Stratigraphy and Vertical Hydraulic Conductivity of the St. Francois Confining Unit in the Viburnum Trend and Evaluation of the Unit in the Viburnum Trend and Exploration Areas, Southeastern Missouri By Michael J. Kleeschulte1 and Cheryl M. Seeger2 Abstract ometric surface of the Ozark aquifer as a result of mining activity. Because of similar geology, The confining ability of the St. Francois stratigraphy, and depositional environment confining unit (Derby-Doerun Dolomite and Davis between the Viburnum Trend and the exploration Formation) was evaluated in ten townships (T. 31– areas, the Viburnum Trend may be used as a perti- 35 N. and R. 01–02 W.) along the Viburnum Trend nent, full-scale model to study and assess how of southeastern Missouri. Vertical hydraulic con- mining may affect the exploration areas. ductivity data were compared to similar data col- Along the Viburnum Trend, the St. Francois lected during two previous studies 20 miles south confining unit is a complex series of dolostones, of the Viburnum Trend, in two lead-zinc explora- limestones, and shales that generally is 230 to 280 tion areas that may be a southern extension of the feet thick with a net shale thickness ranging from Viburnum Trend. The surficial Ozark aquifer is the less than 25 to greater than 100 feet with the thick- primary source of water for domestic and public- ness increasing toward the west. Vertical hydraulic water supplies and major springs in southern Mis- conductivity values determined from laboratory souri. The St. Francois confining unit lies beneath permeability tests were used to represent the St. the Ozark aquifer and impedes the movement of Francois confining unit along the Viburnum water between the Ozark aquifer and the underly- Trend. The Derby-Doerun Dolomite and Davis ing St. Francois aquifer (composed of the Bon- Formation are statistically similar, but the Davis neterre Formation and Lamotte Sandstone). The Formation would be the more hydraulically Bonneterre Formation is the primary host forma- restrictive medium. The shale and carbonate val- tion for lead-zinc ore deposits of the Viburnum ues were statistically different. The median verti- Trend and potential host formation in the explora- cal hydraulic conductivity value for the shale tion areas. samples was 62 times less than the carbonate sam- For most of the more than 40 years the ples. Consequently, the net shale thickness of the mines have been in operation along the Viburnum confining unit along the Viburnum Trend signifi- Trend, about 27 million gallons per day were being cantly affects the effective vertical hydraulic con- pumped from the St. Francois aquifer for mine ductivity. As the percent of shale increases in a dewatering. Previous studies conducted along the given horizon, the vertical hydraulic conductivity Viburnum Trend have concluded that no large decreases. cones of depression have developed in the potenti- The range of effective vertical hydraulic conductivity for the confining unit in the Vibur- 1 num Trend was estimated to be a minimum of 2 x U.S. Geological Survey -13 2Missouri Department of Natural Resources, 10 ft/s (foot per second) and a maximum of 3 x Geological Survey and Resource Assessment Division 10-12 ft/s. These vertical hydraulic conductivity Abstract 1 values are considered small and verify conclusions INTRODUCTION of previous studies that the confining unit effec- Initial ore production from the first Viburnum tively impedes the flow of ground water between area mine began in the 1960’s. Lead is the primary ele- the Ozark aquifer and the St. Francois aquifer ment extracted, but substantial amounts of zinc, copper, along the Viburnum Trend. and silver also are mined. Other major ore bodies were Previously-collected vertical hydraulic con- discovered by 1964 along a 30-mi (mile) linear zone ductivity data for the two exploration areas from that is now referred to as the Viburnum Trend (Whar- ton, 1979; fig. 1). By 1970, two new smelters and five two earlier studies were combined with the data new mine-mill complexes were in operation. From the collected along the Viburnum Trend. The nonpara- early 1970’s into the early 1990’s, lead and zinc pro- metric Kruskal-Wallis statistical test shows the duction from the Viburnum Trend reached then record vertical hydraulic conductivity of the St. Francois highs. Throughout the late 1970’s, the area was the confining unit along the Viburnum Trend, and largest lead producing area in the world, accounting for west and east exploration areas are statistically dif- more than 15 percent of the total recorded world out- put. ferent. The vertical hydraulic conductivity values The Bonneterre Formation of Upper Cambrian generally are the largest in the Viburnum Trend age is the primary host formation for the lead-zinc ore and are smallest in the west exploration area. The deposits of the Viburnum Trend, and together with the statistical differences in these values do not appear underlying Lamotte Sandstone forms the carbonate to be attributed strictly to either the Derby-Doerun rock (dolostone and limestone) and sandstone St. Fran- cois aquifer (figs. 2 and 3). The formation ranges from Dolomite or Davis Formation, but instead they are about 400 ft (feet) below land surface in the northern caused by the differences in the carbonate vertical part of the Viburnum Trend to about 1,000 ft below hydraulic conductivity values at the three loca- land surface in the southern part (fig. 3). The St. Fran- tions. cois confining unit overlies the St. Francois aquifer and The calculated effective vertical hydraulic consists of dense carbonate and shale of the Derby- Doerun Dolomite and Davis Formation. The confining conductivity range for the St. Francois confining -13 -12 unit is considered the barrier that confined ascending unit at each location is: 2 x 10 to 3 x 10 ft/s ore-forming hydrothermal solutions to the Bonneterre -14 for the Viburnum Trend; 3 x 10 (minimum Formation. Formations of Upper Cambrian and Lower reporting level) to 1 x 10-12 ft/s for the west explo- Ordovician age consisting of the Potosi Dolomite to the ration area; and 3 x 10-13 to 2 x 10-12 ft/s for the Roubidoux Formation are exposed at land surface east exploration area. Based on the calculated ver- along the Viburnum Trend and overlie the St. Francois confining unit. These rocks form the Ozark aquifer, the tical hydraulic conductivity ranges, the St. Fran- primary source of water for private and public-water cois confining unit is considered ‘tight’ at all supplies and major springs in southern Missouri. The locations. However, in relation to each other, the geologic names used in this report follow the nomen- west exploration area is the tightest, and the most clature used by the Missouri Department of Natural conductive area is the Viburnum Trend. No appar- Resources, Geological Survey and Resource Assess- ment Division (GSRAD), formerly known as the Divi- ent large cones of depression have developed in sion of Geology and Land Survey. the potentiometric surface of the Ozark aquifer as Mine dewatering before ore extraction is part of a result of mining activity in the Viburnum Trend. normal mine operation. Twenty-six million gallons of Therefore, using similar mining practices as those water per day were pumped from the St. Francois aqui- along the Viburnum Trend, no large cones of fer in 1971 (Warner and others, 1974) and in 1999 the depression in the Ozark aquifer would be expected total pumpage was slightly larger at 27 million gallons per day (Denis Murphy, The Doe Run Company, writ- in the exploration areas, unless preferred-path sec- ten commun., 2000). These withdrawal rates from the ondary permeability has developed along faults or St. Francois aquifer are typical for the Viburnum Trend fractures or resulted from exploration activities. and have been occurring for most of the more than 40 2 Vertical Hydraulic Conductivity of the St. Francois Confining Unit in the Viburnum Trend and Exploration Areas, Missouri Introduction 3 4 Vertical Hydraulic Conductivity of the St. Francois Confining Unit in the Viburnum Trend and Exploration Areas, Missouri Introduction 5 6 Vertical Hydraulic Conductivity of the St. Francois Confining Unit in the Viburnum Trend and Exploration Areas, Missouri years the mines have been in operation. Previous stud- From the 1960’s to the end of the 1990’s, lead ies conducted along the Viburnum Trend to assess the and zinc exploration occurred in two exploration areas effects of mine dewatering in the St. Francois aquifer in the Doniphan/Eleven Point Ranger District of the on water levels in the surficial Ozark aquifer have con- Mark Twain National Forest (fig. 1). These exploration cluded that no large cones of depression have devel- areas are 20 mi south of the Viburnum Trend, and a oped in the potentiometric surface of the Ozark aquifer possible southern extension of the Trend. The explora- as a result of mining activity. However, some localized tion peaked in the late 1970’s and early 1980’s, result- leakage of water from the Ozark aquifer into the St. ing in several hundred exploration holes being drilled Francois aquifer probably is occurring at mine shafts, in the National Forest. The exploration areas lie within ventholes, and inadequately plugged exploration drill a larger region of well-developed karst terrain with an holes. Therefore, small areas of drawdown may exist extensive network of solution-enlarged fractures rang- (Warner and others, 1974; Miller and Vandike, 1997; ing from small channels to large conduits. The two Kleeschulte, 2001). largest springs in Missouri (Big Spring and Greer Fletcher (1974) states that faults along the Vibur- Spring, fig. 1) are in this area, and discharge from these num Trend can be grouped into three systems: the springs helps sustain flow in two nationally designated Palmer Fault system to the north, which includes the streams; the Current River (Ozark National Scenic Riv- Conway Fault; the Black Fault in the east central part; erway) and the Eleven Point River (Eleven Point Wild and the Ellington Fault to the south (fig.