KENTUCKY GEOLOGICAL SURVEY UNIVERSITY OF KENTUCKY, LEXINGTON SERIES X, 1974 Wallace W. Hagan, Director and State Geologist

A SYMPOSIUM ON THE

GEOLOGY OF FLUORSPAR

)ROCEEDINGS OF THE UlNTH FORUM ON GEOLOGY OF NDUSTRIAL MINERALS

SPECIAL PUBLICATION 22 UNIVERSITY OF KENTUCKY Otis A. Singletary, President Alvin L. Morris, Vice President for Administration Lewis W. Cochran, Vice President for Academic Affairs Wimberly C. Royster, Dean of Graduate School and Coordinator of Research James Y. McDonald, Executive Director, University of Kentucky Research Foundation KENTUCKY GEOLOGICAL SURVEY ADVISORY BOARD Elmer C. Dyer, Chairman, Lexington David E. Bayer, Prestonsburg Nicholas C. Kieffer, Jr., Louisville J. Edward Parker, Lexington Henry A. Spalding, Hazard Ralph N. Thomas, Owensboro

KENTUCKY GEOLOGICAL SURVEY Wallace W. Hagan, Director and State Geologist Preston McGrain, Assistant State Geologist Administrative Division Finance Section: Jo M. McGurk, Administrative Accounts Clerk Clerical Section: Linda S. Collins, Departmental Secretary Sydney Johnson, Secretary Juanita G. Smith, Secretary, Henderson field office Publications Section: Donald W. Hutcheson, Geologist and Head, Editor Roger B Potts, Chief Draftsman Gary Creighton, Draftsman John B. Gragg, Principal Clerk

Economic Geology Division Coal Section: Gilbert E. Smith, Geologist and Head Allen D. Williamson, Geologist, Henderson field office John G. Beard, Geologist, Henderson field office Industrial and Metallic Minerals Section: Preston McGrain, Assistant State Geologist and Head Garland R. Dever, Jr., Geologist Lucille Canter, Senior Laboratory Assistant Nelda N. Mitchell, Laboratory Assistant Oil and Gas Section: Edward N. Wilson, Geologist and Head Howard R. Schwalb, Geologist, Henderson field &ice Donald G. Sutton, Geologist Lorene Teater, Records Librarian Glenna A. Wiley, Senior Laboratory Assistant Charles E. Wright, Laboratory Assistant

Environmental Geology Division Areal Geology Section: Martin C. Noger, Geologist and Head Ronald L. Norris, Geologist, Owensboro field office Louis R. Ponsetto, Geologist Avery E. Smith, Geologist, Owensboro field office Russell Ping, Assistant Geologist Sydney Johnson, Secretary Water Section: David C. Bayha, Geologist and Head Terry Hounshell, Draftsman KENTUCKY GEOLOGICAL SURVEY UNIVERSITY OF KENTUCKY, LEXINGTON SERIES X, 1974 Wallace W. Hagan, Director and State Geologist

A SYMPOSIUM ON THE GEOLOGY OF FLUORSPAR

Donald W. Hutcheson, Editor

; Proceedings of the Ninth Forum on Geology of Industrial Minerals

April 26-28, 1973 Sponsored by Paducah, Kentucky Kentucky Geological Survey l llinois State Geological Survey

SPECIAL PUBLICATION 22 LETTER OF TRANSMITTAL

March 25,1974

Dr. Wimberly C. Royster Dean of Graduate School and Coordinator of Research University of Kentucky

Dear Dr. Royster:

The Illinois-Kentucky fluorspar district has produced seventy-five per- cent of the total United States production. Fluorspar is used as a in the steel industry, in industrial chemicals, in the processing of aluminum, and in ceramics.

World-wide interest was generated by this Forum on the Geology of Industrial Minerals. Six of the papers include discussions on fluorspar in Kentucky. These papers should assist in exploration and development of this important mineral, thus aiding in the economic development of Ken- tucky.

Respectfully submitted,

Wallace W. Hagan V ~irectorand State Geologist CONTENTS

Fluorine Resources-An Overview Gill Montgomery ...... The Environments of Deposition of Fluorspar R. M. Grogan, P. K. Cunningham-Dunlop, H. F. Bartlett, and L. J. Cxel ...... 4 Geology of the Fluorspar Deposits, 1. E. Mason ...... 10 Geology of Mexican Fluorspar Deposits Greenleaf W.Pickard ...... Geology of Fluorspar Deposits of the Western United States Ronald G. Worl ...... 31 Some -Barite 'Deposits in the Mississippi Valley in Relation to Major Structures and Zonation Allen V. Hey1 ...... 55 Illinois-Kentucky Fluorspar District Robert D. Trace ...... Structure of the Fault Systems in the Illinois-Kentucky Fluorspar District John W.Hook ...... 77 Geology and History of Pennwalt Corporation's Dyers Hill Mine, Livingston County, Kentucky John S. Tibbs ...... The Eagle-Babb-Barnes Fluorspar Project, Crittenden County, Kentucky F. B. Moodie 111 and Preston McGrain ...... : 96 FOREWORD

The Ninth Annual Forum on the Geology of cals which are manufactured for a large number Industrial Minerals was held in Paducah, Ken- of industrial products. tucky, on April 26-28, 1973. The three-day pro- Paducah, located near the northern tip of the gram consisted of a business meeting, a symposium Mississippi Embayment, is only a 30-minute drive of ten invited papers dealing with various aspects from the Illinois-Kentucky fluorspar mining dis- of the geology of both United States and foreign trict. This district, which has been active for more fluorspar deposits, and two concurrent all-day field than a century, has produced approximately 75 trips to the Illinois-Kentucky fluorspar district. percent of the total fluorspar mined in the United The meeting was attended by approximately 200 States. geologists, mining engineers, mining company ex- The papers included in this volume are the ecutives, educators, investment analysts, and printed versions of the talks given at the sympo- sium. They provide an insight into the geological others, representing 29 states and 6 foreign coun- parameters which are related to the occurrence of tries. fluorspar deposits. Thus, they should aid in plan- The Forum on the Geology of Industrial Min- ning future exploration programs. In addition to erals was founded as a means of bringing together assisting in the prospecting for and development persons from industry, government, and academia of fluorspar resources, this volume will be a val- interested in the geological aspects of industrial uable reference to students of earth sciences in- (nonmetallic) minerals and their utilization. The terested in mineral occurrences. first Forum was held in February 1965 in Colum- The last day of the Forum was devoted to two bus, Ohio, with subsequent meetings in Indiana, concurrent field trips to both the Illinois and the Kansas, Texas, Pennsylvania, Michigan, Florida, Kentucky portions of the fluorspar mining district. Iowa, and most recently, Kentucky. The theme of The Illinois excursion was the principal field trip, the meeting is determined by the host organization featuring underground visits to mines of Ozark- and usually reflects the local resource base and Mahoning Company, Mining Division, and Mi- mineral industries. Previous meetings have dis- nerva Oil Company, Fluorspar Division, to observe cussed the geology of such commodities as lime- bedded and vein ore occurrences. The trip to the stone, , cement raw materials, mineral ag- Kentucky portion of the district was arranged for gregates, phosphate rock, building stone, gypsum, those who could not be accommodated on the and clays. A list of publications containing papers Illinois trip. The Kentucky trip was restricted to presented at previous Forum meetings is tabulated salient surface geologic features, including areas inside the back cover of this volume. of Pennwalt's Dyer's Hill mine (now inactive), the The Ninth Forum, hosted jointly by the state new Cerro-FFL project (currently under develop- geological surveys of Illinois and Kentucky, pro- ment), high-calcium ledges of the Fredonia Mem- vided a unique opportunity to hear some of the ber of the Ste. Genevieve Limestone (a prominent world's most experienced fluorspar geologists dis- host rock for fluorspar ore), and exposures of por- cuss various aspects of the geology of stratiform tions of major fault systems. and vein deposits and visit the largest fluorspar- The writers acknowledge with thanks the as- producing district in the United States. sistance and cooperation of the authors of the Fluorspar is the commercial name for the min- papers, field-trip leaders, companies who permitted eral fluorite, the most important source of fluorine. access to properties, fellow staff members, and It has wide application in the production of alumi- others during the preparation for and conduct of num, steel, many ceramics, and a variety of chemi- this symposium on the geology of fluorspar. Preston McGrain, Kentucky Geological Survey Robert L. Major, Illinois State Geological Survey Co-chairmen, Steering Committee Forum on the Geology of Industrial Minerals, 1972-73 PROCEEDINGS OF TECHNICAL SESSIONS OF PREVIOUS FORUMS

Ohio State University Department of Geology, 1966, A symposium on the geology of industrial limestone and dolomite: Ohio Jour. Sci., v. 66, no. 2, p. 97-191. Indiana Geological Survey and Indiana University Department of Geology, 1966, A symposium on geology of cement raw materials: Indiana Geol. Survey, 197 p. Angino, E. E., and Hardy, R. G., eds., 1967, A symposium on indus- trial mineral exploration and development: State Geol. Survey of Kansas, Spec. Dist. 34, 183 p. Brown, L. F., Jr., ed., 1968, Proceedings, fourth forum on the geology of industrial minerals: Texas Bur. Econ. Geology, 174 p. Hoover, K. V., ed., 1970, Proceedings, fifth forum on geology of industrial minerals: Pennsylvania State Planning Bd., Bur. Topo. and Geol. Survey, Min. Res. Rept. M64, 278 p. Kneller, W. A., ed., 1970, Proceedings, sixth forum on geology of industrial minerals : Michigan Dept. Nat. Res., Geol. Survey Div., Miscellany 1, 155 p. Puri, H. S., ed., 1972, Proceedings, seventh forum on geology of in- dustrial minerals: Florida Bur. Geology, Spec. Pub. 17, 229 p. Iowa Geological Survey, 1973, Proceedings, eighth forum on geology of industrial minerals: Iowa Geol. Survey, Public Inf. Circ. 5, 195 p. FLUORINE RESOURCES-AN OVERVIEW GILL MONTGOMERY Vice-President and General Manager Minerva Oil Company, Fluorspar Division Eldorado, Illinois

By the simple and unhonorable process of sary in the synthesis of fluorcarbon polymers such seniority and longevity, I am approaching the as DuPont's Teflon and a whole family of specialty status of "old timer" and guess I am about the plastics and coatings. It is required in the separa- oldest fluorspar operator in the Illinois-Kentucky tion of uranium isotopes, and is, therefore, field, at least in the engineering and management essential to our entire nuclear power program. end of the business. I had my first hand for Substantial quantities are also being used in the fluorspar in churndrill cuttings in Hardin County manufacture of flint glass, fiberglass, enamel frits, in 1941, and enjoyed the unfolding development, and glazes, where it is used as a flux. It is in by drilling, of what has turned out to be one of increasing use as a welding-rod coating and in the largest orebodies in the United States, Miner- several abrasive products. va mine No. 1, north of Cave in Rock, Ill. This Fluorspar, the common name for the mineral mine has produced well over 3 million tons of fluorite (CaF2), is the subject of our discussions fluorspar ore, and at least half this much is blocked today, as we consider where it came from, when it out for future years. Being nurtured all these arrived, what host rocks it favors, and what years by such a wonderful orebody does. not geologic stnlctures have favored its accumulation. qualify me for the title "Mr. Fluorspar"; it just We will also consider how to go about finding it, makes me the oldest fluorspar manager still as we look at increasingly sophisticated methods around. of exploration. However, welcome to the grand old "mother The United States is producing about 20 per- lode country of fluorspar," the Illinois-Kentucky cent of its consumption requirements. Production district, composed essentially of Crittenden and amounts to about 250,000 short tons per year, Livingston Counties, Ky., and Hardin and Pope and we consume about 1,200,000 tons in various Counties, Ill., an area about 60 miles north and forms and grades. Most of our fluorspar is im- south by some 35 miles east and west. In this ported from Mexico, usually either as a ground district, fluorspar has been more or less con- flotation concentrate (97 percent CaF2) or as the tinuously produced since the 1870's, although it lump or gravel form, nlnning between 82 and was only a minor item of commerce until the First 85 percent CaFZ and usually classed as 70 percent World War, when a major demand developed for effective metallurgical fluorspar. Other principal metallurgical gravel fluorspar as a flux in the sources of imported fluorspar, essentially the acid open-hearth method of steelmaking. This con- grade, are, in order of importance, Spain, Italy, sumption continued to be the principal use until , and South Africa. Potential sources of the 1950's, when the rapidly expanding fluorine imports from important new mining areas are chemical business, and the use of synthetic cryo- Thailand, Brazil, Argentina, Tunis, Kenya, Mo- lite and aluminum fluoride in the aluminum zambique, and Southwest Africa. industry, reached major proportions. Today, fluorspar is considered one of the nation's most The price of domestic fluorspar ranges from strategic minerals. Fluorinated hydrocarbons are $87 per ton for acid-grade material dried and in part of our modern way of life, being the refrig- bulk, f.0.b. cars, Rosiclare or Junction, Ill., to erant used in air conditioning and the principal domestic metallurgical gravel (about 82 percent aerosol used in most spray products. Fluorine is CaF2) which sells for $60 per ton. Most of the necessary in the manufacture of high-test fuels ceramic grades are prepared in this district. No. 1 such as alkylated aviation gasoline and is neces- ceramic is classed as 95 percent CaF2, and sells GILL MONTGOMERY at $82 per ton. No. 2 ceramic sells for $77 per ton In the bedded deposits, which usually range in when it is 90 percent CaF2. This same material thickness from 4 feet to over 20 feet, random is also made into pellets and briquettes for the room-and-pillar mining is the rule, and practically basic oxygen process steel plants, and is cast into all of it is now done by rubber-tired diesel equip- bricks at Rosiclare bv the Cleveland ~l~~ Corn- ment. Most of the drilling is done by compressed- pany for sale as flux to the foundry industry. air rock drills, usually on two-boom Jumbos, and most of them are self-propelled by diesel motors. Now, I shall say a few words about the mining Drilling is done mostly with tungsten carbide bits. of fluorspar. Fluorspar deposits are generally of Ammonium nitrate-fuel oil mixtures are used for two principal types: the bedded replacement of blasting the ore in the relatively dry faces, but limestone, usually of Chester or Ste. Genevieve nitro starch and slower dynamites are used in wet age (Late Mississippian), and veins occupying locations. Most loading is now done by rubber- tension fractures. Fluorspar veins of commercial tired diesel muck-haul units, either of the Wagner interest have been found in Lower Pennsylvanian or Eimco types, ranging in bucket capacity from 1 sandstones, throughout the entire Chester section, yard to 5 yards. Most of the hauling is done by and well into the underlying St. Louis limestone. diesel trucks to shaft-bottom crushing stations. The veins usually bottom in with fluorspar These range in capacity from about 6 tons to 18 stringers, indicating a hydrothermal source and tons. Roof bolting carriages, personnel wagons, a vertical zonation of deposition related to favor- underground roadgraders, and utility vehicles are able temperature and pressure for crystallization usually rubber tired and equipped with diesel of fluorite. The bedded formations terminate engines. abruptly at their margins. Most of the favorable bedded deposits are along a band of minor south- Roof spans between pillars vary from as little west to northeast fissures, parallel to the Peters as 8 feet where the roof is shaly, to over 30 feet Creek fault, northwest of Cave in Rock, plus one where there are massive sandstone roofs such as mine near Joy. Compressional structures are ob- the Bethel sandstone. Roof bolting is necessary served in bedded deposits, indicating almost or prudent throughout most of the room-and- horizontal thrustal pressures from the southeast pillar operations. Such mines customarily have which tended to close the fracture systems and comparatively little water in them unless they are inhibit the upward migration of ore-forming solu- close to the surface. Ventilation is by forced air tions through shale sections to form veins. It has through air shafts or drilled ventilation holes, and become interesting to speculate that the plate- in dead-end areas additional air is supplied tectonic movements recently used to explain the through woven plastic ventilating tubing of var- crumpling of the , perhaps ious diameters by booster fans. There 'are no when Africa came over and bumped into North explosive gases present. In several areas, the America, may have exerted horizontal crustal connate waters of freshly drilled orebodies are forces on this district near the end of Paleozoic noted to be saturated with hydrogen sulfide gas, time. The rest of the deposits of the district are and its dispersion requires additional ventilation. essentially fissure veins in tension fracture systems. The mine waters are nontoxic and are used for The major faults seem to contain too much gouge household and stock-watering purposes, as well to favor commercial mineralization. Associated as water supplies for fluorspar-processing plants. with fluorspar in many of the mines are important Three mines are currently under development quantities of zinc, as sphalerite, and lead, as in the district. The Cerro Corporation, Barnes . Barite is a common constituent in various tract development, near Salem, Ky., has recently localities, in both bedded and vein deposits. reached its total depth of 800 feet and is develop- Efforts are now under way to develop economic ing on its haulage level; at the same time it is outlets for barite products. Strontium minerals constructing an adjacent heavy-media separation occur in some barite deposits, as does witherite. and flotation mill. The Ozark-Mahoning Company Limestone of road-rock quality is a byproduct of is developing the haulage levels at its Knight mine the heavy-media separation plants. west of Rosiclare, where it has also constructed a FLUORINE RESOURCES - AN OVERVIEW 3 heavy-media. plant. The Minerva Oil Company, for the U.S. fluorspar industry due to what we Fluorspar Division, is raising an air shaft at its hope is a temporary oversupply situation, world- Spivey development in northern Hardin County wide, with a resulting downward pressure on from the 300-foot level prior to sinking its pro- prices of imported fluorspar. Only 2 or 3 years duction shaft to about 650 feet. ago there was a world fluorspar shortage. This At the present time, only two companies are encouraged much new exploration and mine operating processing plants in the fluorspar dis- development effort, which was all too successful, trict, these being Minerva Oil Company and resulting in a lot of extra production coming onto the Ozark-Mahoning Company. Minerva has its the world market at the very worst time. Within principal mill 5 miles north of Cave in Rock, and the past year, we have seen a sharp dropoff in the a supplemental mill, the Crystal plant, is located consumption of fluorspar by Japan, as well as 4 miles northwest of Cave in Rock. Both have western Europe, and a slowdown in the use of heavy-media preconcentration units followed by fluorspar in the aluminum industry, and in the flotation, and both can also save lead and zinc steel industry to some extent. Now there is a sulfides. Ozark-Mahoning has its central mill at strong business recovery underway, and we can Rosiclare, and most of the ore from its field shafts only hope that this will be worldwide and that is preconcentrated at a heavy-media mill north- it will soak up the surplus supplies which are west of Cave in Rock. This does not apply to the presently giving us a lot of headaches. vein ore from its Barnett shaft. The pressure of cheaper material from the The Calvert City Chemical Co. recently closed Mexican border has been particularly painful to its mill at Mexico, Ky., following the closure of the many small fluorspar producers and potential its Shouse mine near Joy, and its Babb mine near producers in the Western States. There is a lot Salem. The Cerro Corporation is constructing a of fluorspar in Colorado, Idaho, Nevada, Utah, mill north of Salem and plans to be in production New Mexico, Arizona, west Texas, and southern by the end of 1973. On Spar Mountain, north- California. Unfortunately, there is not much west of Cave in Rock, Robin Hastie & Sons are market out there. Most of the market is along the reconstructing a heavy-media mill brought from Gulf Coast, the Atlantic Coast, around the Great Marion, Ky., where it formerly operated for Ken- Lakes, and along the interior waterways. There- tucky Fluorspar Co. Omar Austin & Sons and fore, these western operations have been at a M. L. Conn & Sons both have logwashing plants distinct disadvantage as compared to the Illinois- which may operate this summer. There are Kentucky district, lying as it does on both sides of several other logwasher operations both in Illinois the Ohio River with its barge traffic, and near to and Kentucky which operate intermittently. Much several consumption centers. of their product is sold to flotation plants unless I hope this has given you an overall glimpse of they can make metallurgical gravel fluorspar for the industrial mineral in the proper framework direct sale. for the geological discussions that follow, not all Business at the present time is a little slow of which will essentially agree with one another. THE ENVIRONMENTS OF DEPOSITION OF FLUORSPAR R. M. GROGAN, P. K. CUNNINGHAM-DUNLOP, H. F. BARTLETT, AND L. J. CZEL Geology Section, Purchasing Department E. I. DuPont de Nemours & Company

ABSTRACT Fluorspar deposits with some degree of commercial significance occur throughout the inhabited world. They occur in many kinds of geologic en- vironments, and give indications of having been formed under a wide range of geologic conditions. The commonest environments are fissure veins, stratiform deposits, replacements of carbonate rocks along contacts with acid intrusive rocks, stockworks in tectonically shattered zones, carbonatites, residual concentrations derived from the weathering of primary deposits, and gangue mineral occurrences. Less common modes of occurrence include fillings in breccia pipes, replacements in large inclusions in granite, fillings of cave-like open spaces, and pegmatites. Many fluorspar districts contain several kinds of deposits in close proximity, such as veins, stratiform deposits, and residual concentrations. There is no single characteristic geological mode of occurrence in many localities, so that careful attention should be given to the examination of all possible environments present.

This paper is the joint product of several of The principal reason for giving a paper of this the members of the Geology Section of the Pur- sort is to summarize in collected form features of chasing Department of the DuPont Company, fluorspar deposits which might prove helpful to and most of the data to be presented were de- those of us seeking new deposits in new areas, to veloped by our own people during field inves- help us keep in mind sites of possible ore occur- tigations, with only a small part being taken from rence in established districts, or to help us inter- publications. pret the odd-looking or enigmatic results of The plan for this presentation is to treat some exploratory drilling. In other words, the main generalities first, then to list the common and less concern of this paper is establishing guides to common geologic environments of deposition, and finding and identifying fluorspar deposits. Much then to cite brief examples, with brief descrip- has been said about this subject before, and the tions, of each. Various fluorspar districts and areas basic facts are well known to many of you already. in the Free World, including those to be dealt However, fluorspar comes in so many forms dif- with by following speakers, will be touched upon ficult for the field geologist to recognize and here. However, because of time allowed, it will appreciate that an iteration of characteristically not be possible to go into much detail, and it is hoped thereby that these descriptions will not favorable sites is not amiss, to help keep the conflict with or subtract from those which you senses alert and tuned to fluorspar, as it were. will hear later. When presented with coarsely crystalline masses It is difficult to illustrate a subject such as this of a heavy mineral with the characteristic octahe- because of its very general nature. There will be dral cleavage and the common blue, green, purple, a few slides of fluorspar districts in Spain, Mexico, or yellow colors, one has little difficulty in think- and Brazil, but they are intended more to put ing "fluorspar." But when one is shown dense you in the mood than to illustrate specific features chalcedonic fornls with brown, black, red, or gray of this talk. In most cases there will be no coloration land no cleavage, one may not think commentary devoted to individual slides. "fluorspar" so readily. THE ENVIRONMENTS OF DEPOSITION OF FLUORSPAR 5

The Ozark-Mahoning Company had a display to support mining operations. In considering of fluorspar specimens from deposits all over the new areas, one should keep in mind the fact that world. Many of these specimens were so atypical a combination of types of occurrence may exist. in appearance as to be baffling, and the message Another example of this principle is afforded to be gained was to think "this could be fluorspar" by the Lost River district in Alaska, which has when handling any knife-soft, heavy, chalcedonic- been much featured in the mining press of recent textured materials. months. According to the published accounts, in Fluorspar occurs in many types of geologic en- one area fluorspar has partially replaced limestone vironnlents and has been formed under a wide where it overlies an intrusive granite dome. In range of geologic conditions. Some types of another area it occurs as irregular replacements in environments are not known to have provided brecciated and porous limestone beds adjacent to deposits of conlmercial grade or size. For example, a thnist fault. In a third area the fluorspar occurs fluorite is an accessory mineral in some igneous in veins and pipes in limestone and dolomite, rocks such as the radioactive quartz bostonite of and a fourth deposit consists of a fluoritized zone Central City, Colorado, and the fluoritic granites in slate. In addition, fluorspar occurs locally in of Conway, New Hampshire, and Nigeria. skarn along limestone-granite contacts. The gen- The commonest environments for the deposi- eral background at Lost River is one of a series tion of fluorspar are: of highly faulted and brecciated limestones in- 1. Fissure veins, in many kinds of country truded by stocks and dikes of hydrothermally rock, notably granite and limestone. active granite carrying substantial amounts of 2. Stratifornl deposits in carbonate rocks. fluorine, plus tin, tungsten, and beryllium. 3. Replacements in carbonate rocks along Fissure veins, usually along faults, are probably contacts with intmsive acid igneous rocks. the commonest of all environments in which fluor- 4. Stockworks or fillings in sheared or tecton- spar deposits occur the world over. Silica, calcite ically shattered zones. or other carbonates, iron, lead, and zinc sulfides, 5. Carbonatites and alkalic rock complexes. and in some areas barite, are typically associated 6. Residual concentrations from the weather- with fluorspar deposits. In some vein deposits, as ing of primary deposits. in the Rosiclare district, fluorite appears in many 7. Gangue mineral occurrences. places to have replaced a prior vein filling of Less common, but nevertheless in some cases calcite. In some veins replacement bodies have of nlajor commercial importance, are: formed out into the wall rock at intersections with 8. Fillings in breccia pipes of explosive or favorable beds. In some veins a notable propor- collapse origin. tion of the total tonnage mined comes from these 9. Replacements in massive inclusions in replacement bodies, so much so thlat it is common granite. practice to orient exploratory drill holes so as 10. Fillings in open spaces. to cut the vein at those favorable zones. Ore 11. Pegmatites. shoots are normal features of fissure vein deposits. Still less con~mon,but possibly of some im- Some of the world's great vein deposits include portance, are: the following: the Osor deposit in northeastern 12. Deposits in lake sediments. Spain, the Torgola deposit in northern Italy, the In some areas fluorspar is found in a combina- Muscadroxiu-Genna Tres Montis vein system in tion of environments. A case in point is the nearby Sardinia, the Longstone Edge-Sallet Hole deposit Illinois-Kentucky district where there are fissure in England, and, of course, the Rosiclare-Good- vein deposits as well as stratiform replacement hope vein system in southern Illinois. The prin- deposits, plus some that are a little of both; in the cipal vein in Brazil's Criciuma district is also past there were also rich residual deposits of notable. significant tonnage. As a matter of fact, many of The Osor vein near Gerona, Spain, on the the residual deposits were developed from primary southern flank of the Pyrenees, has been known vein deposits which were found to be too lean since the turn of Ithe century. It is a major east- 6 R. M. GROGAN AND OTHERS west fissure filling in porphyritic granite which 5 to 10 meters in width, with widths up to 18 contains lenticular bodies and schlieren of biotite meters in places. The ore ranges from 50 to 80 gneiss and schist, and which is cut by narrow percent CaF2, with barite and relatively high alaskite and pegmatite dikes. The strike length lead values in some places. Proved and blocked is about 1 kilometer. The dip is nearly vertical out ore reserves along this structure amount to to a depth of 40 meters, where the vein branches some 6 million tons. like an inverted "Y." The north branch, the more The Longstone Edge-Sallet Hole deposit in persistent of the two, continues downward at a Derbyshire, England, is said to be 3% miles dip of 60 to 70 degrees to the north. Widths range long and has been mined both on the surface and up to about 12 meters and probably average over underground. Open-pit widths have ranged 3 meters. Ore shoots are 100 to 300 meters in mostly between 30 and 40 feet, and depths of length, and some are continuous from surface to 120 to 130 feet have been reached in plmaces. The the present bottom level at about 300 meters surface vein material is soft and clayey, and when depth. The north branch of the vein splits into the property was visited in April 1969, the ore several sub-branches in the lowermost workings was running 55 percent CaFz, 11 percent barite, at the west end of the mine. Unmineralized fault and 1.5 percent lead. In underground exposures gouge and highly siliceous breccia occur in the the vein is 20 to 30 feet wide. In 1969 this vein vein system between the ore shoots. system was credited with containing 3 to 4 million The average grade of ore at Osor is 45 percent tons of ore. CaF2, 30 percent SiOz, 6 percent CaC03, and The Rosiclare-Goodhope vein was not quite in small percentages of Zn and Pb and of BaS04. the same class as those described previously, but For 20 years French interests mined the vein for was the richest, most consistently mineralized and lead, but since 1943, under Spanish ownership, productive vein in the Illinois-Kentucky region. it has produced about 1.5 million tons of fluorspar- At least 800,000 tons of finished fluorspar was lead-zinc ore. Nearly 650,000 tons of acid- and taken from it. It occupied a fault having a known metallurgical-grade spar have been produced from length of nearly 2 miles and was worked from Osor to date, together with 40,000 tons of lead the surface to depths of over 700 feet. The and 60,000 tons of zinc concentrates. maximum width of minable ore encountered was The Torgola deposit in northern Italy is now 14 feet and averaged 5 to 6 feet throughout the depleted, or essentially so. Ten to 15 years ago mine. Throughout very large areas this vein con- it was the outstanding individual producer in the sisted of nearly pure spar from wall to wall, and industry, producing nearly 100,000 tons of acid-, ore pinches were remarkably sn~alland localized. metallurgical-, and ceramic-grade fluorspar an- The Criciuma fluorspar district of Brazil, located nually. The deposit consisted of a number of in the state of Santa Catarina, could possibly veins along a fault in a rock of dioritic or grano- represent the longest fluorspar structure known to dioritic composition. The principal vein hcad a date. Five operating mines are situated along a thickness of 8 to 10 meters and was unusually N. 35" E, fault zone which can be traced along consistent in width and grade. In 1959, at the strike for approximately 25 kilometers. The com- time of the last visit by DuPont geologists, it mercial ore bodies occur as discontinuous lenses had been worked through a vertical distance of which pinch and swell both laterally and vertically 245 meters, and drilling had indicated another 150 in a Precambrian quartz monzonite porphyry, and meters of ore below the lowest workings. It almost are located where overlying sedi- certainly produced 1 million tons of ore, and mentary rocks have been eroded to expose the probably considerably more thjan that. basement. The Muscadroxiu-Genna Tres Montis vein The district is separated into two distinct system in Sardinia is particularly notable, and is sectors. The southernmost 10 kilometers is char- currently one of the world's largest individual acterized by coarse clean spar averaging 4 to producers. It is reported that it has a continuous 5 meters in width near the surface and n~nning strike length of some 3,000 meters and averages 70 to 75 percent CaFz, whereas the most northerly THE ENVIRONMENTS OF DEPOSITION OF FLUORSPAR 7

6 to 7 kilometers contains more silica and clay, Stratiform deposits in carbonate rocks are also resulting in a decrease of grade to +40 percent common throughout the world, occurring in CaF2. Vein width decreases to +3 meters in the Illinois, Italy, Spain, Tunisia, South Africa, and northern sector. Throughout the district, vein Mexico, for example. These tabular bodies occur width decreases to about 2 meters at the -100- in favorable carbonate beds, in many places meter level; this thinning with depth is accom- directly beneath a shale, sandstone, or clay cap- panied by an increase in silica content. ping, and normally have long dimensions related The principal vein of the Criciuma district is to some structural feature or features such as typically coarsely crystalline spar with chalcedony joints and fmaults. The same group of associated as the only primary diluent. Reactivation along minerals occurs in the stratiform deposits as in the the northern sector of the fault zone has caused vein deposits. In many instances there is some gouge to be supergenetically introduced into the evidence of net loss of volume in the replaced mineralized zone. Mineralization does not pen- zones with attendant development of gentle syn- etrate the host rock, nor does the spar contain clinal structures in overlying strata or of collapse xenoliths of the quartz monzonite. Contacts are structures, some of which are pipelike in shape. sharp; there is only minor koaliniaation (5 to 10 In some districts, as in southern Illinois, there is cm) along the hanging wall and footwall. Texture- no recognizable connection between the mineral- zoning is characteristic throughout the district, ization and any igneous activity, whereas at with acicular growth near the contacts grading others, such as the Encantada district in northern inwardly to saccharoidal agglomeration. This Coahuila in Mexico, the presence of rhyolite plugs intermediate zone then yields to banquil last-state and sills in the general vicinity of the spar de- subhedral to euhedral textures in the central posits, and the direct association of spar with portion of the vein. diffuse rhyolite injections along bedding planes, It has been estimated that the Criciuma district makes one lean toward associating the two. has produced 1 to 2 million tons of concentrates Stratiform deposits occur in the mountainous of all grades since the beginning of mining. region of southeastern Spain known as the Betic Several other smaller occurrences in the State Cordillera. The major lead-fluorspar deposits are of Santa Catarina indicate &tat the deposition of confined to the smaller mountain chains, called spar in this part of Brazil is confined to a struc- the Alpujarride nappes, which surround the pic- turally controlled environment in a lithologically turesque, snow-capped Sierra Nevada Range distinct host rock. between Granada and Alrneria. The Triassic Two-thirds of the Spanish fluorspar production formation, which contains the deposits and from comes from fissure veins in the Asturias region of which the Phoenicians, Romans, and Moors mined northern Spain, in the area of the Cantabrian lead, is a carbonate series. The mineralization is Cordillera. The local mining centers are Oviedo, specifically related to the dolomitic beds within Caravia, and Ribadesella. The veins occur in the series. The beds have been variably folded faults or joints oriented northwest or northeast and faulted. and having steep dips in both easterly and west- The lead and fluorspar ore occurs at several erly directions. Widths are about 4 to 6 meters, horizons forming irregular and lenticular bodies. but one vein, located at Caravia, is 20 meters The bedded deposits have rhythmic banding of wide. As a rule the veins are wider at the top fluorite and dolomite similar to the "coon-tail" ore and diminish with depth. Lengths are up to of the Illinois district. Small amounts of sphal- about 500 meters. Wall rocks are mostly Carbon- erite, cinnabar, and copper oxide occur with the iferous limestone, but in some places they consist fluorspar. Some parts of the deposit are heavily of Permo-Triassic clays and breccias. The shapes brecciated while other areas are not disturbed. of these vein deposits suggest possible -type Thicknesses are on the order of 1 to 2 meters, solution cavities along fractures. Ore grades in some places 4 to 5 meters, and lengths are 0.5 average 25 to 30 percent CaF2, with 15 to 20 to 1 kilometer. Mining the highly irregular beds percent CaC03 and as much as 50 percent Si02. is difficult ,and expensive. Most fluorspar mining 8 R. M. GROGAN AND OTHERS to date is from the waste dumps left by the past limestone, marble, and quartzite, forming large civilizations. Grades of lead ore in place range lenticular masses of irregular shape. Apatite and from 1 to 5 percent, and fluorspar ore grades from quartz are abundant accessory minerals. Some 10 to 40 percent. Total fluorspar production prob- consider the fluorspar 'to be a manifestation of ably has not exceeded 500,000 tons of acid, contact metamorphism of the sedimentary rocks metallurgical, and ceramic grades. by the nepheline syenite, but this is debatable. On the north coast of Spain in the region west A number of years ago concentrations of fluor- of Ribadesella and east of Oviedo in the Asturias spar in the clayey and sandy residuum left by the district, bedded deposits occur in the Permo- surficial weathering of fluorspar veins were sig- Triassic section which contains calcareous rocks, nificant sources of metallurgical fluorspar in Ken- sandstone, and conglomerate. These mineralized tucky and Illinois. There is a little of this material zones are bounded by clay beds. Thicknesses of still being worked, but not much. Log washers mineralized beds range from 2 to 10 meters, and and jigs were the principal concentrating ma- ore bodies can cover areas of 1 squlare kilometer chinery. Currently a significant amount of fluor- or more. Grades of ore range from 15 percent to spar is still being recovered from this type of 35 percent CaF2, with 20 to 30 percent CaC03 deposit in the Asturias district of northwestern and about 30 percent SiOz. There are no known Spain, but most of the product is being processed igneous intnisives in the fluorspar district of into acid-grade conoentrate for export. As turias. "Gangue mineral occurrences" may seem to be Replacement deposits in carbonate rocks along an odd category for a group of fluorspar sources, the contacts with intrusive rhyolite bodies are but it seems applicable and suitable in a prag- notably well developed in the Rio Verde, San Luis matic treatment of the subject. This covers the Potosi, and Aguachile districts in Mexico. They production of acid-grade concentrate from lead- include some of the individually largest and zinc mine tailings by Minera Frisco in Mexico, for highest grade fluorspar deposits known. The example, and the similarly large production from fluorspar is not thought to be contact metamor- old lead mine dumps near Berja in southern Spain phic in origin. It was probably introduced later, by Minersa, which has already been mentioned. following the contact zone as a conduit and re- In each case, fluorspar occurs as a principal gangue placing the limestone outward from the contact mineral in base metal deposits, and is abundant either massively or selectively along certain beds. enough (averaging 10 to 20 percent CaF2) to be At Aguachile cross sections show ore shoots economically recoverable now. crudely resembling one side of a tree. Breccia pipes with fluorspar fillings occur in the Stockworks and fillings in shear and breccia Thomas Range in Utah, and elsewhere. These zones are fairly common in occurrence. Many are large enough to have been important pro- veins in the western United States are of the ducers of metallurgical-grade spar. stockwork type, and though they may be wide, Of historical, but presently noncommercial, are usually of low overall CaF2 content. interest are the occurrences of fluorspar in the Fluorspar is a common mineral in carbonatite gold-telluride pipe complex at Cripple Creek, and alkalic rock complexes, and is sufficiently Colorado, and in a central breccia pipe or breccia abundant in some to comprise economic or poten- zone at Hicks Dome in southern Illinois. tially economic deposits. The Okorusu deposit in In the classification of replacements of massive South West Africa is the best known of this type of inclusions in granitic rocks, the Buffalo and re- occurrence. This deposit consists of a number of lated deposits owned by General Mining in South bodies of fluorspar in a 900-foot-high curving ridge Africa lare outstanding examples. At the Buffalo made up of limestones, quartzites, and related deposit, fluorspar occurs in the form of abundant rocks which have been intruded and metamor- parallel veinlets in a large body of fine-grained phosed by an alkalic igneous rock complex, includ- pink granite enclosed in coarse red granite which ing a nepheline syenite stock. The fluorspar is part of the Bushveld complex. Apparently the appears to have replaced bedded and brecciated fluoritized fine-grained granite is the metamor- THE ENVIRONMENTS OF DEPOSITION OF FLUORSPAR 9 phosed remnant of a block of banded sedimentary rubbly aggregates. In one place a stalactitic rock, perhaps a quartzite which had been caught growth was observed. The core of this growth up in the coarse granite. The spar veinlets occur was finely crystalline white quartz having a principally along what may have been former central tubular opening like regular calcitic bedding planes and, to a lesser extent, in steeply stalactites. The growth was covered with layered dipping joints. The result is a system of veinlets fluorite. '/s inch to 5 inches thick which contain enough Fluorspar occurs in clayey and sandy pyroclastic fluorspar to give the deposit an overall content of sediments in the beds of several former lakes in 20 to 22 percent CaFg. Monazite and apatite 'are the Caste1 Giuliano area about 25 miles north of accessory minerals. Rome, Italy. One, probably the largest of the The Crystal Mountain deposits in Montana are group, which has received much attention in the another odd occurrence. Large bodies of massive press, is the Soricom deposit. Apparently gases or pure fluorspar containing biotite mica, feldspar, solutions of volcanic origin permeated the lake quartz, and other igneous rock minerals are em- sediments, resulting in the deposition of very bedded in granite and biotite gneiss. They are minute disseminated crystals of fluorspar. Fluor- thought to be of pegmatitic origin, both from their spar makes up 50 to 60 percent of clayey parts and manner of occurrence and from the variety and about 15 percent of the sandy parts of the deposits, kind of minerals present. They have been a major and is accompanied by barite, apatite, and source of metallurgical-grade spar. gypsum. Apparently there are millions of tons of Deposition of fluorspar in open cavities is la fluorspar in these deposits, but the exceedingly relatively rare occurrence. A spectacular deposit fine grain size of the crystals has proved a real of this type is in the San Vicente district of block to developing them. The Soricom deposit Coahuila, on the west side of the Boquillas valley, alone is credited with 8 million tons of material in roughly 60 miles south of the village of Boquillas. a bed 1.65 meters thick. Fluorspar occurs in both veins and mantos in lime- We have briefly considered 12 different types stone as very pure massive incrustations which of depositional environments for fluorspar. Fissure often have spectacul'ar mamillary and stalactitic veins and stratiform deposits are by far the most and stalagmitic structures. There is no doubt that important, at least from the commercial stand- here the fluorspar was deposited in open cavities. point, but the point is that there is no character- Another place where fluorspar was deposited in istic, single, geological mode of occurrence for open spaces is the Fluorspar-Gero-Penber vein system on the Northgate property of Ozark- fluorspar. Similarly, fluorspar may be epigenetic, Mahoning in Colorado. Here fluorspar occurs in and evidently usually is, or it may appear to be botryoidal layers on the walls of open fissures syngenetic. 1.t may be impossible to frame a and as concretionary masses surrounding frag- characteristic depositional environment for fluor- ments of country rock. The lower parts of many spar except by using the parameters of chemistry of the still-open areas of the fissures are partly and physics: the composition of the ore-forming filled with these concretionary pebble-like masses, agents and the temperature and pressure operative which are in places cemented together into porous, in the zone of deposition. GEOLOGY OF THE DERBYSHIRE FLUORSPAR DEPOSITS, UNITED KINGDOM

J. E. MASON Chief Geologist, Laporte Industries, Ltd. Sheffield, England

ABSTRACT An account is provided of the nature and origin of fluorspar mineraliza- tion in the South Pennine orefield where deposits are located on the eastern flank of the Derbyshire dome and restricted stratigraphically to Visean limestones of the Carboniferous System in a structurally controlled environ- ment. The main deposits are of fissure-vein type but fluoritization of lime- stone in fractured or well-jointed zones has given rise to replacement deposits especially in the vicinity of impervious volcanic rocks and Namurian shales. The existence of fluorite infillings associated with cave deposits provides another facet of what is shown to be a polyphase mineralization which commenced in the early Permian, after the Hercynian orogeny, and possibly extended through to the Triassic Period. Extensive erosion and peneplana- tion of the Carboniferous strata was taking place at this time, and its effects together with those of subsequent geological events on the mineralization history of the area are considered. Current views on the origin of the ore- forming fluids are examined, and a juvenile source for the elements Pb, Zn, F, and Ba possibly mixed with connate brines is favoured. The juvenile fluids are thought to have emanated from a magmatic source which was also responsible for the increase in geothermal gradient necessary to pro- mote hydrothermal activity.

INTRODUCTION gressively younger strata of the Carboniferous Fluorspar occurrences in the United Kingdom System on three sides and unconformable Triassic are quite numerous and distributed over a wide sediments to the south. area extending from the northeast of Scotland, It is an upland region of outstanding natural where they occur as narrow veinlets and dis- beauty, generally 800 feet or more above sea seminations in the Helmsdale granite and adjacent level, and one of contrasting scenery where rolling Devonian arkoses (Gallagher and others, 1971), limestone pastures give way to open moorland to the southwest of England where fluorspar is and precipitous gritstone crags rising to over an important gangue mineral associated with old 1,500 feet. The hills are separated by often deeply lead mines in the Tamar Valley (Dunham, 195213). incised river valleys, particularly the Derwent, Major fluorspar deposits of economic significance Wye, Dove, and Manifold which flow into the are restricted to the North and South Pennines River Trent at the southern end of the county where they occur in limestones and associated (Fig. 1). The northern part of Derbyshire is in sediments of Lower Carboniferous age. fact referred to as the and lies within The present paper is concerned exclusively with the Peak District National Park. fluorspar in the South Pennine orefield which lies PREVIOUS WORK within the county of Derbyshire and covers an area of approximately 200 square miles. Here The first detailed geological account relating the Series, the oldest specifically to fluorspar in Derbyshire was given rocks exposed in the area, occupy the centre of by Wedd and Drabble (1908). The Geological a complex dome-like structure flanked by pro- Survey memoir on fluorspar by Dunham (195213) GEOLOGY OF THE DERBYSHIRE DEPOSITS, UNITED KINGDOM

Figure 1. Location map and physical features. 12 J. E. MASON is a more recent account of the Derbyshire occur- of Castleton to an area of subsidence and a cor- rences, but the most up-to-date paper is by Ford responding change of facies from pale massive and Ineson (1971) on the fluorspar mining po- limestone with a coral-brachiopod fauna to thinly tential of Derbyshire. It provides a detailed bedded limestones and shales with a goniatite- description of individual veins and properties, a lamellibranch fauna. The marginal zone between general account of the stratigraphy, structure, and the shelf and basin facies in characterized by the mineralization of the district, information about presence of extensive coral reefs. This reef belt the old lead-mining laws and customs, and a is well developed on the western and southern comprehensive list of references. There are two edges of the block near and Brassington. recent 1 inch to 1 mile Geological Survey maps A wide range of lithological types has resulted and related memoirs which provide detailed from these varying conditions of sedimentation, geological accounts of the north and southeast and bioclastic limestones containing brachiopod parts of the orefield (Stevenson and Gaunt, 1971; and crinoid debris in well-defined bands can be Smith and others, 1967). contrasted with pale massive limestones and dark The present paper does not aim to add signif- bituminous limestones. Chert is well developed icantly to the amount which has already been at certain horizons and occurs either as discrete written on the nature and origin of mineral nodules or layers up to 1 foot thick interbedded deposits in Derbyshire. It has been prepared with the limestone. specifically for this symposium and to a certain Contemporaneous volcanic rocks are common extent reflects the views of the author which have throughout the area where they form a series of developed over the past 4 years while being con- impervious layers within the limestone succession. cerned with the exploration and mining of fluor- Unfortunately, rapid lateral variations in thickness spar. and lack of continuity make it difficult to correlate GEOLOGICAL FRAMEWORK individual volcanic horizons across the orefield. Stratigraphy Two composite stratigraphic columns are pro- vided to indicate the limestone subdivisions found Mineral deposits in Derbyshire are associated in the north and south of the area together with with the highest member of the Carboniferous the more important volcanic units (Fig. 2). Limestone Series (Visean); the overlying Mill- stone Grit Series (Namurian) and Lower Coal The volcanic rocks include lavas, tuffs, and Measures ( Westphalian) are rarely mineralized. agglomerates. Typical lavas are grey-green olivine basalts with calcite- and chlorite-filled amygdales Carboniferous Limestone Series when fresh, but many have suffered secondary The Visean rocks exposed in the area are essen- alteration through chloritization and carbonation. tially limestones with interbedded chert and They are usually underlain and overlain by green contemporaneous volcanic rocks, known locally as to ochreous volcanic clays. Individual lava flows toadstones. They attain a maximum exposed attain thickness of up to 250 feet in the north thickness of approximately 1,500 feet, but a recent of the area but rapid lateral variations are com- borehole sunk by the Institute of Geological mon. The Upper Miller's Dale Lava, for example, Sciences near has intersected at least 5,900 decreases in thickness from 60 feet to 8 feet over feet of Carboniferous strata resting unconformably a distance of 400 yards (Stevenson and Gaunt, upon Ordovician mudstone ( Dunham, 1973). The 1971). Similar variations are seen near Masson lowest Visean and underlying Tournaisian rocks Hill where the Matlock Lower Lava and Matlock include dolomites and anhydrite bands inter- Upper Lava are 380 feet and 120 feet thick, bedded with mudstones. respectively, and thin rapidly when traced south- The detailed stratigraphy is complicated by the wards. The greatest volcanic pile occurs further paleogeographic conditions under which the rocks east 'in the vicinity of Ashover where over 900 were deposited. This part of the country acted as feet of lavas and tuffs, broken by two thin lime- a stable block during the deposition of the Visean stone units, suggest close proximity to a volcanic sediments giving way northwards in the vicinity centre. GEOLOGY OF THE DERBYSHIRE DEPOSITS, UNITED KINGDOM 13

Peak Forest Area Matlock Area ma or t h) (SOU t h) Sc.alc ~n Shales illst stone Grit series) Shales feet 0 - Eyam Shales Cawdor Shales "2 Cawdor Lstc. + Eyam Lste. + -- MUL } M;iE;k 1D2 - LT - 500 C DL 0,;/ /My } HoptonLste. Wood ] / Griffe Grange Bed IS2 UMDL / /' LMDL - 1000 Bee Low / EXPLANATION LT, Litton Tuff LSteS.* / CDL, Dale Lava UMDL, Upper Miller's Dale Lava / LMDL, Lower Miller's Dale Lava / MUL, Matlock Upper Lava MLL, Matlock Lower Lava m * Limestone with knoll reef development in - places LWoo Dale Beds L 1500

Figure 2. Composite sections of the Carboniferous Limestone Series.

Bedded pyroclastic rocks vary from 100-foot- Volcanic vents occur at a number of localities thick units down to thin clay wayboards of less including Bonsall Moor and Grangemill west of than 1 foot. They are grey-green, calcitized, Matlock and Monksdale in the north of the area. " variably textured rocks which frequently exhibit They are composed of coarse agglomerates and repeated gradational changes from coarse lapilli lapilli tuffs with limestone and volcanic fragments tuffs to fine volcanic clays. Lateral variations in embedded in a greenish matrix. thickness are common and are thought to be Contemporaneous intrusive igneous rocks of partly due to contemporaneous erosion. similar composition are olivine dolerite sills. There are five in the north of the area, of which trending anticline which provides a link between the Peak Forest sill is the largest, and two in the the two limestone inliers of Crich and Ashover south at Bonsall and Ible. Age determinations and can be traced further north in the overlying on one of the northern sills, using the K-Ar Millstone Grit. Fold axes with a similar trend method, gave an average age of 311+6 m.y. which are present on the western flank of the dome. puts the intrusive episode at about the Namurian- The fold structures are accompanied by ex- Westphalian boundary (Stevenson and others, tensive faulting and jointing. The dominant fault 1970). trend throughout the area is easterly to east- northeasterly, and this is accompanied by a set Millstone Grit Series of west-northwesterly to northwesterly faults. The The limestones are overlain unconformably by latter are of importance southwest of Matlock an alternating series of shales, sandstones, and where the Bonsall and Gulf faults have throws of gritstones which are approximately 1,300 feet over 400 feet in places, and a graben is developed thick in the south and southeast of the area, between the two. increasing to over 4,000 feet in the north and Many of these faults and joints with a similar northwest (Fig. 3). The lowest member of the trend are mineralized. Initially the majority were Millstone Grit succession is a 500- to 800-foot- normal faults with a measurable vertical displace- thick, impervious formation of dark-grey pyritous ment, but the presence of brecciated vein material marine mudstones and shales with thin limestone with horizontally slickensided surfaces indicates and siltstone bands. that post-mineralization wrench faulting has taken place along many of them. Structure The main structural features of the area are Post-Hercynian Evolution of the District the product of the Hercynian earth movements The geological history of the area after the which took place at the end of the Carboniferous Hercynian orogeny was one of almost continuous Period, but the main limestone block and sur- uplift and erosion accompanied by periodic earth rounding basinal areas were in the process of movements along existing planes of weakness. The development from Visean times onwards. The initial uplift of the Pennine massif led to the present limestone outcrop represents the broad removal of several thousand feet of Upper Car- axial region of the so-called Derbyshire dome. It boniferous strata so that by late Permian times is an area of gently undulating strata with a peneplanation had progressed sufficiently to allow number of well-defined fold structures flanked to ingress of marine conditions from the east. Solu- the east and west by much stronger folding on a tions derived from this Zechstein sea are thought general north-south axis (Fig. 3). by Dunham (1952a) to have been responsible for The dominant structure in the northern part the dolomitization of the Carboniferous Lime- of the limestone outcrop is the Peak Forest anti- stones prior to mineralization. Unfortunately cline, a north-northwest-trending fold with a there are no Permian deposits preserved in the gentle plunge to the north and south, but on the area to support this view nor remnants of later eastern flank of the dome the major fold axes Mesozoic and Tertiary rocks with the exception trend east-west. Here the easterly plunging of so-called pocket deposits of clays, silica sands, Abney, Chatsworth, and Stanton synclines are and gravels which represent late Tertiary infilling occupied by Millstone Grit Series rocks. A major of collapsed cave systems developed in the lime- anticlinal structure with a similar trend in the stone. northern part of the area is the Longstone Edge Evolution of the present land surface can be monocline which has a steeply dipping southern traced back to Tertiary times, but it is reasonable limb; the Matlock anticline is an important east- to assume that cavernization of the .limestone erly plunging fold in the limestones further south. commenced much earlier than this. Pre-mineral- A contrasting structure to the east of the dome ization cavernization is present in the area, but is the tight, sinuous, northerly to northwesterly most of the orebodies provide evidence of ex- GEOLOGY OF THE DERBYSHIRE DEPOSITS, UNITED KINGDOM 15

Figure 3. General geology of the Derbyshire orefield. tensive post-mineralization solution and erosion. development of calcite crystals in vugs and on Solution features ranging from narrow gullies and the surface of limestone boulders and transported water channels to cathedral-like cave systems are mineral-bearing sediment backfill, both of which common, and the majority of these exhibit de- reflect variations in ground-water level and rates positional features as well. These include the of flow. 16 J. E. MASON

MINERALIZATION mitization, silicification, and fluoritization are the General Features processes involved but the latter will be described elsewhere. The mineralization is restricted from a strati- The effects of dolomitization can be seen in the graphic viewpoint to the Carboniferous Lime- south of the orefield near Brassington and Wirks- stone Series, although there are rare examples worth and also in the Bonsall Moor-Masson Hill where it extends into the overlying Millstone Grit area where dolomitized limestone can be traced and Coal Measures (Stevenson and Gaunt, 1971). in a general west-northwesterly direction for a The location of mineralization within the lime- distance of 10 miles. Dolomitization in this area stone is largely controlled by the fracture pattern appears to be a near-surface phenomenon and resulting from the Hercynian earth movements. transgresses bedding planes. The contact between This has given rise to vein-type deposits which dolomite and underlying limestone is sharp. In follow the main lines of structural weakness and some areas an interfingering between the two can are known locally as rakes. be seen and occasionally lenses of dolomite are The more important vein systems such as Huck- developed in the limestone (Smith and others, low Edge, Longstone Edge, Long Rake, Coast 1967). Rake, and Great Rake all exhibit a general east- Dolomitized limestones in the north of the area west trend and extend for several miles (Fig. 3). are not common. They are located approximately They appear to be located on or near the crests 35 feet above the dolerite sill at Peak Forest in an of structural highs, and in this respect the Long- area where the limestones immediately above the stone Edge vein system is unique because of its intrusion are marmorized and accompanied by association with a major monoclinal structure. the development of secondary nodules of silica Where these veins are traced in an easterly direc- (Stevenson and Gaunt, 1971). tion they disappear beneath the shale-gritstone cover but do not extend upwards into it. Silicification of limestones is usually restricted Smaller veins and joint infillings, rarely exceed- to the wall rocks adjacent to mineral veins and - ing 2 feet in width, have been called scrins by the therefore could be considered as part of the old lead miners. Also the terms flat and pipe have mineralization process, but more extensive silic- been used to describe tabular and elongate re- ification has taken place in the Bonsall Moor area placement orebodies which have developed where it can be traced for a distance of 2% miles selectively parallel to the bedding and along along the axial region of the Matlock anticline, enlarged joint systems, respectively. in addition to the walls of major veins such as The main minerals contained in these veins and Great Rake. other deposits are fluorite, , calcite, quartz, The boundary between fissure veins and lime- and galena. Other sulphides including sphalerite, stone wall rock is in many cases clear cut with no pyrite, and chalcopyrite are present in the area visible signs of alteration attributable to the but are limited in their abundance and distribu- mineralization process. Ineson ( 1969, 1970), in tion. The relative proportion of the main gangue his study of wall rocks in Derbyshire found minerals varies across the orefield, but as a general evidence of calcite recrystallization, impregnation rule the fluorite content of the main veins de- with quartz, and dolomitization in some instances. creases from east to west. There are a large The dispersion of some trace elements showed a number of additional minerals known to occur in logarithmic decay pattern with increase in dis- the orefield, and a list has been compiled by Ford tance from the vein to form distinct aureoles. and Sarjeant ( 1964) in their mineral index of the The Hucklow Edge vein exhibited a 35-foot-wide Peak District. Zr and F aureole, with Pb and Zn not quite at- taining this width. Dispersions were more erratic Host Rock Alteration in areas where micro-fractures had allowed ex- Secondary alteration of the limestone country tensive migration into the wall rocks. Two com- rock has taken place in well-defined areas either mon features were the decrease in Sr adjacent to prior to or as part of the mineralization. Dolo- the veins, said to be due to the dissociation on GEOLOGY OF THE DERBYSHIRE DEPOSITS, UNITED KINGDOM 17 1

recrystallization of calcite in the wall rock, and and a 6-foot wide complex core of admixed the increase in Zr which was considered to reflect fluorite, baryte, and galena. Here irregularly a magmatic source for the ore-forming fluids. orientated blocks of colloform baryte are em- Type of Deposit bedded in a coarsely crystalline matrix of fluorite which also penetrates the baryte wall zone as The fluorspar deposits have been divided into narrow veinlets indicating a polyphase mineraliza- three main groups for descriptive purposes: vein tion. deposits, replacement deposits, and cave deposits, Barytic wall zones are not always developed. but in actual fact all three are interrelated. The eastern end of Hucklow Edge vein, for Vein Deposits example, is composed of crystalline aggregates of colourless fluorite with small amounts of inter- Vein deposits may be either simple or complex. grown baryte, calcite, and galena. Fluorite-rich Simple vein deposits are narrowjoint and fissure veins in the Ashover area also fail to show any fillings from less than 1 inch up to 2 feet in marked zonal arrangement. On Shuttle Rake near thickness. They frequently exhibit a zonal ar- Bradwell inlpersistent remants of fluorite, calcite, rangement of minerals with crystalline fluorite and baryte wall-zone mineralization up to. 1 foot margins, a baryte wall zone, and fluorite-baryte- in width are dominated by a 6-foot-wide core of calcite-galena core. The dominance of one con- successive white calcite crustifications, a charac- stituent over another varies from one part of the teristic feature of the veins in this area. orefield to another, but the most abundant mineral In addition to the contemporaneous earth is either calcite or baryte. Extensive areas of movements and related phases of mineralization Bonsall Moor are criss-crossed by large numbers to account for the disorderly arrangement of the of northwest- and northeast-trending scrins of this vein fill, there is ample evidence of post-mineral- type, but further south near Cromford narrow ization faulting which has resulted in cataclastic fracture fillings cutting dolomitized limestone are deformation of the veins. Brecciated and pulver- colnposed mainly of fluorite. ized, almost mylonitic, fluorite with streaks of The major veins, or rakes, are vertical to near- galena and baryte is a common feature on the vertical complex fissure veins. They range in Hucklow Edge vein, for example. width from 1 foot to 30 feet or more, and in- dividual veins can vary by these amounts in a Replacements Deposits lateral and vertical sense. Many become attenu- The term replacement is used here in its literal ated or appear to pinch out altogether where they sense for deposits which have developed at the are in contact with volcanic rocks, but in most expense of a host rock. They are composed cases narrow fluorite-filled fractures indicate that essentially of pale-brown, fine-grained, crystalline channelways were present during mineralization, aggregates of massive fluorite with occasional thus allowing the passage of mineralizing solutions crystal-lined vugs, but in more advanced stages to more favourable environments of deposition. of replacement more coarsely crystalline fluorite However, there are examples such as White Rake may be present together with varying amounts of near and Great Rake near Matlock baryte and galena comprising a typical vein where widths of veins are hardly diminished assemblage. where they cut across the volcanic units. Unaltered chert nodules are a common feature Although the -mineral distribution in the larger of many replacement bodies, but usually their high veins is extremely complex, some exhibit a simple silica content is due to the presence of micro- zonal arrangement near the vein walls. High crystalline quartz-fluorite intergrowths whose in- Rake on Longstone Edge, for example, in one terrelationships indicate that silicification of the area has an outer l-inch marginal zone of colour- host rock preceded fluoritization. less crystalline fluorite with specks of galena, All known replacement deposits in Derbyshire followed by a l-foot wall zone of pale-brown, have developed in areas where there is some fine-grained colloform baryte studded with small structural control to the mineralization. It is not grains of galena aligned parallel to the banding, surprising, therefore, to find replacement deposits MASON

adjacent to major fissure veins where wall rocks that some of the orebodies were formed in areas are extensively brecciated. Stratigraphic controls where solution and cavernization of limestone are important as well, and the most favourable preceded mineral deposition. The Golconda mine area for fluorspar replacement deposits to be baryte deposit (Ford and King, 1965) and one found is directly above an impervious volcanic of the orebodies at the famous Mill Close lead unit and, less frequently, beneath the impervious mine (Traill, 1939) are two well-documented shale cover. One of the best examples is the examples. replacement deposit associated with the Long Fluorspar deposits of this type are common in Rake fissure vein at Raper mine near Alport de- the north of the area in close proximity to the scribed by Ineson and Al-Kufaishi (1970). They limestone-shale contact. Ford (1955) has de- established a paragenetic sequence based on field scribed the fluorite-rich pipe deposits at Treak mapping and a study of polished sections which Cliff near Castleton where mid-Carboniferous indicated three generations of baryte and five caves and filled with limestone boulders generations of fluorite. Replacement of the lime- contain pockets and vugs of the purple banded stones adjacent to the fissure vein over a width of variety of fluorite known locally as "." at least 150 feet was related to the youngest Even the cavities between the boulders are lined episode of fluoritization and probably preceded with Blue John and some pockets are up to 4 feet by partial dolomitization and silicification. across. Similar cave deposits have been inter- Ineson and Al-Kufaishi (1970) postulated that sected by underground workings at Ladywash the limestone replacement was directly related to mine, approximately 150 feet beneath the shale the presence of a shale caprock which overlies the cover. Here a 100-foot by 30-foot northwest- limestone on the south side of Long Rake. Deep trending, boulder-strewn, 20-foot-high cavern is I opencast operations subsequent to their work partly lined with fluorite and calcite crystals, and have added confirmation to this view, but in the walls are cut in places by narrow fluorite- addition it is clear that a volcanic zone approx- baryte-galena joint infillings and bedding-plane imately 120 feet beneath the shale cover in an flats up to inches in width. The outer surfaces I 6 I area of complex faulting has also played its part of some of the boulders are decomposed, and in controlling the location of the replacement shell-like crustifications of baryte and fluorite are body. developed around them, together with crystal The Masson Hill replacement described by aggregates of twinned calcite scalenohedra. In Dunham (195213) is one of the better known addition, there are deposits of transported fluorite- fluorspar flats in Derbyshire. It lies above the baryte-calcite sand infilling other parts of the cave Matlock Lower Lava where limestones have been floor. Post-mineralization supergene effects, prob- 4 replaced over a maximum proved width of nearly ably including an enlargement of the cavernous 800 feet to a general height of 18 feet and as area, have made it difficult to reconstruct the ;I I high as 50 feet along some joints. The deposit development of these deposits, but pre-caverniza- 1 appears to have developed from the mineraliza- I tion and post-cavernization mineralization are i tion of a belt of northwest-trending scrins and a suspected. conjugate set more or less at right angles cutting A well-exposed west-northwest pipe develop- 11 dolomitized limestone. Similar replacement de- ment can also be seen in Smalldale near Bradwell posits overlie the Matlock Lower Lava at Jugholes where fissured joint surfaces and bedding planes Wood 0.5 mile northwest of Masson Hill and 1 are occupied by radial intergrowths of coarsely more or less on the same line of strike. crystalline, colourless to pale-mauve fluorite up Cave Deposits to 2 feet in diameter, accompanied by some Derbyshire like most limestone areas is noted galena and baryte. These flattened, pillow-shaped, for its natural caverns which owe their origin interconnecting structures are thought to repre- to solution along preferential lines of weakness sent solution channels developed in the limestone such as joints, fault planes, and the more suscep- prior to mineralization and then subsequently tible lithologic units. There is evidence to suggest infilled. GEOLOGY OF THE DERBYSHIRE DEPOSITS, UNITED KINGDOM 19

Distribution of Fluorspar in the Orefield from east to west with a corresponding increase As long also as 1908, Wedd and Drabble in- in the other gangue minerals, there are sufficient dicated that workable deposits of fluorspar were exceptions to warrant a reappraisal of the zonal restricted to the eastern margin of the orefield and concept, a task which has already been started by also in the limestone inliers further east of Crich Firman and Bagshaw ( 1973). and Ashover. Westwards the vein mineralization Age of Mineralization became progressively richer in baryte and calcite Stevenson and others (1970) have stated that at the expense of the fluorspar. They produced a the youngest rocks in the district cut by mineral map with a line showing the approximate western veins are of Lower Coal Measures age. The limit of workable fluorspar deposits which was mineralization is also later than the intrusive revised in 1952 by Dunham (1952b) based on dolerite sills, one of which gave a whole rock more up to date information. It was also stated K-Ar age of 311 t- 6 m.y. (post-Millstone Grit that this mineral zoning was confused in places and pre-Coal Measures). where extensive alteration of the limestone had Determinations by Moorbath ( 1962) on occurred. from the Matlock district giving a mean model In 1954, Mueller departed from the commer- age of 180 + 40 m.y. suggested a Triassic age cial concept of mineral zoning by attempting to for the mineralization, but doubts have been cast show from a study of the composition of the on the validity of these results by Mitchell and master veins, and the variety of fluorite developed Krouse ( 1971). They recalculated Moorbath's in them, that thermal zones could be demonstrated data for comparative purposes and concluded that in the area. He delineated the individual north- the Pennine mineralization took place from late south trending zones based on the following data Carboniferous to early Permian (280 m.y. ago). obtained from old records and the sampling of Fitch and Miller (1964) have also suggested that available exposures. the primary mineralization was associated with Percent - CaF? BaSOa CaCOa Pbs ZnS CuFeS FeSz the Hercynian orogeny which took place at this Fluoritic Zone 10-50 2-10 40-85 1-5 '/2-3 0-10 0-5 Baritic Zone 1-10 10-40 55-85 1/2-3 0-1 - - time. Calcitic Zone 0-1 0-10 80-99 0-3 0-119 - - Ineson and Mitchell (1973) published data (~ftwG- Mueller) based on samples of highly altered basic lavas Fluorite in the fluoritic zone along the eastern and pumice tuffs from areas adjacent to mineral- margin of the orefield was a colourless variety ization. Age determinations were carried out on with inclusions of pyrite and chalcopyrite. West- clay-mineral concentrates using the K-Ar method. wards this gave way to a second colourless but The results suggested that the clay minerals had turbid variety extended as far as the western limit been affected by repeated hydrothermal altera- of his fluoritic zone. Fluorite in the adjacent tion which reflected at least two episodes of barytic zone was found to be purple, and it mineralization, one at 270 m.y. (early Permian) maintained this characteristic across to the central and the other at 235 m.y. (late Permian). Some area of the limestone plateau. dates as recent at 180 m.y. indicated the continua- Mueller considered that coloured tion of hydrothermal events up into the late Trias. formed at lower temperatures than the colourless varieties and their association with the barytic Nature and Origin of the Mineralizing Solutions and calcitic zones supported the thermal-zone don- Fluid inclusion studies on fluorite by Roedder cept. Also, the higher temperature fluoritic zone (1967) indicate a range of filling temperatures was located nearer the source of the mineralizing from 140°C to 60°C which means that the min- fluids to the east of the orefield. eralizing solutions must have entered the areas Subsequent discovery of fluorspar deposits out- of deposition at higher temperatures. The salinity side the zone boundary and problems over the of these fluids varies from 18 to 30 percent by distribution of coloured varieties of fluorite weight of NaCl in primary inclusions from Masson indicate that although- there is a general tendency Hill, Bradwell Moor, and Treak Cliff, down to for the fluorspar content of major veins to decrease between 1 and 3 percent by weight for other pri- 20 J. E. MASON mary inclusions at Treak Cliff. Published data The discovery of Lower Carboniferous evap- on Na/K ratios have not been found for the orites at depth- in the orefield offers an attractive Derbyshire fluorites, but it is understood that alternative which could gain support if brines current workers are finding slightly higher values with a high metal content were proved to have than the North Pennine fluorites which Sawkins existed, in the area. Unfortunately, ground-water (1966a) puts at 6.8 to 12.4. studies so far have shown that this is not the case, Possible sources for these mineral-bearing brines and the only acceptable source for the mineral- include connate waters trapped and buried with izing elements Pb, Zn, F, and Ba would appear to sedimentary formations (fossil sea water), the be a juvenile one. It is acknowledged that these solution of evaporite deposits by circulating juvenile fluids could have blended with connate ground water, and finally juvenile fluids of deep- brines to form the mineralizing solutions, and it seated origin. is possible that sulphate ions may have been. Exploratory drilling for oil has proved the leached out of the Lower Carboniferous evap- existence of saline ground water in the Car- orite~. boniferous Limestone, Millstone Grit, and Coal ORIGIN OF THE MINERALIZATION Measures occurring below the Mesozoic rocks of the . Analytical results of ground- When Wedd and Drabble (1908) came to water samples from the Carboniferous Limestone account for the origin of the fluorspar mineraliza- tion, they listed facts and observations which had have been studied by Downing ( 1967) who found that the concentration of dissolved solids increased some bearing on the question and then suggested in an east-northeasterly direction away from the the most reasonable hypothesis to fit them. 4 Derbyshire dome up to a maximum of 100,000 similar procedure is adopted in the present paper.' ppm. This increase in salinity was accompanied 1. Age determinations indicate that the min- by a change in composition from bicarbonate to eralization history spanned at least 100 sulphate and finally chloride. Downing concluded million years with the first major hydrother- that these brines were connate waters-fossil mal event taking place towards the end of Carboniferous Limestone and Millstone Grit sea the Hercynian orogeny. Field and labora- water-diluted by meteoric water which had tory studies support this Permo-Triassic moved downdip from west to east from post- polyphase mineralization. Cretaceous times onwards. It is possible that 2. Stratigraphically the known mineral deposits similar connate brines undiluted by meteoric are restricted to the upper part of the Car- water could have existed in the Derbyshire lime- boniferous Limestone Series; occurrences in stone at the time of mineralization, but their the overlying Millstone Grit - and Coal ability to provide adequate concentrations of Pb, Measures are rare. Recent borehole ev- Zn, F, and Ba is doubted. idence near Eyam has proved that the min- Other sources have been suggested for the Der- eralization is underlain by over 5,000 feet byshire mineral-bearing brines. Davidson ( 1966) of Lower Carboniferous strata with dolomite favoured the leaching of overlying Permian and anhydrite occurring near the base of evaporites by circulating ground water. The main the succession. objections to this view include the lack of evidence 3. The greatest accumulation of contempora- to substantiate the former existence of evaporite neous volcanic rocks is located on the eastern deposits in the area, the fact that known Permian flank of the orefield near Ashover, but evaporites have a low metals concentration, and numerous volcanic vents together with late finally one of timing. Since the primary mineral- Carboniferous dolerite sills indicate a high- ization is considered to be post-Carboniferous to level penetration of the main limestone early Permian in age, ground-water brines from a block by intrusive igneous rocks and the Zechstein source could only have been of signif- existence of more than one emanative centre. icance in the later phases of hydrothermal activity 4. The mineralization is. restricted in its loca- in the area. tion to joints and fissure systems in the GEOLOGY OF THE DERBYSHIRE DEPOSITS, UNITED KINGDOM 2 1

limestone or their immediate vicinity where be related to events which commenced in early local depositional factors, in addition to Permian times and a comparison is made with structural controls, have enabled more ex- two of these to put the genesis of Derbyshire tensive areas to be mineralized, resulting in deposits into perspective. the formation of replacement pipes and flats In southwest England some 250 miles away, and also cave-type deposits. metalliferous deposits and associated gangue 5. A common depositional environment for minerals are clearly related to hydrothermal fluids replacement mineralization is the upper of juvenile origin that emanated from the cooling surface of volcanic units. These impervious Hercynian granites. Fluid inclusion studies by rocks are generally poor hosts, but the Sawkins (1966b) have shown that the filling existence of narrow fracture fillings and temperatures for fluorite from this area were in much wider veins where the volcanic rocks the 100°C and 200°C range, the salinity was 12.8 are cut by major rakes indicates that min- to 13.5 percent by weight NaC1, and the NaIK eralizing solutions were capable of passage ratio was 6.7 to 9.5. through them. This has led to fluorine In the North Pennines, 120 miles away, where metasomatism of the overlying limestones. fluorspar-rich veins cut similar Lower Carbonifer- 6. Limestone country rock in mineralized areas, ous rocks, but in a different geological setting, particularly in close proximity to major Sawkins has indicated that fluorite was deposited fissure veins or scrin development, has between 100°C and 20O0C, the salinity of the undergone dolomitization and silicification hydrothermal solutions was approximately 20 as well as fluoritization. Trace-element percent by weight NaC1, and the NaIK ratio was studies in wall-rock zones of some mineral 6.8 to 12.4. Baryte crystallized at temperatures veins provide evidence of fluorine, lead, and down to 50°C from solutions with a NaIK ratio zinc migration into the wall rocks, whereas of 15.3 to 46. a strontium decrease and a zirconium in- There is still a lot to learn about the origin of crease have taken place adjacent to the the Derbyshire fluorspar mineralization, and it is veins. hoped that further information from fluid in- 7. Colour variations and the concentration of clusion studies, particularly the NaIK ratio, and fluorite on the eastern side of the orefield other geochemical data will throw more light on reflect a thermal zoning and an easterly the nature of the ore-forming fluids. The writer derivation for the mineralizing solutions, but favours the view that the mineralizing elements the existence of additional fluorite-rich areas Pb, Zn, F, and Ba came from below and were away from the eastern margin suggests the related to a magmatic source. It is possible that presence of more than one source and a connate waters and the rocks through which the more complex mineralization history. mineralizing solutions passed could have con- 8. Fluid inclusion studies on fluorite indicate tributed to the chemical makeup of these solutions filling temperatures of 140°C to 60°C and a by the time they reached the environments of de- salinity of 18 to 30 percent by weight of position. An increase in geothermal gradient NaC1. The mineralizing solutions which sufficient to promote movement of hydrothermal give rise to them are considered to be a solutions is also considered to be related to a mixture of juvenile fluids carrying Pb, Zn, deep-seated magmatic source located in areas F, and Ba and connate brines. where -previous volcanic activity has indicated CONCLUSIONS crustal instability,. particularly- on the eastern The foregoing summary provides sufficient ev- flank of the mefield. idence to support the view that fluorspar deposits ACKNOWLEDGEMENTS in Derbyshire were epigenetic and the product of a telethermal primary mineralization in a The writer would like to thank the organizers structurally controlled environment. There are for inviting him to present a paper at their many areas in Britain where mineralization can symposium and also Laporte Industries Limited 22 J. E. MASON for allowing him to do so. He would also like to Derbyshire orefield: Inst. Min. Met. Trans., v. 79, acknowledge the kind assistance of Miss M. Gill p. ~238-~245. for preparing the script and R. E. Smith and his Ineson, P. R., and Al-Kufaishi, F. A. M., 1970, The min- eralogy and paragenetic sequence of Long Rake vein colleagues for drafting the figures. at Raper mine, Derbyshire: Mercian Geol., v. 3, p. 337-351. Ineson, P. R., and Mitchell, J. G., 1973, Isotopic age REFERENCES determinations on clay minerals from lavas and tuffs of the Derbyshire orefield: Geol. Mag., v. 109, p. Davidson, C. F., 1966, Some genetic relationships between 501-512. ore deposits and evaporites: Inst. Mining Met. Trans., Mitchell, R. H., and Krouse, H. R., 1971, Isotopic com- 75, Bull. NO. 717, p. B216-B225. position of sulfur and lead in galena from the Green- Downing, R. A., 1967, The geochemistry of ground waters how-Skyreholme area, Yorkshire, England: Econ. in the Carboniferous limestone in Derbyshire and the Geol., v. 66, p. 243-251. east Midlands: Geol. Surv. Gt. Brit., Bull. No. 27, Moorbath, Stephen, 1962, Lead isotope abundance studies p. 289-307. on mineral occurrences in the British Isles and their Dunham, K. C., 1952a, Age-relations of the epigenetic geological significance: Roy. Soc. London Phil. mineral deposits of Britain: Geol. Soc. Glasgow Trans., ser. A, v. 254, p. 295-360. Trans., v. 21, p. 395-429. Mueller, George, 1954, The distribution of coloured vari- -1952b, Flourspar: Geol. Surv. Gt. Brit., Mem., eties of fluorite within the thermal zones of Derby- Spec. Rept. Min. Res., v. 4, 143 p. shire mineral deposits: Int. Geol. Cong., 19th, Algeria, 1973, A recent deep borehole near Eyam, Der- C. R. sec. 13, fasc. 15, p. 523-539. byshire: Nat. Phys. Sci., v. 241, p. 84-85. Roedder, Edwin, 1967, Environment of deposition of Firman, R. J., and Bagshaw, C., 1973, A re-appraisal of stratiform (Mississippi Valley-type) ore deposits, mineral zoning in Derbyshire: Research Colloq. from studies of fluid inclusions, in Genesis of strati- Univ. Leics. form lead-zinc-barite-fluorite deposits (Mississippi Fitch, F. J., and Miller, J. A., 1964, The age of paroxysmal Valley-type deposits)-A symposium: Econ. Geol. Variscan orogeny in England, in The Phanerozoic Mon. 3, p. 349-362. time-scale: Geol. Soc. London Q. J., v. 120, Suppl., Sawkins, F. J., 1966a, Ore genesis in the North Pennine p. 159-175. orefield, in the light of fluid inclusion studies: Econ. Ford, T. D., 1955, Blue John fluorspar: Yorkshire Geol. Geol., v. 61, p. 385-401. SOC.Proc., v. 30, p. 35-60. 1966b, Preliminary fluid inclusion studies of the Ford, T. D., and Ineson, P. R., 1971, The fluorspar mineralization associated with the Hercynian granites mining potential of the Derbyshire orefield: Inst. of southwest England: Inst. Min. Met. Trans., v. 75, Min. Met. Trans., v. 80, No. 777, p. B186-B210. Bull. NO. 714, p. B109-B112. Ford, T. D., and King, R. J., 1965, Layered epigenetic Smith, E. G., Rhys, G. H., and Eden, R. A., 1967, Geology galena-barite deposits in the Golconda mine, Brass- of the country around Chesterfield, Matlock and ington, Derbyshire, England: Econ. Geol., v. 60, p. Mansfield: Geol. Surv. Gt. Brit. Mem., 430 p. 1686-1701. [explanation of geological sheet 112; new series]. Ford, T. D., and Sarjeant, W. A. S., 1964, The Peak dis- Stevenson, I. P., and Gaunt, G. D., 1971, Geology of the trict mineral index: Bull. Peak Dist. Mines Hist. country around Chapel en le Frith: Geol. Surv. Gt. SOC.,v. 2, p. 122-150. Brit., Mem., 444 p. [explanation of geological sheet Gallagher, M. J., Michie, U. McL., Smith, R. T., and 99, new series]. Haynes, L., 1971, New evidence of uranium and Stevenson, I. P., Harrison, R. K., and Snelling, N. J., 1970, other mineralization in Scotland: Inst. Min. Met. Potassium-argon age determination of the . Water- Trans., v. 80, p. B150-B173. swallows sill, Buxton, Derbyshire: Yorkshire Geol. Ineson, P. R., 1969, Trace-element aureoles in limestone Soc. Proc., v. 37, p. 445-447. wallrocks adjacent to lead-zinc-barite-fluorite mineral- Traill, J. G., 1939, The geology and development of Mill ization in the northern Pennine and Derbyshire ore- Close mine, Derbyshire: Econ. Geol., v. 34, p. 851- fields: Inst. Min. Met. Trans., v. 78, Bull. No. 747, 889. p. B29-B40. Wedd, C. B., and Drabble, G. C., 1908, The fluorspar 1970, Trace-element aureoles in limestone wall- deposits of Derbyshire: Inst. Min. Engrs. Trans., v. rocks adjacent to fissure veins in the Eyam area of the 35, p. 501-535. GEOLOGY OF MEXICAN FLUORSPAR DEPOSITS GREENLEAF W. PICKARD Assistant Chief Geologist, Asarco Mexicana Parral, Chihuahua, Mexico

ABSTRACT Mexico has been the world leader in production of fluorspar since 1956. The main producing districts are in the states of San Luis Potosi, Guanajuato, Coahuila, Chihuahua, and Durango. The contact between the Lower Creta- ceous limestones and the Tertiary intrusive and extrusive rocks of rhyolitic composition has been very favorable for the deposition of large chimneys and cave fillings of high-grade fluorspar. l mportant production comes from narrow high-grade mantos and veins in the upper section of the Georgetown limestone. Flotation mills in the Parral district produce acid-grade con- centrates from lead-zinc tailings which average from 15 to 20 percent f luorspar.

INTRODUCTION In Coahuila, the bulk of the production comes Mexico began shipping fluorspar to the United from narrow, high-grade mantos and wide veins of lower grade. The Lower Cretaceous George- States in 1938, and by 1956 had become the world town (Aurora) limestone is by far the most favor- leader in production and exportation of metallur- able host rock. Some high-grade chimneys have gical and acid-grade fluorspar, with a total of been found at the contacts between acid intrusive almost 1,300,000 meric tons during 1970 and 1971, or 23 percent of the world production. rocks and dikes and the Georgetown limestone. In Chihuahua and Durango, narrow, high-grade Because of lessening demand in 1972, the produc- veins are found in the middle to late Tertiary tion dropped about 18 percent, to a little over volcanic series. Fluorspar is a major gangue one million tons. material in the lead-zinc veins of the Parral dis- The United States now consumes roughly 36 trict. The tailings being processed by two acid- percent of the fluorspar produced in the world, grade flotation plants average 15 to 20 percent while accounting for only about 5 percent of the fluorspar. world fluorspar production. Because of its prox- Mexico's reserves are conservatively estimated imity to the U.S., and the moderate import duty at 32,000,000 short tons, averaging well over 35 on fluorspar, Mexico continues to ship over 90 percent fluorspar. Improvements in mining meth- percent of its production to the United States. ods, mechanization, milling procedures and trans- The steady rise in demand and price of fluor- portation facilities in the last two decades have spar since 1940 stimulated widespread exploration enabled Mexico to greatly increase its productiv- in Mexico. Many large deposits, averaging over ity. 65 percent fluorspar, and innumerable small, high- Governmental policy in the last few years has grade orebodies were discovered. The main pro- favored the construction of flotation mills and ducing districts are in the states of San Luis hydrofluoric acid plants, which has led to a cor- Potosi, Guanajuato, Coahuila, Chihuahua, and responding drop in the exportation of metallur- Durango (Fig. 1). gical. spar. In San Luis Potosi and Guanajuato, the contact between the Lower Cretaceous Cuesta del Cura DESCRIPTION OF PRINCIPAL DISTRICTS limestone and Tertiary intrusive and extrusive rocks of rhyolitic composition has been very State of Coahuila favorable for the deposition of large chimneys and The state of Coahuila now produces approx- cave fillings, averaging 65 to 85 percent fluorspar. imately 30 percent of the total fluorspar produced 24 GREENLEAFW. PICKARD

NEW MEXICO \

UNITED STATES

t

TEXAS

Figure 1. Index map of Mexico. GEOLOGY OF MEXICAN FLUORSPAR DEPOSITS 25

in Mexico. Commonly associated minerals are 80 percent; CaC03, 12 percent; SiOn, 5 percent; calcite, quartz, barite, hematite, limonite, celestite, and bertrandite (Bel(OH)zSiO,), 0.3 percent. Out- and bertrandite. side of Aguachile, other known deposits contain less than 50 parts per million of beryllium. The STRATIGRAPHICCOLUMN Mexican government declared beryllium a na- Approximate tional reserve in 1952, and special permission must Series and Grow Formation Thickness (Meters) Gulf Series, Eagle Boquillas limestone 1 150-200 be obtained to work these deposits. Ford Group Buda limestone 25 Production since 1966 has exceeded 100,000 tpy (tons per year) of combined acid and metal- Comanche Series De1 Rio Shale 1 1 lurgical spar. A 400-ton-per-day mill processes (Upper Albian), Georgetown (Aurora) Washita Group limestone fluorspar from the Aguachile and Cuatro Palmas Kiamichi limestone 3;i? mines. Comanche Series Fredericksburg- The Cuatro Palmas and La Facil orebodies are (Middle Albian) Edwards located several kilometers northwest of Aguachile, limestone and have produced a substantial tonnage from Comanche and open-pit operation, averaging over 70 percent Walnut Park fluorspar. Both deposits are localized along the formations faulted contact of a 1.8-kilometer rhyolite dike Pico Etereo District and strongly brecciated Georgetown limestone. The Aguachile deposit is located in northwest- The ~uatroPalmas deposit is in the form of an ern Coahuila near the Big Bend National Park in inverted cone, with a 90-meter diameter on the Texas. From 1953 to 1960, this area shipped over outcrop. Mineralization occurred in several stages, 250,000 tons of metallurgical spar by rail to with a rhythmic replacement of the limestone and Marathon, Texas. by direct precipitation in voids. La Facil deposit is a relatively small and This deposit has been described as an example shallow, tabular orebody, measuring about 60 by of intrusive doming, followed by cauldron sub- 15 meters, with a fluorspar content of 85 percent. sidence and the development of ring and arcuate The Ma1 Abrigo deposit is located northeast of dikes of rhyolitic composition. A plug of quartz Aguachile along the faulted contact between an microsyenite subsequently intruded the :south- intrusive rhyolite porphyry and the Georgetown central portion of the sunken block. limestone. The vein has been worked along strike The largest fluorspar deposits occur in limestone for over 300 meters, with oreshoots up to 10 along the contact with dikes of rhyolite porphyry. meters in width. Total production has exceeded These deposits occupy fault zones in local, in- 50,000 tons of highly sorted metallurgical spar. tensely brecciated areas in contact zones along the downthrown side. The Edwards, Georgetown, El Tule District Buda, and Boquillas limestones served as host Located in north-central Coahuila, the El Tule rocks in one part or another, but the most im- district covers an area of 80 square kilometers. portant orebodies were formed by a combination Total production of highly sorted fluorspar from of replacement and void filling in the Georgetown narrow mantos has exceeded 50,000 tons. limestone. The Buda limestone was the second The ore zone is in the top few meters of the best host. Some orebodies are chimney shaped; Georgetown limestone, and in places the fluor- others are elongated parallel to the contact, ex- spar partially or completely replaces the thin Del tending irregularly out into the contact zone. Rio shale. The beds are almost flat, and the fluor- Three stages of mineralization have been de- spar occurs as discontinuous mantos averaging termined. The rhyolite and fluorspar probably about 0.6 meter in width and from 50 to 80 percent came from the same source at different stages of fluorspar. Celestite (SrS04) is a very common the magmatic cycle; the quartz microsyenite may gangue material with minor calcite and barite. be a differentiate of the same parent magma. The Certain deposits contain a high percentage of average composition is as follows: CaF2, 60 to silica. As water is very scarce in the region, dry 26 GREENLEAF W. PICKARD classification using compressed air has been The veins are wide and continuous, averaging attempted in a pilot plant at the San Miguel mine several meters in width; some oreshoots are up to to separate the fluorspar from the celestite. 12 meters wide. A number of veins have been The orebodies are small and not adaptable to mined through a vertical distance of 100 meters. large-scale operation. Extraction of the ore is The veins average 50 to 60 percent fluorspar and by means of short crosscuts and shallow winzes. are usually associated with high calcite gangue, Careful hand sorting of the ore yields a high-grade requiring separation by flotation. product. The principal deposits all have been worked All of the deposits in the district have been out, and the area at present has very limited pro- found by mapping of the Del Rio shale and the duction. Georgetown limestone, and the sinking of numer- ous 'shallow prospect pits. Areas where the Del State of Sonora Rio shale is thickest have proven most favorable Esqueda District for the deposition of the widest and better grade The Esqueda district is located in the north- mantos. western part of Sonora and is the only major Encantada-Buenavista District producer in this state. Prior to 1960, a limited This district, which comprises about 500 square amount of metallurgical spar was produced from kilometers, cqntinues to be the most important selective mining of a wide vein in the Tertiary producer of fluorspar in Coahuila. The Muzquiz volcanic series. A 125-ton-per-day flot.ation mill, plant has a capacity of 600 tpd (tons per day) installed in 1960, produces acid-grade concen- and produces 150,000 metric tons of fluorspar per trates. year. The oreshoots on veins have been mined for The fluorspar occurs as discontinuous mantos over 200 meters along strike; they average several averaging about 1.5 meters in width, and in places meters in width and in places open out to a 20- attaining 6 meters in width. The ore zone is near meter width. Narrow sections of the veins are the top of the Georgetown limestone and in a mined by open stoping and wider sections by cut few places extends into the Del Rio shale. and fill. Extraction of the ore is by means of a As in the Tule area, there is no apparent rela- 100-meter shaft and by adit. tion of ore to intrusive rocks. Some geologists States of Chihuahua and Durango believe the fluorspar to be of possible sedimentary origin, although all the other fluorspar deposits Of major importance in Chihuahua are some throughout Mexico are clearly of hydrothemral 40,000,000 metric tons of tailings, averaging from origin. 15 to 20 percent fluorspar. 'The three principal Mining operations are similar to those in the mines in the Parral district, Santa Barbara, San Tule district. Prospecting in the Del Rio shale Francisco del Oro, and La Prieta, have quartz and the Georgetown limestone is often compli- and fluorspar gangue in the lead-zinc veins which cated by an extensive capping of caliche which occur in shale and andesite. The fluorspar is masks signs of fluorspar mineralization. present through a vertical range of more than 700 meters. A second stage of mineralization formed Paila-San Marcos District narrow veins of quartz, fluorspar, and calcite Located in southeastern Coahuila and covering which cut the sulfide veins, filling open fractures an area of some 1,300 square kilometers, this dis- in and along the vein and extending for short trict produced an important amount of fluorspar intervals into the vein walls. from 1953 to 1965. The ore was obtained from Asarco Mexicana's plant in Parral produces ap- narrow, high-grade mantos and wide fluorspar proximately 50,000 metric tons of acid-grade con- veins with a high content of calcite gangue. The centrates yearly from the old tailings and will mantos are confined to the upper section of the complete a 50-percent expansion in 1974. Georgetown limestone, average about 0.5 meter The Compaiiia Minera Frisco mills 2,000 tpd of in width, and contain over 85 percent fluorspar. current tailings, combined with 200 tpd of high- GEOLOGY OF MEXICAN FLUORSPAR DEPOSITS 27 grade custom ore to produce some 100,000 tpy consolidated conglomerate. Water problems have of acid-grade concentrates. A new plant is under hampered the development of these deposits construction to process the old tailings. below the 40-meter horizon. Frisco is in partnership with E. I. DuPont de States of Zacatecas, Aguascalientes, and Jalisco Nemours & Company and the Mexican govern- ment in the construction of Mexico's first hydro- f rio District, Zacatecas fluoric acid plant at Matamoros, Tamaulipas, at a The Josefina mine, located 10 kilometers east of cost of 37.5 million dollars. The plant is scheduled Sombrerete, produced over 60,000 tons of 60- to be in production by January 1975. At its percent fluorspar from 1944 to 1953; the mine has capacity of 75,000 tpy of hydrofluoric acid, it been inactive for many years. The fluorspar was will need approximately 160,000 tpy of acid-grade deposited along a series of persistent faults in concentrates. Most of this concentrate will be Lower Cretaceous limestone. The main oreshoots supplied by Frisco. Under government regula- are 2 to 4 meters in width and reach a depth of tions, this plant and others now in the planning 90 meters. stages will have priority on any of the acid-grade concentrates needed to keep the plants running Jalpa District at capacity. In recent years a number of small mines have In the Parral area, stripping operations close to been producing metallurgical spar in an extensive the Esmeralda mine produce about 100 tpd for area covering southern Zacatecas and Aguascalien- Frisco. Vein-like concentrations of over 65 per- tes. The veins are in tuffs and flows of rhyolitic cent fluorspar are localized along a wide dike of composition of Tertiary age. They average less rhyolitic composition. The country rock is shale than 2 meters in width, but are persistent along and monzonite and the vein outcrops range from strike and contain approximately 60 percent 3 to 8 meters in width. Diamond drilling results fluorspar. One of the mines produces from a showed a marked weakening of vein structure and depth of 90 meters. A plant for the production increase in silica content at less than 50 meters of acid-grade fluorspar, with a 100-ton-per-day below the outcrop. capacity, is being constructed in Jalpa. A number of small mines produce high-grade metallurgical spar from narrow veins in the Bolanos Mine, lalisco Tertiary volcanic rocks in the transition zone Located in northern Jalisco, this old silver camp between the Central Plateau and the Western was recently reactivated, and a 400-ton-per-day Sierra Madre in south-central Chihuahua, mill produces concentrates of lead, zinc, and In the Bermejillo, Durango;area a small pro- fluorspar. The sulfide "vins average over 20 per- duction of high-grade fluorspar is obtained from cent fluorspar, and high-grade fluorspar, mined narrow mantos in the Lower Cretaceous lime- from narrow veins in the north end of the district, stone. is added to the mill feed. The Rodeo-Indk area in western Durango pro- duces a regular tonnage of fluorspar from veins States of Son Luis Potosi and Guanajuato 0.5 to 3.0 meters in width in the Tertiary volcanic Extensive, high-grade fluorspar deposits were rocks, often associated with wide rhyolitic dikes. discovered in the Zaragoza and Rio Verde districts Upgrading of these ores is by mechanical con- in the early 1950's. Since that time, constant centration, jigs, washing plants, and by hand exploration and development work has promoted sorting to yield over 80 percent fluorspar. a steady increase in the production, which now La Colorada property is located in west-central exceeds 55 percent of the total fluorspar produced Durango and has a production in excess of 40,000 in Mexico, principally of metallurgical grade. The tpy of over 80 percent fluorspar with about 13 faulted and brecciated contact between the Lower percent silica. The veins are persistent for more Cretaceous limestone and Tertiary volcanic rocks than a kilometer in length and vary from 1.0 to is considered to be the major control of the min- 10 meters in width. The country rock is a well- eralization. 28 GREENLEAF W. PICKARD

Zaragoza District orebodies have horizontal dimensions of 50 by La Consentida and Esperanza deposits are lo- 40 meters and are separated by 30 to 40 meters. cated 40 kilometers southeast of the city of San of barren ground. A major new orebody to the Luis Potosi and have been worked by Pennwalt south is said to have been discovered by gravi- since' 1955. Both orebodies are located along a metric studies, followed by diamond drilling. persistent, northwestward-trending fault which Mining is by a rill-type, cut-and-fill method, and has dropped the rhyolitic extrusive rocks relative by shrinkage stoping. to the nearly horizontal Cuesta del Cura lime- A recently completed mill produces some 30,000 stone. La Consentida deposit was formed by tpy of acid-grade fluorspar from fines and low- replacement of the intensely brecciated limestone grade ore. In 1971 Las Cuevas produced 202,000 and rhyolite, as well as by open-space deposition tons of metallurgical spar. The reserves are said in large solution caves. The orebody strikes north- to exceed 3,000,000 tons of ore that is over 65 westward, plunges steeply to the southwest, and percent fluorspar. measures approximately 110 by 80 meters. It has Rio Verde District been mined by open-pit operation to a depth of El Refugio mine, the principal producer in the 100 meters. Diamond drilling below the bottom state of Guanajuato, is located 45 kilometers of the pit showed tapering roots which terminate southwest of the town of Rio Verde, on the south about 60 meters below the floor of the pit. This bank of Rio Santa Maria, the main river in the remaining ore will be mined by means of a ramp area. Transportation of the ore from the mine and truck haulage. The estimated grade is about to the mill over 62 kilometers of winding, narrow 70 percent fluorspar with 16 percent silica. road is difficult and expensive. The Esperanza orebody is located 300 meters El Refugio orebody is believed to be a breccia to the northwest along the strike of the contact pipe almost completely replaced by fluorspar. It of La Consentida deposit. It is much smaller than occurs at the contact between limestone and a La Consentida, with a length of about 50 meters small intrusive body of rhyolite. Rhyolite flows and a width of about 20 meters. A tunnel driven cap the limestone in the immediate vicinity of the at 60 meters below the operating pit floor shows mine. The orebody measures 70 by 40 meters and a considerable increase in size. The estimated has an easterly plunge ranging from 45 to 90 grade is about 75 percent fluorspar with 20 percent degrees. Diamond drilling shows a vertical ex- silica. Diamond drilling of the contact between tension of about 300 meters. The ore grade is the two orebodies failed to find any ore. approximately 85 percent fluorspar with 4 percent The fluorspar is crushed to 2 or 3 inches, hand silica. sorted on picking belts, and screened to remove The upper section of the orebody was mined the fines. Hand sorting removes about 5 percent by open-pit methods; the present production is of the waste rhyolite and limestone fragments. from underground mining and exceeds 100,000 This product is trucked to a storage yard in San tpy, of which 60,000 tons are acid-grade con- Luis Potosi where the fluorspar is further crushed, centrates. Industrias Peiioles and Allied Chemical, screened, jigged, and washed to remove the fines. the owners of the mine, plan to double the mill The ore is assayed and blended in the yard to capacity as well as the production of metallurgical meet market specifications. Unmarketable fines spar. No serious water problems have been en- are sold to flotation mills. countered in mining operations at considerable The Cuevas mine is affiliated with the Noranda depth below the river level. Mines of , and is located about 1.5 kilo- El Zapote mine is the property of the Compaiiia meters south of La Consentida. This deposit also Minera La Valenciana and is located about 25 occurs on the faulted rhyolite-limestone contact, kilometers south of Rio Verde. The orebody is but the bulk of the mineralization is in the highly a nearly vertical chimney, approximately 60 altered and fractured rhyolite. A series of ore- meters in diameter, in the Lower Cretaceous shoots have been developed on the 70- and 120- limestone close to the contact with Tertiary vol- meter levels, driven from a vertical shaft. These canic rocks. Underground mining has reached the GEOLOGY OF MEXICAN FLUORSPAR DEPOSITS 29

107-meter level. The ore is hand sorted at the La Azul orebody occurs close to the contact of mine and tn~ckedto a washing plant in Rio Verde. the Morelos limestone and dolomite of Early The production is about 60,000 tpy of 60 to 80 Cretaceous age with the overlying Balsas con- percent fluorspar. glomerate and the Tilzapota rhyolite series of La Ilusion mine is located near the Zapote mine Eocene-Oligocene age. Major northeastward- and has very similar characteristics. The orebody trending faults traverse the area. is over 10 meters in width and is worked by open- A small, irregular body of rhyolite intruded the pit methods. The owners are Industrias Peiioles limestone; subsequent brecciation and shattering and Fluorita de Mexico (Continental Ore Co.). of the margin of the intnisive rock and the lime- La Rosita mine is located 38 kilometers south- stone provided a favorable locus for the fluorspar west of Rio Verde and is under the same owner- mineralization. The main chimney has a diameter ship as La Ilusion mine. Industrias Peiioles plans of 12 to 20 meters and plunges 70 to 80 degrees to double the production from both of these to the northeast. The average grade is 63 percent mines. fluorspar, 27 percent SiOz, and 2.5 percent CaC03. The orebody is an elliptical chimney over 15 The orebody was worked by open-pit mining and meters in width in a highly folded Lower Creta- partially explored by short levels from a 55-meter ceous limestone. Rhyolite flows are present about shaft. Some diamond drilling was done from the 300 meters to the south of the mine. The produc- surface. Estimates of reserves range from 200,000 tion is about 150,000 tpy of metallurgical spar, to 500,000 metric tons. processed by mechanical concentration. A part of this production will be converted to acid-grade EXPLORATION FOR FLUORSPAR concentrate at a new plant under construction. Although some major ore deposits have been State of Mexico discovered in Mexico by untrained prospectors, most of the large, successful fluorspar operations Zacualpan District have been the result of diligent geological explo- The first flotation mill in Mexico for acid-grade ration. This includes regional and areal recon- fluorspar was a 70-ton-per-day plant at Zacualpan; naissance and mapping and utilization of aerial it started production in 1951. A number of wide, photos to delimit areas for more detailed studies. persistent veins have been worked in the region These may consist of geological mapping with to a depth of 200 meters. More than 100,000 topographic controls, trenching, sampling, di- metric tons were produced from 1938 to 1962. amond drilling, and development work by pros- The orebodies contain 60 to 70 percent fluor- pect pits, shafts, adits, etc. spar, and are localized within fault zones in Meso- Obviously, the most successful exploration has zoic sericite schists, quartzites, and shales. A been in determining the extensions of known variety of Cenozoic intrusive bodies occur in the mineral trends, intersections of major structural area. features, and along the contact between acid Although large reserves remain in the various igneous rocks and favorable limestone units. Map- veins, the district has been inactive for a number ping of the Del Rio shale and the Georgetown of years due to legal problems in the claim owner- limestone in northern Coahuila and the studies ship. The abundant barite gangue is said to cause of structural features and alteration along the serious difficulties in the flotation process. extensive contact between Tertiary volcanic rocks State of Guerrero and the Lower Cretaceous limestones throughout the Central Plateau, followed by diamond-drilling Taxco District programs or development work in the more La Azul and El Gavilin deposits are located promising areas, have led to the discovery of about 10 kilometers northeast of Taxco. They many commercial fluorspar deposits. produced over 100,000 tons of fluorspar during the Gravimetric studies have had some limited period 1939 to 1948. Both deposits have been success in determining local extensions of large, inactive since 1948. massive fluorspar deposits in the Cuevas mine. 3 0 GREENLEAF W. PICKARD

Geochemical sampling and analysis of soil, rock, panies (about 51 percent). Special subsidies are and stream sediments have proven useful in the granted to small mines and to newly formed search for new fluorspar deposits or to locate companies. possible extensions of known ore zones, using the PRICES most commonly associated elements such as Hg, Ag, Pb, Cu, Zn, Be, and Sr. Mexican fluorspar, short ton f.0.b. 1973 ,I .-Tan.-. -- - 1, "Ian. 1971 U.S. TARIFF ON FLUORSPAR Metallurgical (effective I c~F~,70 pe;cent) Since June 1951 the following U.S. tariff has Tampico, vessel 1 $50.00 1 $31.15 been in effect: Mexican border, cars 1 $48.50 1 $30.15 1 Long Ton ( Short Ton Acid grade (97 percent) I Over 97 percent CaF, $2.10 $1.88 Eagle Pass, bulk $64.50 1 $52.00 97 percent, or less, C~F~1 $8.40 1 $7.50 SELECTED REFERENCES MEXICAN TAXES ON FLUORSPAR Grogan, R. M., 1960, Fluorspar and cryolite, in Industrial There is a 3-percent production tax levied on minerals and rocks: Am. Inst. Mining, Metall., and the value per ton of fluorspar, according to the Petroleum Engineers, p. 363-382. Igueravide, Javier, 1972, Estudio geol6gico del prospecto official price set by the Mexican government. de fluorita de Guadalupe, Mpio. de Taxco, Guerrero: There is a 15-percent export tax, plus a 2-per- Tesis profesional, Universidad Aut6noma de San Luis cent surcharge, which is levied on the value per Potosi. ton of metallurgical or acid-grade spar, according McAnulty, W. N., and others, 1963, Aguachile beryllium- to the official price set by the Mexican govern- bearing fluorspar district, Coahuila, MBxico: Geol. ment. Soc. America Bull., v. 74, no. 6, p. 735-743. VanAlstine, R. E., Estrada, Samuel, and de la Garza, One-half of the government portion of these Ernesto, 1962, Investigaci6n de 10s principales dis- taxes, which amounts to about 85 percent of the tritos de fluorita en MBxico: Mbxico Consejo Recursos total, is refunded to the Mexican-owned com- Nat. no Renovables Bol. 62, 62 p. GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES1 RONALD G. WORL U.S. Geological Survey Denver, Colorado

ABSTRACT The Western United States is one of the fluorine-rich provinces of the world, and it contains numerous districts and mines that have produced some fluorspar. However, few have had major or sustained fluorspar pro- duction. The Western States have accounted for approximately 20 percent of the total U.S. production of CaF2 to date. Fluorine in nature is dominantly in the combined form and tends to concentrate in specific geologic environments in the crustal rocks of the Western United States. Preferred igneous associations are silicic and alkalic extrusives and intrusives, complex pegmatites, carbonatites, and contact aureoles of these. Sedimentary rocks containing concentrations of fluorine are volcaniclastic, lacustrine, evaporite, marine carbonate, and marine phos- phorite beds. Major concentrations of fluorine in the West occur in hydro- thermal deposits distributed among a wide variety of geologic environments in the form of veins, mantos, pipelike bodies, stockworks, and disseminations. Two general groups of Tertiary late-magmatic and hydrothermal fluorite- bearing deposits are recognized in the Western United States: (1) those associated with intrusive igneous rocks and (2) those not associated with intrusive igneous rocks. Each group contains a wide variety of types of deposits ranging from metal deposits with minor fluorite gangue to fluorspar deposits with trace amounts of metals. Similarities in geology and geo- chemistry suggest that the two groups formed from the same kind of magmatic-hydrothermal system; the first group represents deposition at depth and the second group represents deposition at or near the surface. The first group includes fluorite within or directly associated with alkalic or silicic-alkalic intrusives. Fluorite in these deposits formed at temperatures ranging from 150°C to 500°C, and from solutions that were relatively saline (A 20 weight percent) and in part magmatic, in part pneumatolytic, and in ijart hydrothermal. Economically important fluorspar deposits of this type are pipelike bodies in large breccia zones and massive fine-grained bodies in tactites. The second group includes fluorite not associated with larger bodies of intrusive igneous rock. Although some of this fluorite is within or directly associated with minor hypabyssal bodies or with extrusive bodies of basalt or rhyolite, much has no apparent igneous connection. Fluorite in these deposits formed at temperatures under 200°C and from very dilute fluids. Economically important fluorspar deposits of this type include large veins and mantos in silicic igneous and metamorphic rocks and calcareous sedimentary rocks, and dispersed fluorite in highly silicified rocks. Fluorspar deposits with most promise for future exploitation are the Tertiary late-magmatic and hydrothermal deposits. Other types of fluorine concentrations that deserve consideration are complex pegmatites, car- bonatite complexes, marine phosphorites, and lacustrine and volcaniclastic sedimentary rocks. The possibilities are excellent in all these for developing large low-grade deposits with possible coproducts or byproducts.

1 Publication authorized by the Director, U.S. Geological Survey. 32 RONALD G. WORL

INTRODUCTION 1901 to 1914, hand-sorted crystals and pure screen- This report is a review and summary of the ings of fluorite from the Castle Dome lead dis- geology and geochemistry of fluorine in crustal trict, Yuma County, Ariz., were shipped to Cal- rocks of the Western United States. A compre- ifornia to be used as a flux in producing cement hensive report on the subject, with emphasis on clinker (Van Alstine and Moore, 1969, p. 349). the mineral fluorite and on resources of fluorspar, Several other districts reported fluorspar produc- is being prepared by the U.S. Geological Survey tion during this period but gave no indication of (D. R. Shawe, editor); descriptions, relative sizes, the destination or use of the ore. The first major locations, and references to each individual fluor- fluorspar production came during World War I spar deposit are presented by Worl, Van Alstine, when 42,000 tons of CaF2 were shipped in 1918 and Hey1 (1973). Production information can be (Fig. 5), mainly from Colorado with lesser amounts obtained from the U.S. Bureau of Mines annual from New Mexico, Utah, Arizona, Nevada, and yearbooks; MacMillan (1970) reported a current Washington. From the end of World War I until summary of domestic uses and the political dis- World War 11, fluorspar production in the West tribution of production and consumption of flu- was sporadic and minor, generally less than 10,000 orine.\ In the present report, fl~~orsparrefers to tons CaF2 annually. During World War I1 many mineral deposits in which fluorite is a major districts in Colorado, New Mexico, Utah, Nevada, component whether or not the deposit is now a Arizona, Idaho, Texas, California, and Wyoming commercial fluorine source, and fluorite occurrence produced fluorspar, and all known deposits were refers to mineral deposits in which fluorite is a explored and evaluated. Following the end of minor or trace component even though it may World War 11, fl~~orsparproduction in the West have possible byproduct potential. The CaF2 remained relatively high during the 1950's and content is the grade of fluorspar ore, and produc- increased to an alltime annual high of 182,000 tion and consumption figures are given in terms tons CaFz in 1958. This tonnage was about 55 of short tons of CaF2. percent of the U.S. total shipments that year (Fig. 5). However, this production dropped sharply the The Western United States is one of the fluorine- following year because several mines in the West rich provinces of the world as indicated by large ceased operations. During the 1960's fluorspar areas containing an abundance of fluorspar de- shipments from the West remained static at about posits and fluorine occurrences (Figs. 1, 2, and 3) 50,000 tons CaFz annually, mostly from three and the fact that these are also areas of fluorine- mines located in Colorado, Montana, and Nevada. rich igneous rocks (D. R. Shawe, personal With the recent renewd interest in fluorspar as commun., 1973). Many deposits in the West have a commodity and a concurrent price rise, ship- produced ore or are currently producing fluorspar ments from the West have more than doubled in (Fig. 4). However, very few have produced more the last few years and currently account for than a few hundred tons of CaFz, and the major roughly 30 percent of the U.S. total fluorspar producers each have total production figures of production. Still, the shipments from the West only around 750,000 tons CaFz. Production of account for only 6 percent of the total U.S. fluorspar in the Western United States to 1970 consumption. amounted to 2,674,600 tons CaF2, or about 20 percent of the total U.S. production to that date. Although crustal rocks in parts of the Western The major producing states have been Colorado, United States are fluorine rich, there are few large Montana, Nevada, New Mexico, and Utah. fluorspar districts located here and very few dis- Production of fluorspar before 1900 was for tricts with any sustained production. Fluorspar local consumption as a flux in smelters. Fl~lorspar production in the West is affected by price fluc- was reportedly taken, for use in local smelters, tuations, distance to markets, competition (both from the Jamestown and Evergreen districts, foreign and domestic), and, most importantly, the Colorado, as early as 1873 (Van Alstine, 1964, very nature of the type of fluorspar deposits p. 163) and from the Gila district, New Mexico, exploited to date. Most are hydrothermal deposits in 1880 (Williams, 1966, p. 3). During the period that form isolated pods and veins or high-grade GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES

I ~UTHDAKOTA!

I ------1 \ t- w- ( I L, I n 1 NEBRASKA \

\! to I KANSAS

I ( OKLAHOMA I k-, -L,p*/*

TEXAS Distribution- of f luorspar deposits in the western United States "\a 10\ ', -\ \ * '- Fluorspar deposit 0

Fluorite nrral rrnnr~ 0, 500 MILES Figure 1. Map showing Tertiary late-magmatic and hydrothermal fluorspar deposits and fluorite occurrences associated with intrusive rocks. pods and veins within larger but uneconomic hydrothermal fluorspar present, generally within fluorspar deposits. Although high in CaF2, most producing districts, has been unproductive of these deposits are small (a few thousand tons), because of low grade, beneficiating problems discontinuous and isolated, and, not uncommonly, mainly owing to the intimate intergrowth of conlpletely mined out within a short time. Other fluorite and silica, or the lack of recognition of 3 4 RONALD G. WORL

\ \ NORTH DAKOTA ------_--- \ I

KANSAS

TEXAS Distribution- of f luorspar deposits in the western United States

Fluorspar deposit 0- 500 MILES Figure 2. Map showing Tertiary hydrothermal fluorspar deposits not associated with intrusive igneous rocks. the presence of fluorite. The deposits exploited producers. Some of the recent exploration activity to date are best suited to relatively minor but in the West has been directed toward finding or steady mining operations such as the present outlining large-tonnage, low-grade deposits with operations at the Crowell mine, Fluorine district, possible coproducts or byproducts. Nevada, and the Burlington mine, Jamestown dis- In any discussion of fluorine in the Western trict, Colorado, both longtime and continuous United States, consideration must be given to GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 3 5

KANSAS

TEXAS Distribution- of f luorspar deposits in the western United States 0 Fluorite occurrence \ '\ I \ 0 500 MILES 111111 ' '--L Fig ure 3. Map showing Tertiary hydrothermal fluorite occurrences not associated with intrusive $-igneous rocks. the total distribution of fluorine, not just to the GEOLOGIC ENVIRONMENT OF FLUORINE commercially important late-magmatic and hydro- Geochemistry and Mineralogy thermal deposits. Although poorly documented and generally unexplored in the West, other types Fluorine is a volatile element, ,and large amounts of fluorine occurrences constitute commercial de- of gaseous fluorine are given off in some active posits elsewhere in the world and deserve con- volcanic areas. Most fluorine in nature, however, sideration here. is found combined in solid form, either in fluoride RONALD G. WORL

NORTH DAKOTA

------

WYOMING /------

NEBRASKA ------

KANSAS

-- -_

TEXAS Dist ri- but ion of f luorspar deposits in the western United States

Fluorspar mine or district with production

Better known mine or district

0 500 MILES I I I I 1 I

Figure 4. Fluorspar mines or districts with past or present production. 1, Crystal; 2, Meyers Cove; 3, Thomas Range; 4, Indian Peaks; 5, Northgate; 6, Jamestown; 7, Wagon Wheel Gap; 8, Browns Canyon; 9, Baxter mine; 10, Crowell mine; 11, Duncan area; '12, Zuni Mountains; 13, Sierra Caballo; 14, Tortugas; 15, Cooks Peak; 16, Fluorite Ridge; 17, Gila; 18, Burro Mountains; 19, Redrock area; 20, Eagle Mountains. GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 37

Figure 5. Graph showing fluorspar (CaF2) production in Western United States and total U. S. production: 191 0- 1970.

Distribution of Fluorine in Crustal Rocks minerals or as a substitute in silicate or phosphate- - The radius of the fluoride ion is very minerals. Although fluorine is widespread throughout close to that of the hydroxyl and oxygen ions, the lithosphere, it tends to be concentrated in allowing easy substitution of one for the other in fairly specific igneous, sedimentary, metamorphic, the si1icat.e ,and phosphate minerals. Fluorite (CaF2) is geologically the most abundant and and hydrothermal environments (Worl, Van Al- economically the most important fluorine mineral stine, and Shawe, 1973). For purposes of discus- in the Western United States: the other fluoride sion, the distribution of fluorine has been classed minerals are very rare. Topaz (A12Si04(F,OH)2) into fluorine associated with igneous rocks, sed- is common, but not yet a commercial source of imentary rocks, metamorphic rocks, and fluorine fluorine. Carbonate fluor apatite (Ca5(P04,C03)RF), in hydrothermal ( hot water ) deposits. The classes the ore mineral of phosphate rock, is widespread overlap and intergrade somewhat but still ~rovide in the Western United States, and is a potential a convenient basis for further discussions. source of fluorine as a byproduct of the processing In igneous activity fluorine is considered as a of phosphate rock. characteristic component of the volatile phase of 38 RONALD G. WORL magmatic differentiation. More specifically, flu- 39). Fluorite-bearing veins at Trout Creek, Utah, orine is concentrated in salkalic and silicic plutonic, composed primarily of carbonate, quartz, mica, hypabyssal, and extrusive rocks and related hydro- and sulfides, .are pegmatitic. The Snowbird fluor- thermal deposits, in complex pegmatites, in car- spar deposit, Montana, contains abundant quartz bonatites, and in alteration zones, including and carbonate and minor parisite (rare-earth flu- greisens, associated with alkalic, silicic, and car- orocarbonate), and is thought to be a carbonatite bonatite intrusive rocks. pegmatite (Clabaugh and Sewell, 1964, p. 268). Precambrian plutonic rocks throughout Colora- Quartz and the carbonate mineral crystallized do contain minor fluorite. The Pikes Peak Granite, from a carbonatit'e magma and the fluorite and a massive rock composed of microcline perthite, other minerals from a late hydrous solution. The quartz, and sodic plagioclase, has accessory flu- large and very rich fluorspar deposits at Crystal orite in amounts generally less than 1 percent. Mountain, Mont., seem to be complex pegmatites. Similar rocks in northern Colorado locally contain The Crystal Mountain deposits are tabular bodies as much as 2 percent disseminated fluorite. Three of fluorite in coarse-grained biotite granite and general types of fluorite are noted: anhedral consist mainly of dark-purple fluorite, but also grains interstitial to or including mafic and felsic contain biotite, sphene, quartz, oligoclase, rare- minerals; crosscutting veinlets with microcline, earth-bearing apatite, green amphibole, grains of sphene, and epidote; and within sericitized feld- metamict fergusonite, and the rare scandium min- spar with calcite (G. L. Snyder, personal commun., eral thortveitite (Parker and Havens, 1963). 1973). Carbonatite complexes are notably enriched in Fluorite, other fluorides, and fluorine-bearing fluorine which, however, is mostly dispersed minerals such as tourmaline, topaz, and the micas through the rock in silicates, apatite, and rare- are common minerals in pegmatites. Fluorite in earth carbonates. Fluorite generally seems to be pegmatites is generally considered a late-stage or a late-stage mineral either in the carbonatite, its hydrothermal-stage mineral. The better known contact aureole, or in related hydrothermal veins. fluorine-bearing pegmatites in the West are Pre- Carbonatites of the Bearpaw Mountains, Mont., cambrian pegmatites located in Colorado and New contain about 0.5 percent fluorine in apatite and Mexico. The Yard pagmatite, Fremont County, rare-earth carbonates, fluorite being rare (Pecora, Colo., is typical of many of the Colorado pegma- 1962). The Precambrian rare-earth carbonatite at tites in that it has a central core composed of pods Mountain Pass, Calif., contains about 1 percent of milky quartz and crystalline microcline and a fluorine, mostly in the form of bastnaesite, but wall zone of graphic granite, quartz, microcline, fluorite forms rare massive pods within small and minor magnetite (Heinrich, 1948, p. 65). carbonatite veins (Olson and others, 1954). Flu- Buff-colored fluorite, along with rare-earth min- orite is also present in related granites and erals and muscovite, occurs as replacement pods shonkinitic dikes as a late-magmatic mineral or a along the margin of the core, and purple fluorite, postmagmatic alteration mineral. The Goldie car- quartz, chlorite, and hematite veinlets cut altered bonatite, Colorado, is mainly limonite-stained cal- rocks of the wall zone. Fluorite is present in 91 cite with local masses of barite (Heinrich and percent of the pegmatites of the Petaca district, Dahlem, 1966). Within the carbonatite are re- New Mexico, as pale-green rounded masses in the placement nodules of deep-purple fluorite and wall zone and as deep-purple pods and veinlets some alumino fluoride minerals, mainly cryolite. throughout (Jahns, 1946, p. 62). The fluorine minerals are late magmatic or post- Some fluorite-bearing veinlike deposits, general- magmatic. Fluorite is also a minor constituent ly of unknown age, probably represent complex in one of four types of related carbonatite dikes pegmatites or hydrothermal deposits derived di- found in the area (Parker and Sharp, 1970). rectly from pegmatites. The scheelite, alkali feld- Fluorite, topaz, and apatite are common min- spar, beryl, mica, and fluorite deposits at Oreana, erals in contact aureoles around many intrusive Nev., are generally pegmatitic but grade into bodies, mainly silicic ,and alkalic rocks and car- fluorite-rich and quartz-rich veins (Kerr, 1946, p. b0natit.e con~plexes. The fluorine minerals occur GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 3 9 in tactite and also in post-tactite hydrothermal clay minerals (Noble and others, 1967). The high- veins and replacement bodies. Fluorite is a fluorine glass-rich volcanic rocks are restricted in common constituent of alkalic and silicic-alkalic geographic distribution and are predominantly in intrusive bodies in the West and occurs in con- a belt in central Colorado and west-central New centrated amounts, in some places economic, in Mexico, in the Big Bend region of Texas, and in their contact aureoles. The modes of occurrence southeastern Idaho, western Utah, and north- are as disseminations within the intrusive rock; eastern Nevada (Coats and others, 1963, p. 941). veins, stockworks, and mineralized breccias within Some fluorine occurrences in sedimentary rocks and surrounding the intrusive body; massive re- appear to be genetically related to the enclosing placement of wall rocks (metasomatic); and dis- sediments, but many may be of hydrothermal or seminations, pods, and stringers in tactites and metasomatic origin. Fluorine minerals occur in silicified wall rock. volcaniclastic sedimentary rocks, lacustrine de- High fluorine content is a characteristic of most posits, and marine carbonate and marine phos- greisens. Quartz-topaz greisens in the central phate rocks. In general, economic concentrations York Mountains, Alaska, are in or near altered of fluorine minerals do not occur in detrital ac- biotite granite, and are spatially and genetically cumulations. related to beryllium-rich fluorite tactite deposits Although volcanic ash commonly contains flu- of the Lost River area, Alaska (Sainsbury, 1968). orine in glass shards and adsorbed on tephra, Greisenization consisted of the destruction of feld- commercial or potential deposits of fluorine in spar in the granite and the formation of topaz, volcaniclastic sedimentary rocks appear to be fluorite, and fluorine-bearing micas along with either interbedded deposits of lacustrine origin or tin, tungsten, and beryllium minerals. Chemical disseminated deposits of probable hydrothermal changes were the loss of K20, NazO, and SiOn origin (for example, Spor Mountain, Utah, de- and the addition of fluorine, A1203, total iron, and scribed later in this report). Fluorite-bearing sulfur along with tin, tungsten, and beryllium. lacustrine deposits near Rome, Oreg., are inter- Some of the greisens, as well as unrnineralized bedded with volcaniclastic sediments. Here flu- granite, were later subjected to argillization and orite occurs as submicroscopic, nearly spherical sericitization, and in extreme cases were converted grains in tuff, tuffaceous mudstone, and mudstone to masses of kaolinite with minor fluorite and of Tertiary lacustrine deposits (Sheppard and residual ore minerals (Sainsbury, 1968, p. 1564). Gude, 1969). Fluorite is nonuniformly distributed Beryllium mineralization near Lake George, Colo., through about 60 feet of section, but occurs in occurred in pipelike and irregular masses of abundance (as much as 16 percent) in one con- greisen within and $along the contact of Precarn- spicuous zeolitic tuff. The rocks do not appear to brian plutonic rocks ( Hawley, '1969). The greisens have been hydrothermally altered. Zeolites, clay are composed mainly of quartz, muscovite, flu- minerals, quartz, potassium feldspar, #and calcite orite, and topaz, with minor pyrite, sphalerite, making up the tuffaceous parts of the fluorine- molybdenite, wolframite, galena, chalcopyrite, bearing rocks seem to be the result of reaction bertrandite, arsenopyrite, and sooty pitchblende. between silicic shards and crystal fragments and saline and alkaline pore water during diagenesis. Fluorite and topaz occur in some silicic volcanic Most constituents of the mudstone are detrital. rocks of the Western United States, where they The depositional environment for these rocks are dispersed through the rock and within vugs must have been saline and alkaline, and also at in the rock (Shawe, 1966, p. C-209). Glass-rich some time enriched in fluorine, such as waters of volcanic rocks of silicic composition in the West some piesent-day lakes in the rift valleys of Africa contain 20 to 4,900 ppm fluorine (Coats and (Sheppard and Gude, 1969, p. D72). The fluorine others, 1963). These values may give a rough may have been deposited originally as villiaumite indication of the fluorine content of the original (NaF), an evaporite mineral which was later magma. It must be noted, however, that some changed to fluorite by calcium-bearing water that fluorine is possibly lost during hydration, and infiltrated the lacustrine rocks after deposition. much is lost upon devitrification and ,alteration to In any case, the fluorite was authigenic. 40 RONALD G. WORL

Marine carbonates and evaporites in the investigation as an ore of rutile, especially since U.S.S.R. contain as much as 30 percent fluorite as it might also yield topaz or topaz and sillimanite fine disseminations and crystal aggregates. Ac- as byproducts (Sheridan and others, 1968). cording to experimental data (Kazakov and Fluorite-bearing hydrothermal deposits are Sokolova, 1950), the fluorite probably formed as a abundant in the Western United States (Figs. 1, precipitate from sea water that had been con- 2, and 3) and represent much of the past and centrated three or four times. Similar deposits in future fluorspar resources. Fluorite is generally the Western United States may be present in the the only fluorine mineral present and its abun- Bighorn Mountains, Wyo., where dolomitic lime- dance ranges from nearly 100 percent down to stone containing 12 to 15 percent fluorite has trace amounts. Hydrothermal fluorite occurs in been recorded (Gulbrandsen and Reeser, 1969, p. many types of host rock, but is especially comn~on C55). Fluorite in the Pennsylvanian and Permian in sedimentary carbonate, silicic igneous, and Minnelusa Formation near Custer, S. Dak., occurs silicic metamorphic rocks. Form is the standard as minute crystals in vugs, and as masses within basis of classification and in general hydrothermal gypsum patches in dolomite (Roberts and Rapp, fluorspar deposits can be grouped into veins, 1965, p. 87). In the same area the Permian Minne- mantos, pipelike bodies and stockworks, and dis- kahta Limestone, a thinly laminated pink to red seminated deposits. Most commercial fluorspar anhydritic limestone, contains purple fluorite as deposits in the West have been hydrothermal subhedral grains, 0.1 to 0.25 mm in diameter, veins, many with associated mantos, pipelike along certain laminae. The fluorite grains are bodies, and stockworks. Disseminations of fluorite surrounded by fine-grained calcite or are within are common in hot springs deposits and in large gypsum crystals. masses of hydrothermally altered rock. The ore mineral of sedimentary phosphate rock GEOLOGY AND GEOCHEMISTRY OF TERTIARY is carbonate-fluorapatite with ratio of F to PzOa LATE-MAGMATIC AND HYDROTHERMAL FLUORITE about 1 to 10. Phosphate rock contains as much as 4 percent F and 40 percent Pz05, although Most known fluorspar deposits and fluorite oc- lower grade deposits are now mined for their currences in the West are late-magmatic and phosphate content. Fluorite is comnlon in minor hydrothermal deposits of Tertiary age; exceptions amounts in these deposits and occurs within and are fluorite in pegmatites, carbonatites, sedimen- among the carbonate-fluorapatite pellets. Other tary rocks, and Precambrian batholithic rocks. minor components present are zircon, tourmaline, This section deals exclusively with the Tertiary rare metals, and the rare earths. Fluorite in the late-magmatic and hydrothermal fluorite occur- phosphorites is secondary and apparently the rences and fluorspar deposits. The others are dis- product of a diagenetic reorganization of car- cussed in the section on geologic qnvironment of bonate-fluorapatite ( Gulbrandsen and Reeser, fluorine. Tertiary fluorite in the West occurs in 1969). deposits of many forms, including veins, pods, Topaz and tourmaline are common in metamor- mantos, pipelike bodies, stockworks, dissemina- tions, and irregular fine-grained replacement phic rocks, and in places where abundant they (metasomatic) bodies, and it formed in a great may represent future sources of fluorine. For diversity of environments by deposition from a example, a Precambrian topaz-quartz-sillimanite variety of solutions. gneiss in the central part of the Front Range, The amount of fluorite present ranges from Colo., contains major amounts of topaz (Sheridan nearly 100 percent down to trace amounts. A and others, 1968). This unit, part of a high-grade very basic, but debatable, assumption is made in metamorphic gneiss and granitic plutonic com- this report that the major difference between the plex, is 11 to 100 feet thick and crops out along Tertiary group classed as fluorite occurrences and strike for 7,000 feet. Three composite chip that classed as fluorspar deposits is the relative samples of this unit were found to contain 67, 23, abundance of the constituents. The two are very and 3.6 weight percent topaz and 4.2, 3.9, and similar in distribution (Figs. 1, 2, and 3), age, 2.2 weight percent n~tile.The gneiss may warrant mineralogy, geochemistry, alteration types, igne- GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 4 1 ous associations, and geologic settings. In detail, those deposits not associated with intrusive rocks however, many subtle differences between fluor- represent deposition from this system at or near spar deposits and fluorite occurrences probably the surface. exist which, when defined, may be important Fluorite Associated with Intrusive Igneous Rocks exploration and evaluation guides. For the purpose of discussion, Tertiary fluorspar Examples of fluorspar deposits and fluorite oc- deposits and fluorite occurrences have been sub- currences of this type occur throughout the flu- divided into two general types: those deposits orine-rich areas of the West (Fig. 1) but are not within or associated with intrusive igneous rocks nearly as common as those deposits not associated with igneous intrusive rocks (Figs. 2 and 3). Flu- and those deposits not associated with intrusive orite related to intrusive rocks (not including igneous rocks (hot-spring, epithermal, and vol- hypabyssal dikes and sills) occurs within the in- canic types). In this evaluation small hypabyssal trusive, its contact aureole, or in close proximity igneous bodies such as dikes and sills are not con- to the intrusive, and is genetically related to at sidered as associated intrusive rocks because, least part of the intrusive complex. The modes of although genetically related, they do not represent occurrence are as disseminations in the intrusive the source of the ore-forming solution. This is an rock; veins, stockworks of veinlets, and mineral- arbitrary breakdown but serves the purpose well ized breccia zones within and surrounding the to illustrate the general range of conditions under intrusive; pods and stringers in skarns and tactites; which fluorite formed. A complete gradation and irregularly shaped fine-grained replacement exists between the two types, and some deposits bodies (metasomatic). and districts exhibit characteristics of. both. Alkalic rocks in many small Tertiary intrusive The geologic and geochemical characteristics of bodies contain fluorite as an ,accessory mineral. each type are summarized in Table 1. Note the A small stock of silicic-alkalic composition asso- similarities in geochemistry, mineralogy, altera- ciated with fluorspar deposits of the Jamestown tion types, and igneous associations. Differences district, Colorado, contains as much as 4 percent in mineralogy, texture, and nature of the ore-form- fluorite as interstitial grains and in veinlets with ing solutions reflect differences in environment of chalcedonic quartz, molybdenite, and potassium deposition. Differences in age reflect the depth feldspar. In the Little Rocky Mountains, Mont., of exposure; the older deposits expose a relatively fluorite is sparsely disseminated throughout a deeper environment of deposition. Although porphyritic syenite and makes up 2 to 3 percent diverse in some aspects, the many aspects in of the rock; it also occurs with quartz and tellu- common among all Tertiary fluorite-bearing de- rides in highly mineralized breccias within the posits suggest that they all formed from a similar syenite (Sahinen, 1962, p. 34). Fluorite occurs as magmatic-hydrothermal system, each individual disseminated grains and as replacements of pre- deposit representing one segment of that system viously altered plagioclase along minute fractures (Worl, 1971). This does not imply a single source in an intrusive leucorhyolite in the South Moccasin for the water or for many of the other constituents, Mountains, Mont. ( Sahinen, 1962, p. 32). Fluorite as it is apparent that fluorite and related minerals is also a constituent of hydrothermal deposits and were deposited from waters that were dominantly alteration zones in sedimentary rocks surrounding either magmatic, connate, or meteoric. It does the intrusive. Fluorite in the three intrusives dis- imply, however, that most of the fluorine present cussed here, as in most studied, seems to be a late- in these deposits had an ultimate deep-seated magmatic or post-magmatic alteration mineral. source. In general all Tertiary fluorite-bearing Fluorite in the Gallinas Mountains, N. Mex., hydrothermal deposits formed from similar mag- occurs in irregular breccia zones, pipelike breccia matic-hydrothermal systems characterized by a bodies, and fissure veins in quartzitic sandstone restricted group of associated elements, alteration next to alkalic intrusives. The breccia zones types, and related igneous activity (see Table 1). range in width from a few inches to as much as The deposits associated with intrusive rocks rep- 30 feet and in length from a few feet to many resent deposition from this system at depth, and tens of feet (as much as 600 feet in one place) 42 RONALD G. WORL

Table 1.-CHARACTERISTICSOF FLUORITEASSOCIATED WITH INTRUSIVEIGNEOUS ROCKS COMPARED WITH THOSEOF FLUORITENOT ASSOCLATEDWITH IGNEOUSROCKS

CHARACTERISTICS FLUORITE ASSOCIATED WITH FLUORITE NOT ASSOCIATED WITH INTRUSIVE IGNEOUS ROCKS INTRUSIVE IGNEOUS ROCKS TYPES OF Tactites Stockworks Veins Pipelike bodies DEPOSITS Breccia pipes Disseminated Mantos Disseminated Calcite Potassium-bearing Calcite Iron oxides Barite minerals common Barite Celestite MINERALOGY Quartz in both altered Chalcedony Potassium feldspar Rhodochrosite and mineralized Manganese oxides rock Crystalline aggregates Banded Breccias, water Breccias Crustified courses, and vugs TEXTURE Corroded crystals Reniform common common Mammillary Coarsely crystalline, commonly containing Columnar, rarely containing trace metals trace metals Fine mixture of fluorite, Fine-grained massive FLUORITE Porcelaneous chalcedonic quartz, pyrite, Earthy jarosite, biotite, sericite, or feldspar. Contains trace metals Silicic Argillic Silicic, very common1 ALTERATION Feldspathic Feldspathic, argillic, sericitic, minor Deposition consisted of a few Deposition consisted of many monomineralogic PARAGENESIS polyrnineralogic stages stages, and a few polymineralogic stages (earthy and porcelaneous fluorspar) ASSOCIATED Ag, Au, Ba, Be, Fe, Mn, Mo, Pb, Sn, Te, Ag, Au, Ba, Be, Fe, Li, Mn, Mo, Pb, Sr, Sn, METALS U, W, and Zn Te, U, V, and Zn Alkalic (K-rich) and silicic-alkalic Mainly no igneous association; a few with IGNEOUS intrusive complexes hypabyssal bodies and flows of bassalt and ASSOCIATION rhyolite 30 to 20 m.y. before present; some older Post-20 m.y. and pre-6 m.y. before present AGE in California, Nevada, and Utah TEMPERATURE 150°C to 500(?)OC (maximum) 7S0C(?) to 250°C OF FORMATION NATURE OF Ascending, variable, and complex; Ascending and convective; generally dilute ORE-FORMI NG generally saline SOLUTION STRUCTURAL Major tensional faults, Rio Grande rift system, CONTROL Basin and Range faults

(Perhac, 1970, p. 41). The extensive fluorspar breccia zones. The average grade of ore produced deposits at Jamestown, Colo., are in breccia veins from the breccia deposits at Jamestown is about and breccia zones that radiate from a small silicic- 50 percent CaFz, although many high-grade alkalic intrusive body. The larger and higher pockets containing 75 to 95 percent CaFz have grade fluorspar deposits are lenticular pipelike been mined. The silica content is high, 10 to 40 bodies, 10 to 100 feet wide, as much as 500 feet percent, but is easily removed because the fluorite long, and at least 1,400 feet deep, within the major is not intimately intergrown with the silica (God- GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 43 dard, 1946, p. 20). Most of the silica is present lead and zinc sulfide-rich contact-metamorphic in the form of feldspar and quartz in wall-rock deposits of the Alta district, Idaho (Umpleby and fragmen,ts. Some .of the flourspar deposits in the others, 1930); and fluorite in contact aureole Star Range, Utah, are in a large-scale stockwork quartz veins of the Blue Wing district, Idaho, within and surrounding a silicic intrusive. with orthoclase, rhodochrosite, huebnerite, pyrite, Abundant fluorite is present in an iron-rich molybdenite, and tetrahedrite (Anderson and Van tactite formed by replacement of Paleozoic lime- Alstine, 1964). stone at the contacts with small intrusive bodies Fluorite associated with intrusive igneous rocks of granite, rhyolite, and aplite at Iron Mountain, is generally either in coarsely crystalline aggre- N. Mex. The tactite is mainly coarsely crystalline gates with other minerals or in very fine-grained magnetite, andradite garnet, hedenbergite, and massive material which is a replacement of cal- hematite. Fluorite, apatite, scheelite, and sulfides careous sedimentary rocks (metasomatic). Cor- are later than the major rock-forming minerals. roded crystals and replacement textures are Most of the fluorite is crystalline and is inter- common. Sugary-textured fluorspar (sugar spar) at layered with magnetite, specular hematite and Jamestown, Colo., Gallinas Mountains, N. Mex., silicates in masses of "ribbon rock" in the form of Judith Mountains, Mont., and elsewhere is com- thick pods, pipelike bodies, and thin tabular bodies posed of highly corroded and rounded grains of in earlier formed tactite (Jahns, 1944, p. 55). fluorite set in a matrix of clay minerals, sericite, Flborite is sufficiently abundant here to warrant and fluorite. Very fine-grained intimate inter- investigations as a resource. At the Tootsie Creek growths of fluorite land other constituents, mainly deposits, Sweetgrass Hill, Mont., fluorspar is silica, are confined to the fine-grained massive re- present as irregular pods and fine-grained replace- placement (metasomatic) deposits. ment seams in or adjacent to marbleized Madison Hydrothermal alteration consisted of several Limestone in the contact zone of an intrusive types characterized by the development of mus- alkalic syenite (Ross, 1950). The Tootsie Creek covite, sericite, potassium feldspar, biotite, albite, fluorspar bodies are generally small, the largest pyrite, fluorite, clay minerals, and fine-grained being 10 feet wide land 50 feet long, but are silica. Hydrothermal alteration was in addition to, scattered throughout an area 2,000 feet long and and commonly imposed upon, contact metamor- several hundred feet wide. The average grade of phism that had already taken place. Alteration typical better ore is about 50 percent CaFz and 30 around fluorite occurrences of this type has been percent silica (Ross, 1950, p. 196). Removal of the well studied in some districts 'such as Climax, silica from this ore w~uldrequire very fine grind- Colo. (Wallaqe and others, 1968), Questa, N. Mex. ing because much of it is intimately intergrown (Carpenter, 1968), and Bishop, Calif. (Gray and with the fluorite. others, 1968). However, the alteration effects Fluorite occurrences associated with intrusive around fluorspar deposits of this type have not igneous rocks include the fluorite in stockworks been studied in detail. In general it seems that and malteration zones associated with molybdenum clay minerals, biotite, sericite, and secondary feld- spars are the common alteration products within deposits at Climax, Colo. (Wallace and others, and around the larger coarse-grained bodies of 1968) and Questa, N. Mex. (Carpenter, 1968); fluorspar, while silicification and pyritization were fluorite in tungsten skarns at Piute, Nev. e em more prevalent within the intrusive rock and along (Buseck, 1967) and the Bishop district, California smaller veins and stockworks away from the larger (Gray and others, 1968); fluorite with gold tellu- bodies. Silicification seems to have been common rides as a stockwork of veinlets in the Little Rocky in many fine-grained replacement (metasomatic) Mountains, Mont. (Sahinen, 1962); fluorite in fluorspar bodies as it was in the deposits in tungsten- and beryllium-bearing pyrometasomatic Brewster County, Tex. (McAnulty, 1967). skarn deposits in the Victorio dtstrict, New Mexico Common associated minerals in the fluorspar (Warner and others, 1959, p. 122); fluorite in iron- deposits are calcite, quartz, barite, rhodochrosite, rich contact-metamorphic deposits of the Alder biotite, potassium feldspar, molybdenite, galena, Creek district, Idaho (Umpleby, 1917); fluorite in sphalerite, and pyrite. Associated elements com- 44 RONALD G. WORL mon in both fluorspar deposits and fluorite occur- and away from the main molybdenum mineral- rences include silver, gold, barium, beryllium, ization or is a later stage of the same episode of iron, manganese, molybdenum, lead, the rare mineralization. However, enough fluorite was earths, tin, tellurium, uranium, tungsten, and zinc. deposited with the molybdenum mineralization in The extent and reliability of the relationship some areas to warrant investigation as a possible between fluorite and some of these elements is so byproduct. Fluorspar deposits in the Gallinas well established that fluorite is ofen used as an Mountains, N. Mex., contain bastnaesite (rare- exploration guide for those elements. The genetic earth fluorcarbonate) in nearly commercial quan- relationship of fluorite to some of the other tities. These same deposits have been worked in elements is sporadic and questionable. Most gold the past for lead-silver, gold, and copper; this telluride deposits and many, but not all, gold- example is a rare instance of copper mineralization quartz deposits contain abundant fluorite gangue. associated with fluorite. Fluorspar deposits at Many, but not all, tungsten-rich tactites and skarns Jamestown, Colo., have been worked for lead- contain generally minor amounts of fluorite as do silver and gold. A late-stage solution in the many iron-rich tactites. Most uranium mineral fluorite mineralization at Jamestown also intro- deposits in the intrusive environment have minor duced anomalous amounts of beryllium, lantha- fluorite gangue as do similar deposits containing num, molybdenum, vanadium, uranium, scandium, the rare earths, tin, and beryllium. Many, but not and the rare earths. In deposits of this type, many all, lead-silver deposits in the intrusive environ- of the metals are restricted in their mineralogy; ment contain fluorite. Almost all molybdenum sulfides are dominant, gold is commonly in tellu- deposits of this type, both stockwork and contact rides, iron in pyrite or magnetite, manganese in metamorphic, contain abundant fluorite gangue. carbonates or silicates, and uranium in pitch- These same deposits may have anomalous con- blende. centrations of manganese and barium. Fluorspar Lindgren (1933, p. 153) noted the frequent as- deposits contain many of the elements listed, sociation of fluorite with intrusive rocks of alkalic locally in possible economic proportions, but com- type, but offered no explanation of the significance monly in trace amounts only. of the numerous alkalic intrusive centers that do All fluorite analyzed from the Western States not have related fluorite. Indeed, most of the contained trace amounts of barium, manganese, intrusive bodies directly related to fluorspar de- strontium, and yttrium. Gold telluride deposits posits-the Sweetgrass Hills and Judith Mountains, in the Sweetgrass Hills, South Moccasin Moun- Mont. (Sahinen, 1962, p. 26); Bear Lodge Moun- tains, and Judith Mountains, Mont, have abun- tains, Wyo., Jamestown district, Colorado (God- dant purple fluorite gangue, and the nearby and dard, 1946); Gallinas ~ountiins,N. Mex. (Perhac, genetically related fluorspar deposits carry trace 1970); and Eagle Mountains (Gillerman, 1953) amounts of gold ( Sahinen, 1962, p. 26). Fluorspar and Christmas Mountains ( McAnulty, 1967), Tex. deposits in the Chinati Mountains, Tex., are -are allcalic at least in part. These intrusives, plus fluorite-lead-zinc-silver-gold veins in jointed or many others related to fluorite occurrences, have one aspect in common: the crystallization stage sheeted zones within, and presumably related to, genetically related to the fluorite mineralization a laccolithic intrusive ( McAnulty, 1972a). Con- and alteration was late in the magmatic sequence. tact-metamorphic lead-zinc deposits in the Star This stage was generally alkalic in nature and in Range, Utah, contain abundant fluorite gangue, some cases was superimposed upon silicic and and related fluorspar deposits lare locally rich in silicic-alkalic rocks of earlier stages. It is difficult sulfides (Thurston and others, 1954, p. 19). to distinguish between products of late-magmatic Possible commercial amounts of fluorite occur in alkalic activity and post-magmatic hydrothermal iron-rich tactites at Iron Mountain, N. Mex., the activity, but much of the fluorite seems to be post Alder Creek district, Idaho, and in the Blawn magmatic and hydrothermal. Still, the amount of Mountain area, Utah (Whelan, 1965). Fluorite in fluorite in the deposit does have a direct relation- molybdenum porphyries or stockworks is generally ship to the presence and amount of late-magmatic related to an alteration phase that formed above alkalic activity. GEOLOGY OF FLUORSPAR DEPOSITS (3F THE WESTERN UNITED STATES 45

Many of the intrusive bodies with related town, Colo., was deposited during two of the three fluorite occurrences have been radiometrically major depositional stages (J. T. Nash and C. G. dated. The intrusives at Climax, Colo. (Wallace Cunningham, oral commun., 1972). The first stage and others, 1968); Questa, N. Mex. (Carpenter, deposited quartz and sulfide minerals from a hot 1968); Magdalena, N. Mex. (Kottlowski and and relatively saline (26 weight percent) fluid. others, 1968); Organ Mountains, N. Mex. (Kottlow- The second stage was major fluorite deposition ski and others, 1969); and Gallinas Mountains, N. from a complex and variable solution. Temper- Mex. (Perhac, 1970) have radiometric dates theat atures ranged from 275" to 375OC; salinities fall between 30 and 22 million years before the generally ranged from 26 to 32 weight percent present. Unpublished dates from a few alkalic although in a few places they were as high as 40 weight percent, and the CO2 content ranged intrusives related to fluorspar deposits indicate from very high to low. The final stage was a that they also fall into this general range of ages. relatively cool (about 250°C) and dilute (less Some intrusive igneous rocks and related fluorite than 26 weight percent) fluid which corroded the occurrences in California, Nevada, and Utah are existing fluorite, deposited clay minerals, sericite, probably older, but are generally of unknown age. biotite, sulfides, and fluorite, and introduced The ore-forming solutions were generally com- anomalous amounts of gold, beryllium, lanthanum, plex and variable, in some stages or places dense molybdenum, scandium, vanadium, uranium, cesi- and hot and in other stages or places dilute and um, and neodymium. cool; the solutions were in part magmatic, in part pneumatolytic, and in part hydrothermal. The Fluorite Not Associated With Intrusive Igneous Rocks paragenetic sequence of several deposits suggests relatively few stages of deposition, with eakh stage Fluorite not associated with intrusive igneous depositing several minerals nearly simultaneously. rocks is the most abundant and commercially most In the Bishop tungsten district, California, the important type of fluorite in the West. Fluorspar earlier ore-forming solutions were pneumatolytic deposits of this type have commonly been termed and formed calc-silicates, fluorite, scheelite, and hot-springs type, epithermal, or banded. Some quartz, whereas later solutions were hydrothermal fluorite of this type is within or related to minor and deposited base-metal sulfides, pyrrhotite, hypabyssal dikes and sills or extrusive igneous sericite, biotite, quartz, pyrite, molybdenite, and rocks, but much is isolated from any associated fluorite (Gray band others, 1968). Fluorspar de- igneous rocks. The modes of occurrence are veins, posits in the Gallinas Mountains, N. Mex., were mantos, irregular breccia deposits, pipelike bodies, deposited in two hydrothermal stages; fluorite is disseminations, and coatings in recent hot-springs not present in earlier iron-rich contact-metaso- deposits, and as disseminations through altered matic deposits. The first hydrothermal stage de- rock. posited quartz, barite, sulfide minerals, fluorite, Veins 'are the most common. Fluorspar deposits bastnaesite, and minor calcite; the second stage, in the Northgate district, Colorado, consist of two following local fracturing, deposited barite, flu- large parallel veins in Precambrian rocks about 2 orite, local calcite, and minor chalcedony. Studies miles apart. One vein system is mineralized for ) of the fluid inclusions in bastnaesite indicate de- a length of about 1mile, and the other for a length positional temperatures of 175" to 185OC ( Perhac, of over 2 miles, although sparsely in places. Flu- 1970, p. 46). At Tem Piute, Nev., fluorite, along orite occurs throughout a known vertical range with base-metal sulfides and quartz, occurs in the of more than 1,000 feet. Fluorspar-bearing brec- outer part of a garnet-pyroxene skarn, whereas ciated fault zones as much as 70 feet wide are minerals in the inner zone consist of p~rrhotite, common, as are fluorspar ore-grade zones 20 feet magnetite, and molybdenite. Scheelite and pyrite wide. The CaF2 content of zones 8 to 11 feet occur throughout. Rough estimations of the wide ranged from 10 to 90 percent and averaged temperature of deposition are as much as 500°C 40 to 50 percent (Steven, 1960, p. 399). Fluorspar for the inner zone and about 200°C for the outer deposits at the Baxter mine, Broken Hills district, zone (Buseck, 1967, p. 347). Fluorite at James- Nevada, occur along a single but bifurcating fault 46 RONALD G. WORL zone in altered Tertiary volcanic rocks. Fluorspar tens of feet in length, occur in diffuse breccia did not extend far below the 700-foot level of the zones in volcanic rocks (Williams, 1966, p. 34). mine, and along much of the vein system it did Manto deposits are not as common in the not extend below the 400-foot level; the ore zones Western United States as they are farther south narrowed with depth. Before 1951, production in Mexico. The known mantos are generally small averaged 85 percent CaF2 and after 1951 it aver- or of low grade and have not been major pro- aged 46 percent CaF2. This deposit was reported ducers. Deposits in the Quinn Canyon Range, as exhausted in 1957 (Matson and Trengove, Nev., occur in a variety of forms. In limestone 1957). Within the Zuni Mountains, N. Mex., an country rock the deposits occur as small replace- elongate dome of Precambrian rocks, there is a ment bodies that extend from rhyolite dikes and mineralized zone 20 miles long and 3 miles wide as large irregular replacement bodies and breccia that contains hundreds of steeply dipping fluor- fillings that extend from fault zones and rhyolite spar veins ranging in length from a few feet to dikes. The CaFz content ranges from 16 to more almost a mile and in width from a few inches to than 90 percent, but the silica content is as much 15 feet. The ore bodies mined to date have been as 74 percent in some zones and averages high 15 inches to 6 feet wide in most places, but locally throughout (Sainsbury and Kleinhampl, 1969, p. they have been as much as 15 feet. The two C7). Fluorspar, barite, and lead deposits in the major producing mines have been explored to Hansonburg district, New Mexico, occur along depths of 700 and 380 feet. These veins contain northward-trending faults in the form of lenticular as much as 95 percent CaF2, but the ore shipped and blanketlike replacement bodies. The indi- from the mines has ranged from 17 to 86 percent vidual deposits extend from the faults for distances CaFz. A mill head of 40 percent CaFz was main- of generally less than 50 feet, but extend along the tained (Goddard, 1966). The Browns Canyon faults as much as 300 feet (Roedder and others, district, Colorado, contains several veins, one that 1968, p. 336). At Bishop Cap Hills, N. Mex., has been mined for 1,600 feet in length. The veins much of the fluorite, barite, calcite, and minor at Browns Canyon range in size from lenses tens sulfide mineralization formed pods, stringers, of feet long and inches thick to sheeted zones veins, and cavity fillings in silicified fault and 1,000 feet long and 25 feet thick. The average breccia zones in fractured limestone. Mineraliza- mining thickness was less than 10 feet. Mined tion was not confined to fractured rock, however, bodies ranged in grade from less than 25 percent as some limestone units were extensively silicified CaF2 to as much as 75 percent, with some large and mineralized with fluorite, barite, pyrite, areas containing 50 to 55 percent (Van Alstine, siderite, and calcite for some distance away from

1969.' ID. 37). faults. Some zones are radioactive and others contain as much as 150 ppm silver. These min- Many fluorspar districts have numerous veins of insufficient size to warrant exploitation. The eralized zones seldom exceed a few feet in thick- ness and the CaFz content is generally low White Signal and Gold Hill districts and the (Kramer, 1970). At the Wells Cargo deposit, Soldiers Farewell Mountain area, western Grant Lincoln County, Nev. (Horton, 1961, p. 13), most County, N. Mex., contain numerous small high- fluorite is in veins land stringers along fault zones, grade fluorspar veins along major graben faults, but some occurs as massive crystalline pods ex- but none is of sufficient size to warrant extensive tending outward from the veins into the limestone development. Most are no more than 100 feet in country rock; in a few places fine-grained gray length and 2 feet in width, although these lenses fluorite, similar in color and texture to the country in one place are scattered along a fault zone for rock, has replaced the country rock for unknown a length of 3,200 feet and are almost pure fluorite distances away from the faults. with minor quartz and sulfides (Gillerman, 1952). Many districts contain pipelike fluorspar bodies In one part of the Cooks Peak district, New localized along faults or fissure veins. Excellent Mexico, hundreds of small irregular lenses and examples occur in the Thomas Range, Utah, and pods of fluorspar are scattered over a surface area the Fluorine district, Nevada (Peters, 1958, p. of about 80 acres. These lenses, as much as la few 672). In the Daisy mine, Fluorine district, Nevada, GEOLOGY OF FLUORSPAR DEPOSITS (3F THE WESTERN UNITED STATES 47

the fluorspar deposits occur as veins and irregular p. 30). Brecciated zones .and permeable strata of steeply dipping pipelike lenses in highly deformed sandstone have been kaolinized, some completely, and fractured dolomite or limestone near major to compact masses of clay wi,th minor amounts of faults (Cornwall and Kleinhampl, 1964, p. J19). magnetite, pyrite, sericite, fluorite, orpiment, The size of the pipelike bodies varies greatly, realgar, gypsum, and opaline quartz. from pods 20 feet across to masses 350 feet long, In many areas, intensely silicified rocks contain with minable widths as much as 65 feet (Thurston, dispersed fluorite. These rocks include jasperoid 1944). The ore mined through 1961 averaged (silicified limestone) and jasperized igneous rock about 75 percent CaFz with less than 2 percent in which most of the fluorite is erratically distrib- silica (Cornwall and Kleinhampl, 1964, p. J21). uted in vugs, fractures, and breccias. Some flu- Pipelike fluorspar bodies in the Thomas Range, orite, along with chalcedonic quartz, occurs as a Utah, are oval to irregular in shape and tend to fine-grained replacement of wall-rock fragments. narrow with depth. Deepest mining has been about 200 feet below the surface. The pipelike Although fluorspar in hydrothermal alteration bodies range in size from pods less than 1 foot in zones tends to be low grade and irregularly dis- diameter to masses 155 feet long by 106 feet wide. persed, some areas of silicified rock may contain The ore ranges in grade from 65 to 95 percent commercial concentrations of fluorine ( McAnulty, CaF2, but it is generally siliceous. Mine shipments 197213). Bulk samples of jasperoid (silicified lime- during 1944-56 averaged 72 to 82 percent CaF2 stone) mined for fluorspar content in the Winkler (Staatz and Carr, 1964, p. 143). anticline, New Mexico, averaged 33.42 percent Small amounts of fluorite occur as dissemina- CaF2 (McAnulty, 1972b, p. 2). In the Quinn tions in travertine deposits of some recent hot Canyon Range, Nev., small pods, stringers, and springs. A travertine deposit, some 500 feet above veinlets of fluorite in large tabular bodies of brec- the present hot springs at Ojo Caliente, N. Mex., ciated and silicified volcanic rocks are being contains nearly 1 percent CaF2 (White, 1955). exploited (Sainsbury and Kleinhampl, 1969, p. Small fluorite veins occur along the same fault C18). The Grand Reef, Aravaipa district, Arizona structure and just above the present springs. (Ross, 1925, p. 59), is a zone several miles long Fluorite-bearing travertine, formed from thermal and a few hundred feet wide of intensely brec- waters at Poncha Springs, Colo., consists of about ciated and silicified rock, chiefly in intrusive 95 percent calcite with minor amounts of manga- rhyolite. Mineralization consisted mainly of the nese oxide, chalcedonic quartz, opal, quartz, chlo- formation of veins, stringers, and irregular pods rite, muscovite, and fluorite (Van Alstine, 1969, of quartz, fluorite, and sulfides within the silicified p. 35). zones. More importantly, fluorite is also present Fluorite and minor tourmaline occur in argil- as a very fine intergrowth with chilcedonic quartz lized rocks associated with uranium deposits in in a rock that resembles chert or jasperized rock; the Marysvale district, Utah (Kerr and others, fluorite is detectable by X-ray diffraction analysis 1957). During progressive stages of alteration, only. fluorite first formed as veinlets when kaolinite and In the Western United States many areas of montmorillonite became the major alteration hydrothermally altered volcanic rock, agglomer- products and the previously resistant orthoclase ates, volcaniclastic sediments, and unconsolidated became partly sericitized; fluorite continued to be clastic sediments contain dispersed fluorite. The formed during alteration to a rock composed fluorite-beryllium deposits near Spor Mountain mainly of fine-grained (in part recrystallized) and the Honeycomb Hills, Utah, are good ex- quartz and sericite, with kaolinite, illite, pitch- amples (McAnulty and Levinson, 1964). Altered blende, pyrite, and black fluorite. Fluorite in the water-laid tuff near Spor Mountain, Utah, con- less altered rocks tends to be green or clear in tains commercial amounts of beryllium and about color but is dark purple to black in the highly 4 percent CaF2. Microscopic fluorite is dispersed altered rocks and veins. Fluorite is a minor con- through altered tuff and in a fine-grained inter- stituent of hydrothermally altered rocks in the growth with opal and chalcedony in nodules as South Moccasin Mountains, Mont. (Sahinen, 1962, much as 30 cm in diameter. Although some flu- 48 RONALD G. WORL orite in these deposits may have been derived common in some districts and argillization of from leaching of fluorine from the included vol- feldspars occurred in a few. In the Zuni Moun- canic ash, most of the fluorine along with beryl- tains, N. Mex., mild silicification occurred in zones lium, lithium, manganese, uranium, and trace ranging in width from 1 inch along some fluor- amounts of niobium, cesium, and yttrium, was spar veins to 1,000 feet along several others (God- introduced by laterally spreading hydrothermal dard, 1966). Wall-rock alteration, mainly silicifica- solutions (Staatz and Griffitts, 1961; Lindsey and tion and fluoritization, was not extensive in the others, 1973). Browns Canyon district, Colorado, and extended Fluorite occurrences not related to intrusive no more than several inches on either side of the igneous rocks are numerous and most are listed vein (Van Alstine, 1969). Material within the in Anderson and Van Alstine ( 1964), Dasch (1964), breccia pipes in the Thomas Range, Utah, is Geach ( 1963), Horton ( 1961), Thurston and others silicified and argillized, but the wall rocks adjacent (1954), Van Alstine and Moore (1969), and Van to the pipes are unaltered. Alteration in the North- Alstine (1964, 1965, and 1966). Good examples gate district, Colorado, consisted of a zone of are the fluorite gangue in gold telluride deposits mild silicification, pyritization, and fluoritization of Cripple Creek, Colo.; gold-quartz veins at in the form of a very fine-textured and pervasive Jarbridge, Nev.; barite deposits at Rowley, Ariz.; network of veinlets composed of chalcedonic beryllium deposits at Spor Mountain, Utah; man- quartz, fluorite, pyrite, and occasionally molybde- ganese deposits of the Luis Lopez district, New nite centered on the fluorspar vein (Worl, in U.S. Mexico; lead-silver veins of the Castle Dome lead Geological Survey, 1970, p. AS). Massive silicifica- mine, Arizona; molybdenum-lead-manganese-sil- tion was common in some areas (McAnulty, 1972b) ver veins of the Trigo Mountains, Ariz.; and the and covered a much larger area than the related uranium deposits at Marysvale, Utah. fluorite deposits. (See discussion of fluorite in Fluorite not related to intrusive igneous rocks is alteration zones in previous section.) Alteration generally columnar in habit, massive porcelaneous, types, other than silicification, are generally not or in earthy masses. Columnar fluorite is made up extensive, although fluorspar deposits in the Clark of acicular fibers or massive columns of fluorite Mountains, Calif., consist of fluorite disseminated generally perpendicular to vein walls or radiating through highly sericitized dolomite (Crosby and from fragments (Peters, 1958, p. 672). The porce- Hoffman, 1951), and fluorite in the Marysvale, laneous and earthy varieties are actually a very Utah, district is in veins and disseminations in fine grained mixture of fluorite, chalcedonic highly argillized volcanic rocks. quartz, and commonly pyrite, jarosite, biotite, Commonly associated minerals in fluorspar de- sericite, clay minerals, and feldspar. Monominer- posits not associated with intrusive igneous rocks alogic layering, with crustiform and mammilary are calcite, chalcedonic quartz, barite, celestite, textures, is common, as are massive fine-grained, potassium feldspar, hypogene iron, and manga- essentially featureless masses. Water courses and nese oxides; less common minerals are jarosite, vugs are common, as are pseudoinorphs of fluorite wulfenite, galena, pyrite, and secondary uranium after calcite and other minerals. minerals. Associated elements are silver, gold, Hydrothermal alteration in and around fluor- barium, beryllium, iron, lithium, manganese, mo- spar deposits not related to intrusive igneous rocks lybdenum, lead, strontium, tellurium, uranium, varies greatly in degree; in some areas the wall vanadium, and zinc. As with the other type of rocks are little altered, or not at all, but in other Tertiary fluorite deposits, association with some areas they are extensively altered. Many small elements is quite strong, whereas it is somewhat fluorspar veins like those in the Soldiers Farewell questionable with others. Examples of fluorite Mountain, Redrock, and El Rito areas, New gangue in metal deposits have already been listed. Mexico, have had no associated alteration; the Nearly all gold, barite, beryllium, molybdenum, wall rocks next to fluorite in the fissures are un- and lead-zinc-silver deposits not associated with altered. Silicification is the predominant type of intrusive igneous rocks have fluorite gangue, com- alteration associated with fluorspar deposits. Pyrit- monly in abundance. Most hypogene manganese ization, sericitization, and feldspathization were and iron oxide deposits contain minor amounts of GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 49 fluorite ( Hewett, 1964). Fluorite is a local gangue veins in a major fault zone. The veins ,are adjacent mineral in the Terlingua mercury district, Texas, to and parallel to a rhyolite dike that contains and cinnabar is a minor constituent of fluorspar pods, segregations, and dissen~inationsof fluorite. in the Fluorine district, Nevada; however, mercury The large fluorspar veins northeast of Winston, N. and fluorite are not commonly associated. All ,the Mex., are within the same structure and parallel elements listed occur in at least trace amounts in to a large fluorite-bearing rhyolite dike. Fluorite many fluorspar deposits, and barium, manganese, mineralization in southern New Mexico has been strontium, and yttrium ,are consistently present. related to late Tertiary volcanism ( Rothrock, 1970, Fluorspar deposits containing trace metals, or p. 125), and the distribution of this type of fluorite grading into associated metal deposits, are too (Figs. 2 and 3) is similar to the distribution of nuillerous to list. It is commonly the earthy and fluorine- and fluorite-rich volcanic rocks (D. R. porcelaneous varieties of fluorspar in breccia Shawe, personal commun., 1973). zones that contain anomalous amounts of metals. The age of fluorspar deposits of this type can Anomalous amounts of molybdenun~occur within be determined only relatively by crosscutting and around a fluorspar vein in the Northgate dis- relationships; none of the deposits have been trict, Colorado. The source of the anomaly is a radiometrically dated. It does seem, however, that minor depositional phase of porcelaneous material most formed roughly 5 to 20 million years ago, composed of chalcedonic quartz, fl~~orite,pyrite, during the same general time span as some of the and scattered molybdenite. This same material volcanism in parts of the West. Several minor pervasively entered and altered the wall rocks for occurrences of fluorite in hot-spring deposits are distances up to 50 feet (Worl, in U.S. Geological probably younger. Fluorite, manganese, gold, Survey, 1970, p. AS). Gold veins in the Steeple uranium, and silver mineralization in southwest Rock district, New Mexico, contain fluorite New Mexico occurred in late Miocene or Pliocene gangue, and genetically related fluorspar veins in as contrasted to earlier Tertiary base-metal sulfide the same district contain trace amounts of gold. mineralization (Gillerman, 1970, p. 118). Numer- Fluorspar deposits in the Vulture Mountains, ous fluorspar deposits in New Mexico and south- Ariz.; Sierra Caballo, N. Mex,; and Yankee Fork eastern Arizona occur within the extensive district, Idaho, are related to lead-silver and gold Pliocene and Pleistocene Gila Conglomerate, and deposits that occupy the same stn~ctures. For in the Redrock area, New Mexico, fluorspar veins many more examples of fluorspar deposits con- extend into basalt flows (presumably Pliocene or taining concentrations of other elements, see Worl, Pleistocene) overlying the Gila Conglomerate. Van Alstine, and Hey1 ( 1973). Many fluorspar deposits in this region are situated Igneous associations with this type of fluorite within basin and range faults that are younger are difficult to define; many deposits such as those than 20 m.y. (Elston, 1970, p. 150). Several de- in the Northgate district, Colorado (Steven, 1960), posits in southwestern Arizona cut the Pliocene are many miles from any known Tertiary igneous Bouse Formation, and in the Trigo Mountains ,they activity, and many deposits that do occur within apparently cut even younger volcanic flow rocks. volcanic rocks have not been proved to be genet- The basalt and andesite in the Cady Mountains, Calif., that contain veins and disseminations of ically related to that rock or even to the volcanic fluorite are Miocene or possibly younger (Dibblee event that was the source of the rock. In a few and Bassett, 1966). Fluorspar veins at several places, however, it seems that the fluorite is locations in Nevada crosscut a sequence of vol- genetically related to the enclosing volcanic rock. canic rocks radiometrically dated as 16 to 10 m.y. In the Cady Mountains, Calif., fluorite stringers, old (for example, see McKee ,and Silberman, veinlets, and pods occur through breccia zones in 1970). Fluorite-bearing gold deposits at Jarbridge, basalt and andesite flows. The basalt and andesite Nev., are considered to be late Miocene (Roberts contain disseminated fluorite, mainly as a filling and others, 1971, p. 29). The extensive fluorspar of vesicules (Dibblee and Bassett, 1966). The deposits in the Browns Canyon district, Colorado, Moneymaker fluorspar deposit, Burro Mountains, were probably formed during the late Miocene N. Mex. (Williams, 1966, p. 49), is composed of (Van Alstine, 1969, p. 37). 50 RONALD G. WORL

Fluorite not associated with intrusive igneous pyrite, and lesser amounts of barite, manganese rocks formed by deposition from relatively cool oxides, and molybdenite. The ore-forming solu- and generally dilute hydrothermal fluids, probably tions were very dilute fluids (salinities less than not greatly different from the waters issuing from about 2 weight percent). Temperatures of the many present thermal springs. It is commonly fluids at the time of deposition were 130" to thought that the great bulk of the water was 175°C as determined by homogenization temper- meteoric and probably slightly alkaline. Fluorine, atures of fluid inclusions (J. T. Nash, oral and possibly some of the other constituents, prob- commun., 1970). ably had a deep source, either volatiles escaping The direct connection between fluorspar de- from a crystallizing magma #at depth or derived posits and extinct hot springs can be seen in directly from a deep crust or upper mantle source. several areas. Fluorite-manganese oxide veins in The concentration of fluorine in the waters at the the Animas Mountains (Elston, 1965, p. 212) and time of deposition is unknown. Thermal waters the Redrock area, New Mexico, pass upward, now depositing very minor fluorite or associated within a few feet, into banded travertine at the with fluorspar deposits at Ojo Caliente, N. Mex., surface. Fluorspar .deposits along the west side and Poncha Springs and Browns Canyon, Colo., of the Burro Mountains, N. Mex. (Gillern~an,1964, contain 12 to 16 ppm fluorine (White, 1955, p. p. 72), consist of small veins extending a short 143). distance away from a major fault zone. The fluor- The paragenetic sequences of several districts spar veins grade along strike into banded traver- indicate numerous depositional stages generally tine and apron deposits of extinct hot springs. separated by brecciation. Most depositional stages The Madrasco deposit, Nevada (Horton, 1961, p. were monomineralogic; the exceptions were those 9), consists of fluorite pods and dissenlinations in that deposited porcelaneous and earthy fluorspar rock of extinct hot springs aprons. (both a mixture of fluorite, chalcedonic quartz, Fluorspar deposits not associated with intrusive and other minerals). Deposits at Hansonburg, N. igneous rocks are in many areas related to zones Mex., formed from several stages of deposition, that have undergone tensional faulting. These the first producing sphalerite, pyrite, galena, and zones trend mainly north to northwest or north- chalcopyrite, and the last calcite. All the interme- east, but in southwestern Arizona and southeastern diate stages were primarily fluorite. Temperatures California they trend east. The distribution of of deposition, as determined from homogenization basin and range faulting in the West coincides temperatures of fluid inclusions, during the early closely with the distribution of this type of fluorite fluorite stages were 205" to 180°C and decreased (Figs. 2 and 3). The 'alignments of fluorspar de- during the later stages to about 140°C. The salin- posits closely parallel the structural zones; deposits ity increased from 10 to 16 weight percent during occur both within the structural zone and nearby fluorite deposition (Roedder, Heyl, and Creel, in subsidiary structures. Numerous deposits occur 1968). Fluorspar in the Browns Canyon district, along faults of the Rio Grande rift system in New Colorado, was deposited in many stages from Mexico (Rothrock, 1970, p. 241, and Elston, 1970, slightly alkaline solutions at temperatures of 119" p. 147) and its northern extension into Colorado. to 168"C, as determined by honlogenization of Faults of this system probably extend to the north fluid inclusions. The ore-forming solutions were and include the mineralized faults in the North- very dilute and probably a mixture of meteoric gate district, Colorado (Tweto, 1968, p. 582). water with minor amounts of hydrothermal waters Most of the deposits in the Silver City 'area, New (Van Alstine, 1969, p. 37). Fluorspar veins at Mexico, are aligned along major northwest-trend- Northgate, Colo., formed by deposition during ing fault zones and along less distinct northeast- several stages and substages often interrupted by trending fault zones. periods of brecciation. Most stages of deposition In some areas the alignment of deposits and the were monomineralic, forming layers of columnar structure of the deposits reflect major structures fluorite, but several stages, usually during and that may be older than the north-trending range- following ~eriodsof brecciation, produced fine- bounding faults and the structural grain of the grained mixtures of fluorite, chalcedonic quartz, Basin and Range province. Fluorspar deposits in GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 5 1 the Lovelock area, Nevada (Hor,ton, 1961, p. 21) rich volcanic rocks, massive silicified rock, 'and are mainly within and aligned along major fault recent and extinct hot-springs activity are also systems that trend N. 20"-40" W. These faults good exploration guides. are transverse to the attitude of the enclosing Other types of fluorine concentrations that de- nlountain ranges and to the major north-trending serve consideration are complex pegmatites, car- structural grain of the region. Deposits in the bonatite complexes, and lacustrine sand volcani- Indian Peaks area, Utah, are aligned along a clastic sedimentary rocks. Complex pegmatites northwest-trending fault system that does not exploited in Montana, the Crystal, Spar, and parallel the general north-trending structural grain Snowbird properties, are not well studied in terms of the region. In addition, the Indian Peaks de- of age, mode of emplacement, origin, geochem- posits are just one of many districts that are istry, and structural control. Similar unrecognized aligned along a well-defined northeast-trending deposits may exist in other parts of the West. zone of mineralized, altered, and intrusive centers. Carbonatite complexes exist in the West but none (See Worl, Van Alstine, and Heyl, 1973.) have been a conlmercial source of fluorine. Lacus- CONCLUSIONS trine deposits similar to those near Rome, Oreg. (Sheppard and Gude, 1969), deserve serious con- A large part of the Western United Stfates is sideration as future fluorine resources. Beds that underlain by crustal rocks relatively enriched in coincide in time and space with hydrothermal fluorine. The fluorine concentrations within the fluorite and fluorine-rich volcanism may contain rocks are of several types. The most abundant fluorite concentrations. and most promising for future exploitation are Tertiary late-magmatic and hydrothermal deposits Several factors will have to be overcome before of two general types: those associ'ated with in- the production of fluorspar increases substantially trusive igneous rocks, and those not associated in the Western United States. Transportation is with intrusive rocks. The similarities and differ- a problem in many areas as there is a lack of large ences of the two types are summarized in Table local consumers and the distance to the present 1. Exploration for these deposits should be pri- large consumers may be great. Many known marily within the fluorine-rich areas and should deposits ,are many miles from the nearest com- be oriented toward the important geologic param- munity or railhead. Foreign competition, espe- eters as outlined in Table 1. Exploration for cially from large deposits being exploited in Africa deposits associated with intrusive rocks should be and South America, will become increasingly directed toward intrusive centers characterized strong. These stable sources will probably be able by late-magmatic activity of an alkalic nature that to supply fluorspar to the major United States exhibited an abundance of volatiles during that consumers in the near future more cheaply than stage. Silicified rock, fluorite, and secondary can the fluorspar deposits currently being ex- sericite, biotite, or potassium feldspar within or ploited in the Western United States. However, near an intrusive are favorable indicators, as are the incentive for increasing fluorspar production stockworks of these same minerals. The most in the West is present. The United States is favorable hosts are carbonate sedimentary and currently producing only 20 percent of the ap- silicic igneous and metamorphic rocks. The silicic proxinlately 1,600,000 tons of CaF? consumed rocks make an excellent host for large mineralized annually. Large areas of the West contain rel- breccia zones, and the carbonates are excellent atively fluorine-rich crustal rocks, and the possi- hosts for large massive replacement bodies as well bilities are excellent for developing large low- as mineralized breccias. grade deposits with coproducts or byproducts. Important factors to be considered in searching for deposits not associated with intrusive rocks REFERENCES CITED are large Tertiary fault systems th~atare generally Anderson, A. L., and Van Alstine, R. E., 1964, Fluorspar, tensional in nature. Most favorable hosts are again in Mineral and water resources of Idaho: U.S. 88th brecciated calcareous sedimentary and silicic ig- Cong., 2d sess., Senate Comm. Interior and Insular neous and metamorphic rocks. Areas of fluorine- Affairs, Comm. Print, p. 79-84. 52 RONALD G. WORL

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'L., 1968, Bishop tungsten district, California, in stracts for 1963: Geol. Soc. America Spec. Paper 76, Ridge, J. D., ed., Ore deposits of the United States, p. 268-269. 1933-1967 (Graton-Sales Volume), v. 2: New York, Coats, R. R., Goss, W. D., and Rader, L. F., 1963, Am. Inst. Mining Metall. and Petroleum Engineers, Distribution of fluorine in unaltered silicic volcanic p. 1531-1554. rocks of the western conterminous United States: Gulbrandsen, R. A,, and Reeser, D. W., 1969, An occur- Econ. Geology, v. 58, no. 6, p. 941-951. rence of Permian manganese nodules near Dillon, Cornwall, H. R., and Kleinhampl, F. J., 1964, Geology of Montana, in Geological Survey research 1969: U.S. Bullfrog quadrangle and ore deposits related to Bull- Geol. Survey Prof. Paper 650-C, p. C49-C57. frog Hills caldera, Nye Cdunty, Nevada, and Inyo Hawley, C. C., 1969, Geology and beryllium depositsof County, California: U.S. Geol. 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India, p. 37-44, nardino County, California: U.S. Geol. Survey Misc. [1967]. Geol. Inv. Map 1-467. Hewett, D. F., 1964, Veins of hypogene manganese oxide Elston, W. E., 1965, Mining districts of Hidalgo County, minerals in the Southwestern United States: Econ. New Mexico, in Guidebook of southwestern New Geology, v. 59, no. 8, p. 1429-1472. Mexico 11: New Mexico Geol. Soc. 16th Field Conf., Horton, R. C., 1961, An inventory of fluorspar occurrences 1965, p. 210-214. in Nevada: 'Nevada Bur. Mines Rept. 1, 31 p. 1970, Volcano-tectonic control of ore deposits, Jahns, R. H., 1944, Beryllium and tungsten deposits of the southwestern New Mexico, in Guidebook of the Iron Mountain district, Sierra and Socorro Counties, Tyrone-Big Hatchet Mountains-Florida Mountains New Mexico, with a section on the Beryllium min- region: New Mexico Geol. Soc. 21st Field Conf., erals, by J. J. Glass: U.S. Geol. Survey Bull. 945-C, 1970, p. 147-153. p. 45-79. Geach, R. D., 1963, Fluorspar, in Mineral and water re- 1946, Mica deposits of the Petaca district, Rio sources of Montana: U.S. 88th Cong., 1st sess., Arriba County, New Mexico, with brief descriptions Senate Comm. Interior and Insular Affairs, Comm. of the Ojo Caliente district, Rio Arriba County, and Print, p. 65-67. the Elk Mountain district, San Miguel County: New Gillennan, Elliott, 1952, Fluorspar deposits of Burro Mexico Bur. Mines and Mineral Resources Bull. 25, Mountains and vicinity, New Mexico: U.S. Geol. 289 p. Survey Bull. 973-F, p. 261-289. Kazakov, A. V., and Sokolova, E. I., 1950, Usloviya 1953, Fluorspar deposits of the Eagle Mountains, obrazovaniya flyuorita v osadochnykh porodakh (flyu- Trans-Pecos, Texas: U.S. Geol. Survey Bull. 987, oritovaya sistema) [Conditions of the formation of 98 p. fluorite in sedimentary rocks]: Akad. Nauk SSSR -1964, Mineral deposits of western Grant County, Geol. Inst. Trudy, v. 114, Geol. Ser. 40, p. 22-64 New Mexico: New Mexico Bur. Mines and Mineral [English translation, U.S. Geol. Survey Trace Ele- Resources Bull. 83, 213 p. ments Inv. Rept. TEI-386, 76 p., 19511. 1970, Mineral deposits and structural pattern of Kerr, P. F., 1946, Tungsten mineralization in the United the Big Burro Mountains, New Mexico, in Guidebook States: Geol. Soc. America Mem. 15, 241 p. of the Tyrone-Big Hatchet Mountains-Florida Moun- Kerr, P. F., Brophy, G. P., Dahl, H. M., Green, Jack, GEOLOGY OF FLUORSPAR DEPOSITS OF THE WESTERN UNITED STATES 53

and Woolard, L. E., 1957, Marysvale, Utah, uranium Pecora, W. T., 1962, Carbonatite problem in the Bearpaw area: Geol. Soc. America Spec. Paper 64, 212 p. Mountains, Montana, in Petrologic studies-A volume Kottlowski, F. E., Weber, R. H., and Willard, M. E., in honor of A. F. Buddington: Geol. Soc. America, 1969, Tertiary intrusive-volcanic-mineralization epi- p. 83-104. sodes in the New Mexico region: Geol. Soc. America Perhac, R. h4., 1970, Geology and mineral deposits of the Abstracts with Programs for 1969, pt. 7, p. 278-280. Gallinas Mountains, Lincoln and Torrance Counties, Kramer, W. V., 1970, Geology of the Bishop Cap Hills, New Mexico: New Mexico Bur. Mines and Mineral Dona Ana County, New Mexico: El Paso, Tex., Texas Resources Bull. 95, 51 p. Univ, unpub. M.S. thesis. Peters, W. C., 1958, Geologic characteristics of fluorspar Lindgren, Waldemar, 1933, Differentiation and ore de- deposits in the western United States: Econ. 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Mining Metall. and of halogens from crystallized and glassy silicic vol- Petroleum Engineers, p. 1555-1572. canic rocks: Geochim. et Cosmochim. Acta, v. 31, Sainsbury, C. L., and Kleinhampl, F. J., 1969, Fluorite no. 2, p. 215-223. deposits of the Quinn Canyon Range, Nevada: U.S. Olson, J. C., Shawe, D. R., Pray, L. C., and Sharp, W. N., Geol. Survey Bull. 1272-C, 22 p. [1970]. 1954, Rare-earth mineral deposits of the Mountain Shawe, D. R., 1966, Arizona-New Mexico and Nevada- Pass district, San Bernardino County, California, with Utah beryllium belts, in Geological Survey research a foreword on History of the discovery at Mountain 1966: U.S. Geol. Survey Prof. Paper 550-C, p. Pass, California, by D. F. Hewett: U.S. Geol. Survey C206-C213. Prof. Paper 261, 75 p. Sheppard, R. A., and Gude, A. J., 3d, 1969, Authigenic Parker, R. L., and Havens, R. G., 1963, Thortveitite as- fluorite in Pliocene lacustrine rocks near Rome, sociated with fluorite, Ravalli County, Montana, in Malheur County, Oregon, in Geological Survey re- Short papers in geology and hydrology: U.S. Geol. search, 1969: U.S. Geol. Survey Prof. Paper 650-D, Survey Prof. Paper 475-B, p. B10-B11. p. D69-D74. Parker, R. L., and Sharp, W. N., 1970, Mafic-ultramafic Sheridan, D. M., Taylor, R. B., and Marsh, S. P., 1968, igneous rocks and associated carbonatites of the Gem Rutile and topaz in Precambrian gneiss, Jefferson and Park Complex, Custer and Fremont Counties, Colo- Clear Creek Counties, Colorado: U.S. Geol. Survey rado: U.S. Geol. Survey Prof. Paper 649, 24 p. Circ. 567, 7 p. 54 RONALD G. WORL

Staatz, M. H., and Cars, W. J., 1964, Geology and mineral Comm. Interior and Insular Affairs, Comm. Print, deposits of the Thomas and Dugway Ranges, Juab p. 199-204. and Tooele Counties, Utah: U.S. Geol. Survey Prof. 1969, Geology and mineral deposits of the Paper 415, 188 p. Poncha Springs NE quadrangle, Chaffee County, Staatz, M. H., and Griffitts, W. R., 1961, Beryllium-bearing Colorado, with a section on Fluorspar mines and tuff in the Thomas Range, Juab County, Utah: Econ. prospects, by R. E. Van Alstine and D. C. COX: Geology, v. 56, no. 5, p. 941-950. U.S. Geol. Survey Prof. Paper 626, 52 p. Steven, T. A., 1960, Geology and fluorspar deposits, North- Van Alstine, R. E., and Moore, R. T., 1969, Fluorspar, in gate district, Colorado: U.S. Geol. Survey Bull. Mineral and water resources of Arizona: U.S. 90th 1082-F, p. 323-422 [1961]. Cong., 2d sess., Senate Comm. Interior and Insular Thurston, W. R., 1944, The Daisy fluorspar deposit near Affairs, Comm. Print, p. 348-357. Beatty, Nye County, Nevada: U.S. Geol. Survey Wallace, S. R., Muncaster, N. K., Jonson, D. C., Macken- Strategic Minerals Inv. Prelim. Rept. 3-209. zie, W. B., Bookstrom, A. A., and Sulface, V. E., Thurston, W. R., Staatz, M. H., Cox, D. C., and others, 1968, Multiple intrusion and mineralization at Climax, 1954, Fluorspar deposits of Utah: U.S. Geol. Survey Colorado, in Ridge, J. D., ed., Ore deposits of the Bull. 1005, 53 p. United States, 1933-1967 (Graton-Sales Volume), v. 1: New York, Am. Inst. Mining Metall. and Tweto, Odgen, 1968, Geologic setting and interrelation- Petroleum Engineers, p. 605-640. ships of mineral deposits in the mountain province 'Warner, L. A., Holser, W. T., Wilmarth, V. R., and of Colorado and south-central Wyoming, in Ridge, Cameron, E. N., 1959, Occurrence of nonpegmatite J. D., ed., Ore deposits of the United States, 1933- beryllium in the United States: U.S. Geol. Survey 1967 (Graton-Sales Volume), v. 1: New York, Am. Prof. Paper 318, 198 p. Inst. Mining Metall. and Petroleum Engineers, p. Whelan, J. A., 1965, Hydrothermal alteration and mineral- 551-588. ization, Staats mine and Blawn Mountain areas, Umpleby, J. B., 1917, Geology and ore deposits of the central Wah Wah Range, Beaver County, Utah: Mackay region, Idaho: U.S. Geol. Survey Prof. Utah Geol, and Mineralog. Survey Spec. Studies, no. Paper 97, 129 p. 12, 31 p. Umpleby, J. B., Westgate, L. G., and Ross, C. P., 1930, White, D. E., 1955, Thermal springs and epithermal ore Geology and ore deposits of the Wood River region, deposits, in Pt. 1 of Bateman, A. M., ed., Economic Idaho, with a description of the Minnie Moore and geology, 50th anniversary volume, 1905-1955: Ur- near-by mines, by D. F. Hewett: U.S. Geol. Survey bana, Ill., Econ. Geology Publishing Co., p. 99-154. Bull. 814, 250 p. Williams, F. E., 1966, Fluorspar deposits of New Mexico: U.S. Geological Survey, 1970, Geological Survey research U.S. Bur. Mines Inf. Circ. 8307, 143 p. 1970: U.S. Geol. Survey Prof. Paper 700-A, 426 p. Worl, R. G., 1971, Spatial and time distributions of fluorite Van Alstine, R. E., 1964, Fluorspar, in Mineral and water occurrences in the western United States and their resources of Colorado: U.S. 88th Cong., 2d sess., relationship to metalization [abs.] : Mining Eng., Senate Comm. Interior and Insular Affairs, Comm. v. 23, no. 12, p. 80. Print, p. 160-165. Worl, R. G., Van Alstine, R. E., and Heyl, A. V., 1973, 1965, Fluorspar, in Mineral and water resources Fluorite in the United States: U.S. Geol. Survey of New Mexico: U.S. 89th Cong., 1st sess., Senate Mineral Inv. Resource Map MR-60 (in press). Comm. Interior and Insular Affairs, Comm. Print, Worl, R. G., Van Alstine, R. E., and Shawe, D. R., 1973, p. 260-267. Fluorine, in Brobst, D. A,, and Pratt, W. P., eds., 1966, Fluorspar, in Mineral and water resources Mineral resources of the United States: U.S. Geol. of Washington: U.S. 89th Cong., 2d sess., Senate Survey Prof. Paper 820, p. 223-235. SOME FLUORITE-BARITE DEPOSITS IN THE MISSISSIPPI VALLEY IN RELATION TO MAJOR STRUCTURES AND ZONATION1

ALLEN V. HEYL U.S. Geological Survey Denver, Colorado

Many of the fluorite-barite deposits in the barite, and sphalerite occur with the same mineral eastern parts of the Mississippi Valley lie along habits and trace elements as in central Kentucky. major basement lineaments or at the intersections Large breccia pods and blankets of fluorite and of lineaments. An east-trending lineament that barite and some sphalerite, #as well as sphalerite extends approximately along the 38th parallel of alone, occur in the Knox Dolomite. Small veins latitude from western Virginia into south-central similar to those in central Tennessee are above in Missouri (Heyl, 1972) is the most important the Middle Ordovician limestones (Jewell, 1947). commercially. The Illinois-Kentucky and the New fluorspar deposits should be looked for in Central Kentucky districts lie along this lineament major domes and arches east of the Mississippi at its intersection with other major structures. River, and along major lineaments. Promising The Illinois-Kentucky district ( Grogan and areas include: (1) the southern part of the Nash- Bradbury, 1968) is centered around greater Hicks ville dome, (2) the crest of the Cincinnati arch in dome, just south of the intersection of the 38th southern Kentucky, (3) the crest of the Findlay parallel lineament and the New Madrid fault arch south of Toledo, (4) the Ste. Genevieve fault zone (Fig. 1). The galenas of the district contain zone in Illinois and Missouri, (5) the Mt. Cannel more silver and antimony near Hicks dome, but fault zone in southern Indiana, and (6) the became progressively leaner in these elements Frontenac arch in southern Ontario and western peripherally, especially toward Princeton, Ken- New York. tucky. The zonal pattern suggests areas favorable for discovery of new deposits beneath the over- lying Pennsylvanian strata northward, northeast- ward, and northwestward from the center of the dome. REFERENCES CITED The Central Kentucky district (Fig. 2) lies on Grogan, R. M., and Bradbury, J. C., 1968, Fluorite-zinc- the crest of the Lexington dome at the intersection lead deposits of the Illinois-Kentucky mining district, of the 38th parallel lineament and the Cincinnati in Ridge, J. D., ed., Ore deposits of the United States, arch. The vein district is zoned with fluorite, 1933-1967 (Graton-Sales volume), v. 1: New York, Am. Inst. Min. Metall. and Petroleum Engineers, p, which is more abundant centrally, and with 379-399. strontian-barite, and galena, which are more Heyl, A. V., 1972, The 38th parallel lineament and its abundant peripherally (Jolly and Heyl, 1964). relationship to ore deposits: Econ. Geology, v. 67, Similar mineral deposits extend southward at p. 879-894. intervals along the Cincinnati arch and in fault Jewell, W. B., 1947, Barite, fluorite, galena, sphalerite veins of middle Tennessee: Tennessee Div. Geology zones which occur at intervals along its crest into Bull. 51, 112 p. Tennessee (Taylor, 1962). Jolly, J. L., and Heyl, A. V., 1964, Mineral paragenesis The Central Tennessee district is on the crest and zoning in the Central Kentucky mineral district: of the Nashville dome. Here, fluorite, strontian- Econ. Geology, v. 59, p. 596-624. Taylor, A. R., 1962, Geology of the Amandaville quad- 1Publication authorized by the Director, U. S. Geological rangle, Kentucky: U. S. Geol. Survey Geol. Quad. Survey. Map GQ-186. 0 2 5 50 100 MILES I I I I

EXPLANATION X Perm~an.Devon~an and Cam- Occurrences of galena. sphalerlte, bar~te,fluor~te br~anlntruslons of per~dot~te Ant~cl~nalaxis Tertlary and Cretaceous rocks Precambrian rocks

A u b t a5 ...... - Fault Large m~neraldlstr~ct .. . Shnunw relnt~uemovement Synclinal axls 3 Ill~no~s-Kentucky PermIan and Pennsylvan~an Pre-Pennsylvan~anrocks @ 4 Southeast M~ssoun rocks of Paleozo~cage -Monocl~nalaxls Cryptoexplos~onstructure 5 Northeast Arkansas Figure 1. Major structures of the Illinois-Kentucky district and surrounding region. (Reproduced from Economic Geology, 1972, vol. 67, p. 886.) 0 25 50 100 MILES I I I I

EXPLANATION ---..--*.------Inferred basement fault Th~stfault ------0' I.....i:::::] Concealed fault in basement Central Kentucky mlneral dlstrlct /::::::::I A U 7 D Anticlinal axis 0' Permian and Pennsylvanian nmks Fault 4 Cumherland R~vrrm~nrrnl d~stnrt Shewiny dir~rtivnvf ruleliur t rlt,orvn,pnl Synclinal axis

u @ Occurrences of galena, sphalerite. Pre-Pennsylvanian rocks Cryptoexplosion structure barite. fluorite

Figure 2. The Central Kentucky district and major structures which control the district. (Reproduced from Economic Geology, 1972, vol. 67, p. 883.) ILLINOIS-KENTUCKY FLUORSPAR DISTRICT1 ROBERT D. TRACE U.S. Geological Survey Madisonville, Kentucky

ABSTRACT

The Illinois-Kentucky fluorspar district is the largest producer of fluor- spar in the United States. The deposits occur in sedimentary rocks of Middle and Late Mississippian and Early Pennsylvanian age. Some mafic dikes and sills and dike- or plug-like bodies of breccia intrude the sedimen- tary rocks. The fluorspar is localized either as veins along a series of complex northeast-trending, steeply dipping normal fault zones or as bedding-re- placement deposits principally along three horizons in rocks of Mississippian age. A structural high, centered at Hicks dome in Illinois, crosses the area in a northwesterly direction. The deposits are composed principally of calcite and fluorite, with sub- ordinate quantities of sphalerite, galena, and barite. Abnormally high quantities of thorium, beryllium, and rare earths are present in the breccias near.Hicks dome. Most geologists consider that the deposits are epigenetic and that the ore elements mostly were carried upward by hot connate water as a result of deep-seated igneous activity. A syngenetic origin for the deposits also has been proposed. As a result of several discoveries within the last several years, and the still substantial amount of inadequately tested or untested ground, potential production of fluorspar from the area is considered good.

LOCATION, HISTORY, AND PRODUCTION Illinois -part of the district, and the U. S. Geolog- ical Survey, in cooperation with the Kentucky More than three-fourths of the fluorspar pro- Geological Survey, has published several geologic duced in the United States has come from the maps and has completed the field work for geo- Illinois-Kentucky district. Substantial quantities logic maps of the remaining five quadrangles in of zinc and some lead and barite also have been the Kentucky part of the district (Fig. 3). produced, usually as a byproduct of fluorspar The earliest mining in the district was for lead mining. and was done at the Columbia mine, Crittenden The Illinois-Kentucky fluorspar district is in County, Ky., in 1835 (Ulrich and Smith, 1905, p. Hardin and Pope Counties in southeasternmost 115). Lead mining started in 1842 in Illinois Illinois and in adjacent Crittenden, Livingston, (Bastin, 1931, p. 10; Norwood, 1866). From 1835 and Caldwell Counties of western Kentucky (Fig. to the early 1870's little fluorspar was mined. 1). Nearly all the mines or mineralized areas are Only small amounts were produced from the early within the boundaries of 17 7.5-minute quad- 1870's to about 1890, when an expanded market rangle maps that comprise an area of about 1,000 was created by the development of the basic open- square miles (Fig. 2). The Illinois State Geolog- hearth steel furnace in which fluorspar was used ical Survey has published geologic maps of the for flux. Production since 1890 has been erratic but in general has risen. Production during World wars and land the Korean conflict 1 Publication authorized by the Director, U. S. Geological I I1 Survey. rose sharply, but because of rising imports during ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 59

Figure 1. Major structural features of the Illinois-Kentucky fluorspar district (compiled from 17 published and un- published geologic maps of 7.5-minute quadrangles, 1962-1972, by the Illinois State Geological Survey and U. S. Geological Survey).

1953-58, production in the district decreased. been produced at intervals. Lead has been a Production rose in 1970 over 1969 and will prob- minor liyproduct in recent years, as have silver, ably increase further in the near future. Available cadmium, land germanium. fluorspar production figures are summarized in Until the early 193OYs,almost the entire pro- Table 1. duction from the district was from vein ores. Zinc has been produced for many years, and Since then, the amount of ore produced from since 1940 the district has become a major source bedding-replacement deposits near Cave in Rock, of zinc, some as a byproduct, some as a main Ill., has risen so that by the middle to late 1960's, product. Substantial quantities of barite have this type of ore constituted more of the Illinois 60 ROBERT D. TRACE

EXPLANATION

d9' Bedding replacement d Ve~n

Figure 2. Illinois-Kentucky fluorspar district, showing mineralized areas.

production than vein ore. The rise in the ratio of ment ore near Joy has been known since the 1950's bedding-replacement ore to vein ore was in part and was put into production in 1970. due to the depletion of some of the large vein deposits- near Rosiclare. Within the last few GEOLOGIC SETTING years, however, the Illinois production from veins Stratigraphy

has increased and mav soon eaualA the A~roduction from bedding-replacement deposits. In Kentucky, Most of the sedimentary rocks that crop out practically all production has been from veins, in the district range in age from Late Devonian although a substantial deposit of bedding-replace- through Early Pennsylvanian, although in the ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 6 1

TABLE1.-FLUORSPAR SHIPMENTS FROM ILLINOIS more productive areas, the rock units at the AND KENTUCKY(FHOM U. S. BUR.MINES MINERALS surface are the Meramecian and Chesterian Series YEARBOOK). of Late Mississippian age. Lower Pennsylvanian Illinois TONS rocks are present also in several places, and small Through 1963 ...... 6,163,345 amounts of unconsolidated sand, silt, clay, and 1964 ...... 127,454 1965 ...... 159,140 gravel of Cretaceous and Tertiary age and loess 1966 ...... 176,175 and alluvium of Quaternary age are present 1967 ...... 210,207 locally. 1968 ...... 188,325 The stratigraphic column of exposed formations 1969 ...... 88,480 in the district, as summarized by Grogan and 1970 ...... 148,208 Bradbury ( 1968, Fig. 2), is given in Figure 4. The 1971 ...... 141,000' Total 7,402,334 stratigraphic col~imnfor the Kentucky part of Kentucky the district is shown in Figure 5. The lithology Through 1963 ...... 3,016,980 in Illinois and Kentucky is generally similar, but 1964 ...... 38,214 stratigraphic nomenclature differs. 1965 ...... 31,992 Most of the vein and bedding-replacement ores 1966 ...... 28,725 occur where the wall rocks are of either early 1967 ...... 32,952 1968 ...... 17,050 Chesterian or late Meramecian age. (See Figs. 1969 ...... 10,000f 4 and 5. ) 1970 5,000f ...... Dikes, Sills, and Breccias 1971 ...... (Expected to incr,ease) Many mafic dikes and, less commonly, sills are Total 3,180,913 present in the district; in Illinois, dike- or plug- ' Bur. of Mines estimate t Writer's estimate like bodies of breccia (Fig. 1) occur in rocks of Paleozoic age. The mafic dikes and sills have been called mica peridotites and lamprophyres (Koenig, 1965). Most are so highly altered that they defy precise classification; available analyses indicate they are mafic alkalic rocks. The dikes and sills are mostly dark gray to dark greenish gray, finely crystalline, and commonly slightly porphyritic. They are composed primarily of carbonates-both dolomite and calcite-serpentine, chlorite, and biotite (gen- erally phlogopitic). Small quantities of magnetite, leucoxene, marcasite, fluorapatite, garnet, perov- skite, and goethite are commonly present. Olivine and pyroxene occur as primary constituents, but in most of the dikes, these minerals have been largely altered to serpentine (Clegg and Brad- bury, 1956; Koenig, 1956; Trace, 1962a). Princeton @ Rarely, the mafic rock is medium to coarsely crystalline (sample no. 197 in Zartman and others, 1967) or is light gray and free of chlorite or 1-1 1-1 Published maps serpentine. Oesterling (1952, p. 324) described light-green dike material composed "... nearly ...... r-'J...... Field mapping completed entirely of fine-grained calcite. The phlogopite has been completely replaced by calcite; there is Figure 3. Status of geologic mapping of 7.5-minute quad- no indication that olivine or pyroxene phenocrysts rangles in the Illinois-Kentucky fluorspar district. were ever present. ..." 62 ROBERT D. TRACE

PENNSYLVANIAN

NEW ALBANY GROUP

Figure 4. Stratigraphic column of exposed formations in the Illinois-Kentucky mining district. Range of deposits columns are scaled to correlate with lithology column, e.g., the three main bedded horizons are the top part of the Downeys Bluff, top part of the Ste. Genevieve, and the Spar Mountain Member. (From Grogan and Bradbury, 1968, fig. 2, p. 375, as adapted from Baxter and others, 1967, pl. 1. Reprinted courtesy AIME.) Chemical and semiquantitative spectrographic a sample from 'a similarly altered dike in the east- analyses of samples from the Illinois dikes and central part of the Sa1,em quadrangle, Kentucky sills were reported by Bradbury (1962) and (Trace, 1962a), showed that the Robinson dike chemical analyses of similar samples from Ken- contained much larger quantities of rare earths tucky by Koenig ( 1956). Semiquantitative spec- than did the Kentucky dike (see Table 2). trographic analyses of a sample from the highly The number of identified dikes and sills has weathered Robinson dike on Hicks dome, de- increased considerably in the district in the last scribed by Bradbury and others (1955, p. 8), and two decades, principally because of an increase ILLI NOIS-KENTUCKY FLUORSPAR DISTRICT 63

DESCRIPTION

PENNSYLVANIAN

Limestone, cherty, partly oolitic

Limestone, cherty; containing lithostrotion colonies

Warsaw Limestone Limestone, large Echinocrinus spines at top

Limestone, mostly dark gray and very cherty or silty; locally, upper part is light gray

Figure 5. Generalized stratigraphic column of exposed formations in the Western Kentucky fluorspar district. 64 ROBERT II. TRACE

TABLE2.-SEM~QUANTITATIVE SPECTROGRAPHIC more than 2,000 feet (Brown and others, 1954, ANALYSESOF WEATHEREDMAFIC DIKES, ILLINOIS p. 897-900; Hey1 and others, 1965, p. B11; Brad- AND KENTUCKY. bury, 1962, p. 6-8; Trace, 1960). Minerals occur- Fowler dike ring in the breccia include fluorite associated with Robinson dike (east-central part of Salem Precento (near Hicks dome, Illinois 1 quadrangle, Kentucky rare-earth elements, sphalerite, galena, barite, More than 10 Si Si monazite, florencite, calcite, quartz, pyrite, brook- 5-10 Fe, A1 Fe, A1 1-5 Ti, Mg Mg, Ca ite, biotite, mtile, xenotime, pyroxene, hornblende, 0.5-1 Ca, K, Na Ti, K feldspar, and apatite; the breccias also contain 0.1-0.5 Ni, Y, Ba, Ce Ni, Cr above-normal concentrations of beryllium, tho- 0.05-0.1 Mn, Nd - 0.01-0.05 La, Sr, V, Co, Cr, Zr, Cu Mn, Ba, Na, Sr, V, Cu rium, niobium, and zirconium. 0.005-0.01 Nb, Zn, Ga. Co, Ga Before the early 196d's, the dikes, sills, and 0.001-0.005 Yb, Pb, Mo, Sc, Be La, Nb, Y, Pb, Nd, breccias were dated as post-Middle Pennsylvaniail Zr, Mo, Sc - on the basis of stratigraphic relations. Zartman 0.0001-0.0005 1 Ag Yb, Ag, Be and others (1967, p. 860-861) studied samples of * Analyses by Mona Frank, U. S. Geol. Survey, Sept. 1955. biotite, phlogopite, and hornblende from the dikes, sills, and breccias; on the basis of radio- in diamond-drill exploration. Some in Illinois isotope studies they reported that: "All the ages have been found during mining. A few have been lie within experimental uncertainty of each other found during areal mapping in Kentucky (Amos, and given an average Early Permain age of 267 1966; Trace, 1966) and in Illinois. Probably many million years." more have not been found because mafic rock on Alteration exposure decomposes within a few years ,and is silicification is the most striking ch,ange in the difficult to recognize. Where continuously washed wall rocks of veins along faults. Where at least clean, as it is by Claylick Creek near the eastern one fault wall is a Chester sandstone, the ' sand- edge of the Salem quadrangle (Trace, 1962a), stone close to or within the fault zone is altered inafic dike rock superfically resembles a dark-gray to quartzite. Indeed, the tracing of "quartz reefs" limestone. or fragments of quartzite is the best means of Many breccias and brecci'a "dikes" have been mapping faults in some 'areas. Study of a few thin mapped in the Illinois part of the district by sections of quartzite from the Comnlodore area Baxter and Desborough (1965) and by Baxter in the Salem quadrangle suggests that little or no and others (1967), and have been described in secondary silica has been added to the sandstone. some detail (Clegg and Bradbury, 1956; Brown Pore space in the quartzite is essentially non- and others, 1954). According to Baxter and Des- existent, and the rock consists of tightly grouped borough (1965, p. 28), "The breccias consist of and embayed angulcar to subrounded quartz sand angular- to subrounded fragments- of sedimentary, grains. Hardin (1955, p. 24) suggested that in the metamorphosed sedimentary, and igneous rocks Babb area in the Salem quadrangle the "secondary in a matrix of finely ground rock and mineral silicification appears to have been of more signif- fragments. The mineral fragments include quartz, icance than pressure in the conversion of sand- pyroxene, augite, hornblende, apatite, mica, and stone to quartzite." feldspar." Grogan and Bradbury (1968, p. 376) The 'alteration ,of limestone wall rocks generally described fine-grained- nepheline-feldspar rock in is slight to moderate. In places, many small doubly one of the breccias. terminated quartz crystals and small masses of Many of these bodies of breccias, which are chalcedony have been reported (Hardin, 1955, p. roughly circular or elliptical in plan and as much 24; Trace, 1962b, p. 17; Trace, 1954, p. 70) where as 1,000 feet in diameter, are pipes or small stocks. limestone is adjacent to a vein. Fragments of Some of the breccia masses are vertical or steeply dolomitic limestone, which is a relatively common dipping linear bodies which resemble dikes. country rock of the area, are present within the Many of the breccias contain a variety of veins. No secondary dolomitization of the wall minerals, both on the surface and to depths of rocks of vein deposits has been reported, but very ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 65 little research has been completed on this possi- Structure bility to date. According to Heyl and Brock (1961, p. D3), Hall and Heyl (1968, p. 661) described visibly "The Illinois-Kentucky mining district is centered altered wall rocks as much as 100 feet laterally in the most complexly faulted area in the central from a bedding-replacement deposit. According craton of ,the United States. Structural studies to them, geochemical and clay-mineral studies suggest that the mining district lies within a h'ave shown that alteration includes solution thin- collapsed, block-faulted, sliced, and partly rotated ning, silicification, dolomitization, and clay-min- domal anticline that is located at and near the era1 alteration. Brecke (1962, p. 525-530) de- intersections of several major fault lineaments." scribed the alteration of country rock, primarily (See Fig. 6.) Heyl (1972) has related the fluor- within the mineralized zones, as decalcification, spar district to the intersection of the 38th parallel dolomitization, and silicification. According to lineament with the New Madrid fault system. Pinckney and Rye (1972, p. 4), limestone wall- Within the fluorspar district (see Fig. 1) the rock alteration in the Hill mine near Cave in rocks are complexly broken by a series of steeply Rock, Ill., included dolomitization, recrystalliza- dipping to vertical normal or gravity faults that tion of limestone, and silicification of both lime- trend dominantly northeast and break the area stone and dolomite. into elongated northeast-trending blocks. Many

EXPLANATION

l2szfEl +-- -7- B.se of Cretaceous mks Fault MormIina Slrounng dtp and darectlrm of ,/wpiocemnt whars knmun, darhrd where ~nfemdor Bare of Pennsylm~u%meks dsd rn

0 IntenselyQ diaturbd CBrnbrim lhmugh Mi.aiaaippim mcka bali.sd uplift -f- Anticline

Figure 6. Major structural features near the Illinois-Kentucky mining district. Geology compiled from many pub- lished sources by A. V. Heyl, Jr., J. L. Jolly, C. E. Wells, and M. R. Brock. (From Heyl and Brock, 1961, fig. 294.1.) 66 ROBERT D. TRACE cross faults that trend north to northwest are occupied in places by mafic dikes. Near the east edge of the Kentucky part of the district, the faults trend more to the east; in Illinois, radial and arcuate faults surround Hicks dome. Hicks dome is a structural high with about 4,000 feet of vertical uplift that is centered in the south- west part of the Karbers Ridge quadrangle, Illinois (Baxter and Desborough, 1965). Brown and others (1954) described the dome as an incipient crypto- volcanic structure on the basis of breccias in an oil-test hoIe, nearby exposed arcuate faults, and the unusual quantities of rare earths, thorium, and beryllium in ithese breccias. As ,a result of an aeromagnetic survey, McGinnis and Bradbury (1964, p. 11) stated that Hicks dome is not under- lain by a laccolithic intrusion, but they observed that: "A broad magnetic anomaly of relatively low 0 100 FEET intensity centered about 5% miles northeast of Figure 7. Cross section of Babb area, Crittenden County, Hicks dome and the featureless configuration of Ky., showing dip of vein. (From Hardin, 1955, port of contour lines around the anomaly suggest a large pl. 4.) igneous body overlain by a thick sedimentary rock section." subparallel and sinuously intersecting fractures. The southeasterly extension of the dome is These zones are commonly a few hundred feet partly obscured by a 4- to 5-mile-wide fault zone, wide, although at places they (are more than 1,000 largely a downdropped area known as the Rock feet wide. The total displacement attributable to Creek graben. Southeast of the graben, the struc- a fault zone is commonly distributed irregularly tural high reappears as the Tolu dome or arch, among the several individual faults-as step faults which is centered about a mile east of Tolu, Ky., and also as small grabens within the flault zone. in the Cave in Rock quadrangle (Baxter and In places, the bounding faults of the zone may others, 1963; Trace, unpub. data). dip toward each other (Fig. 8). Minor faults may Southeast of the Tolu arch is another series of occur outside of, but within a few hundred feet of, grabens (Weller and Sutton, 1951), bounded on the major fault zones-most comn~only on the the south by the Tabb fault system (Rogers and hanging-wall side. Hays, 1967). Because of the many faults within Data regarding a dominant direction of move- this part of the district, the structural high is more ment along the northeast-trending faults are con- difficult to trace; a possible extension is shown flicting, perhaps suggesting that both vertical and on the Salem quadrangle (Trace, 1962a) between some horizontal movement may have taken place. the Levias-Crittenden Springs and the Moore Vertical displacement generally is considered to Hill fault systems. Further south, in the Dycus- have been the dominant direction of movement burg quadrangle, mapping (see Fig. 1) suggests along the major northeast-trending faults in the three more possible segments of the arch (D. H. district; some evidence of an unknown amount of Amos, written commun., 1972). horizontal movement, however, has been noted Nearly all faults in the district are called (Weller and Sutton, 1951). Clark and Royds (1948) normal and dip generally 75' to vertically; rarely and Hey1 and Brock (1961) suggested that a are they inclined as low as 45". Loclally, the horizontal component of movement may be sig- direction of dip of a fault or vein may be reversed, nificant. as shown in Figure 7. Along the edges of many Field mapping has shown that perhaps as much of the larger grabens, fault zones consist of several as 3,000 feet of vertical displacement has taken ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 67

All wfltings pqctad to pl*m of ¶utlon

EXPLANATION

9.;.0.,.:6 Fault breccia Fluorspar

Figure 8. Cross section of Davenport area, Crittenden County, Ky. (From Thurston and Hardin, 1954, part of pl. 14.)

place. Positive evidence for substantial horizontal The amount of vertical displacement of the movement is not obvious. For example, a dike faults varies widely. The greatest amount of dis- swarm extending from the Glendale Church are1a placemen't is reported in Kentucky in the south- southeast through the Columbia mine area to the east corner of the Smithland quadrangle (Amos, Claylick Creek area in the Salem quadrangle of 1967) and in the southwest corner of the Burna Kentucky (Trace, 1962a) is reasonably continuous quadrangle (Amos, oral commun., 1971). At the even though it is crossed by two major fault zones. locality in the Burna quadrangle, sandstone of the The relations suggest at best only a little post-dike Caseyville Formation of Pennsylvanian age is horizontal movement. On the other hand, pre- next to the Fort Payne Formation of Early liminary mapping of the Hicks-Tolu structural Mississippian age. The general thickness of the high southward through the Cave in Rock quad- Mississippian rocks above the Fort Payne is about rangle (Trace, unpub. data) and the Dycusburg 2,400 feet; hence, the minimum total displacement quadrangle (D. H. Amos, unpub. data) suggests would be 2,400 feet. Considering that the Fort horizontal offsetting, or at least bending, of the Payne is about 600 feet thick and the Caseyville axis of the structural high (see Fig. 1). is a few hundred feet thick, displacement might 6 8 ROBERT D. TRACE be as much as 3,000 feet. In general, displacement Ordovician (Brown and others, 1954). A related is much less, commonly ranging from a few feet fluorite deposit cementing breccia has been mined to a few hundred feet. at the Rose mine near Hicks dome. Little information is available regarding the amount of fault displacement in the subsurface Veins below depths of 1,000 feet. A few drill holes in the Crittenden Springs and Commodore areas of Most of 'the vein ore deposits are along north- Ken'tucky indicate that the amount of displace- east-trending faults, although la few veins are ment at depths of nearly 2,000 feet below the along northwest- and north-trending fissures or surface is about the same as that at the surface. faults that are in places occupied by mafic dikes. Field evidence suggests that at least some and The distribution of mineralized areas is shown in probably most of the major northeast-trending Figure 2. Mines are shown by Hey1 and others faults {areyounger than Hicks dome and the mdc (1965, pl. 2). dikes, and, therefore, are post-Early Permian in The fluorspar veins commonly are fissure fillings age. The major displacement along these faults along faults and in fault breccia, accompanied by may have been completed by middle Cretaceous replacement of vein calcite and some limestone time, although some movement has continued wall rock. A typical vein is lenticular, pinches through Cretaceous and Tertiary time to the and swells erratically, and is comnlonly a mixture present (Rhoades and Mistler, 1941; Ross, 1963; of fluorite with highly variable quantities of calcite McGinnis, 1963; Amos, 1967). and country-rock fragments. Loclally, the vein Locally some f'ault movement may have started may be either entirely calcite or fluorite. Com- during Early Pennsylvanian time. For example, monly, contact with vein walls is sharp; however, in the northern part of the Golconda quadrangle, at places, veinlets of fluorite and calcite extend a the lowermost Pennsylvanian Lusk Member of the few hundred feet beyond a vein into slightly Caseyville Formation in an oil test within the broken wall rock. In many veins, sphalerite, Rock Creek graben is about 130 feet thick, where- galena, and barite are accessory minerals; in a few as the unit is only 50 feet thick where exposed veins they are major constituents. A few veins of along the eastern margin of the graben (Amos, sphalerite and pyrite without fluorite have been 1966). Possibly the easterly thinning and westerly productive, and a few barite veins are known. thickening are due, respectively, to movement The fluorite varies from fine and medium and graben fill that began in Early Pennsylvanian crystalline in small, commonly purple, veinlets to time. coarsely crystalline in commonly brown, white, or colorless, more massive veins. In many places, the CHARACTERISTICS OF ORE BODIES veins are complexly brecciated and/or sheeted. Most fluorspar ore bodies occur either as steeply Rude banding parallel to vein walls is present dipping to vertical vein deposits along faults or locally. Shaly fault gouge, presumably dragged in as very gently dipping to nearly horizontal bed- along the faults from shale units of the Chesterian ding-replacement deposits along certain strati- Series, is common in places. graphic horizons in limestone of Late Mississip- Width of most veins averages 3 to 10 feet pian age (Fig. 4). Numerically, the known bed- (Hardin and Trace, 1959; Trace, 1962b), although ding-replacement deposits consist of probably less a width of as much as 45 feet is reported (Grogan than a quarter of the total number of deposits; and Bradbury, 1968, p. 379). Length of mined ore most of the deposits are veins. A few deposits, shoots commonly ranges from 200 to 400 feet, especially in Illinois, are made up of a combina- although in many places, particularly in the tion of vein and bedding-replacement-type ore Rosiclare area of Illinois, greater lengths are and so-called gravel deposits thtat resulted from common. The average height of ore shoots is 100 concentrations of fluorite in residuum above vein to 200 feet, although ore shoots extending from deposits. Disseminated fluorite is present in the the surf,ace to a depth of nearly 800 feet were breccias of Hicks dome as deep as the Middle reported by Grogan and Bradbury ( 1968, Fig. 10). ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 69

Bedding-Replacement Deposits Most bedding-replacement deposits and mines occur in the Cave in Rock, Ill., area, in the north- east part of the district (Fig. 2). Another area (and one operating mine) is present in Kentucky, beginning just southwest of, and across the Ohio River from, Rosiclare, Ill., and extending south- ORE BODY SYMMtlRICAL 4BOUT CENTRAL FISSURE ward to near Joy, Ky. Probably labout two-thirds of the mined bedding-replacement ore has been from the uppermost ore horizon near the top of the Renault or "Downeys Bluff Limestone (Fig. 4). The stratiform or bedding-replacement deposits are elongated bodies that trend northeastward I ORE BODY ON ONE SIDE OF MINOR FAULT sc.Lc and, less commonly, southeastward (Fig. 9). Most Figure 10. Characteristic cross sections through strati- of these deposits "are localized along a network of form deposits and enclosing strata. (Reproduced from fractures and minor faults parallel to and half a Economic Geology, 1949, vol. 44, p. 608.)' mile distant from the Peters Creek fault. . . ." (Grogan and Bradbury, 1967, p. 41-42). In cross 515-525) as banded, imperfectly banded, and section, they are crescentic or wedge shaped (see breccia. The imperfectly banded and breccia Figs. 10 and 11). A few pipe-like breccia-zones types constitute most of the deposits. are mineralized (in places, with commerci'al-grade The ore bodies are commonly 50 to 200 feet ore) and may be the conduits for ore solutions wide and 5 to 20 feet thick; the length is highly (Brecke, 1962, p. 511-514; Grogan and Bradbury, varimable, from 200 feet to 2 miles. The distribu- 1968, p. 393-394). tion of the mineralized trends is shown in Figure 9. The texture of the bedding-replacement de- The bedding-replacement deposit being mined posits has been described by Brecke (1962, p. in Kentucky is believed to be approximately 2 miles long and 150 to 250 feet wide. It has an Cove in Rock Fluorspor Dislricl / I average thickness of 7 feet and contains about 30 Hardin County, lll~nols / percent CaFz and small quantities of zinc and Legend barite (J. S. Tibbs, oral commun., 1971). Bethel Hor~zon Ros~clareHor~zon Depth of Ore Sub Rosiclare - Breccia Pipe Dcldned The deepest mined fluorspar is 800 to 900 feet Possible Breccio Pope C Sulfide Orebody & below the surfiace in the Fairview mine in ithe Rosiclare area, Ill. (Grogan and Bradbury, 1968, p. 380). The deepest mine in the Kentucky area is about 700 feet (Dyer Hill mine for fluorspar and Hutson mine for sphalerite). Several holes drilled in the Rosiclare area (Muir, 1947) have inter- sected the veins more than 1,300 feet below the surface, but the veins at that depth are dominantly calcite and wall-rock fault breccia. A few deep holes drilled in Kentucky to depths of almost 2,000 feet have penetrated similar calcite veins.

Grade of Ore Figure 9. Cave in Rock fluorspar district, Hardin County, Ill. (Reproduced from Economic Geology, 1967, vol. 62, The average grade of ore mined from the de- p. 381.) posits has varied. Thirty years ago, the ore mined ROBERT D. TRACE

commonly contained at least 45 percent CaF2, but gradually the ore cutoff grade has dropped and now is probably 25 to 40 percent CaF2. Various factors have influenced the ore grade, such as the selling price of the finished product, the amount of byproduct zinc and lead (see below), and also the varying costs of mining, which are determined primarily by type of deposit ,and in part by mine depth, amount of water, and degree of stability of mine walls or roof. The sphalerite, galena, and barite content of the mined veins and bedding-replacement deposits varies erratically. A substantial number of de- posits, however, contain an average of about 2 to 3 percent zinc and 1/2 to 1 percent lead. Some contain almost none or only negligible quantities of these minerals. At the other extreme, a few deposits are dominantly sphalerite or barite, with little or no fluorite, and may contain as much as 15 percent zinc and 30 to 40 percent barite. Rarely, galena is the dominant mineral. The uppermost ore horizon of the bedding- replacement deposits, although the largest pro- ducer among the bedding-replacement deposits, is characterized by a lower average content of CaFa and Pb but is higher in Zn and its contained germanium and cadmium than the other two principal ore horizons (see Fig. 4). Cadmium is reported by Grogan and Bradbury (1968, p. 384) to average 1 percent in zinc concentrates from an Illinois bedding-replacement deposit. The galena in the Illinois part of the district contains as much as 1,000 ppm silver; that in the Kentucky part contains much less, 5 to 45 ppm (Hall and Heyl, 1968, p. 656).

Mineralogy al- .-C Quantitatively, the principal minerals in the E P vein deposits are calcite and fluorite. In places, 0 LC minable deposits of only sphalerite or barite are 6 present, although more commonly the sphalerite, i .-0 barite, and galena occur in small quantities with &u al the fluorite. Minor quantities of quartz, ferroan In In dolomite, pyrite, marcasite, chalcopyrite, and 8 locally the zinc, lead, or copper alteration products 3 (cerussite, pyromorphite, smithsonite, hemimor- -C phite, greenockite, cuprite, and malachite) are ?! ?! - a present. Celestite occurs in one locality in Ken- .-0 Y tucky (Hardin and Thurston, 1945). ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 7 1

The vein and bedding-replacement deposits Oldest Rhombohedral calcite I contain essentially the same suite of minerals. I The principal difference is in the quantity of Yellow fluorite I - White fluorite calcite, which is very abundant in the vein de- Blue fluorite posits and common, although not abundant, in the Early purple fluorite bedding-replacement deposits. Chalcopyrite Fluorite is the principal mineral in the bedding- Quartz replacement deposits. Sphalerite, galena, and Sphalerite Galena barite are locally very abundant but in places Late purple fluorite they are uncommon. Small quantities of calcite Bitumen and quartz are persistent. Coarse quartz, how- Scalenohedral calcite ever, is so abund'ant in a few deposits, such as the Barite southwest end of the Deardorf mine (Illinois) Witherite that it prevents profitable mining' Ferroan Figure 12. Paragenetic sequence in the Cave in Rock is an abundant gangue in the district. Illinois. (Reproduced from Economic Geology. walls of most bedding-replacement ore babes and 1963, 58, p. 891.) occurs in small fissure veins in the Oxford mine (Illinois). Witherite occurs in such quantities in one Illinois orebody that it made concentration of vapor bubbles in fluid inclusions, indicate a fluorite difficult. range of 90" to 140°C. Chalcopyrite, marcasite, pyrite, witherite, stron- The composition of fluid inclusions in the ore tianite, smithsonite, cerussite, malachite, bitumen, and gangue minerals of the Cave in Rock area and pyromorphite have been reported by Grogan has been studied by Hall and Friedman (1963), and Bradbury (1968, p. 384-385). Park (1967) who reported that the general composition of the reported that bravoite and vaesite occur in very fluid inclusions suggests that the fluorite was de- small quantities locally in Illinois. posited from a concentrated Na-Ca-C1 brine, According to Hall and Heyl ( 1968), the fluorite probably of connate origin, to which F has been in the district is remarkably pure except that found added. Fluid inclusions in quartz, however, con- in breccias at Hicks dome which contains abun- tain smaller concentrations of solids than do dant rare-earth elements. Sphalerite of the district other gangue minerals and have a higher ratio contains rather high amounts of cadmium, ger- of K/Nma, Ca/Na, Cl/Na, and S04/Na, and a manium, and gallium. Galena here contains as lower relative deuterium concentration. Possibly much as 1,000 ppm silver and antimony; the part of the fluids in the quartz period of deposi- highest silver concentration is around Hicks dome, tion and the fluorine were derived from magmatic with lesser quantities outward. water. The paragenesis of vein and bedding-replace- Zoning ment deposits appears to be similar. Of the more abundant minerals, the time of most calcite em- No apparent district-wide zoning of the fluorite, placement was earliest and was overlapped 'and sphalerite, and galena has been reported. Brecke followed by emplacement of fluorite. Some calcite (1964a) suggested that barite is more common on is a late mineral. Sphalerite and galena emplace- the fringes of the district, but the relative ment generally appears to overlap and follow abundance of barite in the Lola, Ky., area obscures fluorite, and barite is the youngest main mineral. the broad picture. Hall and Friedman (1963, p. 891) reported in Heyl (1969) suggested a zonation pattern for more detail on the paragenesis of the Cave in the occurrence of silver and antimony in galena Rock deposits (Fig. 12). around Hicks dome (see also Heyl and others, Depositional-temperature studies by Freas 1966) and a systematic change in lead isotopic (1961) and by Grogan and Shrode (1949), who ratios for the area extending from Hicks dome used a method based on the disappefarance of southeastward into Kentucky. 72 ROBERT D. TRACE

Age indicates a primary monazite derived from the Accurate dating of the age of mineral deposi- mantle. tion here is difficult. Stratigraphic relations indi- CONCLUSIONS cate that the minerals were deposited after the Ore Controls Lower to Middle Pennsylvanian rocks were laid down. To the writer's knowledge, no fluorite has The general location of the Illinois-Kentucky been found along faults where at least one fault district may be structurally coiltrolled by the wall is of Cretaceous or younger age. Thus, the intersection of northeast-trending faults of the age of mineralization is post-Early or Middle New Madrid system (Fig. 6) with a large north- Pennsylvanian and pre-Late Cretaceous. west-trending structural uplift, northwest-trend- The fluorspar, on the basis of field relations, is ing mafic dikes, and the 38th-parallel lineament. younger than the mafic rocks and the major north- This east-trending lineament of igneous activity east-trending faults. These faults are probably described by Snyder and Gerdeinann (1965) and younger than the mafic rocks, as no mafic rock is by Heyl (1972) passes through the district and is known along any of these faults. The mafic rocks intersected by the fault systems. hlave been dated isotopically as Early Permian; Faulting was the primary factor within the thus, both the major faults and fluorspar are post- district that controlled location of ore deposits, Early Permian. particularly vein deposits. Faults served as solu- Heyl and Brock (1961, p. D6) reported a lead- tion channelways for ore and provided space for alpha age of 90 to 100 million years (middle deposition of ore bodies. Fractures and minor Cretaceous) for the monazite found near the faults apparently were also significant factors in surface at Hicks dome. If this is a valid determinia- the localization of the bedding-replacement de- tion (see below), and if the monazite and fluorite posits, although their control on the shape of these are of the same approxin~ateage, as perhaps deposits is somewhat less obvious than on vein suggested by the relative abundance of rare deposits. Strata with low permeability, breccia earths in the fluorite near Hicks dome, then the pipes, and unconformities have been suggested as age of the fluorite could be middle Cretaceous, a factors that localized bedding-replacement de- theory that does not conflict with known strati- posits ( Brecke, 1962; Grogan and Bradbury, 1968). graphic relationships. Exploration and identifying individual vein de- Heyl ( written commun., 1972), however, sug- posits that contain minable fluorspar are costly gested that the lead-alpha date on the monazite and difficult because the veins contain highly is so open to question because of the material varying quantities of calcite and fluorite. So far available that it should be discarded. Earthy as the writer is aware, there are no guides to monazite (land florencite), strikingly similar )to the predict the calcite/fluorite ratio of a given vein earthy Hicks dome monazite (and florencite), was prior to subsurface exploration. described from Magnet Cove, Ark., by Rose and One broad factor land a few more specific ones others (1958); they believe that the Arkansas that might exercise some control of vein widths monazite is a secondary product of weathering of along the faults have been suggested by Grogan rare-earth-bearing apatite. Fluorapatite has been and Bradbury (1968), Thurston and Hardin (1954), identified by X-ray analysis by the writer in the and Trace (1954, 1962b). For example, most of mdc rocks of Kentucky, and apatite is present in the ore has been mined from veins where at least some of the Hicks dome breccia. If the monazite one wall, and commonly both walls, include the is secondary, its value in dating the deposits is Cypress, Paint Creek (Ridenhower), Bethel, reduced considerably. Renault, Ste. Genevieve, and St. Louis Formations On the other hand, W. C. Overstreet (oral of Mississippian age. The combined thickness of commun. to A. V. Heyl, 1968) has disagreed with these units is about 1,000 feet. Possibly this strati- Rose and others and does not believe that weather- graphic control was effective because these units ing-product monazite exists and that the composi- are donlinantly competent and massive in contrast tion (i.e., enrichment in yttrium and thorium) to the units of post-Cypress age which contain ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 73 many beds of incompetent shale, siltstone, and Sequence of Events and Genesis thin-bedded sandstone. Openings formed by The sequence of events and genesis of the faults where the walls are composed of Cypress Illinois-Kentucky fluorspar district has been dis- Sandstone or older rocks probably remained open cussed by Amstutz and Park ( 1967), Brecke ( 1962, and received vein fillings; incompetent shaly 196413, 1967), Brown (1970), Grogan and Brad- material would less likely be dragged into and bury ( 1968), Hall and Friedman ( 1963), Hall and fill the fault zone. Also, the faults may steepen Heyl ( 1968), Heyl and others ( 1965), Heyl ( 1969), in dip where they intersect the more competent Oesterling (1952), Park and Amstutz (1968), and beds; this local steepening along normal faults Snyder and Gerdemann (1965). There is no con- could have allowed more space for mineral de- sensus of opinions. Most geologists consider the position. Similarly, where competent beds are deposits to be epigenetic; Amstutz and Park (1967) involved, the total displacement of the f'ault consider them to be syngenetic. system is taken up by many faults, thus creating more space, rather than by a few faults that The exact timing of events and the origin of created less space and steeper drag-folded walls, many of the unusual geologic features of the as in places where post-Cypress units are involved. district are debatable. However, as a result of considerable research and field mapping in the The amount of fault displacement may have last two decades by the Illinois State Geological influenced vein width. Thurston and Hardin Survey, the U. S. Geological Survey in coopera- (1954, p. 98) suggested that "extreme dislocation tion with the Kentucky Geological Survey, and may produce excessive breccia and fault gouge." by several mining company geologists, much has Perhaps a displacement of 25 to 500 feet was been added to the geologic knowledge of the dis- optimum for wide veins, as suggested byhGrogan trict. and Bradbury (1968, p. 390-392). Many of the structural and mineralogical events A change in the general strike of a fault system must have overlapped and recurred, thus con- may influence the location of deposits. Possible fusing and frustrating many a geologist! In gen- examples include, in Kentucky, the Babb area eral, however, the geologic history can be divided (Trace, 1962a) and Dyers Hill area (Amos, 1967) into three broad phases, all probably occurring and, in Illinois, the Rosiclare area (Baxter and principally within the interval of post-Middle Desborough, 1965; Amos, 1965). Pennsylvanian to pre-middle or Late Cretaceous. The spatial relation of mafic dikes to zinc de- The oldest events were the structural arching and posits and fluorspar deposits hlaving substantial formation of Hicks and Tolu domes, the intrusion byproduct zinc and lead is well known. This of mafic dikes and sills, and the formation of type of metallic sulfide mineralization may occur breccias. According to Zartman and others ( 1967), either along northwest- or north-trending faulted these events appear to be approximately Permian mafic dikes or along northeast-trending faults that in age. Next came most of the movement along are near mafic dikes. A deposit that contains the northeast-trending faults, followed by mineral abundant sphalerite and is rather close ito a mafic deposition. dike was recently discovered in Livingston Coun- The deposits are considered by most geologists ty, Ky. (Mining Record, Denver, Colo., Dec. 23, (Brown, Grogan and Bradbury, Heyl and asso- 1970). ciates, and the writer) as epigenetic, the ore Brecke (1967, p. 387) thinks that zinc sulfide elements being carried by hot connate water, deposition may be related to the iron sulfide of which was heated by deep-seated igneous activity, the mafic rocks. Oesterling (1952, p. 332) sug- upward along the faults to the present locations. gested that sphalerite was deposited where dikes At least some of the ore elements presumably were offset by faults after deposition of fluorite. were contributed to connate water by deep-seated According to Hardin (1955, p. 23), "the distribu- igneous activity. Heyl (oral commun., 1972) and tion of sphalerite is controlled to some extent by Hall and Friedman (1963) suggested that much the cross and subparallel faults" of the fault zone; of the calcite, dolomite, silica, and even the lead, thus he implied late-stage faulting. zinc, and barium (but not fluorine or silver) may 74 ROBERT D. TRACE have been derived from the connate brines and/or quadrangle in Kentucky: U. S. Geol. Survey Geol. the rocks through which they passed. Quad. Map GQ-546. 1967, Geologic map of part. of the Smithland Amstutz and associates suggested a syngenetic quadrangle, Livingston County, Kentucky: U. S. origin, and Brecke suggested that warm connate Geol. Survey Geol. Quad. Map GQ-657. water picked up the ore elements from the sed- Amstutz, G. C., and Park, W. C., 1967, Stylolites of iments and moved them laterally into the district diagenetic age and their role in the interpretation of from the southwest, without recourse to igneous the southern Illinois fluorspar deposits: Mineralium Deposita, v. 2, no. 1, p. 44-53. activity. Bastin, E. S., 1931, The fluorspar deposits of Hardin and Pope Counties, Illinois: Illinois State Geol. Survey Potential Bull. 58, 116 p. The imminent death of the fluorspar district has Baxter, J. W., and~esborou~h,G. A,, 1965, Areal geology of the Illinois fluorspar district-Part 2, Karbers Ridge been predicted verbally for many years-even in and Rosiclare quadrangles: Illinois State Geol. Survey 1942, when the writer first worked in the area. Circ. 385, 40 p. Although no comprehensive survey of fluorspar Baxter, J. W., Desborough, G. A,, and Shaw, C. W., 1967, reserves has been made since 1956 (Fluorspar Areal geology of the Illinois fluorspar district-Part 3, Reserves of the United States Estimated, press Herod and Shetlerville quadrangles: Illinois State release, Office of Minerals Mobilization and Geol. Survey Circ. 413, 41 p. Baxter, J. W., Potter, P. E., and Doyle, F. L., 1963, Areal Geological Survey, Nov. 23, 1956), a brief survey geology of the Illinois fluorspar district-Part 1, Saline in the district by the author suggests that under mines, Cave in Rock, Dekoven, and Repton quad- 1971 economic conditions and continued current rangles: Illinois State Geol. Survey Circ. 342, 43 p. production, reserves are still substantial and Bradbury, J. C., 1962, Trace elements, rare earths, and probably adequate for #at least 15 to 20 years. chemical composition of southern Illinois igneous They are by far the largest fluorspar reserves in rocks: Illinois State Geol. Survey Circ. 330, 12 p. Bradbury, J. C., Ostrom, M. E., and McVicker, L. D., the United States, far surpassing any other district 1955, Preliminary report on uranium in Hardin Coun- or region. ty, Illinois: Illinois State Geol. Survey Circ. 200, 21 p. New finds of near-surface "gravel" deposits of Brecke, E. A,, 1962, Ore genesis of the Cave in Rock fluorspar probably will be rare, and results from fluorspar district, Hardin County, Illinois: Econ. Geology, v. 57, no. 4, p. 499-535. deep (more than 1,000 feet) exploration have -1964a, Barite zoning in the Illinois-Kentucky been only slightly to moderately encouraging. The fluorspar district: Econ. Geology, v. 59, no. 2, p. very large number of faults within the district not 299-302. adequately tested at intermediate or, even in 1964b, A possible source of solutions of the places, shallow depths, however, suggests to the Illinois-Kentucky fluorspar district: Econ. Geology, writer that the district will be a source of fluorspar v. 59, no. 7, p. 1293-1297. 1967, Sulfide and sulfur occurrences of the for many years. Currently, exploration is increas- Illinois-Kentucky fluorspar district: Econ. Geology, ing, and several new discoveries of ore have been v. 62, no. 3, p. 376-389. made in the last few years. Brown, J. S., 1970, Mississippi Valley type lead-zinc ores; The fluorite occurrences in the breccias around a review and sequel to the "Behre Symposium": Hicks dome currently are too low grade to mine. Mineralium Deposita, v. 5, no. 2, p. 103-119. Brown, J. S., Emery, J. A., and Meyer, P. A., Jr., 1954, Under more favorable economic conditions and Explosion pipe in test well on Hicks dome, Hardin with recovery of the byproduct minerals, large- County, Illinois: Econ. Geology, v. 49, no. 8, p. scale mining of these breccias might be under- 891-902. taken some time in the future. Clark, S. K., and Royds, J. S., 1948, Structural trends and fault systems in Eastern Interior basin: Am. Assoc. ~etroliumGeologists Bull., v. 32, no. 9, p. 1728-1749. REFERENCES CITED Clege;, K. E., and Bradbury,. -J. C., 1956, Igneous- intrusive Amos, D. H., 1965, Geology of parts of the Shetlerville rocks in Illinois and their economic significance: and Rosiclare quadrangles, Kentucky: U. S. Geol. Illinois State Geol. Survey Rept. Inv. 197, 19 p. Survey Geol. Quad. Map GQ-400. Freas, D. H., 1961, Temperatures of mineralization by 1966, Geologic map of the Golconda quadrangle, liquid inclusions, Cave in Rock fluorspar disbict, Kentucky-Illinois, and a part of the Brownfield Illinois: Econ. Geology, v. 56, no. 3, p. 542-556. ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 75

Grogan, R. M., 1949, Structure due to volume shrinkage McGinnis, L. D., 1963, Earthquakes and crustal movement in the bedding-replacement fluorspar deposits of as related to water load in the Mississippi Valley southern Illinois: Econ. Geology, v. 44, no. 7, p. region: Illinois State Geol. Survey Circ. 344, 20 p. 606-616. McGinnis, L. D., and Bradbury, J. C., 1964, Aeromagnetic Grogan, R. M., and Bradbury, J. C., 1967, Origin of the study of the Hardin County area, Illinois: Illinois stratiform fluorite deposits of southern Illinois: Econ. State Geol. Survey Circ. 363, 12 p. Geology, Mon. 3, p. 40-50. Muir, N. M., 1947, Daisy fluorite mine, Rosiclare Lead & 1968, Fluorite-lead-zinc deposits of the Illinois- Fluorspar Mining Co., Hardin County, Illinois: U. S. Kentucky mining district, in Ridge, J. D., ed., Ore Bur. Mines Rept. Inv. 4075, 16 p. deposits of the United States, 1933-1967 (Graton- Norwood, J. G., 1866, Report on the Rosiclare lead mines: Sales volume), v. 1: New York, Am. Inst. Mining, Illinois Geol. Survey, v. 1, p. 366-372. Metall., and Petroleum Engineers, p. 370-399. Oesterling, W. A,, 1952, Geologic and economic signif- Grogan, R. M., and Shrode, R. D., 1952, Formation icance of the Huston zinc mine, Salem, Kentucky-its temperatures of southern Illinois bedded fluorite as relation to the Illinois-Kentucky fluorspar district: determined from fluid inclusions: Am. Mineralogist, Econ. Geology, v. 47, no. 3, p. 316-338. v. 37, no. 7-8, p. 555-566. Park, W. C., 1967, Early diagenetic framboidal pyrite, Hall, W. E., and Friedman, Irving, 1963, Composition of bravoite, and vaesite in the Cave in Rock fluorspar fluid inclusions, Cave in Rock fluorite district, Illinois, district, southern Illinois: Mineralium Deposita, v. and Upper Mississippi Valley zinc-lead district: Econ. 2, no. 4, p. 372-375. Geology, v. 58, no. 6, p. 886-911. Park, W. C., and Amstutz, G. C., 1968, Primary "cut and Hall, W. E., and Heyl, A. V., 1968, Distribution of minor fill" channels and gravitational diagenetic features: elements in ore and host rock, Illinois-Kentucky Mineralium Deposita v. 3, p. 66-80. fluorite district and Upper Mississippi Valley zinc- Pickney, D. M., and Rye, R. O., 1972, Variation of lead district: Econ. Geology, v. 63, no. 6, p. 655-670. 01*/O16, Cl3/C12, texture, and mineralogy in altered Hardin, G. C., Jr., 1955, Babb fault system, Crittenden limestone in the Hill mine, Cave in Rock district, and Livingston Counties, in Fluorspar deposits in Illinois: Econ. Geology, v. 67, no. 1, p. 1-18. western Kentucky: U. S. Geol. Survey Bull. 1012-B, Rhoades, R. F., and Mistler, A. J., 1941, Post-Appalachian pt. 1, p. 7-37. faulting in western Kentucky: Am. Assoc. Petroleum Hardin, G. C., Jr., and Thurston, W. R., 1945, Celestite Geologists Bull., v. 25, no. 11, p. 2046-2056. from Livingston County, Kentucky: Am. Mineral- Rogers, W. B., and Hays, W. H., 1967, Geologic map of ogist, v. 30, no. 9-10, p. 639-640. the Fredonia quadrangle, western Kentucky: U. S. Hardin, G. C., Jr., and Trace, R. D., 1959, Geology of Geol. Survey Geol. Quad. Map GQ-607. fluorspar deposits, Big Four fault system, Crittenden Rose, H. J., Jr., Blade, L. V., and Ross, Malcolm, 1958, County, Kentucky: U. S. Geol. Survey Bull. 1042-S, Earthy monazite at Magnet Cove, Arkansas: Am. p. 699-724. Mineralogist, v. 43, no. 9-10, p. 995-997. Heyl, A. V., 1969, Some aspects of genesis of zinc-lead- barite-fluorite deposits in the Mississippi Valley, Ross, C. A., 1963, Structural framework of southernmost U.S.A.: Inst. Mining and Metallurgy (London) Illinois: Illinois State Geol. Survey Circ. 351, 28 p. Trans., Sec. B, v. 78, Bull. 756, p. B148-B160. -1964, Geology of the Paducah and Smithland -1972, The 38th parallel lineament and its rela- quadrangles in Illinois: Illinois State Geol. Survey p. tionship to ore deposits: Econ. Geology, v. 67, p. Circ. 360, 32 879-894. Seeland, D. C., 1968, Geologic map of part of the Repton Heyl, A. V., and Brock, M. R., 1961, Structural frame- quadrangle in Crittenden County, Kentucky: U. S. work of the Illinois-Kentucky mining district and its Geol. Survey Geol. Quad Map GQ-754. relation to mineral deposits: U. S. Geol. Survey Prof. Snyder, F. G., and Gerdemann, P. E., 1965, Explosive Paper 424-D, p. D3-D6. igneous activity along an Illinois-Missouri-Kansas Heyl, A. V., Brock, M. R., Jolly, J. L., and Wells, C. E., axis: Am. Jour. Sci., v. 263, no. 6, p. 465-493. 1965, Regional structure of the southeast Missouri Thurston, W. R., and Hardin, G. C., Jr., 1954, Fluorspar and Illinois-Kentucky mineral districts: U. S. Geol. deposits in western Kentucky: Part 3, Moore Hill Survey Bull. 1202-B, 20 p. fault system, Crittenden and Livingston Counties: Heyl, A. V., Delevaux, M. H., Zartman, R. E., and Brock, U. S. Geol. Survey Bull. 1012-E, p. 81-113. M. R., 1966, Isotopic study of galenas from the Upper Trace, R. D., 1954, Fluorspar deposits in western Ken- Mississippi Valley, the Illinois-Kentucky, and some tucky; Part 2, Mineral Ridge area, Livingston and Appalachian Valley mineral districts: Econ. Geology, Crittenden Counties: U. S. Geol. Survey Bull. v. 61, no. 5, p. 933-961. 1012-D, p. 59-79. Koenig, J. B., 1956, The petrography of certain igneous -1960, Significance of unusual mineral occurrence dikes of Kentucky: Kentucky Geol. Survey, ser. 9, at Hicks dome, Hardin County, Illinois: U. S. Geol. Bull. 21, 57 p. Survey Prof. Paper 400-B, p. B63-B64. 76 ROBERT D. TRACE

-1962a, Geology of the Salem quadrangle, Ken- well Counties, Kentucky: U. S. Geol. Survey Geol. tucky: U. S. Geol. Survey Geol. Quad. Map.GQ-206. Quad. Map GQ-880. -1962b, Geology and fluorspar deposits of the Ulrich, E. O., and Smith, W. S. T., 1905, The lead, zinc, Levias-Keystone and Dike-Eaton areas, Crittenden and fluorspar deposits of western Kentucky: U. S. County, Kentucky: U. S. Geol. Survey Bull. 1122-E, Geol. Survey Prof. Paper 36, 218 p. 26 p. Weller, Stuart, and Sutton, A. H., 1951, Geologic map of 1966, Geologic map of the Marion quadrangle, the western Kentucky fluorspar district: U. S. Geol. Crittenden and Caldwell Counties, Kentucky: U. S. Survey Mineral Inv. Field Studies Map MF-2. Geol. Survey Geol. Quad. Map GQ-547. Zartman, R. E., Brock, M. R., Heyl, A. V., and Thomas, H. H., 1967, K-Ar and Rb-Sr ages of some alkalic Trace, R. D., and Palmer, J. E., 1971, Geologic map of intrusive rocks from central and eastern United the Shady Grove quadrangle, Crittenden and Cald- States: Am. Jour. Sci., v. 265, no. 10, p. 848-870. STRUCTURE OF THE FAULT SYSTEMS IN THE ILLINOIS-KENTUCKY FLUORSPAR DISTRICT JOHN W. HOOK Reynolds Metals Company Salem, Kentucky

ABSTRACT The Illinois-Kentucky fluorspar district is a gentle arch broken by north- east-trending fault systems. The fault systems are complex zones of step, antithetic, and cross faults between major horsts and grabens. The faults are predominantly normal and have dips ranging from 45 to 90 degrees. Vertical displacements range from a few feet to over 1,500 feet. The cumu- lative heave components of the normal faults indicate that the district has been extended about 1 mile in a northwest-southeast direction. Basement spreading related to minor rifting along the New Madrid fault zone is the probable cause of the crustal tension and gravity collapse. As the major grabens moved downward in a keystone manner to fill the voids, minor blocks broke loose along the edges creating the complex fault systems. The minor blocks were subject to both gravity movement and the downward drag of the grabens. The structure of the district is further complicated by strike-slip move- ment. The magnitude of the strike-slip faulting is difficult to meosure, but it is probably minor in comparison to that of the gravity faulting.

INTRODUCTION by basic dikes. This paper will deal primarily The Illinois-Kentucky fluorspar district is a with the structure of the northeast-trending fault gently arched, block-faulted area in the deepest systems. part of the Illinois basin. The block faulting is of MAJOR STRUCTURAL FEATURES the horst-and-graben type. The faults are pre- dominantly normal and have northeasterly strikes. Figure 1 is a composite from many published The term "fault system" as commonly used in the and unpublished sources. It shows the prominent fluorspar district refers to wide zones of multiple structures in and around the fluorspar district. / faulting between horst and graben blocks. For The Cretaceous and younger formations are example, the Moore Hill graben in Kentucky is omitted because most of the faulting predates the bounded on the northwest by the Moore Hill fault Cretaceous and is masked by it. system and on the southeast by the Claylick Creek The Shawneetown-Rough Creek fault zone fault system. The fault systems vary from a single along the northern edge of the district is described fault to complex zones of step, antithetic, and cross as a high-angle reverse fault. It is considered by faults as much as 1,500 feet wide. The vertical some geologists to be a thrust fault and by others displacements between the horsts and grabens to be a wrench fault. Heyl (1972) related this are commonly 500 to 1,500 feet, with a maximum structure to the 38th parallel lineament, a major of about 3,000 feet. basement lineament stretching from the Appala- The vein-type deposits of fluorspar are usually chians to the Ozarks, and possibly to the Rockies. along faults in the northeast-trending fault sys- The New Madrid fault zone in the Mississippi tems. Some economic deposits of fluorspar, and embayment projects northeastward through the especially zinc, are found along north- to north- Illinois-Kentucky fluorspar district to the faults west-trending faults of minor displacements. The along the Wabash River. Heyl and Brock (1961) latter are usually referred to as "dike faults" viewed the northeast-trending faults of the fluor- because some of these faults have been intruded spar district and the Wabash River faults as the 78 JOHN W. HOOK

lished and unpublished sources. FAULT SYSTEMS IN THE ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 79

New Madrid fault zone. The subsidence of the east-trending faults in the fluorspar district are embayment area, the block faulting of the fluor- predominantly normal. The average dip is 70 to spar district, and the igneous intrusions along 75 degrees which produces about 100 feet of this lineament are suggestive of incipient rifting. heave for each 300 feet of vertical displacement. Hicks dome, described by Brown and others The writer estimates that the cumulative north- (1954) as a cryptovolcanic structure, is near the west-southeast heave component of the normal intersection of the 38th parallel lineament and faults of the district is roughly 5,000 feet. This the New Madrid fault zone. The dome is about indictates that the district was stretched about 1 9 miles in diameter and has 4,000 feet of struc- mile. Excluding the Shawneetown fault zone, tural relief. Diatremes with sedimentary and strike-slip faulting and other compressional fea- igneous breccia are found in the dome. tures within the district are of minor structural Basic igneous dikes and sills are found in the consequence in comparison to the extensional fluorspar district and in the coal fields north of features. the Shawneetown-Rough Creek fault zone. The It is the thesis of this paper that multiple dikes are in fracture zones that trend slightly west rupturing under tension and the subsequent of north. gravity adjustments caused the northeast-trending Except for the locally disturbed uplift at Hicks block faulting in the Illinois-Kentucky fluorspar dome, the axis of the district arch is nearly north- district. As the stretching progressed and the south from the Tolu dome to Kuttawa. The arch major grabens moved downward, many minor is broken by the block faulting, and the crest is blocks broke loose along the edges to form the offset from one block to the next. The offset is complex fault systems. These minor blocks within not consistently to the right or the left. the fault systems have gravity movement along a Excluding the unusual structure at Hicks dome, series of step, antithetic, and cross faults (Hook the district arch is 25 to 30 miles wide and has and Winans, 1962). The actual faults thus created about 2,000 feet of structural relief. The arch is are usually wide zones of gouge, breccia, and a very gentle structure, and the formations have vein minerals. Only rarely do the walls fit closely low dips except for locally tilted fault blocks and together, forming a clean-cut fault. The down- drag folding along the faults. ward movement of the grabens produced both drag folding along the faults and rotation of the The major graben blocks generally trend north- minor fault blocks within the fault systems. eastward, but some change direction locally; some are discontinuous, or offset. Some of the grabens Figure 2 is a schematic sketch of the horst-and- hinge within the district, and most are hinged, graben stndture, illustrating a fault system with or nearly so, at the edge of the district. The Rock step faults on the left and a fault system with Creek graben changes sharply in direction from antithetic faults on the right. The chaotic nature N.30°E to N.55OE. near Rosiclare, Ill. It hinges of the faulting is omitted. Actually, both anti- thetic and step faults are usually present in a in the edge of the district arch north of Cave in Rock. Mapping of sub-cretaceous units indicates given fault system. The step faults have down- thrown sides toward the grabens and the antithetic that the Rock Creek graben h'as also lost most of faults have downthrown sides toward the horsts. its displacement before reaching the Ohio River a few miles north of Paducah. The Lockhart Bluff graben is offset from the Griffith Bluff graben. Step Faults The Moore Hill graben hinges near the crest of The displacement in the fault systems is pre- the district arch, but the bounding fault systems dominantly along step faults and their associated continue to the southwest, each containing minor drag zones. These are apparently gravity faults grabens within the fault systems. which displace multiple fault blocks within the fault systems in a step-like manner from the horsts DESCRIPTION OF THE FAULTS to the grabens. They 'are usually normal faults The horst-and-graben structure of the district that dip toward the grabens, but local reversals is indicative of extensional tectonics. The north- of dip occur. In most cases, such reversals are JOHN W. HOOK

ANTITHETIC FAULT BETWEEN MASTER STEP FAULTS

HORST

ANTITHETIC FAULT

WITH STEP FAULTS

FAULT SYSTEM' WlTH ANTITHETIC FAULTS

Figure 2. Diagrammatic sketch of a horst-and-graben structure, illustrating a fault system with step faults on the left and one with antithetic faults on the right. along local segments of what is otherwise a steep- produced ,additional minor step faults, while angle normal fault. The step faults usually dip movement along the tension fractures developed from 60 to 90 degrees and, where reversed, are antithetic faults. seldom more than-5 degrees from vertical. Both the strikes and dips along the step faults are un- Antithetic Faults dulating and can change as much as 15 to 20 The antithetic faults are usually found in the degrees within a few hundred feet. tilted blocks between step faults as previously The fault systems in some places pinch down mentioned, but they also occur in the drag zones to what is essentially a single major step fault, of the major grabens. In either case they were but multiple step faults are the rule. A relatively developed along tension fractures dipping op- common occurrence in the district is to find two posite to the bedding of the stratigraphic units. master step faults forming the outer boundaries Due to local drag, the formations dip toward the of a fault system. In these cases, the fault adjacent graben while the antithetic faults dip toward the to the horst is locally termed the "footwall fault" horst. The strike of the antithetic faults is gen- and the one adjacent to the graben, the "hanging- erally parallel to the fault system. The antithetic wall fault." faults usually have relatively low angles of dip, Intervening blocks between two master step 45 to 65 degrees, whereas the step faults usually faults have been subjected to considerable drag dip 60 to 90 degrees. The antithetic faults which caused rotation toward the graben. Such terminate downdip against step faults. The blocks usually have yielded to additional frac- wedge-shaped blocks thus created are minor turing and faulting. Caught in the forces of a grabens within the fault systems. couple between the up-drag on the footwall The antithetic faults apparently developed in master fault and the down-drag on the hanging- response to, and along with, continued movement wall master fault, both tension and shear fractures on the master step faults. As the stretching of developed. Movement along the shear fractures the district continued, gravity movement occurred FAULT SYSTEMS IN THE ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 8 1 along the tension fractures between step faults, had differential downward displaceinent which and also in the drag zones in the grabens. The caused rupturing and consequent cross faulting. gravity n~oveinentwas augmented and possibly In either the major grabens or the smaller fault even initiated by the rotation of the fornlations blocks within a fault system, there is often a toward the grabens. longitudinal componeilt of tilting. Where this I11 other words, the minor blocks between step component of tilting is uneven, the blocks rupture faults were caught in the forces of a couple which along cross faults. Both the step faults and the caused rotation toward the graben. This de- antithetic faults may be terminated or be dis- veloped tensioil fractures dipping away from the placed by cross faults or vice versa. The longib- step faults. Further movement of the step faults diilal component of dip may also cause hinging initiated the inovemeilt on the tension fractures. along which step or antithetic faults may die out, Further stretching due to extensional tectonics but termination at cross faults seems to be more perinitted gravity movemeilt on the antithetic common. faults. Northwest-Trending- (Dike) Faults The heave conlponents of the antithetic faults The basic dikes of the fluorspar district are augmented the heave conlponents of the step along north- to northwest-trending faults. These faults in filling the voids created by the exten- faults have very little vertical displacement; ap- sional tectonics. The step faults permitted the parently the ~novementwas primarily strike slip inajor grabens to partially fill the voids by a as indicated by the slickensides. These clean-cut, keystone type of movement, and the antithetic northwest-trending faults with nearly straight faults further added to the fill by dropping minor strikes and dips are in sharp contrast to the un- grabens within the fault systems. The remaining dulating, chaotic faults of the northeast-trending space was filled by the added volume created by fault systems. fractured and brecciated rock and vein mineraliza- Oesterling ( 1952) believed that the dikes along tion along individual faults. Two prominent these northwest-trending faults are older than the examples of antithetic faults are the Blue Dig- northeast-trending block fiaulting, but that the gings vein at Rosiclare, Ill., and at the Davenport zinc deposits along these structures were due to mine near Salem, Ky. much later ( post-fluorite ) movement. The dikes Figure 3 is a block diagram of the Moore Hill are offset by northeast-trending faults. The dikes fault systenl at the Watson and Davenport mines. do not intrude the northeast-trending faults, but The fluorspar ore in these mines was localized Oesterling ( 1952) found post-fluorite movement along step and antithetic faults. The net vertical along the dike (northwest-trending) faults which displacen~entof the Moore Hill f'ault system at displaced northeast-trending faults at the Hutson this point (the stratigraphic displacement between mine. the Moore Hill graben and the Salem Valley horst) is 600 feet; the cumulative heave is 360 feet. Strike-Slip Faulting Figure 3 also shows cross faults, the third type The northwest-trending (dike) faults seem to of fault found in the northeast-trending fault have predominantly strike-slip movement. Slick- systems. ensides along the northeast-trending faults also indicate components of lateral movement. Bastin Cross Faults (1931) described slickellsides along the nearly As the name implies, the strike of the cross vertical Daisy vein at Rosiclare which are inclined faults is couilter to the strike of the fault system. from 10 degrees north to 80 degrees south. The cross faults are normal gravity faults resulting Slickensides with inclinations ranging from hor- from differential downward nlovement in blocks izontal to vertical have been observed throughout which were caught between step faults or between the district. Thus, in addition to the gravity a step and an antithetic fault. In addition to the movement of the major grabens and the associated cross faults within the intermediate blocks of the northeast-trending fault systems, there bas also fault systems, some of the major grabens have been a component of wrenching. 82 JOHN W. HOOK

Figure 3. Block diagram of the Moore Hill fault system at the Watson and Davenport mines. Stratigraphic units are: Msl, St. Louis; Msg, Ste. Genevieve; Mr, Renault; Mb, Bethel; Mpc, Paint Creek; Mc, Cypress; Mg, Golconda; and Mh, Hardinsburg. Length of block, 3,500 feet; width, 1,700 feet. FAULT SYSTEMS IN THE ILLINOIS-KENTUCKY FLUORSPAR DISTRICT 83

The amount of strike-slip movement on the major blocks. It illust account for the major dip- major northeast-trending faults is unknown. It slip components including about a mile of cumu- is the writer's opinion that the strike-slip com- lative heave. ponent of movement is relatively minor in com- Five tectonic mech~anismshave been proposed parison to the dip slip on the major fault blocks. in the literature, singly or in combinations, as the A swarm of dikes extending intermittently from forces which created the block faults. Basically, the Glendale area on the Commodore fault system the five mechanisms involve (1) expanding magma, southeastward to the Claylick fault system on the (2) shrinking magma, (3) release of lateral com- Salem quadrangle (Trace, 1962) crosses three pression from the southeast, (4) northwest-south- major fault systems without appreciable lateral east extension due to southwest compression, and displacement. (5) strike-slip movement along the Shawneetown However, some of the northeast-trending faults fsault zone. with minor vertical displacement are predom- Expanding Magma inantly strike slip. The Gaskins mine in the Em- pire district on the west side of Hicks dome has Weller (1927, p. 94) related the fault systems predominantly horizontal slickensides and tension to extension and uplift during a deep-seated in- fractures indicating left-lateral movement. The trusion: "All of these faults are of the normal or vein splits into two segments in the central part tensional type, and have been formed by the of the mine but is otherwise a nearly straight, stretching of this segment of the earth's crust." uncomplicated structure in comparison to the He related the basic dikes in the district to the undulating veins along the gravity faults in the intrusion. district. Oesterling (1952) discounted this theory on the Baxter and Desborough (1965) suggested that basis that the dikes are older than the block the relative importance of strike-slip and high- faulting. However, Oesterling's evidence does not angle reverse faulting as compared to normal preclude arching and extension due to la post-dike faulting in the fluorspar district has probably been intmsion. underestimated. However, while strike slip is a Of the five mechanisms, Weller's theory is the factor to be considered seriously, I would also only one which proposes active tension. Other caution that it not be overestimated. In general, theories propose a conlponent of tension as a strike slip seems to be more of a factor in Illinois, byproduct of compressional forces. closer to the 38th parallel lineament, than in the Shrinking Magma Kentucky portion of the district. Both left-lateral and right-lateral movement Hey1 and Brock (1961) and Grogan and Brad- have been observed in the Cave in Rock area of bury (1968) suggested that the shrinkage of a the district (Don Saxby, personal commun.). The cooling magma contributed in part to the block minor faults associated with the bedded deposits faulting. This implies ,thlat the shrinkage removed are predominantly strike slip. support and contributed to the collapse. How- The relative importance of strike slip as com- ever, would shrinkage of the magma not have pared to normal faulting needs further study. The tended to shrink ,the area of the overlying sed- study should also compare the relative amount of iments also? How could shrinkage of the intrusion right-lateral movement to left-lateral movement. have produced the extensional characteristics of The role of the Shawneetown fault zone (the 38th the normal faulting? parallel lineament) relative to the other'haults of Release of Lateral Compression From the South the district should be examined more closely. Weller (1940), Oesterling (1952), and Grogan ORIGIN OF THE FAULT SYSTEMS and Rradbury (1968) suggested that relaxation of The origin of the fault systems is speculative. the compressive stresses which formed the Shaw- A viable mechanism to explain the block faulting neetown fault zone contributed in whole or in must be compatible with the structure of the part to the block faulting. Oesterling (1952, p. existing fault systems and the gentle dips of the 329) added the opinion that ". . . in view of the 84 JOHN W. HOOK extensiveness and complexity of the faulting, the neetown fault zone, which compressed and rotated release of pressure was quite sudden, as might be the north end of the fold in a counterclockwise expected to result from the Shawneetown-Rough direction to develop the numerous northeast- Creek thrust faulting." trending fault blocks." Some shattering could possibly result from the This theory proposes a considerable strike-slip sudden release of compression las Oesterling sug- component for the northeast-trending faults. To gested, but how could relaxation develop the offset the anticlinal axis of the Tolu-Kuttawa arch extensional tectonic structures of the district? to Hicks dome would require a cun~ulativestrike Unless the relaxation of compression was followed slip of about 5 miles. Heyl 'and Brock (1961, p. by rebound or withdrawal to produce tension, how D-6) indicate that a gaseous explosion took place could this mechanism produce the normal faults on the apex of the structure to form the smaller of the district? This theory calls for relaxation of dome (Hicks dome) and its diatremes. I agree compression; if tension is implied, it should be with this proposed origin of Hicks dome except so stated. that the explosion probably occurred on the flank Northeast-Southwest Extension Due to Southwest of the district arch rather than at the apex. With Compression the latter interpretation, no robation is required. In ,the preceeding paper, Trace (this symposium) This theory proposed that the extensional tec- shows offset of the arch in both directions, not tonic features of the block faulting were the result consistently to the left as would be the case if of bulging when pressure was applied from the there were substantial left-lateral strike slip on southwest. Brecke (unpub. ms.) states: "The the northeast-trending faults. forces producing the faults were apparently com- pressional from the southwest. Such forces tend Other evidence against strike-slip movenlent of to produce shortening of the crustal layers. the magnitude indicated by this theory is that: Evidence of this shortening is found in three (1) the basic dikes which probably predate the forms: folding, shearing, and overthrust. Thrust block faulting apparently have little offset along faulting and the arcuate faults of the Kentucky the northeast-trending faults, (2) drag folding in part of the district indicate overriding pressure the district indicates predominantly dip-slip from the southwest. The Shawneetown-Rough movement, and (3) the irregular, chaotic nature of Creek fault is a high-angle overthrust and prob- the northeast-trending fault systems is more in ably the largest relief feature of the system." keeping with gravity collapse due to tension than Except for steeper dips at Hicks dome and the the organized, clean-cut nature of strike-slip drag folding and tilting near normal faults, the faulting. formations of the district have low dips. Had Later studies by Heyl (1972) indicate that the there been enough shortening in a northeast- Shawneetown fault zone is part of the 38th parallel southwest direction to produce the approximately lineament which has right-lateral n~oven~ent. 1 mile of northwest-southeast extension, the com- Right-lateral movement on the Shawneetown pressionla1 structures should be more pronounced. fault zone would not produce the northeast-trend- ing tension fractures with left-lateral n~ove~nent Strike-Slip Movement Along the Shawneetown as the earlier theory proposed. However, it would Fault Zone produce northwest-trending fractures with the This theory proposes that the northeast-trend- general trend of the dike faults. ing fault blocks were formed by left-lateral itrike- Discussion slip movernent along the Shawneetown fault zone. Heyl and Brock (1961, p. D-6) combined this Right-lateral movement on the 38th parallel theory with the shrinking magma theory as lineament prior to the period of block faulting follows: "Subsequent cooling and shrinkage of could have opened the northwest-trending tension the igneous rocks partly lowered the anticline. fractures which were intruded by the basic dikes. This action was combined with a compressive Renewed periods of movement could have re- force-couple acting along the Rough Creek-Sh,aw- opened these structures during the periods of FAULT SYSTEMS IN THE ILLINOI S-KENTUCKY FLUORSPAR DISTRICT 85 fluorite and sphalerite mineralization proposed by faulting was due to extensional tectonic forces Oesterling (1952). which caused crustal stretching and gravity col- Movement along the 38th parallel lineament lapse. has probably been intermittently active since Torsional forces have oaused both right-lateral Precambrian time (Heyl, 1972). The major period and left-lateral movement along some of the north- of block faulting probably occurred about the east-trending faults. The magnitude of this move- close of the Faleozoic. Thus, torsional forces ment is mostly unknown but it is believed to be producing the northwest-trending (dike) faults relatively minor in comparison to the normal and the strike-slip- movement on the northeast- faulting. trending structures may have been active before, The northwest-trending (dike) faults are prob- during, and after the period of block faulting. ably tension fractures related to right-lateral Such movements could have set the northeast- movement along the 38th parallel lineament. trending pattern and produced the later strike-slip These fractures were opened prior to the period slickensides found in the fault systems. However, of block faulting when the basic dikes were em- it is my opinion that the major block faulting was placed, and reopened subsequent to the block primarily gravity movement due to stretching of faulting dniing perods of fluorite and sphalerite the crust. Although the torsional forces were mineralization. active over a greater period of time, the strike-slip movement seems minor in comparison to the dip- REFERENCES slip movement produced by the tensional forces. Bastin, E. S., 1931, The fluorspar deposits of Hardin and The New Madrid fault zone (including the Pope Counties, Illinois: Illinois State Geol. Survey block faulting in the fluorspar district and the Bull. 58, 116 p. faults along the Wabash River) is suggestive of Baxter, J. W., and Desborough, G. A., 1965, Areal geology of the Illinois fluorspar district-Part 2, Karbers Ridge a zone of incipient rifting. Basement spreading and Rosiclare quadrangles: Illinois State Geol. Sur- due to a minor plate movement could have vey Circ. 385, 40 p. caused the igneous activity along this zone and Brown, J. S., Emery, J. A., and Meyer, P. A., Jr., 1954, the extensional tectonic structures in the fluorspar Explosion pipe in test well on Hicks dome, Hardin district. The extension may be due in part to a County, Illinois: Econ. Geology, v. 49, no. 8, p. deep intrusion, as suggested by Weller (1927), 891-902. which was associated with the rifting. Grogan, R. M., and Bradbury, J. C., 1968, Fluorite-lead- zinc deposits of the Illinois-Kentucky mining district, The major block faulting occurred between in Ridge, J. D., ed., Ore deposits of the United States, Pennsylvanian and Cretaceous times. The original 1933-1967 (Graton-Sales volume), v. 1: New York, horst-and-graben topography has now been large- Am. Inst. Mining, Metall., and Petroleum Engineers, ly reversed by erosion. The resistant massive p. 370-399. Pennsylvanian sandstone remnants in some of the Heyl, A. V., 1972, The 38th parallel lineament and its grabens now form the highest ridges in the relationship to ore deposits: Econ. Geology, v. 67, p. 879-894. district, while the St. Louis and Ste. Genevieve Heyl, A. V., and Brock, M. R., 1961, Structural framework areas of the horsts form much of the present of the Illinois-Kentucky mining district and its rela- lowlands. However, some later movement has tion to mineral deposits: U. S. Geol. Survey Prof. occurred as reflected in Cretaceous and possibly Paper 424-D, p. D3-D6. Eocene sediments (Ross, 1963). Both the New Heyl, A. V., Brock, M. R., Jolly, J. L., and Wells, C. E., Madrid land Shawneetown fault zones are still 1965, Regional structure of the southeast Missouri active. and Illinois-Kentucky mineral districts: U. S. Geol. Survey Bull. 1202-B, 20 p. CONCLUSIONS Hook, J. W., and Winans, T. R., 1962, Structure of a fault system in the Western Kentucky fluorspar district The major movement on the northeast-trending (abs.): Geol. Soc. America, Spec. Paper, No. 68, p. fault systems probably occurred during a relatively 73-74. short period in ~ost-penns~lvaniantime, but Matthews, S. W., 1973, This changing earth: Natl. Geog., some minor nlovenlent has continued. The block v. 143, no. 1, p. 33. 86 JOHN W. HOOK

McGinnis, L. D., and Bradbury, J. C., 1964, Aeromagnetic Kentucky: U. S. Geol. Survey Geol. Quad. Map study of the Hardin County area, Illinois: Illinois GQ-206. State Geol. Survey Circ. 363, 12 p. Weller, J. M., 1940, Geology and oil possibilities of Oesterling, W. A,, 1952, Geologic and economic sig- extreme southern Illinois: Illinois State Geol. Survey nificance of the Hutson zinc mine, Salem, Kentucky- Rept. Inv. 71, 71 p. its relation to the Illinois-Kentucky fluorspar district: Weller, J. M., Grogan, R. M., and Tippie, F. E., 1952, Econ. Geology, v. 47, p. 316-338. Geology of the fluorspar district of Illinois: Illinois Ross, C. A., 1963, Structural framework of southernmost State Geol. Survey Bull. 76, 147 p. Illinois: Illinois State Geol. Survey Circ. 351, 28 p. Weller, Stuart, 1927, Geology of the Cave in Rock quad- rangle: Kentucky Geol. Survey, ser. 6, v. 26, p. Trace, R. D., 1962, Geology of the Salem quadrangle, 1-128. GEOLOGY AND HISTORY OF PENNWALT CORPORATION'S DYERS HILL MINE, LIVINGSTON COUNTY, KENTUCKY

JOHN S. TIBBS Consulting Geologist Marion, Kentucky

ABSTRACT Pennwalt Corporation's Dyers Hill mine, located northeast of Smithland, Livingston County, Kentucky, was operated between 1956 and 1968. During this period it was one of the most important fluorspar mines in the Western Kentucky district. The ore, a vein-type deposit, consisted of clear, white, and brown fluorite with inclusions of galena and sphalerite. Mining was carried on between depths of 350 and 690 feet.

The Dyers Hill mine is located 3.5 miles north- Many of the faults are scissor or "purse" faults; east of Smithland, Livingston County, Ky., at an that is, they die out at one or both ends, with the elevation of about 500 feet. It is reached by maximum throw occurring at one end or in the driving northeast from Smithland along U. S. middle. Where this diminishing of throw occurs, Highway 60 for 4.5 miles and then traveling on subparallel faults occur, opening up in the op- a gravel road for another 1.2 miles to the shaft. posite direction to keep the overall throw about The shaft location is shown on the 7.3minute the same for long distances; the surface forma- Smithland quadrangle topographic map. The tions within any given fault block remain almost area is one of small, highly eroded hills, with uniform. many small sandstone bluffs, lying between the The igneous dikes are narrow, being from a Ohio River flood plain and the normal plateau, few inches up to perhaps 20 feet in width, but some 300 feet higher in elevation. may be several miles long. They were apparently The rock formations are, for the most part, intruded at a slow rate, because in places they sedimentary and of Pennsylvanian and Missis- are composed of almost pure calcium carbonate sippian ages; they are cut by many faults having which was dissolved by the intrusive mass and throws of up to 3,000 feet. Most of these faults pushed ahead of it across the country rock. are normal and have northeasterly strikes; dips are Three types of ore deposits are found in the from 70" to 90'. Intruded across this fault system area: (1) gravel, or residual deposits, (2) manto, are a series of basic igneous dikes which trend in or replacement deposits, and (3) vein deposits. a north to northwest direction. The Pennsylvanian Vein deposits are the most common type, and rocks are all of a siliceous nature, with inter- this is the type that is found in the Dyers Hill bedded shales and coal. The Mississippian rocks mine. These vein deposits are the result of fissure are composed of interbedded .sandstones, lime- filling by ascending pneumatolitic solutions from stones, shales, and minor amounts of coal. which the fluorite and other minerals crystallized The faults, which in general trend from about at the correct conditions of temperature and N.lSOE.in the western part of the area to about pressure, when the elevation of a good host S.60°E. in the southeastern part, would have a horizon was reached. In the Illinois-Kentucky combined length in the order of thousands of area, if fluorspar is found in a vein, it will be miles in the roughly 40 by 30 mile area that makes found at the elevation of the Fredonia limestone. up the Illinois-Kentucky fluorspar district. The It may be found opposite other limestones; but strike of the faults in the Dyers Hill area varies if it is, it will also be found at the elevation of from about N.25"E. to N.60°E. the Fredonia. 88 JOHN S. TIBBS

The ore is normally found in areas along the A highly weathered igneous dike was found stcke of a fault at the elevation of the Fredonia some 1,500 feet southwest of the shaft. Strike of limestone, on one or both sides of the fault. The the main vein was N.28"E. northeast of the dike, ideal case is at points where the throw of a fault and S.47"W. southwest of the intrusive. almost, but not quite, offsets the Fredonia. Where Two other areas of minable mineralization were this situation exists, a continuous vertical ore found associated with the "Number One" deposit. deposition of from 200 to 500 feet may be The "L" vein, a mineralized tension fracture expected. Ore deposits are now found by di- having little or no displacement, splits off the amond core drilling since virtually all of the main fault some 400 feet southwest of the shaft deposits that are exposed at the surface have and strikes S.70°W. for 1,500 feet, where the already been found. mineralization terminates in an open water-filled Vein deposits are found by drilling angle holes cavity, 300 feet long, containing a few limestone of 45" to 60" from the hanging-wall side of the boulders. In this vein the ore extends only from fault to intersect the vein at the elevation of the 50 feet below the 350-foot level down to below Fredonia limestone. In cases where the Fredonia the 690-foot level, where it becomes too narrow is offset, it may be necessary to drill the structure to mine. The ore in this vein ranges in width at the elevation of the Fredonia on each side of from 0.5 to 8 feet. the fault. Drill holes deviate as much as IS0, An antithetic fault dips through the main shaft both vertically and horizontally; therefore, a good at an angle of 75" to the southeast; this fault borehole survey is ,a must. intersects the main vein at a depth of 500 feet and runs parallel with the main fault. Its south- To date, three ore deposits have been found in west end abuts against the "L" vein. The ore cut the Dyers Hill area of Livingston County, Ky. in the shaft was 6 feet wide from a depth of 260 Only one of .these, the so-called "Number One" feet down to 320 feet; however, it had pinched to deposit, has been mined. It is with this "Number nothing at the 350-foot level and only opened up One" deposit that this paper is concerned. to about 15 inches at a depth of 400 feet. In The deposit was found by diamond drilling on order to protect the shaft, this ore was not mined. the Frank 0. Werner farm in March 1950. When The major components of the main vein were four holes had been completed in the discovery fluorite, calcite, shale, limestone, sandstone, fault area, a drilling program was set up to test the gouge, and a narrow band of aragonite that main branch of the Dyers Hill fault to the south- practically filled the final void. In addition, there west toward the Ohio River, but without success. were minor concentrations of barite near the top In the spring of 1951 a new program was set up of the economic mineralization, which occurred to prospect updip to the northeast of the discovery some 200 feet below the surface. The fluorite ore point along the strike of the fault. The first hole contained about 1 percent galena; southwestward cut 17 feet of high-grade fluorspar, sphalerite, and from the main shaft the amount of sphalerite in galena ore. Good minable ore was cut in 15 of the ore increased gradually to perhaps 3 percent the next 16 holes, covering a distance of 3,200 in the vicinity of the dike. This sphalerite was feet to .the northeast. This drilling program was nornlally concentrated along the hanging-wall completed early in 1952. The main Dyers Hill side of the vein and in many places impregnated fault was found to be mineralized with fluorspar the first few inches of the hanging wall itself. for a distance of 4,200 feet overall, and varied The sphalerite concentrate contained almost 1 from 1 foot to over 30 feet in width. It had an percent cadmium and 0.06 to 0.09 percent of both economic minable depth of about 400 feet. germanium and gallium. At .the surface, the northwest wall of the fault The ore varied in width both horizontally and is Golconda limestone, ,and the southeast wall is vertically; hard, clear to white fluorite, containing Bethel sandstone. The average fault movement inclusions of galena with varying amounts of was about 235 vertical feet along the fault plane calcite, were predominant in the northeast end that has a dip of about 75" to the northwest. of the mine. This ore graded through brown GEOLOGY AND HISTORY OF DYERS HILL MINE 89 fluorite, containing galena and increasing amounts 6-inch oak cribbing, were jacked up as the soft of sphalerite, to soft gouge-like material contain- gouge-like ore was removed from above through ing fluorite, galena, and sphalerite as the mine sliding trap doors in the hoods. From the stope progressed to the southwest. The material in the area, the ore was trammed to the shaft loading last 1,200 feet at the southwest end of the mine pockets, where measuring pockets were located, was very soft, and the walls and back were difficult in 2-ton side-dump cars pulled by Mancha battery- to hold. There was very little crystalline fluorite operated locomotives on 18-inch gauge rails. present in the mine; however, in some of the voids The decision to open Dyers Hill mine was made in the vein in the northeast end of the mine there in 1954, and early in 1955 the access road was were many dogtooth calcite crystals as much as located and the dewatering well was drilled. The 18 inches in length. main shaft was started in August 1955, with com- The ore in Dyers Hill mine was reached by a pletion to 350 feet, where the first level was shaft, sunk in the hanging wall of the vein, 180 turned off, in January 1956. The planned oper- feet northwest of the fault outcrop; a dewatering ating tonnage of 85 tons per day was reached well was drilled 27 feet southeast of the shaft. in May of that year. In February 1958 a winze Levels were turned off from the shaft at 350 feet was started from the 350-foot level to prepare and 520 feet, with one more level at 690 feet, for the raising of the shaft from the 520-foot level which was reached from the 520-foot level by a to the 350-foot level. At this time the production winze located 30 feet northwest of the shaft was 165 tons of raw ore per day. The raise from (Figs. 1-6). the 520-foot level was started in January 1959 The usual mining method was shrinkage stop- and completed in October of that year. At this ing with free-floating cribbed manways at 150- time production was set at 210 tons per day and foot intervals and loading shoots at 25-foot spac- increased to 300 tons in March 1962. In May ings. As the mine progressed to the southwest, 1963 a winze was started 30 feet northwest of the increasingly incompetent walls were encountered. shaft on the 520-foot level to open the 690-foot As a result, many other methods were tried. level. This was completed in November 1964. Some cut-and-fill stoping was done, and we also Daily production reached over 550 tons of raw tried underhand stoping from sublevels. In the ore per day in early 1965, and then began to extreme southwest end of the mine, half-inch-thick decrease. The mine became unprofitable to op- pyramidal steel hoods, supported on 6-inch by erate and was closed in June 1968. JOHN S. TlBBS

SCALE ):::::I 0 300 600 Feet

Figure 1. Plan of Dyers Hill mine. For further details see Figures 2-6. GEOLOGY AND HISTORY OF DYERS HILL MINE . .-:>------==

. -.-.-. 0 0 0 0 Z PLAN Z

Feet SECTION + 300

. . _._._._.~.~__.~__._._._.__~.___._____.__~__.-__._.-._._. . . . LU//Ld&/IL//L//////14..-.-.-.-.-.-.-.-.-.---.---- -. I2 - 2- .-. - .- .- - - !?L .-. - .- .

-100

II II _-----A __-_----- L-A --L- - 200 0 100 200 -.-.-. 350' Level I Feet 520' Level Stoped-out Area ----- 690'Level

Figure 3. Plan and section of northeast end of mine. !. / 9 oooL P % '! ',-0 00 \%* 2 % Shaft %2

Feet +300

+ 200

+ 100

0

- 100

-200 -.-.-. 350' Level 0 100 200 I '520' Level ~toped-out Area Feet ----- 690' Level

Figure 4. Plan and section of shaft area. , r, -0' 000 2

oooC \\.

Feet + 300

+ 200

+ I00

0

-200 0 100 200 -.-.-. 350' Level I Feet 520' Level Sloped-out Area ----- 690 ' Level

Figure 5. Plan and section of mine southwest of shaft. 00% 0 ?Oo \o. O+ PLAN

Feet SECT l ON + 300

+ 200

+ 100

0

- 100

- 200 0 100 200 I I I 520' Level Stoped-out Area Feet

Figure 6. Plan and section of southwest end of mine. THE EAGLE-BABB-BARNES FLUORSPAR PROJECT, CRITTENDEN COUNTY, KENTUCKY

F. B. MOODIE Ill Exploration Consultant, Cerro-FFL Group,' Salem, Kentucky PRESTON McGRAlN Assistant State Geologist, Kentucky Geological Survey, Lexington, Kentucky

ABSTRACT Core drilling on two properties along the Babb fault system in south- western Crittenden County, has disclosed a potentially commercial vein-type fluorspar ore body. Drilling data suggest that about 1,000,000 tons of fluor- spar ore in indicated and inferred categories exist in the deposit. Prepara- tions are currently under way for developing the ore body.

INTRODUCTION Prospecting by pits and drilling, and develop- The announcement by Cerro-FFL Group of ment activity by shallow pits and shaft mining plans to construct a new multi-million dollar was done on the Eagle-Babb-Barnes by as many fluorspar mine and mill in Crittenden County, as 10 different companies, individuals, and orga- (Mining Engineering, 1972, p. 19) has once again nizations between 1899 and 1967. According to focused attention on one of the well-known min- available records from public and private sources, eral areas in the Western Kentucky fluorspar 22 holes were drilled on the Eagle-Babb tract and district. 25 on the Barnes tract. Three shafts with depths The project area is located on the Babb fault of 200 feet or more were sunk on the two prop- system about 2 miles north of Salem, Livingston erties. Eagle No. 1 and Eagle No. 2 shafts on the County (Fig. 1). The area of the Babb fault has Eagle-Babb were reportedly sunk to depths of been known for more than 70 years as a potential 552 feet and 200 feet respectively. The Howard mineral region. In 1905, Ulrich and Smith (1905, shaft on the Barnes property was reportedly sunk p. 83, 201-202) recognized a mineralized fault in to a depth of 234 feet (Fig. 2). For a summary the area and reported that Eagle Fluorspar Com- of the development and exploratory activity pany operated on the Ramon Babb property in between 1899 and 1946, the reader's attention is 1899 and 1900. This consisted of two shafts and invited to the discussions by Hardin (1955, p. several prospects, the main shaft being 80 feet 33-35) and Swanson and Starnes (1950, p. 10-13). Hardin (1955, p. 35) wrote that because of the deep. At one time the Babb area was considered one of the most productive in the district ( Hardin, stratigraphy and the character of the fault he 1955, p. 1). believed that fault 2 on the Barnes property The area under discussion in this report covers offered the best possibility for prospecting. His two properties which have long been known in analysis was prophetic. local mining circles as the Eagle-Babb and Barnes GEOLOGIC AND GEOGRAPHIC SETTING tracts. Although there have been several changes The E'agle-Babb-Barnes project is in the south- over the years in land and mineral rights owner- western portion of the Salem 7.5-minute quad- ship, the present operators have retained the rangle which is covered by geologic (Trace, 1962) earlier designations and refer to the project as the and topographic maps, both at a scale of 1:24,000. "Eagle-Babb-Barnes." It will now be operated as The topography is rolling and of moderate relief, a single property. varying from 410 to 540 feet above sea level. In the vicinity of the project area, several sandstone- 1 FFL Group: Frontier Resources, Five Resources, J. Fred Landers, and F. B. Moodie 111. capped hills 'and ridges attain elevations of 700 EAGLE-BABB-BARNES FLUORSPAR PROJECT

ILLINOIS

Figure 1. Map of portion of the Illinois-Kentucky fluorspar district showing the location of the Eagle-Babb-Barnes project in Crittenden County, Ky. 98 F. 6. MOODIE Ill AND PRESTON McGRAlN

that a thorough study be made of all available HOWARD SHAFT information on the Eagle-Babb and Barnes prop- (obondomd) ------erties. This included both published information Menord and record; in the hands of the owner. Study of available data led to the conclusion

Woltersburg that the Eagle-Babb property had been drilled

/ - 4 - Vienno but that some of the geologic interpretation might

/ Tor Springs be subject to question. Apparently no thorough -*--- : ---- .-. 0 -- .--.--.--.--.-- exploration program had ever been carried out on the Barnes tract, and the main fault (referred -irk&? ? ? ? to in some earlier literature as fault 2) had not 17been tested here. In fact, there had been little drilling along the strike of the Babb fault system Figure 2. Sketch of the abandoned Howard shaft on on the Barnes property. the Barnes tract. Data compiled from public and private The study revealed that the northeast portion sources. of the Barnes property contains two distinct faults, to 800 feet. Sandy Creek and its westward- and one Cypress against Fredonia, and the other southwestward-flowing tributaries drain the area. Menard against Cypress. It was this latter fault Rocks of Late Mississippian age occur at the that was believed to be the main fault, and it was surface; however, few outcrops are present. The this fault that past drilling had failed to properly Babb fault system extends for more than 2 miles explore on this property. Earlier drilling on the in a northeast-southwest direction across portions Barnes property had apparently followed the of Crittenden and Livingston Counties (Trace, Cypress-Fredonia fault. 1962). The footwall block of the Babb system Evaluation of the information available at this consists mainly of the Ste. Genevieve Limestone. stage in the study led to the conclusion that the In the northwest, or hanging-wall, block, lime- Eagle-Babb and Barnes properties contained stones, sandstones, and shales of Chesterian age sufficient fault length under favorable geologic are present at the surface. Some portions of the conditions to produce a potentially commercial Babb system appear to be represented by a single fluorspar ore body. A short tern1 lease-option was fault which may be accompanied by a wide then obtained from the property owner. brecciated or broken zone. Elsewhere along the Contractural obligations did not allow time trace of the system the displacement may be for geochemical or geophysical investigations. distributed among several step faults. The max- Because of the scarcity of outcrops and the avail- imum displacement, between the Ste. Genevieve ability of subsurface and other geological data, Limestone in the footwall and the Menard Lime- new surface geological work was restricted. A stone in the hanging wall, is approximately 950 drilling program, outlined primarily on the basis feet. Figure 3 is a generalized geologic section of earlier exploratory efforts, commenced July 8, of the project area. 1971. The project property is near Kentucky Highway The first core hole (Fig. 4), EBB 1, was located 723, approximately 2 miles north of Salem and to check an earlier drilI log which had reported U.S. Highway 60. The Illinois Central Railroad 8 feet of fluorspar ore. Stratigraphic and structural passes through Marion, the county seat of Crit- relationships as interpreted from data gathered tenden County, about 12 miles to the east. Cum- from the drilling program are shown by a series berland River is 6 miles south of Salem, and the of geologic cross sections (Figs. 5-9). Dimensions Ohio River is 12 miles to the north and west. on the cross sections show the ore or mining widths and not the actual vein widths. Veins may CURRENT PROJECT contain calcite and other materials which may In April 1971, F. B. Moodie I11 recommended not be recovered. A shaft, which is now being to the FFL Group-Cerro Corporation joint venture sunk, and subsequent mining operations will EAGLE-BABB-BARNES FLUORSPAR PROJECT

Figure 3. Generalized geologic column of the Eagle-Babb-Barnes project area. Adapted from company data. F. B. MOODIE Ill AND PRESTON McGRAlN

Geology by F. 0. Moodie Ill

Figure 4. Generalized topographic map of the Eagle-Babb-Barnes area showing location of project core holes. reveal additional details about the ore body and Inore than 1,000 feet at approximately 45 degrees, related geologic controls, which undoubtedly will and bottomed in Fredonia. This was the main refine these interpretations. fault with a con~mercialwidth and grade of ore. Core holes EBB 1 and EBB 2 (Fig. 5) on the This was the first hole on the Barnes tract to Eagle-Babb property indicated a sandstone brec- intersect this fault at a favorable horizon. cia zone outward from the maill hanging wall to Core hole EBB 9 was located to cut the inain be approximately 140 feet wide. This zone is Babb fault about halfway between EBB 7 and highly fractured, faulted, and brecciated. Corre- EBB 3 and EBB 5. This hole encountered 12.2 lation of these holes with records from 'earlier feet (true width) of high-grade fluorspar (see drilling was inlpossible. The only vein that Tables 1 and 2 and cover photograph). At this showed any continuity was the vein that lay point the presence of a potentially commercial immediately adjacent to the main hanging wall. fluorspar orebody was suspected. Subseq~~ent It was decided that the hanging wall of the main drilling further defined the structure and estab- fault (Menard against Cypress at the surface) was lished reserves of ore. the structure that should be followed across the During November and December 1971, four Barnes property, a distance of more than 5,000 drills operated two 10-hour shifts each to outline feet. the deposit. By January 1972, drill results were Core holes EBB 3 and EBB 5 (Fig. 6) imme- encouraging enough to exercise the first phase of diately across the property line on the Barnes the option agreement. Drilling ceased February property found the main Babb fault and good 1972 with the completion of 45 core holes. The mineralization. The faults were better defined. 45 holes, 40 classed exploratory and 5 audit, rep- Two veins with a zone of intense brecciation resented more than 28,000 feet of core taken along between them were encountered. Here the brec- the fault strike over a distance of approximately cia zone narrowed considerably, being only 10 to 5,400 feet. All exploratory tests were angle holes, 20 feet as contrasted with approximately 140 feet ranging from 45,to 60 degrees. Con~putedvertical in the first holes. depths ranged from 250 to 800 feet. Since time was of the essence, core hole EBB 7 Data obtained from the drilling program sug- was located near the north end of the Barnes gest a fluorspar deposit in the order of 1,000,000 tract. It was located so that it would cut the tons in indicated and inferred categories. The east fault (Cypress against Fredonia at the surface) vein, a nearly vertical fissure fill, has an average and continue to the main Babb fault. The first width of 9 feet; height varies from 200 to 400 fault, Fredonia against Bethel, was encountered feet. at 84 feet (on rods). At 913 feet (rod distance) the Calcite and fluorite were the most abundailt hole cut 7 feet (rod distance) of high-grade fluor- minerals encountered in the drilling program. The spar against a hanging wall of Fredonia Liine- fluorite was predominantly white to brown (see stone. The hole was collared in Fredonia, drilled cover photograph). The average sphalerite con- EAGLE-BABB-BARNES FLUORSPAR PROJECT

MENARD

WALTERSBU RG

VIENNA

\ TAR SPRINGS

HARDINSBURG Main fault

GOLCONDA

5.7' (true width economic ore

Quartzite breccia

Sandstone, calcite breccia, shows of Ca F2 and Zn S Geology by F. B. Moodie Ill

Figure 5. Cross section A-A'. An unusually wide zone of highly fractured, faulted, and brec- ciated sandstone was encountered in core hole EBB 2. 102 F. B. MOODIE Ill AND PRESTON McGRAlN

B

EBB 3 and 5

TAR SPRINGS

8.0' (true width/ economic ore

GLEN DEAN

7.5' (true width) economic ore Intensely breccioted zone

Geology by F. B. Moodie Ill Limestone breccia, calcite

Figure 6. Cross section B-B'. The faults were better defined and the brecciated zone thinner than in core hole EBB 2. Good mineralization occurs along the main fault. EAGLE-BABB-BARNES FLUORSPAR PROJECT 103

TABLE1.-LOG OF PORTIONOF COREEBB 9. HOLE WAS COLLAREDAT 65 DEGREES.ALL DEPTHSAND INTERVALSARE DISTANCESON RODS. GEOLOGYBY F. B. MOODIEI11 Depth (in feet) Distance drilled Core recovered Analysis From To (in feet) (in feet) Number Description 549.5 552.2 2.7 2.7 9-A1 Quartzite breccia (Cypress Ss.) with sphalerite and fluorspar. 552.2 557.0 4.8 4.8 9-A2 Limestone breccia (Fredonia (?)) with black gouge, sphalerite and fluorspar. This appears to be in the vein. 557.0 559.0 2.0 2 .O 9-A3 Fluorspar, dark-blue, with gouge and limestone breccia with sphalerite. 559.0 564.0 5.0 5.0 9-A4 Fluorspar, hard, crystalline, amber to brown, with sphalerite. 564.0 569.0 5.0 5.0 9-A5 Same 569.0 574.0 5.0 5.0 9-A6 Same 574.0 581.4 7.4 7.4 9-A7 Same 581.4 586.2 4.8 4.8 9-A8 Fluorspar, crystalline, dark-blue, and limestone breccia. Fault slip at 584.6. 586.2 591.2 5.0 5.0 9-A9 Calcite, petroliferous, with scattered shows of brown fluorite. 591.2 596.2 5.0 5.0 9-A10 Same; brown fluorite at 592.2 and 592.7. 596.2 603.0 6.8 6.8 9-All Same; brown fluorite at 597.3 and 598.6. Purple fluorite veinlet with pale yellow sphalerite at footwall contact 603.0.

TABLE2.-ANALYSIS OF PORTIONOF COREEBB 9. The footwall of the fault apparently had little VALUESOF CONSTITUENTSIN PERCENT. SEE TABLE effect on mineral accumulation. 1 FOR DESCRIPTIONOF SAMPLES The principal continuity along the Babb fault Sample system in the Eagle-Babb-Barnes project area is No. CaF, SiOp CaC03 ZnS R803 the hanging-wall (Menard) side rather than the 9-A1 18.22 58.28 6.12 6.92 - footwall (Fredonia) side. 9-A2 20.48 17.62 50.88 4.78 - As indicated earlier, intense brecciation is - 9-A3 52.08 13.94 16.12 8.43 present in portions of the Babb fault system. The 9-A4 96.79 0.32 0.43 1.19 0.42 PbS 9-A5 94.14 0.43 0.77 2.57 0.51 rocks in the hanging wall, particularly the lime- 9-A6 95.38 0.77 1.59 1.32 0.47 'I stones and more highly indurated sandstones, 9-A7 93.58 0.81 1.13 1.63 1.13 have been highly fractured. The rocks in the 9-A8 57.82 22.16 14.98 0.89 0.56 " footwall have been much less disturbed. Mineral - 9-A9 3.16 5.42 90.62 0.44 accumulation may be related, in part, to the 9-A10 2.94 1.22 95.38 - 0.46PbS broken-rock conditions in the hanging wall. 9-All 7.22 2.32 89.92 - 0.54 I' It has long been accepted that lithologic char- acteristics had marked effect on localizations of tent of the deposit is less than 2 percent, and the veins in the district. The largest fluorspar deposits average galena content less than 0.5 percent. have been associated with the purer limestones of Some pyrite is present but no barite has been the Ste. Genevieve and Renault formations. Since noted. these formations have not been thoroughly tested The main ore starts from the top of the Cypress on the hanging wall of the principal Babb struc- Sandstone and extends down into the lower ture in the Eagle-Babb-Barnes project area, it is section of Chesterian rocks. However, a few holes possible that a substantial reserve of ore is present indicate that at some places along the strike, ore in deeper zones. Further exploration will be shoots may extend upward as high as the Tar necessary to determine the total depth of fluorspar Springs Sandstone, all on the hanging-wall side. ore bodies in the Babb fault system. F. B. MOODIE Ill AND PRESTON McGRAlN C

EBB 30 EBB 13

.WALTERSBURG

Geology by F. B. Moodie Ill Figure 7. Cross section C-C'. Good mineralization continues along the main fault. Differences in thickness of the Cypress formation may be due to unrecognized faults or other structural conditions. EAGLE-BABB-BARNES FLUORSPAR PROJECT

. . Figure 8. Cross section' D-D'. Fluorspar ore of commercial grade and width was encountered in both the main fault and the east fault. As in cross section C-C', differences in thickness of the Cypress for- mation may be due to unrecognized faults or other structural conditions. F. B. MOODIE Ill AND PRESTON McGRAlN

Figure 9. Cross section E-E'. Commercial grade and width fluorspar ore extended along the strike of the main fault to the north end of the Barnes property, a distance of some 5,000 feet. EAGLE-BABB-BARNES FLUORSPAR PROJECT 107

Hardin (1955, p. 24-25) observed that vein States Geological Survey cooperative mapping width increase in the steeper segments of the program are providing an additional tool to use Babb fault system. Drilling on the Eagle-Babb- in prospecting programs. These 7.3minute quad- Barnes properties indicate that the faults were rangle maps, which are now completed or will be steeper where they crossed the massive limestone completed in the near future for the district, are formations, which coincide with principal zones giving earlier geological work an added dimension. of mineral occurrence. However, core drilling is the only way to deter- Differences of indicated thickness of the Cy- mine the presence, size, and shape of an ore body. press formation in Figures 7 and 8 may be due The long-accepted stratigraphic and structural to distortion, dip of beds, unrecognized faults, or considerations are still valid. However, it appears other deformation. that many deeper formations have not been ad- Fault gouge, derived primarily from shales of equately tested. Future drilling programs should Chesterian age, is commonly present in the fault be designed to thoroughly test the deeper units system. It is thought that this material served as in potentially favorable areas. This will mean an a trap for migrating mineral solutions. Earlier increase in exploration costs, but the results exploratory drilling apparently intersected the should be more rewarding. fault zone above or through the gouge material, whereas the current program was designed to test zones beneath gouge accumulations. Thirty-two of the exploratory holes encountered commercial- REFERENCES CITED grade ore. Hardin, G. C., Jr., 1955, Babb fault system, Crittenden Holes collared in the Fredonia Limestone and Livingston Counties, in Fluorspar deposits in commonly encountered cavernous conditions for western Kentucky: U. S. Geol. Survey Bull. 1012-B, p. 7-37. the first 200 feet (on rods at 45 degrees), resulting Mining Engineering, 1972: Mining Engineering, v. 24, in poor core recovery. no. 4, p. 19. Swanson, A. S., and Starnes, X. R., 1950, Investigation of CONCLUSIONS fluorite deposits of Babb vein system, Crittenden and Core drilling on the Eagle-Babb-Barnes pros- Livingston Counties, Ky.: U. S. Bur. Mines Rept. pect has demonstrated that the Western Kentucky Inv. 4677, 30 p. fluorspar district is still capable of yielding com- Trace, R. D., 1962, Geology of the Salem quadrangle, Kentucky: U. S. Geol. Survey Geol. Quad. Map mercial-size bodies of fluorspar ore. Undoubtedly GQ-206. others will be disclosed in the future. Ulrich, E. O.,and.Smith, W. S. T., 1905, Lead, zinc, and The 1:24,000-scale areal geologic maps pro- fluorspar deposits of western Kentucky: U. S. Geol. duced by the Kentucky Geological Survey-United Survey Prof. Paper 36, 218 p.