Abstract More than 400 specimens of galena were collected from the south orebody at the Sweetwater mine, Viburnum Trend, Southeast Missouri to conduct a detailed study of the variations in galena morphology. The specimens were selected for their well crystallized character and their spatial and vertical positions within the orebody. Most of the collected galena crystals belong to the main stage of deposition in the paragenetic sequence, and they are dominated by the octahedral form that shows vaiying degrees of modification by the cubic form. To closely evaluate the relative proportions of octahedral to cubic faces, the sizes of those faces were measured on each crystal. The resulting measurements have shown that main-stage Sweetwater galena crystals exhibit cuboctahedral morphologies over a complete spectrum from those that are almost totally octahedra to those that are nearly perfect cubic forms. In order to statistically test the measured crystal areas for grouping, a cumulative frequency plot method was applied to the measured data. Breaks in the cumulative curve indicate the limits of each group of crystals with similar morphology. The cumulative curve for the measured Sweetwater cuboctahedral galena detected breaks that define nine groups of crystals. These nine types of galena morphology, in terms of their percent octahedral development, listed from dominantly octahedral to dominantly cubic, are: 1) 92-93.5% octahedral (or 6.5-8% cubic), 2) 85-90%, 3) 81-84%, 4) 74-78%, 5) 63-72.5%, 6) 51-62%, 7) 42.6-46%, 8) 36-39.5%, and 9) 24-33%. Although these nine types have been differentiated by detailed crystal measurements and applying cumulative curve techniques, continued study of the specimens has indicated that most of the groups can be distinguished by simple visual examinations of their characteristic proportions of cubic modification of the octahedral forms. With regard to the spatial distribution, six of the galena morphological types were found to be distributed parallel to the length of two ore runs, whereas a seventh galena type is restricted to a circular area at the end of one of the ore runs. These results are interpreted to indicate that the ore fluids traveled along the length of the ore runs and encountered another flow of fluids at the north end of ore runs. Vertically, all nine types of cuboctahedral galena were found to occur at essentially all elevations examined in this study.

Abstract The mine tour will consist of two stops at general mining areas, one each in the north and south orebodies. We will attempt to visit several active mining faces in each area as dictated by the specifics of the situation at the time of the tour. This should provide an opportunity to compare and contrast many of the geologic characteristics of the two orebodies. A more specific description of the geology and location of the stops will be made available to participants at the time of the tour.

Abstract The Asarco Sweetwater Unit, consisting of an underground lead/zinc mine and mill, is the southernmost mine of the Viburnum Trend. lt is located 7.5 miles southeast of Bunker and 13 miles northwest of Ellington, Mo. (Fig. 1). Formerly owned and operated by Ozark Lead Company, a division of Kennecott Corporation, the orebody was discovered in January, 1962. Mine production began in June,1968 and continued for over 15 years until ozark Lead halted production in 1983 due to declining lead prices. In late 1986, Kennecott sold the Ozark mine to ASARCO, Inc. Asarco restarted operations at sweetwater in December, 1987. Current production is at a rate of 3,400 tons of ore a day. At full production, the mine is rated as having the capability of producing 5,000 tons per day of ore grading 4.8% lead and 0.6% zinc.

Abstract The bornite ores in the Viburnum Trend, Southeast Missouri Lead District, have received little scientific attention because of their small volumes and spotty occurrence. These ores, however, are important in providing significant information on the chemical compositions of the earliest ore-forming fluids in the ore district and they mark the focus for early fluid ingress into the Viburnum Trend. Their interesting and complex mineralogy attests to significant variations in the ore fluids through time. Their ore textures vary significantly from one locality to another, indicating that the ore-forming process differed areally at the time of their deposition. The positions of the rare lenses and pods of bornite ores are interpreted to indicate early point sources for the introduction of ore fluid in the district. The early fluids in the Viburnum Trend were ones that dominantly deposited copper sulfide minerals. They also carried significant amounts of cobalt, nickel, and especially arsenic. The replacement of early-deposited gersdorffite by the subsequently deposited copper-arsenic minerals, enargite and tennantite, shows that the chemical character of the fluids that deposited the bornite ores changed through time. Later fluids that affected the bornite pods resulted in the replacement of bornite and chalcopyrite by digenite, anilite, djurleite, and chalcocite. It is significant that bornite ores from different mines exhibit markedly different ore textures. The ores from the Fletcher mine exhibit exsolution-like textures that are interpreted to have formed by exsolution of chalcopyrite from a higher temperature bornite solid solution during cooling. Bornite ores from the Brushy Creek mine exhibit intricate colloform textures in which bornite and chalcopyrite have been rapidly and repetitively deposited., Bornite ores from the Sweetwater mine show replacement textures in which bornite clearly has replaced earlier deposited chalcopyrite. Recendy studied bornite ores from the Casteel mine exhibit a granular intergrowth of the bornite grains. These variations in ore textures appear to reflect differences in the mode of deposition and the rate of crystallization of these ores from place to place. The bornite ores have formed early in the history of deposition of the sulfide minerals in the Viburnum Trend, as shown by the fact that bornite, chalcopyrite and the other minerals forming this association have been enveloped and partly replaced by main stage cuboctahedral galena. Recent ICP analysis of 26 specimens of bornite ores has shown that, in addition to major amounts of Cu and Fe, they contain significant minor to trace amounts of some elements. Specifically, they contain as much as 1.2% Ni, 1.5% As, 0.1% Mo, 1400 ppm Co, and 173 ppm Ag. Trace amounts of Sb and Bi are present in some specimens. Ni, As, Co, and Mo contents are greatest in Fletcher bornite ores, significant in Sweetwater bornite, and less in Brushy Creek and Casteel bornite. Silver concentrations average 64 ppm in the bornite ores and are slightly less than the average for the lead-zinc ores. Chalcopyrite ores associated with the bornite ores have similar trace element signatures, and differ from typical Viburnum Trend chalcopyrite-rich ores that contain less silver. The bornite ores are interpreted to mark the positions of the early plumbing system(s) in the Viburnum Trend. They appear to indicate multiple point sources for the influx of the early ore fluids prior to the more pervasive introduction of the ore fluids into the ore district during subsequent periods of lead-zinc(-copper) ore deposition.

Abstract The Asarco Sweetwater Unit, consisting of an underground lead-zinc mine and mill, is the southernmost mine of the Viburnum Trend. It is located 7.5 miles southeast of Bunker and 13 miles northwest of Ellington, Missouri (Fig. 1). Formerly owned and operated by Ozark Lead Company, a division of Kennecott Corporation, the orebody was discovered in January, 1962. Mine production began in June, 1968 and continued for over 15 years until Ozark Lead halted production in 1983 due to declining lead prices. In late 1986, Kennecott sold the Ozark mine to ASARCO, Inc. Asarco restarted operations at Sweetwater in December, 1987. Current production is at a rate of 5,000 tons of ore per day. The Sweetwater orebody, when considered as a whole, consists of a narrow, sinuous trend of lead, zinc, and minor copper mineralization that extends for a distance of about 7 miles. The trend strikes north and northwest. Mineralization is fairly continuous, but the ore grade, width, and thickness are variable throughout the length. The width ranges from 100 to about 1,000 feet and the thickness from a few inches to over 100 feet.

Abstract This trip traverses Middle Ordovician and Lower Ordovician Knox Group strata enroute to American Smelting and Refining Company’s (ASARCO) Young mine and mill complex (Stop 1). The Young mine, located near the center of the Mascot-Jefferson City zinc district, is the largest of the operating mines. The ore occurs mainly in collapse breccias which will be observed during an underground mine tour led by ASARCO staff. The trip retraces the route to Knoxville, then turns southwest to the Sweetwater barite district traversing mostly Knox Group formations. The Stephens barite mine, the only currently active mine, as well as the largest producer over the district's 100-year history, can be seen in passing. The shaft site for the 1970’s U.S. Borax Company fluorspar project is just down-dip (southeast) from the Stephens site. Turning northeast brings the trip to Stop 2, the Ballard barite mine. This mine, idle since 1958, has the best exposures of rock pinnacles, remnants of upper Knox Group mineralized breccias. As at all the mines in the Sweetwater district, economic ore occurs only in the clay residuum and mining stops when bedrock is reached. Trip returns to Knoxville.

Abstract In the years since the first production from the Viburnum Trend in 1960, consolidation of mining companies and properties has occurred (Fig. 1). Today, two companies control the Viburnum Trend. The Doe Run Company operates six mines: #29, #28, Casteel, Buick, Brushy Creek, and Fletcher. ASARCO operates two mines; West Fork and Sweetwater. These are all underground, room and pillar mines accessed by vertical shafts. Doe Run also operates three mills, one primary lead smelter at Herculaneum, Missouri., and a secondary lead smelter at the site of the former Buick primary smelter. ASARCO has two mills and a primary lead smelter at Glover, Missouri. Through years of mining different parts of the same huge ore deposit, several of the mines have merged together. Today the Magmont Mine is joined on the north by the Casteel Mine and connects with the Buick Mine on the south. These connected mine workings have a combined north/south length of over 8 miles. This length will continue to increase as the Casteel Mine advances to the north and the Buick Mine advances to the south. The Buick Mine and Brushy Creek Mine are steadily mining toward each other, and the West Fork and Fletcher Mines are connected. A major portion of the southern part of the Trend is acquired land of the Mark Twain National Forest. The mineral rights are administered by the Bureau of Land Management. Property is obtained through a process of permit and subsequent lease. Rentals and royalties are paid to the U.S. Government, with royalties based on 5% of the net smelter return.

Abstract This trip traverses Middle Ordovician and Lower Ordovician Knox Group strata enroute to American Smelting and Refining Company's (ASARCO) Young mine and mill complex (Stop 1). The Young mine, located near the center of the Mascot-Jefferson City zinc district, is the largest of the operating mines. The ore occurs mainly in collapse breccias which will be observed during an underground mine tour led by ASARCO staff. The trip retraces the route to Knoxville, then turns southwest to the Sweetwater barite district traversing mostly Knox Group formations. The Stephens barite mine, the only currently active mine, as well as the largest producer over the district's 100-year history, can be seen in passing. The shaft site for the 1970's U.S. Borax Company fluorspar project is just down-dip (southeast) from the Stephens site.

Abstract The first half of today’s trip will traverse nearly flat-lying sediments starting in Middle Ordovician limestones and ending in Pennsylvanian sandstones, shales and coal beds. Along the way, the Gordonsville mining and milling complex will be visited with an underground trip in the Gordonsville mine. The zinc occurs in breccias as open space filling in upper Knox Kingsport and Mascot beds in approximately the same stratigraphic position as the ores in east Tennessee. Much of the sphalerite is of an orangish-brown color as opposed to the usual honey-yellow-color of the east Tennessee sphalerites. Another major difference is the quantity of accessory fluorite, barite and galena, all of which are virtually absent in the east. As the trip continues east from Gordonsville, the ascent from the Central Basin up to the Eastern Highland Rim and on to the Cumberland Plateau begins. Rocks traversed will be from Ordovician to Pennsylvanian in age with some excellent roadcuts to view along the way. At the plateau’s east edge, a fault escarpment makes the contact with the wide expanse ahead, the Great Valley of East Tennessee, a part of the Valley and Ridge province. The second half of today’s trip will cross-cut and parallel some of the numerous valleys and ridges formed by repetition of beds by folding and by thrust faulting from the southeast. Most of these sediments are limestones/dolostones, shales, siltstones and sandstones from Lower Cambrian to Middle Mississippian in age. The Ballard open pit mine is along the easternmost of four belts of Knox that comprise the barite district surrounding the town of Sweetwater. The barite occurs in breccias in the Kingsport formation; although nearly all production has been from the residuum. The Stephens pit has been the most recently active.