the Ozark uplift, and contains timbered uplands bounded by the valley of the Eleven Point River on the west side. Within the study area are several narrow tributary valleys that drain southwestward into the Eleven Point River. Exposed rocks in the study area are nearly flat-lying dolomites and sandstones of Ordovician age having a total structural drop of about 10 ft (3 m) from the northwest to southeast. These Ordovician strata are underlain by about 2,000 ft (610 m) of mostly dolomitic carbonate sedimentary rocks of Late Cambrian age and some beds of older Lamotte Sandstone that lie on a distinctly irregular surface of Precambrian basement igneous rocks. There is no known record of mineral production, development, or prospecting within the study area, although some exploration holes have been drilled just east and north of the area. One prospect for iron ore is in the NW1/4 sec. 28, T. 24 N., R. 2 W., within a private property reentrant into the area. Several Paleozoic rock units that underlie the study area are known to be host rocks for the very important lead-zinc-copper-silver-cobalt deposits of the Viburnum Trend, north of the study area. Precambrian rocks underlying the Paleozoic units could host magnetite deposits as in the Southeast Missouri district to the north and northeast of the study area. Extrapolation of available data, especially from general knowledge of drill holes north of the study area to within a few miles of it, suggests that a high potential for similar mineral resources exists in the Irish Wilderness Roadless Area. The geophysical study of the study area (Moss, in press) indicates that several deeply buried Precambrian hills extend into and underlie the study area. These buried hills could have provided favorable traps for ore forming fluids in the Cambrian rocks that are against and cap these L' ils. A second favorable deeply buried structural feature is a northeast-trending, wide fault zone which crosses the northwest part of the study area. Structural disturbances have taken place in post-Precambrian time along this fault zone as shown by shearing and an abrupt southwest bend of the Eleven Point River. The potential for deeply buried metallic mineral deposits cannot be confirmed or ruled out without information-obtained from drilling deep test holes within and near the study area, especially near or above the buried hills and the fault zone. Other mineral and energy resources either have a low potential in the study area or are more readily available elsewhere. R3W R2W 91°07'30" T25N T24N 36°45'ir .-. .v.X APPROXIMATE BOUNDARY OF IRISH WILDERNESS ROADLESS AREA.::- BM-1,2 ittJIiXJi;..^ , _ _ _ x-XvX-x-x-x-x-xt R3W R2W 2MILES 0 3 KILOMETERS EXPLANATION BM-1,2 US Bureau of Mines sample locality 7> ,DH Drill Hole MISSOURI County highway J Outer margins of buried Precambrian fault zone, and of shattering and shearing in Paleozoic rocks at the surface Figure 1. Index Map of the Irish Wilderness Roadless Area (09221) showing location of buried hills (stippled pattern) that have potential for Viburnum-type lead deposits INTRODUCTION others, in press). The geology was mapped by Heyl, and all of the party collected stream-sediment The Irish Wilderness Roadless Area in southeast samples. The sample preparation was done by Odland Missouri covers 17,322 acres (7,010 hectares) in the and analyses by Mosier and Viets. A geophysical Mark Twain National Forest in northeastern Oregon survey was done by the U. S. Geological Survey (Moss, County just south of the village of Wilderness (fig. 1). in press). The study area is most accessible by County Highway J which partly follows the Oregon and Ripley County ACKNOWLEDGMENTS line along the east side of the study area. U.S. Highway 160 is about 3 mi (5 km) south of the study We wish to thank L. D. Fellows, J. A. Martin, H. area. Good township and county roads form the M. Wharton, and I. R. Satterfield, all of the Missouri northeast and southern boundaries of the study area, Division of Geology and Land Survey, for their help and Forest Service trails, many traversable by with the stratigraphy of the area, for providing notes, pickup or jeep, provide excellent access to the study and for their general assistance in many ways. We also area. wish to thank Stan Freeze, Leon Cambre, William The study area is within the Salem Plateau Alden, James Crates, Gary Cole, and Dean Pennington region of the Ozark uplift. The heavily timbered, of the U.S. Forest Service, Mark Twain National nearly flat uplands are dissected by narrow entrenched Forest, for several useful and constructive conferences tributaries of the Eleven Point River, forming steep and for their cooperation in the study. bluff- and cliff-sided valleys. Numerous small sinkholes and a few caves, typical of karst topography, GEOLOGIC SETTING exist in and near the study area. Maximum altitude is 908 ft (277 m) in the central northern part of the study The study area is located on the southern upper area and along County Highway J in the northeast flank of the Ozark uplift. The three rock units corner. The maximum topographic relief is about 450 exposed are dolomites and sandstones of Ordovician ft (140 m). age which throughout the area appear to be flat lying, but actually have a very gentle southerly dip from PREVIOUS STUDIES northwest to southeast. These rocks are underlain by essentially flat lying sedimentary rocks of Ordovician There is little published information on the study and Cambrian ages and by igneous basement rocks of area. James G. Williams (unpub. data, 1975) of the Precambrian age having an upper very uneven Missouri Division of Geology and Land Survey made a erosional surface. Although Precambrian and survey of the exposed rock formations as viewed from Cambrian rocks do not crop out in the study area, they a boat along the Eleven Point River and located the are exposed in the Eminence Hills about 30 mi (50 km) main units and their contacts. His work was to the north, and they have been identified in drill incorporated as part of "The Geologic Map of Missouri" holes near the north and east sides of the area. In (Anderson, 1979). This work greatly helped in mapping descending order, the exposed geologic units in the the geology of the area. Heller (1954) studied the study area are as follows: Quaternary alluvium as stratigraphy and paleontology of the Roubidoux valley fill, residuum derived from weathering of Formation in the general region. Crane's (1912) report Jefferson City Dolomite, Ordovician Jefferson City on iron deposits of Missouri describes the iron-ore Dolomite, Ordovician Roubidoux Formation (both prospect within the private southern reentrant where sandstone and dolomite), and the upper part of the U.S. Bureau of Mines samples BM 1-2 were taken (see Ordovician Gasconade Dolomite. The subsurface units fig. 1). are the remaining minimum of 200 ft (60 m) of Gasconade Dolomite, about 300 ft (90 m) of Cambrian PRESENT INVESTIGATIONS Eminence Dolomite containing some sandstone, 350 ft (110 m) of Cambrian Potosi Dolomite, 300 ft (90 m) of Fieldwork by the U.S. Bureau of Mines was Cambrian Derby-Doerun Dolomite (of Anderson, 1979), carried out by George S. Ryan, in 1980 and 1981. Land 30 ft (9 m) of Cambrian Davis Formation (mostly status records were checked at the U.S. Forest Service dolomitic shale), 450 ft (140 m) of Cambrian district office for the ownership of mineral rights in Bonneterre Formation, 0-500 ft (0-150 m) of Lamotte the study area. The study area was thoroughly Sandstone, and Precambrian gneiss and granite, traversed and the metallic potential of the exposed thickness unknown.