Mineralogy and Chemistry of Rare Earth Elements in Alkaline Ultramafic Rocks and Fluorite in the Western Kentucky Fluorspar District Warren H

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Mineralogy and Chemistry of Rare Earth Elements in Alkaline Ultramafic Rocks and Fluorite in the Western Kentucky Fluorspar District Warren H. Anderson

Report of Investigations 8 doi.org/10.13023/kgs.ri08.13 Series XIII, 2019 Cover Photo: Various alkaline ultramafic rocks showing porphyritic, brecciated, and aphanitic textures, in contact with host limestone and altered dike texture. From left to right: • Davidson North dike, Davidson core, YH-04, 800 ft depth. Lamprophyre with calcite veins, containing abundant rutile. • Coefield area, Billiton Minner core BMN 3. Intrusive breccia with lamprophyric (al- nöite) matrix. • Maple Lake area, core ML-1, 416 ft depth. Lamprophyre intrusive. • Maple Lake area, core ML-2, 513 ft depth. Lamprophyre (bottom) in contact with host limestone (top). Kentucky Geological Survey University of Kentucky, Lexington

Mineralogy and Chemistry of Rare Earth Elements in Alkaline Ultramafic Rocks and Fluorite in the Western Kentucky Fluorspar District

Warren H. Anderson

Report of Investigations 8 doi.org/10.13023/kgs.ri08.13 Series XIII, 2019 Our Mission The Kentucky Geological Survey is a state-supported research center and public resource within the University of Kentucky. Our mission is to support sustainable prosperity of the commonwealth, the vitality of its flagship university, and the welfare of its people. We do this by conducting research and providing unbiased information about geologic resources, environmental issues, and natural hazards affecting Kentucky.

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© 2019 University of Kentucky For further information contact: Technology Transfer Officer Kentucky Geological Survey 228 Mining and Mineral Resources Building University of Kentucky Lexington, KY 40506-0107

Technical Level

General Intermediate Technical

Statement of Benefit to Kentucky Rare earth elements are used in many applications in modern society, from cellphones to smart weapons systems. The igneous rocks of the Western Kentucky Fluorspar District are slightly enriched in these elements, and although the limited dataset of this study did not reveal economic deposits, there could still be economic quantities in western Kentucky, as well as occurrences of titanium, niobium, iridium, cobalt, molybdenum, zirconium, and lithium.

ISSN 0075-5591 Contents Abstract...... 1 Introduction...... 1 Geologic History and REE-Related Mineralization...... 2 Alkaline Ultramafic Rocks...... 5 Model for the District...... 7 Rare Earth Elements...... 7 REE Concentrations in Alkaline Ultramafic Rocks and Fluorite...... 8 Methods...... 9 Sample Set...... 9 Mineralogy and Petrography...... 9 Elemental Analysis...... 9 Normalization of REE Data...... 13 Standards and Analysis of REE data...... 13 Results ...... 13 Petrology and Major Element Analysis...... 13 Mineralogy of Alkaline Ultramafic Dikes...... 16 REE in Dikes...... 26 Background...... 26 Discussion of Elemental Data From Dikes...... 26 REE in Ore-Stage Fluorite...... 32 Discussion of REE in Fluorite...... 32 Conclusions...... 36 Dike Petrology and Mineralogy...... 37 REE Analysis in Dikes...... 38 Carbonatite Metasomatism and Incompatible Element Ratios...... 39 REE in MVT-Stage Fluorite...... 41 Acknowledgments...... 42 References Cited...... 43 Figures 1. Map showing location of the Western Kentucky Fluorspar District and its faults, dikes, grabens, mineral districts, and sample locations...... 3 2. Photograph of a Rogers Quarry lamprophyre dike, Crittenden County, Ky...... 6 3. Photograph of KGS dike 801, Frontier Spar core 6, located north of the Klondike Mines, Livingston County, Ky...... 6 4. Graph showing results of raw-data analysis by inductively coupled plasma atomic emission spectrometry of various dikes with increasing distance from Hicks Dome, indicating REE enrichment...... 14

5. Ternary composition diagrams showing Al2O3, CaO, FeO (total), and MgO concentrations of intrusive rocks of the Western Kentucky Fluorspar District...... 15 6. Photomicrographs of: A. The Davidson North dike, Crittenden County, Ky., near the northeastern Babb area and north of the Midway area. B. The Davidson North dike, showing lamprophyre containing abundant clinopyroxene phenocrysts with the white titanium mineral leucoxene, and an alteration vein cutting the dike...... 17 7. Photomicrograph showing xenolith in the Minner core...... 18 8. Photomicrograph of moissanite identified by X-ray diffraction in xenolith in core DLP-3 at 329 ft, Crittenden County, Ky...... 18 Figures (continued) 9. Photomicrograph of almandine garnet in an altered dike matrix of calcite, anatase, muscovite, illite, lizardite, and the iron sulfate rozenite...... 19 10. Photomicrograph of core DLP-2, showing the MVT sulfide sphalerite at a depth of 824 ft...... 19 11. Scanning electron microscope photograph of core DLP-2 at a depth of 112 ft, showing the calcium phosphate moazite with iridium enrichment...... 20 12. Graph showing normalized REE concentrations of selected dikes in the Western Ken- tucky Fluorspar District...... 27 13. Graph comparing La/Yb ratios and Tb/Yb ratios is indicative of fractionated melt crystallization and metasomatism of high-titanium alkaline ultramafic magmas in the West- ern Kentucky Fluorspar District...... 27 14. Bivariate linear plot of La/Yb ratio versus Sm/Yb ratio showing significant changes in dike mineralogy for an evolving peridotite melt...... 28 15. Plot of whole-rock La/Yb and Nb/Ta ratios showing elevated concentrations in both superchondritic and subchondritic niobium-rich ilmenite and rutile fields...... 28 16. Bivariate diagram of whole-rock uranium/thorium element fractionation, which is thermal-inducing in magma melts...... 29 17. Plot of Zr/Y and Zr/Hf ratios versus La/Yb ratios, showing superchondritic dikes in both sample sets, which indicates mantle and metasomatic geochemical enrichment in the Western Kentucky Fluorspar District...... 29 18. Plots showing (A) increasing niobium and yttrium concentrations that suggest some variable degrees of partial melting and enrichment in a fractionated titanium-niobium carbonatite near the Coefield anomaly and (B) Ti/Nb ratios, which indicate increasing niobium in response to increased differentiation of high-titanium magma...... 30 19. Plot of Ti/Eu and Zr/Hf ratios, showing increasing differentiation in the magma...... 31 20. Graph showing patterns of REE in fluorite from the Western Kentucky Fluorspar District...... 33 21. Graph showing ratios of REE in fluorite...... 33 22. Graph showing uranium-thorium concentrations in fluorite, which indicates high uranium in fluorite from the Joy Mine and high thorium in fluorite from the Davenport Mine...... 34 23. Graph showing Y/Yb ratios indicates that the Western Kentucky Fluorspar District fluorites are in the hydrothermal category...... 34

Plate 1. Mines, minerals, and magnetics of the Western Kentucky Fluorspar District...... 4

Table 1. Inventory of igneous dikes in the Western Kentucky Fluorspar District...... 10 1 Mineralogy and Chemistry of Rare Earth Elements in Alkaline Ultramafic Rocks and Fluorite in the Western Kentucky Fluorspar District Warren H. Anderson

Abstract Rare earth elements, or REE, are used in modern society in televisions, computers, cellphones, military equipment, and smart weapons systems. These metals are also used by the medical industry in magnetic resonance imaging and in medical products. The igneous rocks in the Western Kentucky Fluorspar District of the New Madrid Rift System are considered alkaline ultramafic rocks that are slightly enriched in REE. These rocks are rare and only occur in several hundred locations in the world. They have a complex history of emplacement, fractionation, metasomatism, and alteration, and are overprinted with Mississippi Valley-type mineralization. They are classified as lamprophyres and peridotites, and the rare mineralogy of the district suggests that there may be other facies of these rocks, such as carbonatite, kimberlite, and lamproite. The rare minerals wüstite and moissanite also suggest a deep lithospheric and asthenospheric mantle contribution to these igneous rocks and raise the level of interest in the igneous complex, which occurs in a Midcontinent rift system. The petrogenesis of these rocks allows them to fractionate and concentrate REE by natural means, and although this study’s limited dataset did not reveal any economic deposits, there could still be economic quantities in western Kentucky. If higher concentrations of REE are found in the igneous dikes in the area, the economics and mining of the dikes might be feasible. Millions of tons of fluorite and thousands of tons of sphalerite, galena, and barite have been mined in the district, and small amounts of REE have been detected in the fluorite. Other elements of interest are titanium, niobium, iridium, cobalt, molybdenum, zirconium, and lithium, which suggest other elemental phases of mineralization. Many of these rare minerals and elements have never been described in the West- ern Kentucky Fluorspar District, and future research is warranted to further classify them.

Introduction goggles, communications, magnets, lasers, batter- Rare earth elements, or REE, are a group of ies, and nuclear propulsion. Other uses for REE chemical elements, called lanthanides, that are of are in cellphones, computers, electronics, magnetic strategic importance to the security of the United resonance imaging, green energy applications, and States. REE, together with other trace metals, are wind turbines. Titanium, an associated element, is critical materials in the modern world, and are a high-strength, lightweight, corrosion-resistant used in the aerospace and military industries in metal used in aviation and jet aircraft. The U.S. precision military weapons systems, night vision Congress has enacted legislation to promote research on strategic and critical minerals, and sever- 2 Inntroduction al National Strategic and Critical Mineral Produc- Geologic History and tion Acts were enacted in 2013 and 2015 to facilitate REE-Related Mineralization the research and development of domestic REE The western Kentucky portion of the Illinois- deposits in the United States. The 2017 House Bill Kentucky Fluorspar District (Fig. 1, Plate 1) occurs was submitted but has not yet been enacted. For in the northern New Madrid Rift Zone in the central many years, the only operating REE mine in the United States, and is part of a failed late Precambri- U.S. was the Mountain Pass Mine in California an continental extensional rift (Braile and others, (Castor, 2008), which was shut down in 2015, but 1986). The New Madrid Rift Zone extends from reopened under MP Materials’ new ownership in the Ouachita Fold Belt in Arkansas northeastward 2018 (www.mpmaterials.com). With the decrease into western Kentucky, where it turns abruptly in Chinese exports of raw REE materials begin- east to form what is locally known as the Rough ning in 2010, the United States’ supply of REE has Creek Graben, and continues directly east farther become unstable and prices have increased dra- into Kentucky (Nelson, 2010). The Rough Creek matically. In addition, limited reserves from other Graben is bounded on both sides by large listric sources make these elements a national security is- normal faults that cut deep into the Precambrian sue. Today, academic, government, and industry basement (Potter and others, 1995). The rift zone personnel are conducting research and exploration has a complex tectonic history: northeast-trending in the U.S. to search for new REE deposits and re- normal faults periodically reactivated throughout duce our reliance on foreign suppliers. the Paleozoic, which induced structural compres- The primary purpose of this study is to evalu- sion, faulting, arching, and an extensional phase ate the mineralogy and elemental chemistry of a during the Alleghenian Orogeny (Kolata and group of REE-bearing alkaline igneous rocks and Nelson, 2010; Nelson, 2010). These magmatic and the associated mineral fluorite (CaF2) in the West- structural events prepared the late Paleozoic rocks ern Kentucky Fluorspar District and the Southern to receive both deep-seated igneous intrusive and Illinois Mineral District (Fig. 1). Combined, the two basinal brine mineralizing fluids during the Perm- districts form the Illinois-Kentucky Fluorspar Dis- ian Period. Snee and Hayes (1992) dated actual em- trict, which was once the largest producer of fluo placement of the northwest-trending igneous dikes rite and base metals in the United States. These and Mississippi Valley-type mineralization (Ohle, igneous rocks are dikes and sills that intrude Pa- 1959) in the district using argon geochronology on leozoic rocks and contain REE. The analytical in- biotite at the Grants Intrusive in Illinois and the formation in this study will help characterize rocks Hutson dike in Kentucky and suggested an age of of the Illinois-Kentucky Fluorspar District for 271–272 Ma; Chesley and others (1994) determined REE to determine if there is an undiscovered re- the age, based on samarium and neodymium source in the Western Kentucky Fluorspar District. yields in fluorite, to be 272 Ma; and Denny (2010) More than 50 distinct alkaline ultramafic igneous and Denny and others (2017) suggested a broader dikes, sills, diatremes, and other intrusions have range of ages between 258 and 281 Ma. Paragenetic been identified and mapped in western Kentucky studies of the mineralization by Hayes and Ander- (Fig. 1, Plate 1). son (1992) suggest early, middle, and late stages of Analytical data were normalized and com- mineralization, which can be used to correlate in- piled into diagrams and bivariant plots that sug- trusion, alteration, and mineralizing fluid events. gest complex metallogenesis for REE in alkaline There is an association between some altered dikes ultramafic rocks from the Western Kentucky and sphalerite mineralization. Pollitz and Mooney Fluorspar District. Various lithofacies of these al- (2014) used mantle viscosity profiles and mantle kaline ultramafic lamprophyre rocks originated in flow in the Midcontinent to describe a weakened the subcontinental lithospheric mantle and have mantle in the study area. These important process- undergone fractionation and metasomatism. The es in the New Madrid Rift Zone influenced mantle most favorable rock types for hosting REE are nio- dynamics, melting, fractionation, and carbonatite bium-bearing carbonatites (Verplanck and others, metasomatism. 2014). Introduction 3

Explanation Igneous diatreme Igneous dike showing trend

area of this map Igneous sample location Fluorite subdistrict

Fluorite mine

Fault Sparks Hill diatreme Highangle reverse fault

Graben

Kentucky Illinois-Kentucky Fluorspar District Hicks Dome Goose Illinois Rose Mine Creek

Empire Grants Annabell Lee Intrusive Cave Rock

Hastie Bros. Mine

t Cave in Rock Interstate

Stewar er Riv Tolu Arch Ohio Dixon Springs Graben RosiclareRosiclare

Coefield Commodore Crittenden Co. Carrsville Intrusive Complex Columbia Mines Joy DLP Minner

Graben Hampton Joy Midway Davidson North Columbia Marion Graben Midway Lady Farmer Bluff Sunderland

Creek Belt Graben Davenport Griffith Clay Lick Grove Dyer Hill Eagle Shady Caldwell Co. Robinson GrabenEagle East Rock Babb Graben Cardin Salem Hill Graben Moore Hill

Dyer Hill Hodge Graben Graben West Bluff Moore Mexico Graben Mexico Farmersville Dome Hodge Klondike Hobby dikes Mineral Tabb Ridge Lockhart Caldwell Fredonia Hutson n Creek e Maple Lake Paducah Graben b a r n Tabb G be s ra s G re ia p on y ed C Fr

Livingston Co.

s Lyon Co. i y o k n c li Princeton Il tu Eddyville n e K

0 4 mi Marshall Co. N 0 8 km

Figure 1. Location of the Western Kentucky Fluorspar District, showing faults, dikes, grabens, mineral districts, and sample locations. 88°30 37°30 25 20 15 10 88°05 h n c Hastie Bros. Mine: Sullivan Bra Hazel KENTUCKY GEOLOGICAL SURVEY actual location north of map. Rock Spring William C. Haneberg, State Geologist and Director T r a UNIVERSITY OF KENTUCKY, LEXINGTON d e Plate 1: Mines, Minerals, and Magne�cs of the w h a Wheatcroft c t n e r a h r c

n R West Wheatcroft B a i r v B e

r k n r o Modified from Hanley and Vorhees (1984), Gaylord and others o y s F e Western Kentucky Fluorspar District y n m a e (1998), and Anderson and Sparks (2012). a d n C A Introduction and galena. Stratabound, or bedded, deposits, also classi ed a as MVT and C r Rive This map is modi ed from Anderson and Sparks (2012). It containsate a layerr of containing uorite, occur mainly in the Joy and Carrsville areas; bedded w Warren H. Anderson e magnetic data compiled from various sources to enhance the understandingra d sphalerite may occur in other areas. The third class is igneous intrusives, similar of the district. Point data were also added to highlight whichT dikes were to Hicks Dome, a carbonatite complex located in Hardin County, Ill. More than analyzed during this study. 50 documented igneous intrusions, including dikes, sills, and diatremes, are 0 ILLINOIS found in the district. These igneous rocks can host rare earth elements, titani- 1 1 2 3 4 5 6 KILOMETERS h Purpose Weston c KENTUCKY n um, and uorite minerals. a The map showsr all the known and identi ed mines, mineral prospects, and

N B

Br. igneous intrusionsg (dikes or sills) in the Western Kentucky Fluorspar District, Mining History n 1 0 1 2 3 MILES o L Dam 50 compiled from thousands of maps and les, creating an up-to-date, compre- The earliest mining in the district was for lead at the Columbia Mine, Critten- RIVER Cave Crab water well hensive catalog for the district. The district has been extensively mined for den County, Ky., in 1835 (Ulrich Virginiaand Smith, 1905, p. 115). Fromo r1835ch to the early ar OHIO d C Sand more than 120 years and was once the largest producer of uorspar (uorite) in 1870s, little uorspar was mined. Only small amounts were producedre from the SCALE 1:50,000 ek the United States. early 1870s to about 1890, when an expanded market was created byFairmont the dike at Cave- Derby Lambert conformal projection, 1983 North American datum in-Rock Ferry development of the basic open-hearth steel furnace, in which uorspar was Kentucky Single Zone Coordinate System Millions of tons of vein ore minerals (uorite, zinc, lead, and barite) have been produced from these mines, and substantial reserves still remain. New mining used for ux. Production since 1890 has been erratic, but in general has risen. and exploration activity has renewed interest in the district, and the industry During World Wars I and II and the Korean conict, production rose sharply, but Webster fluorite because of rising imports from 1955 to 1958, production in the district Camp will bene t from the use of this new map. Historic iron ore mines are also 409 400 754 873 491 Cartography by Terry Hounshell 91 Ainsworth Mine DDH prospect 1201 REPTON decreased. It rose in 1970, but declined rapidly, and all production ceased in ROSICLAIRE BLACKFORD PROVIDENCE (Baldwin shaft) SHETLERVILLE CAVE IN ROCK Baldwin prospect C included because of their immediate proximity to this mapped area. dike location reek Blackford Kentucky by 1985. Sporadic milling of recycled government stockpiles contin- Crittenden Galena shaft 387

N ProcedureM ued into the 1990s. Exploration is intermittent in the district, and currently ea SHADY d 546 546 LOLA DALTON490 The map was compiled from numerous sources,o includingk those resulting from there is one operating mine, near the Klondike Mine complex. 1288 SALEM206 MARION547 GROVE880 w e GOLCONDA open-cut Cre BROWNFIELD trench the U.S. Geological Survey–Kentucky Geological Survey Geologic Mapping Pro- Livingston Caldwell reek Since mining began, the Western Kentucky Fluorspar District has produced ne C ch gram (1960–78), Strategic and Critical Minerals Program (1983), Conterminous urrica ran about 3.5 million tons of uorspar, 70,000 tons of zinc, 12,500 tons of lead, and H B United States Mineral Assessment Program (1987–92), KGS Digital Geologic 657 OLNEY742 KENTUCKY Tolu Arch BURNA1150 1149 607 CRIDER1283 SMITHLAND FREDONIA 45,000 tons of barite concentrate (Anderson and others, 1982). Some trace DYCUSBURG 365 s Mapping Program (1996–2005), and numerous KGS mineral investigations Lyon Area of C e elements, such as silver, copper, cadmium, and gallium, have also been recov- Shell No. 1 Davis r ek h barite-fluorite o re g (1838–present). Some data were from KGS research, and others were collected this map Mico o u 135 k C ered. Thirty percent of the uorspar came from the Tabb Fault System, a major prospect H k Tolu (Cook-Springs) e and donated by mining geologists, eld mappers,e mining companies, federal d e LITTLE ranch Mine r curvilinear fault in southern Crittenden and western Caldwell Counties (Trace 554 731 328 255 WEST EAST B dike location C CYPRESS EDDYVILLE PRINCETON385 PRINCETON1032 Ainsworth South and state geologists, and exploration consultants. Many of the data are in the k ds CALVERTY CITY GRAND RIVERS e drillholes oo and Amos, 1984). C e H t an fluorite r form of surface and underground mine maps, property maps, eld notes, drill et ey C DDH C rn rk occurrence ra 7.5-minute quadrangle index a fluorite o b B F logs, cross sections, summary reports,Nunn and reserve studies. Zinco has been produced since 1940, some as a byproduct of mining uorite. prospects 135 fluorite rc s The hHutson Mine was a primary zinc producer in the district. Substantial quan- m a a prospect r li Database d il

Creek tities ofC baritere have also been produced. Lead has been a minor byproduct in W ek This map is an introduction to the Kentucky Minerals DatabaseT (ww- fluorite mine r fluorite prospect a recent years, as have silver, cadmium, and germanium. w.uky.edu/KGS/minerals/im_database.php). This new GIS database providesd e w SYSTEM a immediate online access to detailed information about the mines on thist map. e dike r

Creek location For some of the larger mines, abundant data are available, but for others,R only

i 25 ° v 37 25 e Franklin Beard limited information or just a reference to a publication or report is available.r 723 Hurricane Group Acknowledgments Furnace prospect Also included in the database is informationFork about the igneous dikes in the lamprophyre dike ney Thanks are extended to Walter Gaylord, Bill Frazer, and T. Ballard, Savage Zinc Inc.; Ed Mines M district, which are important forCa the exploration of ore deposits and other geo- in coreholes 654 a t Hanley, Billiton Metals and Ores USA Inc.; and Boyce Moodie III, Moodie Minerals Inc., fluorite t R o E mine Hurricane o logic studies. There are some identical mine names for dierent properties on IV DDH n Dynamex Resources Corp., and North American Exploration Inc. Additional thanks go R lamprophyre 297 FAULT the map and in the database, along with various spellings of mine names on iron ore Cr. 60 to Terry Hounshell and Thomas Sparks, Kentucky Geological Survey, for cartographic Hurricane sample (T-2-76) k prospect e fluorite DDH the same property, and multiple mine names for thee same property. The data- IO galena in Texas Beard r services. iver CRITTENDEN C R prospect er H Gas No. 1 1668 Mines base will ultimately be the most up-to-date, geospatiallyt accurate catalog for at Hurricane s ew O Arflack o Trad h o Special thanks for the development of this map and database are extended to William nc Mattoon western Kentucky mineral deposits. r a drillhole locations on 135 r Moore DDH ge B FAULT for bedded fluorite Pi R. Frazer, Marion, Ky., who allowed KGS to scan his company’s mining data and make fluorite prospects DDH 1901 prospect Carrsville fluorite prospect by Minerva and Magnetics Mine fluorite Ellis k E them publicly available in the new Kentucky Minerals Database; and Robert D. Trace, ILLINOIS e R SPRINGS American Zinc mine e The magnetic data on this map were compiled from several dierent sources. shaft r O B

d USGS and KGS, whoPiney worked in the district between 1942 and 1985 and provided

l D DDH i Deer g

C 91

KENTUCKY Carrsville e Patmore-Stalion O Cyclone k During the 1980s, Billiton Metals and Ores USA Inc. ew an aeromagnetic M B fluorite l prospect Br. numerous rock samples, maps, notes, sections, and logs of mine data. Trace’s numer- i M lamprophyre Ellis-Carr r r O CRITTENDEN a occurrence h y survey of the district, and their residual magnetic data were acquired by KGS Mine k C n 137 East-West manto T ee k DDH ous maps, publications, and interpretationsc are important components of this new r DDH Crook c h C ed o after Billiton ceased exploration activities. During the 1990s, Savage Zinc Inc. Shell No. 1 Minner Hole in the Craighead-Coates LEVIAS – R database, as is the igneous sample set he archived and donated to KGS. fluorite san (Old Glory) area Su Ground survey M y drilled around the Columbia Mine area and compiled additional total intensity Clement mines il sh Repton area l u (Clemens) Frazer prospect fluorite DDH C r F Irma Sullenger Slick Frazer (Owl re B o aeromagnetic data. From 2006 to 2008, Dynamex Resources Corp. ew anoth- Early mine geologists, including Harry J. Klepser, G.C. Hardin Jr., Stuart Weller, X.B. vein C e r reek Mine Hollow) shaft prospects k k ns C r er aeromagnetic survey and produced a total intensity magnetic map of the ve e DDH Starnes, Dewey H. Amos, and William R. Thurston, contributed vital information and Gi ek k Coe eld portion of the district. To create Plate 1, data from the above sources e Bellman documentation on the early mining activity in the district. Many of them wrote publi-

e GRABENCampbell Crotser r Mine Memphis (North) were overlaid on Anderson and Sparks’s (2012) “Mines and Minerals Map of the vein prospects C prospects cations and contributed to earlier War Minerals and U.S. Bureau of Mines reports. John fluorite fluorite prospect C 297 a DDH Western Kentucky Fluorspar District.” The magnetic data used on Plate 1 are mines ne k Tibbs and many other persons contributed to the understanding of the Western y lamprophyre sill e Loves Chapel re total intensity data and may be somewhat imprecise because of the various 723 in coreholes GRABEN C Kentucky Fluorspar District and therefore have contributed much to the Kentucky shaft B Fo uck rk Little Hurricane generations and scales of data, the quality of which is unknown; only general- Minerals Database. Suit prospect lamprophyre ized magnetic intensity data (highs greater than 2 gammas and lows less than Loves Chapel prospect Fork D Dike in O 2 gammas) are shown because of magnetic data conicts noticed during com- Disclaimer r r Commodore Mines k y c e Shell Oil e er 135 h tl

r u pilation of this plate. The dierences are related to petrologic dierences, mag- Although this map was compiled from digital data that were successfully processed C a Commodore lamprophyre B fluorite prospect Co. No. 1 C

r a Howard Stout Adams d on a computer system at the Kentucky Geological Survey,k no warranty, expressed or v FAULT e lamprophyre netic susceptibility, and alteration events (which aect magnetics) in certain e e core 1668 r fluorite implied, is made by KGS regarding the utility of theC data on any other system, nor shall S Hickory Cane Memphis Howard Stout sample (T-8-76) parts of the district. The Billiton residual data are available via the KGS Minerals f S C dike in Callahan Mining corehole l p Shell No. 1 Adams W prospect ad Mines o r le McDaniels r Mine the act of distribution constitute any such warranty. KGS does not guarantee this map i r e fluorite prospect i W n n e Database (www.uky.edu/KGS/minerals/im_database.php). g C dike Burns Hickory Cane lamprophyre re l ch e k n k Struck- o a h or digital data to be free of errors or inaccuracies. KGS disclaims any responsibility or (Bradshaw) FAULT Glendale w r Hampton Joy Minner It-Rich live B n c prospect C Minner Mines Glendale mica O Bra Br. core oe Mine Mine Mineral Deposit Classi cation n Deanwoodliability for interpretations from this map or digital data, or decisions based thereon. fie alnoite peridotite Freedom North ea fluorite 133 (HJ-10) ld Minner (Coefield) core BMN-7 D Shouse-Skelton KK Mines (Hard) C The locations of three classes of mineral deposits are shown on this map, the r The views and conclusions contained in this document are those of the authors and prospects Gulf Oil (Joy) Mine Minner (Coefield) core BMN-4 Clement Mine lamprophyre e No. 1 Belmar Nine ek rst of which is Mississippi Valley–type hydrothermal mineral deposits (vein Black ek Minner (Coefield) core DLP-2 SHERIDAN should not be interpreted as necessarily representing the ocial policies, either Homer Day D Cre B Acre CREEK Mine e SYSTEMMinner (Coefield) core DLP-3 ranc deposits, bedded deposits, and igneous intrusives). The second class is vein expressed or implied, of the U.S. Government. CREEK e h Mine Joy fluorite 120 L prospect Johnson- r e SYSTEM a prospect n deposits, which are narrow mineralFAULT deposits that extend vertically and hori- 120 n a 654 AY LICK d Quetermous- Gray Mine ic 60 CL Bebout Mine rr G Dalton prospects Gray Hu SYSTEM zontally for hundreds of feet and consist of uorite, sphalerite, calcite, barite, u FAULT Sheridan m Hampton Joy lamprophyre Crystal (Flannery) Freedom South k fluorite 120 e core C mica peridotite 1905 e C Br. r lamprophyre r Hampton Joy e 297 occurrence re (HJ-5) ek Macer Mine Crittenden Springs C e Berrys Ferry dike and May-Black k prospect LOLA Butler Columbia Mine core BCS-2B Tribune corehole Mines area Mines LT (HJ-13) Davidson shaft FAU CRYSTAL Columbia mica peridotites FAULT Butler Horse Lot Mines Deer Creek k FAULT 139 RIDGE BIG Eureka Mine e r lamprophyre e ga (Cartwright) Mines Craighead Mines r u HICKORY B S Columbia South sample 1379a C Good Hope u FAULT ROCKS c Crystal sample TK Block k Atlas Mine BLUFFMary Belle Mines Mary Belle mica peridotite fluorite FAULT Crystal Mines 91 (Morton) FAULT Rogers Quarry dike T prospects Br. Holly mica peridotite HILL prospect ur La Rue Mine Big Deal k key eek Holly Mine Old Jim mica T STOPPING r r e C prospect i Mann- peridotite 1668 ss b e Big Four Mines Ga B zinc r Miller (Daisy Sam r. u McDowell Old Jim core (D-1) HILL n prospect Shady Grove C Zinc) Mines Br. 120 e area F Old Jim Mine l d k Mann a T e n L PALEY 37°20 20 e k t ld r k Marion ° li U FAULT fie Creek fluorite 37 20 e c o r lamprophyre c o A e o o u k CREEK 723 F C Bro C C r prospects Cr ROCK B wn C C eek 137 s Lady Farmer MOORE re r 88°00 e 87°55 e fluorite C k Br. R Franklin mica peridotite 60 iv r U 135 occurrence e O Mines R e Corn (Givens) Mine F Lady Farmer Lucille lamprophyre Utley 133 k KNOB y r p Lucille Mine e e Mine r. in t Ford m BIG Ada Florence Mine B P Creek h a a Stalion-Curnel nc w c Pennsalt F-20 Prospect Bra e 1436 r prospect Lady Farmer d a Haynes n a g core BLF-4 Hill so r u prospect t y T S Mitchell A. Watson T Hick Jones Mine shafts N an Mine COEFIELD prospect 297 E as Bateman-Lola Ben Belt HARDIN Davidson North core (Slick Frazer) le Smith Ford prospect C B P Mines Damron Mine Mines YH-004 (est. loc.) oe John f P i Moore Hill A 1592 e Lola Jim Belt e GRABEN c Sunderland Keystone 641 FAULT Creek k Belt ld lamprophyre R Good Hope Church Mine (Dameron) Mine h h Mines Mine C 506 fluorite nc c (Faulkner) prospect re G Bra n Br. e occurrence a k r MINES Snyder shafts CHURCH FAULT 60 k B POINT Sunderland (Lola) Barnes ee STONY Sunderland sample (T-5-6) r James Cr Bradford Store C POINT y ee lamprophyre lamprophyre k e k c Eaton Midway (Davidson) (Crider) drill tests li in k Wright Mine Mine y P e lamprophyre la 139 e Fowler C STONY r NE Babb Dike North FAULT ks GROVE C k Eaton Midway (Davidson) T-9-76 lamprophyre c Kemper e area lamprophyre la 1608 re B Mine C Larue Levias Guilless Mine Claylick East Claylick East sample T-1136 Mine mica peridotite fluorite Little Midway Guilless samples T-800, T-1-76 HILL k Bonanza O.V. Paris prospect e

Good Hope Bluff andy re h Mine C Br. c South (Robinson- S Claylick West prospect r n Jennings Mine CHAPEL tle ra Vasseur) prospect mica peridotite Claylick West sample T-798 Bu s B GRABEN Larue shaft fluorite n k Dike South e ry e v e n occurrence e w a re lamprophyre SHADY To m C B Creek Johnson re o Eagle prospect Frazer Mine C F Dike South CH 49 (USBM DDH 49) SYSTEM GRIFFITH r Gilland Babb-Barnes o prospect Dike South CH 48 (USBM DDH 48) o Mine Complex m Riggs Mine k

e e Howard Formosa l Standard d

a fluorite Piney Fork Quinn S Eagle Babb shaft (Famosa) prospect C FAULT occurrence 506 Poindexter LIVINGSTON r Mines Mines (Savage Zinc) Mary Kinnin e fluorite prospects dike e Bachelor shaft prospect k fluorite ork C y F r. prospect Kentucky Delhi Mine r B Deer D Summers u SYSTEM BLUFF Babb LICK tle 133 Mine r New eek C Cr Cr. r. Nelson New Brown Hollow P Oxley- re fluorite prospect Salem a Robinson- CLAY (Leander White) c prospect Hampton FAULT Dry Pepperbox h Robinson (Cerro-FFL) Guill Mine shafts e Lasher shafts r 1077 C

lamprophyre Crosson McCune r Mine (T-7-76) 723 e Cr M e s ek Cave property Childress Bluff c Cardin Cardin sample T-1448 H w HILL prospect SYSTEM (Levias) a 641 e lamprophyre l l Nelson Watson (Vein) Cardin sample T-404-2 e FAULT l fluorite occurrence SYSTEM lamprophyre WILSON 135 prospect 60 lamprophyre Tightwad y BRIDGE (Reynolds fluorite shaft Cr. k View prospect (Pennsalt F-14) ree DYER Mining) Butler prospect C u Davenport Eagle-Watson Mines o k Baxter-Loyd prospect Mine Br. y e Mines e Two Brothers shaft a (W.T. Baxter lease) Nelson r area H WILSON 902 B C FAULT fluorite 1608 prospect Roberts Crayne illyard occurrence Orr (Cerro-FFL) and Frazer FAULT C BRIDGE B r B r. FAULT a Baxter-Loyd vein (Tyner) uce Creswell n y View (Lowery) o ou Pace-Linley shafts lamprophyre (T-277) s Harper Ford

ld y B HILL HILL Branch d prospects Sp a Chips C n r r n a in r B a CREEK Eagle- g SYSTEM o Property e fluorite n D a S e 60 C h Lena Wring View c k y LOCKHART B c o occurrence Salem h dike o fluorite prospect k r n u x shaft a Massey a e 902 MOORE n r S FAULT e c DYER HILL GRABEN EASTprospect Susie Beeler r B p h C Lingang prospect C Baxter-Loyd r shaft r i Maxus Exploration Co. e prospect (Loyd n XICO e g No. 1 Ray James ME k fluorite

lease) B Stevens-Butler 139 r a occurrence 70

Baxter Heirs SANDY 723 n prospect Ebby Hodge

prospect c Mosier Mine

h shaft k Enon Quetermous Grimes prospect 855 lic y D Lingang prospect la Clement Creek FAULT 763 Eagle-Cullen C r RICHLAND prospect y 15 (Evening Star) 37°15 n DDH fluorite prospect a Addie D Lingang r F Mexico East m y o k e DDH 60 Manus prospect Nancy Hanks r e l Burna Emmus k re (Crayne) Howard Story o prospects J. Pace C H 1433 Mine Complex Church fluorite Dupont prospect 1077 Bayou 763 DDH DDH Frontier prospect C area mine prospect r fluorite Spar . 137 fluorite prospects D (Little) Reiter Mine ry corehole Lovelace Mines prospects Vinson F ork (Ramage) Hodge prospect shaft fluorite Mine King Mine fluorite GRABEN k fluorite prospect e Eberle e . prospect r r prospect prospect Bibb C B 60 Hutson FAULT prospects k e 1433 North mica n ek DDH Hutson core BH-7 133 re Rufus r re Riley Eagle Mines u C peridotite Brown Mine Pennsalt (F-14) on C k Flat Rock ns b El (BHN 1-4) ton he k P James and Pennwalt ings p Hobby North c h Redd 641 Liv 70 te la el Lovelace prospects MEXICO S (Bethany Church) B ps Lake-Maddux Mines e (Loveless) 902 s mica peridotite C ll prospect oo reek DDH Bisse Mineral Ridge Complex Mines G PITTSBURGH Riley Kirk M fluorite mine Northeast YSTE 70 Mullikin Junction Hutson Mines Mine prospects S Mine Mexico Crider farm sill in DYER HILL GRABEN WEST Hutson shaft sample (T-10-76 Pace Mine Beavers Stephens k prospect e 293 FAULT Pygmy Mine fluorite No. 1 well re Hutson core (T-3-76) Hulet C Needmore Klondike II Wallace Mines Complex SYSTEM prospect Mine C Bradley-Padon Mine Crouch-Simp- Haffaw Tabb a Birdsville Ryan MEXICO prospect Klondike Southwest kins prospect Frances Mine n (Lafayette) e Dyer Hill 1433 prospect fluorite prospect EXPLANATION lamprophyre Mine Mines Mine FAULT y Mine Hutson mica possible dike dike Complex Eva on Complex peridotite Br. MOORE T.C. Campbell fluorite Mary 70 s oe Br. in corehole d C b Mine, surface cut; fluorspar, zinc, or barite TABB Tanguay l e prospects mines Helen a r fluorite Clear Billy Owl Kelley Mine Blue-Marble n e D Yandell Mine Mine o e C Mine Mine Lowery-Ray Farmersville Dome D k Mine, surface cut; iron re prospect Mines TABB ek Tabor Mines Green k r. Fork e Mine (Jones-Brown C ry Mine re Pogue and Buc Mine shaft; underground D C 70 leases) F ha Hutson Matthews Asbridge Mines AU na fluorite Tabb LT n sill in corehole South 723 Mines Fredonia e Prospect activity Grassham shaft Mines oos Mine (Grasen) S.L. Crook Mine G C (McNeely lease) OHIO o Mine iron ore C Occurrence or outcrop Cr. o al 1119 C ek k d r ll re mine w S e i C k e YSTE Farmersville rfie e c M B ia ld k H y fluorite li fluorite mines ll Br y l Dike location at surface D d iron ore a y n la 137 er prospects Spring c CALDWELL a S C prospects k S p ek Cr. r e 139 Dike or sill in corehole PADUCAH GRABEN i r D 641 91 n fluorite C 855 902 fluorite g ry RIVER Cr. mine Marble mine l C Drillhole; DDH, mineral, oil, etc. shaft e Cr. fluorite Ax Mines re Maple Lake area ek Hobby South Lemen occurrence M (Parrish) dike mica peridotite Igneous dike; lamprophyre, peridotite (vein) TE S fluorite Landing Y S SYSTEM prospects k F Mineral vein; fluorite, zinc, lead, barite e fluorite e o r r The Bluff occurrence k Fluorspar mine; includes zinc, etc. C Caldwell Spring Black FAULT s Creek (Dycus- Sulphur fluorite Moxley Pinckneyville dy prospects SYSTEM ad burg) dike (Schwenck) Landing FAULT P Stone prospect Mines Igneous dike intrusives (area) k Vicksburg Maple Lake e Miller Landing k re Bakers iron ore ee C Iron ore mine Mitchell LICK Cumberland iron ore r Walker open cut mine Landing mines mines C w Walker Mine o l y l ingston d Prospect area FAULT Liv Crowder ne 1119 HILL o Maple Lake Ken H Mines core (ML-2) R Petes rp River a Walker Mine u B Magnetic high > 2 gammas Kibbler n lamprophyre dike H 70 Maple Lake Williamson ra Hill CLAY (South lease) nc fluorite Lick (Patton) dike Mines Crowder h Magnetic low < 2 gammas 60 occurrence CREEK Mines Maple Lake dike Royal Silver Atwood Mine iron ore core (ML-1) Senator Mine Mine Fredonia Valley Quarry h mines 70 Complex Fault ranc Complex SANDY MOORE B Tiline C fluorite Creek re D ek prospects k y Concealed fault e e y e

r r SYSTEM r Creek o k C 37° 37°10 l Oak 10 c Inferred fault e i Riley-Clifts fluorite

z t

Hill H Ridge t a prospect lease

prospects a

Parkway H shaft r

s P Parkway fluorite s 902 Oak e 293 Creek r 91 occurrence Ridge p fluorite occurrence FAULT y Dycusburg Bright 60 Mine C U.S. highway Mine Fork Crider 137 1433 State highway fluorite Flynn k fluorite occurrence ree 1113 Hughett Mine Tyrie Mine City boundary prospects C 70 iron CYPRESS GRABEN fluorite prospects ore Phelps LATROBE Creek TEM State boundary fluorite mine TABB SYS occurrence Sugar Cre County boundary FREDONIA GRABEN ek WHITE SULFUR GRABEN 139 FAULT k 295 White fluorite ee k fluorite r Sulphur occurrence e C 866 e

1943 r Crayne Populated place prospects . r me C C S 2232 ra inf n y k Creek r S s g even 7.5-minute quadrangle boundary o l t i S k n

n i

n C 91 H W ILLINOIS u Creek 70 r h D e it KENTUCKY Smithland LYON e Fork

e H C Dry ewlett y k r

Creek a e b Skinframe l Heater i Pond S iron ore mines B u k l fluorite W r p iron ore e e h

e prospect S w

mine r u k s r

n C n o i t M o st n e c Map data current as of October 4, 2017 s g f r E C n k 641 r Creek u i e 1943 a lr g iv e o r r L r m y e iron C e e k e e k y F ore re C e C l Crowtown mines ree s C k n iron ore re C i e re T mine k ek Creek S pr For information on obtaining copies of this iron ore mines ing Pumpkin

map and other Kentucky Geological H 3171 C Center

a r

z e Survey maps and publications call: e r l e 293 e Parkway 62 917 k M h fluorite ky t 373 Kentuc Public Information Center c n C C C . a occurrence re 60 k reek r e o P 1199 866 C k

(859) 257-3896 e

m . e r

453 r Western

Creek

i C Toll free: (877) 778-7827 C c

k 62 s

s 295 W.H. Ford View the KGS website at 1889 e le www.uky.edu/kgs u 819 p C G p . r r r d a e D a n e C e s r g la k y r u h © 2019, University of Kentucky, o y B c S i 62 S H Princeton d fluorite prospect r pr Kentucky Geological Survey a ing R d

n B ran E c ch Eddyville h 62

88°30 25 20 15 10 05 88°00 55 87°50 Introduction 5

Much has been written about the structure, Alkaline Ultramafic Rocks age, and mineral deposits of the fluorspar districts The International Union of Geological Scienc- in western Kentucky and southern Illinois, includes’ Subcommission on the Systematics of Igneous ing studies by Fohs (1907), Grogan and Bradbury Rocks has long debated the classification scheme (1968), Richardson and Pinckney (1984), Trace and for alkaline ultramafic igneous rocks (Streckeisen, Amos (1984), Goldhaber and Eidel (1992), Plumlee 1978; Mitchell, 1986, 1993, 1994; Rock, 1986, 1987, and others (1995), and Potter and others (1995). 1991; Rudnick and others, 1993; Woolley and oth- Previous studies that specifically discuss the REE ers, 1996; Woolley and Kjarsgaard, 2008; Le Maitre, content of the igneous dikes and fluorite in western 2002; Wall and Zaitsev, 2004; Tappe and others, Kentucky are by Bradbury (1962), Richardson and 2006; Zeng and others, 2010; Jones and others, 2013; Pinckney (1984), Hall and Heyl (1968), Mitchell Verplanck and others, 2014). REE-bearing alkaline (1986), Burruss and others (1992a, b), Chesley and ultramafic rocks are classified as lamprophyre others (1994), Barnett (1995), Plumlee and others (alnöite, aillikite, minette), peridotite, carbonatite (1995), Heck and others (2006), Moorehead (2013), (greater than 50 percent igneous carbonates), kim- and Denny and others (2017). These studies all sug- berlite (CO2-rich peridotite), nepheline syenite, gest the presence of REE in the igneous rocks of the lamproite, and orangeite. These alkaline rocks are Illinois-Kentucky Fluorspar District. formed under conditions of ultra-high tempera- Hicks Dome is a major structural feature in the ture and pressure; are rich in calcium, sodium, and Illinois-Kentucky Fluorspar District and has also potassium; and are undersaturated in silica. Frac- been called a cryptoexplosive that has a deep-seat- tional crystallization of a cooling parental magma ed igneous diatreme component to it. It has been is one of the primary causes of formation of car- considered the primary igneous and hydrothermal bonatites that contain silica phases (Bell and others, source of mineralizing fluids in the district, based 1998). By definition, alnöites (Rock, 1986, 1987) and on MVT mineralization, composition, and tem- aillikites (Mitchell, 2008) can grade into carbon- perature studies (Hall and Heyl, 1968; Goldhaber atites, which also have a CO2-rich volatile phase and Eidel, 1992; Taylor and others, 1992; Plumlee (Plumlee and others, 1995). These carbonatites are and others, 1995). Hicks Dome is also the site of of interest in the study area because they are a pri- low-grade metamorphism in surface rocks, it has mary host for REE mineralization throughout the a magnetic signature, and was classified as a car- world and can form from partial melting of base- bonatite by Pinckney (1976), Bradbury and Baxter ment peridotite. Most of these rock types are hyp- (1992), Potter and others (1995), Denny (2010), and abyssal and diatreme intrusions, uniquely forming Denny and others (2017), but questions remain at various depths and pressures within the mantle about this classification because the exposed sur- (Mitchell, 1986, 1993, 2005), and have undergone face rocks are not a classic carbonatite as seen in extensive melting, differentiation, metasomatism, other parts of the world, implying that the carbon- and alteration (Figs. 2–3). Carbon dioxide de atite is at depth. Carbonatites generally contain gassing is a product of carbonatite formation both large amounts of magmatic calcite and igneous tex- before and during the ascent of igneous intrusions, tures in a central igneous plug, although lenticular and is an important process for this investigation. or sheeted intrusive bodies also occur. In addition Many igneous intrusions are composed of different to Hicks Dome, the Kentucky portion of the Illi- geochemical and mineralogical lithofacies, which nois-Kentucky Fluorspar District contains several results in an overlapping intrusion complex rather structural features important to this study, includ- than an isolated single intrusion. The carbonatite ing Tolu Arch and the Coefield Intrusive Complex, formation process covers a broad range of temper- as well as several major faulted graben structures atures and is a direct result of magmatic differen- (Plate 1, Fig. 1). Tolu Arch in northern Crittenden tiation (Lapin, 1982). Carbonatite metasomatism is County, Ky., is a major northeast-trending struc- usually a hybrid between carbonatite and silicate ture aligned with many northeast-trending dike metasomatism, but more analytical data are need- systems in Kentucky, and several magnetic fea- ed to define the silicate component of the metaso- tures related to these dikes are mapped on Plate 1. 6 Introduction

matism; therefore, the focus of this study is on the 1 formation of carbonatite. The association of alkaline ultramafic intrusions and massive amounts of fluorite in the Illinois- Kentucky Fluorspar District is a direct indication of carbonatite formation (Modreski and others, 1995; 2 Kogut and others, 1996; Lee and Wylie, 1998; Yang and others, 2003; Schwinn and Markl, 2005; Den- ny, 2010; Jones and others, 2013; Makin and oth- 3 ers, 2014; Denny and others, 2017). Some of these carbonatites are associated with fluorite, which is mined in the United States, China, Russia, Sweden, Africa, and other parts of the world; many of these Figure 2. Rogers Quarry lamprophyre dike, Crittenden County, Ky. Dike, exposed on the surface in an active limestone quarry, carbonatites are combined with a syenite facies (Xu shows variability in lithology and petrology. The primary facies and others, 2012). Fluorite and hydrothermal fluids present in the dike is subdivided into (1) slightly altered dike, are discussed in Möller and others (1998). Two car- magnetic, containing clinopyroxene and serpentine, progress bonatites occur near the New Madrid Rift Zone: at ing downward into (2) a more highly altered part of the dike Magnet Cove, Ark., where nepheline syenite and a containing serpentine, clinopyroxene, titanium oxides, and abundant calcite veins, changing to (3) a very altered, light diamond-bearing lamproite also occur (Scott Smith green dike, nonmagnetic, composed of calcite, dolomite, and and Skinner, 1984; Rock, 1991), and at Avon, Mo.; ankerite with quartz and calcite veins. both locations contain magmatic carbonates (How- ard and Chandler, 2007; Shavers and others, 2016). Ultramafic rocks at Aillik Bay, Labrador (Tappe and others, 2006), and basalts at Shadong, China (Zeng and others, 2010), are also carbonated peridotites-carbonatites, and are similar to the western Kentucky dikes; they are mentioned here because of their similar petrogenesis. Since there is a paragenetic association of REE with these various rock types, the chemistry of both igneous dikes and fluorite were examined in this study. Lewis and Mitchell Figure 3. KGS dike 801, Frontier Spar core 6, located north of the Klondike Mines, Living (1987) classified igneous ston County, Ky. This unique core shows both a dark green unaltered dike (left), which is rocks in the Illinois-Ken- slightly magnetic, and a light green altered dike (right), which is nonmagnetic. Pyrite occurs tucky Fluorspar District in both altered (less than 10 percent and finely disseminated) and unaltered rock (greater than 10 percent and coarsely disseminated) and is concentrated near their contact. Black as an alnöite lamprophyre clasts are clinopyroxene, and some veins of serpentine (dark colored) and carbonate (light intrusive complex (Plate 1, colored) are also visible. Penny for scale. Figs. 2–3); individual intrusions have been classified as minette by Moorehead (2013), aillikite by Maria and King (2012), and alnöite by Heck and others Rare Earth Elements 7

(2006). An older report by Koenig (1956) identified temperature and pressure minerals; carbonatite serpentine, garnet, perovskite, ilmenite, phlogo- metasomatism also took place. These upwelling pite, and apatite in many Kentucky dikes and clas- magmas underwent fractionation and metasoma- sified them as mica peridotites and lamprophyre. tism during the late Precambrian and early Paleo- Robert Trace (U.S. Geological Survey, written com- zoic, while the magmas were stalled. The fraction- munication, 1960; 1974) detected florencite, mon- ation process started to separate the REE, whereas azite, brookite, and xenotime in the dike rocks of metasomatism concentrated other incompatible the Illinois-Kentucky Fluorspar District and classi- elements in the melts. Extensional tectonics and fied them as altered mafic dikes (Trace and Amos, structural reactivation of faults during the Alle 1984), meaning they essentially contain a mineral- ghenian Orogeny caused the upwelling, fraction- ogy of an alkali ultramafic intrusive complex. The ated, and metasomatized magma fluids to begin Coefield Magnetic Anomaly (Plate 1), a significant intruding into the Paleozoic rocks. About the same geologic and magnetic feature in the Western Ken- time, during the Permian Period, base-metal-rich tucky Fluorspar District, was discovered in the Mississippi Valley-type hydrothermal fluids were 1980s, and several cores (Minner and DLP) from migrating toward the Illinois-Kentucky Fluorspar this feature were used in this study. The intrusion District and began to deposit the mineral veins contains some unusual minerals, such as titanium and to mix with CO2-rich igneous alteration fluids garnets, and is now called the Coefield Intrusive and be emplaced in the Permian faulted structures. Complex because of its varied mineralogy and pe- During these processes, REE and other trace ele- trology and the rare xenoliths and xenocrysts as- ments were mobilized from magmas, and CO2-rich sociated with mantle and basement rock petrology. volatile magma degassing events concentrated the Many of the dikes are north-trending and can ex- REE into subeconomic quantities in the dikes, at tend for miles, and some of the dikes are thin, but the same time altering the igneous dikes and se- several are tens to hundreds of feet wide. Many of lected mineral deposits. Several processes, includ- the dikes in the Western Kentucky Fluorspar Dis- ing the post-crystallization alteration of igneous trict are actually twin dikes (Hutson, Old Jim, Co- dikes and mixing of base-metal-rich MVT miner- lumbia, Midway, Caldwell Creek), consisting of alization with post-emplacement, CO2-rich fluids one dike that is slightly altered and another dike caused some of the lithofacies to form. These im- that is more heavily altered. Some dikes are splin- portant processes created a complex igneous intru- tered or brecciated, and many contain the associ- sion overprint on the mineral paragenesis. Other ated sphalerite mineralization. igneous complexes in the New Madrid Rift Zone of interest for this study are adjacent to the craton Model for the District and have been identified at Magnet Cove, Ark., A model of the geologic processes that formed and Avon, Mo. the Illinois-Kentucky district is based on the results of this study and in part on previous work by Rare Earth Elements Lapin (1982), Mitchell (1986), Lewis and Mitchell Rare earth elements are a group of 15 chemi- (1987), Hayes and Anderson (1992), Hildenbrand cal elements with atomic numbers from 57 to 71: and Hendricks (1995), Plumlee and others (1995), lanthanum, cerium, praseodymium, neodymium, Wall and Zaitsev (2004), Tappe and others (2005), samarium, europium, gadolinium, terbium, dys- and Nelson (2010). prosium, holmium, erbium, thulium, ytterbium, During Precambrian rifting, a thinning litho- lutetium, and promethium. Promethium does not sphere allowed subcontinental lithospheric mantle occur naturally on Earth, but has been detected as magmas to form and ascend toward the crust in a product in nuclear reactions and radioisotopes. response to a thinned lithosphere and reduced Yttrium and scandium are also sometimes includ- lithospheric stress, but full crustal intrusion stalled ed in the REE category because of their 3+ ioniza- when the rift failed to fully develop. Some of these tion and geochemical behavior similar to REE. The magmas were generated in the asthenospheric lower REE atomic numbers (57–60) are referred mantle at depths of the stability field of ultra-high to as light REE (LREE), the middle range (61–67) 8 REE Concentrations in Alkaline Ultramafic Rocks and Fluorite as medium REE (MREE), and the higher atomic Carbonatite deposits typically have abun- numbers (68–71) as heavy REE (HREE). Rare earth dant fluorite and REE mineralization. The genetic elements are not really rare, since they occur in origin of fluorite mineralization and REE in most many rock types and in many minerals. They are carbonatite-type rocks for many mineral districts broadly distributed, including in primitive meteor- throughout the world is discussed in Mariano ites, which are used to normalize terrestrial values (1989), Möller and others (1998), Mitchell (2005), of REE. Because of their similar atomic structures, Makin and others (2014), and Simandl (2015). REE REE usually occur together in ore deposits, which in carbonatite pegmatite, and hydrothermal and makes extraction, separation, and beneficiation sedimentary fluorite, are discussed in Parekh and from host rocks and from each other difficult. Their Möller (1977) and Möller and others (1998); these “rare” designation is because they rarely occur in works interpret the genetic origin of REE in fluo- native form; usually, REE occur as trace elements rites. in other minerals until the concentration becomes Hicks Dome contains significant REE in dark high enough for them to compound and form their purple fluorite (A.V. Heyl, U.S. Geological- Sur own minerals, such as REE-carbonates, -oxides, vey, written communication, 1963); the breccias -phosphates, and -fluorides. REE can be enriched have high concentrations of cerium, lanthanum, in igneous rocks by fractionation and magmatic thorium, niobium, yttrium, and beryllium and differentiation. Along with REE, other important are considered to be both a source and center of elements are considered incompatible in igneous mineralization in the district (Hall and Heyl, 1968; melts, but also demonstrate a propensity to help Burruss and others, 1992a; Plumlee and others, concentrate REE and thus help determine the pet- 1995). The Hicks Dome fluorites from deep cores rogenetic history of magmas. These elements are are clear to dark purple in color, suggesting early zirconium, niobium, hafnium, thorium, uranium, MVT-stage purple fluorites are more enriched in cobalt, molybdenum, chromium, and tantalum; REE than later MVT-stage fluorite in general and they have difficulty entering into a solid crystal exhibit REE zonation within the early fluorite (Bur- structure, will fractionate, sometimes become im- russ and others, 1992b). There may also be tem- miscible, or mix with metasomatized mantle mate- perature zonation of REE, according to Möller and rial to form mineral deposits. others (1998). Purple fluorites from the Rose Mine on Hicks Dome have much higher REE concentra- REE Concentrations in Alkaline tions than other fluorites in the district (Burruss and others, 1992b). Fluorite from the Hamp core, Ultramafic Rocks and Fluorite drilled into Hicks Dome, contains less than 0.5 per- REE concentrations in ultramafic rocks that cent REE and more than 1.5 percent thorium and have differentiated or have been hydrothermal- yttrium, but no uranium was detected (Robert ly enriched would be expected to be higher than Trace, U.S. Geological Survey, written communica- primitive chondrite concentrations, which have not tion, 1960; A.V. Heyl, U.S. Geological Survey, writ- been affected by such Earth processes. Fluorite as- ten communication, 1963). Hall and Heyl (1968) sociated with such ultramafic rocks would also be noted variation in fluorite color and REE content, enriched in REE. Sufficient enrichment could en- and thorium content suggests that the dark purple able a deposit to become anomalously enriched or fluorites have higher thorium and REE concentra- economically mineable. Most economic deposits, tions for the Hicks Dome mineralized fluorite brec- such as at Mountain Pass, Calif. (Long and others, cia. This purple fluorite from the Rose Mine is also 2010), or Bayan Obo, China (Yang and others, 2003), depleted in LREE and enriched in HREE, whereas have whole-rock values greater than 10,000 ppm the blue fluorite from the Rose Mine was depleted for some individual REE and whole-rock total REE in both LREE and HREE, with a maximum value greater than 100,000 ppm. Carbonatites host most for europium (Burruss and others, 1992b). of Earth’s REE and normally have high REE con- Additional analyses of REE in Kentucky-Illi- centrations (greater than 10,000–20,000 ppm) (Cas- nois fluorites by Richardson and Pinckney (1984), tor, 2008), whereas kimberlites and lamproites gen- Trinkler and others (2005), and Denny and others erally have lower LREE concentrations. Methods 9

(2017) demonstrate a convex-downward pattern of prepared depending on the type of analysis: thin enriched MREE. Burruss and others (1992b) noted sections or polished sample surfaces for X-ray dif- examples of REE in colored fluorites in the Illinois- fraction and pulverized whole-rock samples for el- Kentucky Fluorspar District; they found the total emental analysis. REE from the Rose Mine was 10 to 20 times higher than in outlying mines, which suggests REE zona- Mineralogy and Petrography tion and variable REE in fluorite composition. They Optical petrography and photography were suggest LREE and HREE depletion requires ex- conducted in the KGS petrographic laboratory us- tensive fractionation of the original hydrothermal ing a polarizing petrographic microscope and a fluids prior to mineralization. Trinkler and others binocular scope on petrographic slides prepared (2005) worked on yellow fluorite from hydrother- in house. Both transmitted and reflected-light mal veins and determined both MREE enrichment photography were conducted. More than 100 pho- and that optical adsorption irregularities in the tographs were used to record the mineralogy of fluorite lattice contributed to the yellow coloration various dikes, some of which are included in this of fluorite from the Victory Mine in Illinois. Heyl report; additional photographs and data are in the (1983) reported that green fluorite from the Hicks KGS Minerals Database (www.uky.edu/KGS/ Dome area contains yttrium. Blue fluorite from the minerals/im_database.php; accessed 04/22/2019). Rose Mine is depleted in LREE and HREE, accord- An X-ray diffractometer in the KGS labora- ing to Burruss and others (1992b). Robert Trace tory was used to identify minerals in 40 samples, (U.S. Geological Survey, written communication, but the resulting diffractograms are not included 1960; 1974) detected a monazite-like mineral, later in this report. Confidence in the mineral phases identified as brookite, and measured radioactive obtained with X-ray diffraction is high because anomalies at Hicks Dome. Harry Rose of the U.S. most samples were flat and polished, resulting in Geological Survey used an electron microprobe to an accurate X-ray beam angle for acquiring two identify a thorium-, yttrium-, erbium-, dysprosi- theta-angle measurements. These angles were cor- um-bearing fluorine mineral intergrown with fluo- related to a mineral identification and accompa- rite from the Hamp Hole at Hicks Dome and tenta- nying crystallographic system classification in the tively identified it as yttrioparisite, as reported by Bruker crystallographic database (www.bruker. Hall and Heyl (1968). com/products/x-ray-diffraction-and-elemental- analysis/x-ray-diffraction/xrd-software/eva/cod. Methods html; accessed 04/22/2019). Standards were also Samples were collected and analyzed for min- used to calibrate the two theta angles for the X-ray eralogical identification and major, minor, and diffraction scans. rare earth elemental values. REE data were nor- Backscatter image analysis and mineral iden- malized with chondrite values. Geochemical data tification were conducted on a few samples using were compared to data from other locations in the scanning electron microscopes at Northern Ken- world. The samples’ geochemical compositions tucky University and the University of Kentucky. were evaluated in part from how they vary in re- Elemental Analysis lation to distance from Hicks Dome; other work- Cores or rock-outcrop samples from ultramaf- ers have used Hicks Dome as a temperature and ic dikes were collected and crushed for whole-rock mineralization center (Taylor and others, 1992) on elemental analysis, and fluorites were carefully many charts and diagrams. hand-selected for color content, crushed, and ana- Sample Set lyzed for REE. Whole-rock major, minor, and trace Dike samples were collected from 50 locations elements of dikes were analyzed using a sodium (Table 1) in the Western Kentucky Fluorspar Dis- peroxide fused-pellet method with an inductively trict (Plate 1); 30 samples were analyzed with X- coupled plasma atomic emission spectrometer ray diffraction and 12 samples were analyzed for in 2015 by SGS Laboratories of Burnaby, British major, minor, and trace elements. Samples were Columbia, Canada. Some outcrop samples were weathered, which could affect their REE composi- 10 Methods X - ray = Lithology lamprophyre lamprophyre lamprophyre lamprophyre mica peridotite lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre mica peridotite lamprophyre lamprophyre mica peridotite mica peridotite lamprophyre lamprophyre lamprophyre lamprophyre alnoite lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre thin section. X - ray = Trace Minerals Trace database reference. TS database reference. anatase anatase, ilmenite, garnet anatase REE-bearing fluorite, perovskite, rutile fluorapatite, anatase magnetite anatase (Ce), rutile (Nb) altered to calcite and dolomite andradite, schorlomite yttriofluorite, anatase garnet schorlomite garnet andradite zinc with dike anatase = Analysis Type Analysis Type TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS chemical analysis compilation reference. Record No. = Site Name Hurricane lamprophyre dike Little Hurricane lamprophyre dike in core drillhole (Pennwalt) lamprophyre dike in core drillhole Cyclone lamprophyre dike Hobby North lamprophyre dike Midway (Davidson) Eaton northwesternmost lamprophyre Davidson North Eaton dike Guilless dike northeastern lamprophyre Guilless dike lamprophyre Dike South lamprophyre Dike South lamprophyre Dike South lamprophyre Dike South lamprophyre Glendale dike Moore Hill lamprophyre dike Fowler lamprophyre dike Claylick East lamprophyre dike Claylick East lamprophyre dike Cardin lamprophyre dike Cardin dike Childress Bluff lamprophyre dike (Lowery) lamprophyre dike View Shell core (Adams) lamprophyre dike Howard Stout lamprophyre dike lamprophyre dike Claylick West lamprophyre dike Claylick West Robinson lamprophyre dike Sunderland lamprophyre dike

TH - 84? - 799 - 800 - 214 - 804 565 - 2 76 - 9 76 - 1 76 - 4 76 - 8 76 - 7 76 - 5 76 - 1136 - 798b - 1448 - 595? - 798a - 798b - 404 2 T T T T T 597 - V T T T T T T T T T T T T T YH - 004 T - 227 105 (RDT_10) T CH 49 - 165 CH 48 - 198 Field Map/ Analysis ID 78 79 80 81 94 262 262 262 262 279 280 281 282 283 283 284 285 286 302 1061 3017 1385 1401 1401 1273 1064 1064 1366 1367 Record No. Inventory of igneous dikes in the Western Kentucky Fluorspar District. An online database (www.uky.edu/KGS/minerals/im_database.php) is searchable An online database (www.uky.edu/KGS/minerals/im_database.php) Kentucky Fluorspar District. Inventory of igneous dikes in the Western 78 79 80 81 94 261 261 262 262 262 262 279 280 281 282 282 283 283 284 285 286 302 1385 3017 1385 1064 1064 1366 1367 Site No. Table 1. Table by site name. Dikes used in the study are highlighted red. Site No. diffraction. Methods 11 X - ray = Lithology lamprophyre lamprophyre alnoite alnoite alnoite alnoite alnoite alnoite alnoite lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre mica peridotite mica peridotite mica peridotite mica peridotite mica peridotite mica peridotite mica peridotite mica peridotite lamprophyre lamprophyre thin section. X - ray = Trace Minerals Trace database reference. TS database reference. breccia, REE perovskite breccia, REE perovskite anatase, ilmenite anatase, andradite/schorlomite, perovskite double perovskite, andradite (Ti), spinel, magnetite andradite, schorlomite (Ti), Y) Eu, Ta, perovskite (La, Pr, Ta), perovskite (Y, schorlomite (Ti), spinel iridium, fluoro-tetraferriphlogopite astrophyllite, moissanite, zinc in dike, rare garnet, marimotoite anatase, ankerite anatase fluocerite fluorite, anatase zinc in dike, molybdenite = Analysis Type Analysis Type TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS TS, X - ray TS TS, X - ray 341.5 ft depth TS, X - ray TS, X - ray compilation reference. Record No. = Site Name Mann lamprophyre dike Butler lamprophyre dike Minner lamprophyre dike Minner lamprophyre dike Minner lamprophyre dike Minner lamprophyre dike Minner lamprophyre dike Minner lamprophyre dike Minner lamprophyre dike DLP - 2 Kennecott core sample DLP - 3 Kennecott core sample Gray lamprophyre dike Commodore lamprophyre dike 1971 Hickory Cane roadcut, Commodore lamprophyre dike Holly lamprophyre dike Crystal (Flannery) lamprophyre dike Crystal lamprophyre dike Mary Belle Columbia South lamprophyre dike Columbia South lamprophyre dike Columbia North lamprophyre dike Mary Belle Southwest lamprophyre peridotite Lady Farmer lamprophyre dike Lady Farmer lamprophyre dike Old Jim lamprophyre dike Freedom South lamprophyre dike Barnes lamprophyre dike lamprophyre dike Watson

TK RD - 565 - 681 - 796 D - 1 105 BLF 1971 T T T TL - 78 BLF - 4 DLP - 2 DLP - 3 BMN - 1 BMN - 3 BMN - 4 BMN - 7 a KGS - 1380 Field Map/ BMN7 - 227d BMN7 - 227 c Analysis ID BMN7 - 227 b c b d 1368 1369 1370 1370 1370 1370 1371 1373 1284 1377 1378 1378 1380 1402 1381 1383 1383 1384 1267 1389 1390 1370a 1379a Record No. Inventory of igneous dikes in the Western Kentucky Fluorspar District. An online database (www.uky.edu/KGS/minerals/im_database.php) is searchable An online database (www.uky.edu/KGS/minerals/im_database.php) Kentucky Fluorspar District. Inventory of igneous dikes in the Western 1368 1369 1370 1370 1370 1370 1370 1370 1370 1370 1371 1373 1284 1377 1378 1378 1380 1402 1381 1383 1383 1384 1267 1389 1390 1379a Site No. Table 1. Table by site name. Dikes used in the study are highlighted red. Site No. diffraction. 12 Methods X - ray = Lithology mica peridotite mica peridotite mica peridotite mica peridotite mica peridotite mica peridotite lamprophyre lamprophyre lamprophyre lamprophyre lamprophyre mica peridotite mica peridotite alnoite lamprophyre lamprophyre mica peridotite mica peridotite lamprophyre mica peridotite thin section. X - ray = Trace Minerals Trace database reference. TS database reference. astrophyllite, zinc in dike REE fluorapatite, anatase, pyrite rutile rutile, fluorite rutile rutile rutile massive sulfide anatase, diopside, antigorite andradite grossular anatase, rhodochrosite rhodochrosite, anatase, carbonate altered to calcite and dolomite rutile beryllium, titanium copper detected = Analysis Type Analysis Type TS, X - ray TS TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS, X - ray TS TS TS TS TS USGS analysis compilation reference. Record No. = Site Name Hutson core BH - 7 Hutson Mine shaft dike (underground) Hutson North Hutson North Hutson core 228, depth 329 ft Holly South lamprophyre dike 8 Maple Lake dike core 1 Maple Lake dike core 1 Maple Lake dike core 2 Maple Lake dike core 2 Maple Lake dike core 2 Hampton Joy dike Frontier (Little property) BCN - 3 Billiton Crittenden Springs core, 247 ft depth Crittenden Springs Eagle Mine Lucille Mine Orrs Landing, Illinois Mix dike, Illinois Eaton dike Minner dike Minner dike Eaton vein Hampton Joy area, core near Sisco Chapel, Salem quadrangle well in Crittenden County

E LD OL HD - 801 MD - 3 76 - 6 76 - 183 HJ - 5 - 10 76 T T T T BHN - 1 BHN - 4 BCN - 3 T BCS - 2B BCS - 2B ML - 1_420 ML - 1_424 ML - 2_509 ML - 2_510 ML - 2_513 KGS 1390 DLP - 2 152 DLP - 2 824 HJ - 13_277 Maxus well Field Map/ Analysis ID 619 1406 1406 1391 1392 1407 1407 1408 1408 1408 1409 1405 1265 1385 1370 1370 1385 Record No. Inventory of igneous dikes in the Western Kentucky Fluorspar District. An online database (www.uky.edu/KGS/minerals/im_database.php) is searchable An online database (www.uky.edu/KGS/minerals/im_database.php) Kentucky Fluorspar District. Inventory of igneous dikes in the Western 2 1406 1406 1391 1392 1407 1407 1408 1408 1408 1409 1405 1265 1385 1370 1370 1385 Site No. Table 1. Table by site name. Dikes used in the study are highlighted red. Site No. diffraction. Results 13

tion. Some of the analyzed samples were collected ogy is complex. Based on the Al2O3, FeO, and MgO by previous researchers, but precise location infor- ternary diagram shown in Figure 5a, most of the mation was available for all samples. dikes would fit into the alnöite or aillikite lamprophyre category, with some trending toward kim- Normalization of REE Data berlite or carbonatite. Based on the CaO, FeO, and The full suite of REE were analyzed for nu- MgO ternary diagram shown in Figure 5b, some merous dike and fluorite samples, and raw- con dikes would fit into a carbonatite category or have centrations were normalized using Taylor and been influenced by carbonatite fluids; others, near McLennan’s (1985) values for chondrites. REE the Coefield Intrusive Complex, fit into a lampro- concentrations are thus reported as chondrite-nor- phyre-kimberlite and a calcio-ferro-magnesio car- malized, in order to establish a standard for com- bonatite category. The high CaO content (Fig. 5b) parison and to remove elemental odd-even oscil- in some dikes suggests an influence of carbonatite- lations inherent in REE raw data. Chondrites are type rocks or that these dikes have been influenced considered “primitive” in that they have not been by crustal contamination; isotopic work is needed influenced by Earth processes, such as differentia- for confirmation. All Coefield Intrusive Complex tion or hydrothermal mineral enrichment, and so dikes (including Minner, Davidson, and Lady REE values of the reference chondrites (Taylor and Farmer) are rich in iron and magnesium. McLennan, 1985) are considered free of Earth’s The range of Ca/Al ratios (0.29–46) allows concentration influences. Primitive mantle mate- different magma types to be distinguished, and rial should have similar values to chondrites. large variations in strontium (186–960 ppm) sug- Standards and Analysis of REE Data gest crustal contamination of mantle material. Low Apart from determining overall REE abun- calcium concentrations in four calcium-depleted dances and patterns, REE data from igneous rocks mantle dikes (Stout, Davidson Midway, Sunder- are frequently evaluated by using normalized ra- land, and Caldwell Creek), where Ca/Al ratios are tios of light to heavy REE and by comparing com- less than 1, can be distinguished from a second set patible and incompatible elemental data. Ratios of that have Ca/Al ratios greater than 1 (Hampton the REE end-members are one way to measure de- Joy, Davidson North, Cardin, Minner 4, Minner 7, grees of fractionation, metasomatism, enrichment, and Lady Farmer). Two dikes are extremely en- and depletion in an igneous body. The ratios La/ riched in calcium (Maple Lake and Hutson 7); Ca/ Yb, Tb/Yb, Sm/Yb, Nb/Ta, Y/Yb, U/Th, Zr/H, Al ratios are greater than 15. These differences may and Zr/Y are commonly used, and others are also represent influences from carbonatite and silicate used to evaluate the effect of mantle dynamics metasomatic fluids or contamination from crustal and metasomatism in rift systems. Niobium is also materials such as limestone; this study is focused commonly used to evaluate the potential for car- on carbonatite metasomatism, however, since the bonatite formation. Because of their ionic structure, silicate component is considered poorly defined. other elemental ratios of importance are Zr/Hf and Because no true carbonatite has been found in sur- Zr/Y; they measure fractional crystallization and face rocks, the Coefield Intrusive Complex appears metasomatism. to be an altered group of ultramafic rocks and may be the closest to a carbonatite lithofacies in the dis- Results trict. Petrology and Major Element Analysis Some of the lamprophyre subclassifications Whole-rock major-element analyses of the ig- are based on aluminum content; the aillikite fa- neous dikes sampled across the Western Kentucky cies generally contain less aluminum than the al- Fluorspar District (Fig. 1, Plate 1) vary substan- nöites, according to Rock (1991), and by definition tially in calcium, magnesium, iron, potassium, ti- can trend toward carbonatite. The titanium and tanium, chromium, and aluminum concentrations. aluminum concentrations place most of the dikes Whole-rock, major-element compositional data are into the broad ultramafic lamprophyre alnöite and used to determine petrologic classification, and as aillikite categories, but the high titanium content shown in Figures 4 and 5, the variation in petrol- would place some of the dikes into a carbonatite,

14 Results Value (ppm) Value Figure 4. Raw - data analysis by inductively coupled plasma atomic emission spectrometry of various dikes with increasing distance from Hicks Dome, showing REE enrichment. The REE elemental oscillations and gentle negative slope of decreasing values of REE reflect decreasing cosmic abundance of REE. Note high There is (18–521 ppm). (0.35–12 percent), and Zr (1.01–13.7 percent), Fe (0.07–0.47 percent), Mg P percent), Nb (1–199 ppm), (0.04–3.4 Ti elemental values for Th daughter products., Th, particularly Ni, Zn, Ga, Pb, and Co—and in U also variability in other metals—Cr, Results 15 17

ML Calcio-carbonatite BH7 HJ

Sund DM PM=Primitive PM=Primitive DM=Depleted HJ DM=Depleted

Sund Magnesio-carbonatite Ferro-carbonatite Cardin BH Coefield

Lamproite Cardin CC DN BMN-7 Alnӧite DN DM Aillikite ML

PM BMN-7, Coefield PM CC DM DM

Figure 5. Ternary composition diagrams showing Al2O3, CaO, FeO (total), and MgO concentrations of intrusive rocks of the West ern Kentucky Fluorspar District. The heterogeneousWhole nature Rock of the Ternary Kentucky Diagramultramafics fits with the overlapping compositional variations of lamprophyre, kimberlite, and carbonatite. Lamprophyres (including lamproite facies) have low aluminum oxide val Figureues, 5 placing Ternary composition them in diagrams the alnӧite showing Al and2O3, (CaO), aillikite FeO (total), categories. and MgO of intrusiveAlnӧite rocks generally of the WKFD. has The heterogeneous high aluminum nature of concentrations, the Kentucky ultramafics according fit into the overlapping to Rock compositional variations of lamprophyre, kimberlite, and carbonatite. Lamprophyres (including lamproite facies) have low aluminum oxide values placing them in the alnӧite and aillikite categories. Alnӧite generally contains higher(1991). aluminum Kimberlite values according and, to Rockin some (1991). Kimberlitecases, and, carbonatite in some cases, havecarbonatite similar have similar compositions, compositions, but but their theirmineralogy mineralogy excludes some excludes dikes from the some kimberlite dikes classification. from High titaniumthe kimberlite garnets in BMN-7 classification. place this dike into anHigh-titanium overlapping kimberlite, garnets carbonatite, in dike and aillikiteBMN-7 classification, place thiswhile highdike iron into in Caldwell an overlapping Creek suggest a ferro-carbonatite.kimberlite, carbonatite,Primitive and depleted and mantle categoriesaillikite are classification, shown for comparison. whereas Although overlappinghigh iron in composition,in the Caldwell a deep mantle Creek origin isdike the primary suggests common afactor ferro-carbonatite. in the analyzed rocks although Primitive aqueous and and hydrothermaldepleted alterationmantle of these dikescategories may influence are their shown calcium composition. for comparison. Worldwide Althoughbackground data composition for carbonatites fromof the Jones rocks et al. (2013), overlaps lamprophyres several from Rockclassifications, (1991), and kimberlites a deepfrom Mitchell mantle (1986). origin Mantle is values from McDonoughthe primary and Sun common (1995) and Condie factor (1997). in the In some analyzed of the diagrams, rocks; some aqueous of the sample andlocations hydrothermal are abbreviated with alteration their initials orinfluenced first few letters theof the composition.name to conserve space Worldwide and reduce confusion on the diagrams. For example, a Billiton Lady Farmer or Minner sample could be labeled BLF or BMN and a Stout or Cardin dike could be labeled St or Card. background data for carbonatites from Jones and others (2013), for lamprophyres from Rock (1991), and for kimberlites from Mitchell (1986). Mantle values from McDonough and Sun (1995) and Condie (1997).

kimberlite, or lamproite category (Fig. 5). The pres- cent) in seven of the dikes examined in this study ence of titanium and calcium garnets (schorlomite also suggests that a few dikes may trend toward an and andradite) is important during melting and iron-rich ferro-carbonatite, as at Caldwell Creek, or fractionation and is diagnostic for certain aillikite assimilations of high iron-dolomite crustal mate- lamprophyre classifications, which determine car- rial. Only two dikes, Hutson and Maple Lake, had bonatite and ultramafic mantle melt and mixing less than 1 weight-percent iron. scenarios (Tappe and others, 2005; Rogers, 2006). Primary processes are magma melting, mix- The Mg/(Mg + Fe) ratios of the analyzed dikes ing, fractionation, and metasomatism, and second- range from 0.20 to 0.90, and, according to Mitchell ary processes are post-crystallization alteration, (1986), the Mg/(Mg + Fe) ratios of kimberlitic mag- MVT mineralization, and post-MVT alteration. The

ma containing crustal material are less than 0.85. later-stage CO2 volatile event mixed with MVT flu- Higher Mg/(Mg + Fe) ratios (between 0.9 and 0.95) ids to create a series of altered dikes and mineral in biotite in the Billiton Minner lamprophyre core veins in the district. This suggests that the variable were determined to be the result of interaction with whole-rock chemistry is an indicator of complex late-stage high-magnesium alteration fluids (Heck source-rock mixing, fractionation, metasomatism, and others, 2006). Many of the dikes in the Coefield and alteration. The lithologic, petrologic, and min- Intrusive Complex are high in magnesium and fit eralogic similarities of the igneous intrusions and into a magnesium-carbonatite category (Figs. 4–5); fluorite deposits of the Illinois-Kentucky Fluorspar when these values are plotted, the high-magne- District to economic REE deposits elsewhere in the sium values form a semi-concentric zonation in the world (Rock, 1991) raise the level of interest in the complex. The high iron content (greater than 7 per- 16 Results

Illinois-Kentucky Fluorspar District for more ad- cerite, and wüstite. Sphalerite occurrence (Fig. 10) vanced research and exploration for REE deposits. is also notable, since it provides evidence of mixing of MVT fluids and late-stage igneous alteration Mineralogy of Alkaline Ultramafic Dikes fluids. Monazite containing iridium also occurs The mineralogy of the varied lithofacies in (Fig. 11). these dikes was studied by whole-rock X-ray dif- The following mineral identifications and de- fraction (Figs. 6–11). Although the dikes may scriptions are important petrologic indicators of al- appear to be homogeneous, many have subtle kaline ultramafic rocks that trend toward carbon- changes in mineralogy and all of them have been atite and REE enrichment. Minerals are listed in fractionated, altered, or brecciated. The original order of importance and rarity, and some of them alkaline ultramafic olivine mineralogy has under- are alteration minerals from post-crystallization gone post-crystalline alteration to form clinopyrox- stage, MVT stage, and some are ultra-high temper- ene, serpentine, and carbonate minerals (calcite and ature and pressure xenocryst minerals, probably dolomite), including the alteration of the titanium unaltered. The origin of these rare xenoliths and mineral ilmeno-magnetite to rutile and leucoxene, xenocrysts are deep seated and deserve further re- as at the Clay Lick dikes. X-ray diffraction studies search. have noted only one occurrence of olivine, in the 1. Rutile, NbTiO , tetragonal, a niobium and Guilless dike, whereas many of the original olivine 2 has been serpentinized, and altered to clinopyrox- titanium oxide, and its polymorph, anatase (TiO , tetragonal) (Fig. 6); ilmenite ene, serpentine, and carbonate minerals, some of 2 ((NiMg)TiO ) and magnetite (Fe O ) were which are pseudomorphs of the original olivine 3 3 4 orthorhombic morphology. Post-MVT-mineral- noted in several cores from the Davidson ization alteration of sphalerite to smithsonite, and North and Minner dikes. phlogopite to sericite, occurred during the middle Rutile and anatase have been found in paragenetic stage (Hayes and Anderson, 1992), numerous dikes, including the Frontier during the Permian Period; where the sphalerite Spar (core 801), Dike South, Davidson became more reddish orange and accompanied the North, Maple Lake, Crittenden Springs, Lady Farmer, Columbia South, Minner, CO2-rich alteration of the dike material. The high carbonate and oxide mineral contents suggest an Sunderland, Clay Lick, Robinson, and influence by carbonatite-type fluids; the presence Cardin dikes. In four dikes, some of these of abundant ferro-magnesium silicate minerals rutiles and anatases are high in niobium. such as clinopyroxene and garnets is evidence of Cerium-bearing anatase ((TiO2Ce)O2, te- a silica fraction in this alkaline melt. No unaltered tragonal) is present in the Dike South dikes have been observed in the Western Kentucky and Sunderland dikes. Some of the more Fluorspar District, except at Maple Lake. altered dikes have a varied ilmeno-mag-

Alteration of the dikes and the effects of meta- netite mineralogy ((TiFeO4)(NiMg)TiO2, somatism create some areas of mineral enrichment rhombohedron) and various alteration in the Western Kentucky Fluorspar District, partic- titanium minerals such as leucoxene. The ularly near the Coefield Intrusive Complex. Dikes titanium, niobium, and REE were intro- in numerous cores, including from the Minner, duced into the magma melt by volatile Midway-Davidson, and Davidson North dikes and metasomatizing fluids (Haggerty and the Coefield Intrusive Complex, contain abundant Baker, 1967; Haggerty, 1976). Titanium is titanium oxides and REE-bearing perovskites. Al- mobile in alkaline fluids and is altered to though perovskite is common in ultramafic rocks, titanium oxide (rutile). Niobium rutile is REE-bearing perovskites are not as common. Rare essential in one style of metasomatism re- minerals found in the district include perovskite lated to upper-mantle alkaline rocks and and niobium rutile (Fig. 6), astrophyllite (Fig. 7), kimberlites (Haggerty and Baker, 1967; moissanite (Fig. 8), villiaumite, fluoro-tetraferri- Haggerty, 1976) and is stable in high-CO2 phlogopite, almandine garnet (Fig. 9), natrite, fluo- magmas (Barnett, 1995), but becomes de- Results 17

B. Figure 6. A. Reflected-light photomicrograph of the Davidson North dike (analysis ID YH04_800), Crittenden County, Ky., near the northeastern Babb area and north of the Midway area. This lamprophyre shows post-crystallization alteration of ilmenite to red rutile, as well as white titanium oxide minerals such as leucoxene. Both rutile and leucoxene occur along cleavage planes in biotite and phlogopite. B. Davidson North dike, showing lamprophyre containing abundant clinopyroxene phenocrysts with the white titanium mineral leucoxene, and an alteration vein cutting the dike. The alteration vein has abundant red rutile that has crystallized in the titanium-rich groundmass of the dike, and abundant pyrite crystallized when the vein cut a large iron-rich clinopyroxene silicate crystal. This is an example of the post-crystallization alteration phase. 18 Results

Clinopyroxene

Astrophyllite

Calcite Magnesite Schoepite

Figure 7. Xenolith in the Minner core (DLP 3, depth 329–330 ft): lamprophyre breccia, located in the Minner area, Crittenden County, Ky. Intrusive magnetic breccia contains mantle xenolith of yellow calcite with black acicular xenocryst crystals of astro phyllite, a potassium, sodium, iron, titanium silicate that contains niobium. Also detected in this xenolith was the yellow mineral metaschoepite, a uranium oxide, as well as magnesite, a magnesium carbonate. Xenolith is 1 in. wide; reflected-light photomi crograph, 2X.

Figure 8. Moissanite (SiC) identified by X-ray diffraction in xenolith in core DLP-3 at 329 ft; Crittenden County, Ky. Moissanite is a very rare mineral that occurs in extremely reduced rocks in the deep mantle; it is sometimes associated with diamonds. Results 19

Almandine garnet

0.25 in.

Figure 9. Almandine garnet in an altered dike matrix of calcite, anatase, muscovite, illite, lizardite, and the iron sulfate rozenite. Reflected-light microphotograph of the Hurricane dike, Crittenden County, Ky.

Figure 10. Transmitted-light photomicrograph of core DLP-2, showing the MVT sulfide sphalerite (yellow minerals), at a depth of 824 ft. These sphalerite crystals were emplaced when late-stage igneous alteration fluids mixed with middle-stage, MVT, sphalerite-rich fluids when the sphalerite was emplaced in the igneous dike. This is an example of MVT mineralization, although it occurs during a middle-stage mineralization event, and illustrates sphalerite association with light green, altered dikes. 20 Results

Figure 11. Scanning electron microscope photograph of core DLP-2 at a depth of 112 ft, showing the calcium phosphate mona zite with iridium enrichment (red). Blue indicates oxygen and green indicates phosphorus.

stabilized in evolving magmas (Mitchell, ern Kentucky Fluorspar District. Since as- 1986), suggesting that the niobium content trophyllite can be high in niobium and has of rutile and perovskite is important be- the niobium-rich end-member niobophyl-

cause its occurrence can indicate carbon- lite ((K,Na)3(Fe,Mn)6(Nb,Ti)2(Si8(O(OH)

atite formation. Rutile (Figs. 6a, b) occurs F)31, triclinic), more work needs to be done in numerous dikes along biotite cleavage to determine the implications for REE con- planes and is of special interest since it oc- tent. Astrophyllite occurs in opposite ends curs at the Magnet Cove igneous suite in of the district and is significant in determi- Arkansas. nation of a differentiated magma material; 2. Astrophyllite, K Ba (NaCa)(Fe Mn,Mg it also indicates an alkaline-carbonatite 2 3 2 petrology beneath the fluorspar district Na)(Ti,Nb)Si8O14, monoclinic, an ultra- high temperature and pressure, high- and suggests mantle metasomatism. As- magnesium, -potassium, -niobium, -tita- trophyllite also occurs at Magnet Cove, nium, and -sodium silicate (Fig. 7). Ark. (Erickson and Blade, 1963), and its type locality is Laven Island near the Kola Astrophyllite was found in several spheri- Peninsula REE complex in Norway and cal yellow xenoliths in core DLP-3 from Russia. the Minner area of Crittenden County. The astrophyllite occurs as black, acicular 3. Schoepite and metaschoepite, (UO2)4O crystals in a yellow carbonate-syenite xe- (OH)6(H2O), orthorhombic, yellow-green nocryst contained in a matrix of calcium uranium oxides. carbonate. Astrophyllite crystals were Schoepite and metaschoepite were detect- also detected in the pebble breccia in core ed in xenocrysts in core DLP-3 at a depth BH-7 from the Hutson Mine of Livingston of 329 ft. These minerals normally occur County in the southern part of the West- in hydrothermal mineral and uranium Results 21

deposits, and so the schoepite occurrence amonds and meteorites; the type location suggests uraniferious mantle xenocrysts, is in Germany. A potassium richterite,

whereas the metaschoepite suggests hy- K(Na,Ca)Mg5)Si8O22F2, monoclinic, was

dration of schoepite. Uraninite (UO2) was also tentatively identified in the xenolith also detected in core DLP-3. from this core.

4. Moissanite, SiC, hexagonal (Fig. 8), a me- 6. Spodumene, LiAlSi2O6, monoclinic. tallic ultra-high temperature and pressure Spodumene, a lithium aluminum silicate silicon carbide. of the sodium pyroxene group, was de- Moissanite was detected as crystals in xe- tected in the Hutson core BH-7 at 74 ft and noliths in core DLP-3 at 308, 314, 318, and in several xenoliths in core DLP-3. Spodu- 328–329 ft. It is a naturally occurring silica mene is common in peralkaline granitic in- carbide metal (Fig. 8) and is very rare, oc- trusive pegmatites and has been mined in curring naturally only in the deep mantle the Black Hills of South Dakota. Its occur- material, usually in kimberlites and some- rence in core BH-7 is rare, and the lithium times as inclusions in diamonds (Nixon, in fluoro-tetraferriphlogopite indicates a 1987). Moissanite is very hard (H = 9.5) possible lithium phase in the fluids. and only occurs in reducing alkaline ul- 7. Fluorides. tramafic facies in sublithospheric upper- Numerous fluorides, CaF , isometric, cu- mantle rocks, kimberlites, and in some 2 bic, were found in the ultramafic dikes. meteorites. The type locality is the Can- These unusual fluorides were detected yon Diablo meteorite from Arizona. The within the altered or brecciated dikes, and origin of moissanite has been suggested to their relation to the main ore-stage fluorite be either from a primordial early mantle indicates there were various cations in the near the core-mantle boundary (Mathez fluids to replace calcium in the fluoride and others, 1995) or from a highly frac- crystal structure. Also notable are visible tionated, organic-carbon-rich, extremely and microscopic inclusions within the reducing ultramafic environment with fluorites examined; some barite inclusions little to no iron components (Schmidt and were visible to the naked eye, so these in- others, 2014). Its presence in a xenolith in clusions may influence elemental analysis core DLP-3 from 300–329 ft is significant of fluorites. in that it indicates deep mantle rocks were

thrust to near-surface exposure in west- a. Fluocerite, (La,Ce,Nd)F3, hexagonal, ern Kentucky. Further research should be a rare REE neodymium fluoride, was conducted on wüstite and moissanite in identified at the Columbia Mine ina western Kentucky. breccia clast of dike rock. The fluocerite was identified via red fluorescence 5. Wüstite, FeO, cubic, iron oxide. under ultraviolet light, and its pres- Wüstite is also an ultra-high temperature ence was confirmed with whole-rock and pressure mineral, and was detected X-ray diffraction analysis. The fluocer- by X-ray diffraction in a xenolith in the ig- ite occurs in a calcite crystal, suggest- neous breccia of core DLP-3, box 2, at 308 ing an intergrown fluorite and calcite and 328–329 ft. Wüstite is very rare and mineralogy that dates from a late- only occurs in reduced, oxide-poor rocks stage dike alteration and brecciation in the lower mantle near the iron/wüstite involving CO -rich fluids. boundary, where many peridotites, kim- 2 b. Villiaumite, NaF , isometric, a rare so- berlites, carbonatites, and other ultramaf- 3 dium fluoride, was found in a pebble ic alkaline rocks originate (Arculus and breccia in core BH-7. Delano, 1987). Wüsite is found in kimberlites (Nixon, 1987) and as inclusions in di- 22 Results

c. Yttrium-bearing fluoride, (CaY)F2, Chakhmouradian, 1996). These rare

and cadmium-bearing fluoride, CdF2, micas are usually bladed in appear- were also detected in this sample. An ance, and more detailed work on the unnamed sodium- and REE-bearing micromineralogy is needed to de-

fluoride, (Ca9Na,Eu,Lu(PO4(SiO2))F, iso termine evolving trends toward car- metric, was detected in the Davidson bonatite or lamproite facies. This is a

North dike, and yttrium fluorite, YF3, rare bladed mica whose petrogenesis orthorhombic, was detected in the is complex, but it forms during late- Cardin dike. stage fractionation, and usually in- Fluorides bearing rare earth elements dicates an evolving reduced magma (neodymium, europium, and yttrium) in which phlogopite evolves to tetra- occur in some of the altered dikes, and ferriphlogopite containing iron and their relationship to the massive fluorite titanium and incorporating fluorine mineralization needs more research to de- and barium in the crystal structure termine the proper paragenetic sequence while displacing aluminum. Tetrafer- and any specific REE-bearing fluoride riphlogopite is known to occur in ol- paragenesis. Fluorescent mineralization ivine lamproites (Mitchell, 1993). An- was observed in calcite-fluorite crystals at nite, a potassium iron-rich member the Columbia Mine, and X-ray diffraction of the mica group, was noted in core analysis showed fluocerite, a REE fluoride. DLP-3. The presence of fluorine sug- The abundance of fluorides in the dikes, gests an abundant fluorine source, as consisting of calcium fluorides, cadmium does the occurrence of lithium and so- fluorides, sodium fluorides, REE-bearing dium, and further suggests a depleted fluorides (fluocerite), and yttrium-bearing aluminum source is available for these fluorides, indicates abundant REE in the micas to form.

melt system that allowed them to replace b. Vermiculite, Mg3(Si,Al)4O10(OH)24H2O, the calcium in the fluorine crystal struc- monoclinic. ture. The dike fluorite may be an initial Vermiculite, an aluminum clay min- phase or prolonged phase of the hydro- eral, is an altered form of biotite mica thermal-metasomatic fluorite mixing with commonly found in carbonatite de- MVT fluids. Sodium-rich fluorite, such as posits. It was found in the Guilless villiaumite, may have been a component Mine, Minner Mine, Caldwell Creek of the silica and carbonate fluids formed area, and DLP core xenoliths. Garnier- by liquid immiscibility during metasoma- ite, (Ni,Mg3)Si2O5(OH4), a green nickel tism. magnesium layered silicate, was de- 8. Mica. tected in core MLK-1 at a depth of a. Fluoro-tetraferriphlogopite, 424 ft, and barium mica was noted in core BMN-7. K(Mg3LiNa)(Si3,FeO10)F2, monoclinic. Fluoro-tetraferriphlogopite is a rare 9. Garnets.

fluoro-mica and was identified in the a. Schorlomite, Ca3(Ti,Fe)2((SiTi)O4)3, iso- Davidson North dike, Robinson dike, metric, a titanium garnet; andradite,

and in core DLP-2 at 112 ft by X-ray Ca2(Fe,Ti,Al,V,Mn,Na)2(SiO4)3, isomet- diffraction. The type locality for this ric. mineral is the Bayon Obo Complex Both schorlomite and andradite are in China (Miyawaki and others, 2011) high-titanium garnet and sometimes and it has also been described in the synonymous with each other in alka- Lovozero ultramafic complex in the line ultramafic rocks. Schorlomite oc- Kola Peninsula, Russia (Mitchell and curs in cores BMN-7 and DLP-3, and Results 23

Koenig (1956) identified titanium gar- kimberlite fraction; however, the carbon- net in the Shell No. 1 Adams core from rich nature of the magma and metasomat- the Minner area in the Coefield Intru- ic events could influence diamond forma- sive Complex. The high-titanium gar- tion. There were also several garnets in net is generally associated with REE core DLP-3 at depths of 332 and 338–339 ft in carbonatite, including at the type that were not properly characterized or locality in Magnet Cove, Ark. An iron named. andradite was found in the Stout dike. 10. Sphalerite, Zn(Fe)S2, isometric. b. Grossular and hibschite garnet, Sphalerite has been found in or associated Ca3Al2Si3O12, isometric. with numerous dikes in the Western Ken- These garnets have been found in the tucky Fluorspar District, including five BMN-7 and DLP cores; aluminum an- altered dikes: Old Jim, Hutson, Robin- dradite has been found in the Frontier son, Minner, and Sunderland. Sphalerite Spar core north of the Hutson Mine was also detected in core DLP-2 at 824 ft dike. (Fig. 10). These dikes contain visible sphal- +2 erite, sometimes abundant, both brown c. Almandine garnet, Al2Fe (SiO4)3, isometric. and reddish orange, and the presence of sphalerite in the altered dikes indicates a Almandine has been found in the mixing of MVT fluids and CO igneous Hurricane (Fig. 9), Fowler, and View 2 fluids, causing dike alteration. A carbon dikes, and in the Shell No. 1 Adams dioxide alteration of the dike at the Old and Hampton Joy 13 (at 277 ft) dike Jim Mine suggests alteration of both the cores. dike rock and the accompanying sphal- d. Morimotoite, (Ca2MgNa)(Ti,Fe,Al,Zr, erite (zinc sulfide) mineralization, which Mg,Mn)Si3O12. altered to smithsonite, a zinc carbonate. Morimotoite, an iron titanium sodium Smithsonite occurs in several dikes. garnet, type locality in Japan, has been a. The Old Jim dike has been mined for found at Magnet Cove, Ark., and was smithsonite (ZnCO3, trigonal) and detected in core DLP-3 at 318 ft. This sphalerite. Arsenopyrite, FeAsS2, mono- high-iron garnet contains less titanium clinic; pyrite, FeS2, isometric; and mo- than schorlomite and is derived from lybdenite, MoS2, hexagonal, were also a low-oxygen fugacity magma (Henmi detected in the Old Jim dike by scan- and others, 1995). ning electron microscope backscatter analysis. and abundant coarse- e. Uvarovite, Ca3Cr2(TiSi3O12). Pyrite Titanium chromium uvarovite garnet and fine-crystalline calcium carbonate was detected in core DLP-3 at 339 ft. were readily observed in thin section. The high-titanium garnets schorlomite b. The Hutson Zinc Mine and dike were and andradite; a high-calcium garnet, mined for sphalerite. Core examina- grossular; and a high-iron garnet, alman- tion and X-ray diffraction analysis of dine, might suggest the original melt was the dike confirmed sphalerite, and un- a peridotite-nepheline syenite material usual REE-bearing fluorides and sodi- that underwent some element partition- um and barium carbonates were also ing or that could be an overlapping al- identified. nöite-aillikite-kimberlite-carbonatite type c. The Robinson dike is altered and con- of body (Fig. 5). A manganese garnet, hen- tains large quantities of brown sphal- ritermierite, was also detected. The lack of erite, easily visible in hand samples pyrope garnet is not encouraging for the of core, and the dike is high in nio- potential discovery of diamonds in any bium. X-ray diffraction confirmed fer- 24 Results

roan sphalerite and several sodium c. Witherite, BaCO3, orthorhombic,

zinc sulfates: gordaite, NaZn4(SO4) a barium carbonate; smithsonite,

(OH)6Cl · 6H2O, trigonal; and the iron ZnCO3, hexagonal, zinc carbonate. sulfate rosenite, FeSO4(H2O)4, mono- Witherite was detected at the Clay clinic. Lick dike and in the Hutson Mine d. Core DLP-2 at a depth of 824 ft, lo- core BH-7. Traces of rhodochrosite

cated in the Minner area, contains yel- (MnCO3, rhombohedral), a manga- lowish orange sphalerite crystals in an nese carbonate, have been detected in altered dike (Fig. 10), and langbeinite, a Billiton core (BCS-2B) from Critten- an iron sulfate, at a depth of 824 ft in den Springs. the DLP-2 core. These sulfates indicate d. Smithsonite, ZnCO3, hexagonal. The oxidation of sulfide mineral deposits Old Jim dike is an oxidized igneous and are interpreted to be a result of dike containing smithsonite, a large late-stage CO2 alteration of the dikes. zinc deposit in a carbonate-rich vein Zinc concentrations in dikes (Figs. 4, 10) deposit. This vein contains coarse- ranged from 10 to 350 ppm, and there are crystalline carbonate and very fine- numerous associations of dikes and zinc crystalline replacement carbonate deposits occurring as a mid-stage MVT containing abundant smithsonite. Nu- deposit, in which both brown and reddish merous dike/vein combinations con- orange sphalerite occurred in altered dike tain smithsonite. intrusion material. Previous paragenetic In addition to the ubiquitous calcium studies (Hayes and Anderson, 1992) indi- and magnesium carbonate in many cate that the MVT fluids introduced sphal- altered dikes, the presence of anker- erite into the dike alteration fluids during ite (MgFeCO ) and rhodochrosite a middle paragenetic sequence of brown 3 (MnCO3) and all carbonate minerals to reddish orange sphalerite mineraliza- indicates a variable carbonate influ- tion. ence in the dike system. 11. Carbonates. 12. Perovskite, CaTiO3, orthorhombic. Some of the igneous xenoliths in cores A high-pressure mineral, perovskite is DLP-2 and DLP-3 contain calcite, dolo- common in lamprophyres, but in sev- mite, and magnesite, which could be ig- eral of the dikes of the Western Ken- neous carbonates; more isotopic work is tucky Fluorspar District, REE-bearing needed on these minerals. Carbonates of perovskite occurs, which is more unusual. interest are: The REE-enriched perovskites are simi-

a. Magnesite, MgCO3, hexagonal. lar to those at their type localities, which Magnesite was detected in the DLP are in the Kola Peninsula, Russia (Mitch- cores. ell and Chakhmouradian, 1996). For example, numerous forms of perovskite b. Natrite, Na CO , monoclinic, sodium 2 3 occur in core BMN-7: cubic (Ba(InW) carbonate. O3,Ba2YTaO6), monoclinic (Pr,Na,MnO3), Natrite is found in core BH-7 and is a orthorhombic (La(NiO3)), and ortho- common mineral in peralkaline rocks rhombic (Eu3InO) europium perovskite in continental rift basins such as the oxides—some of which are double New Madrid Rift. The type locality perovskites (Ba2Na(ReO6)). Other varia- for natrite is the Lovozero ultramafic tions occur that incorporate lanthanum, yt- complex in Russia. trium, tantalum, niobium, and nickel such Results 25

that they mimic the loparite perovskites Jim Mine. Topaz, Al2SiO4(OH)F, was de-

((Ce,Na,Ca)(TiNb)O3, cubic) solid solution tected in the Stout dike, and manganite,

series. High-REE perovskites have been Mn2O3H2O, monoclinic, and a manganese found in kimberlites and are common in oxide were detected in core BH-7-74 from carbonatites (Mitchell, 1986). These oxides the Hutson Mine. Spodumene, a lithium form a layered structure, and many have silicate, represents a lithium phase, and the been identified as double perovskites. phosphates are important carriers of REE. Perovskites are important REE carri- Other metallic minerals of interest, in-

ers during fractionation in magma melts cluding jamborite (Ni,Co(OH)(SO4)H2O),

(Beyer and others, 2013). The perovskites cooperite (PtS), carlinite (Ti2S), wairauite in the Western Kentucky Fluorspar Dis- (CoFe), zinc nickel ferrite ((Zn,Fe)(Ni,Fe)

trict should be compared to those from the O4), and hibonite ((Ca,Ce)(Al,Ti,Mg)12O19) Lovozero deposit in Russia because of the were detected in an igneous breccia in high REE content in loparite, a member of core DLP-3 at a depth of 300–340 ft. Wol-

the perovskite solid solution series. Some lastonite, CaSiO3, was detected in several of the REE-rich perovskites in core BMN- xenoliths in core DLP-3. Pyrite, arseno- 7 are similar to loparite and suggestive of pyrite, chalcopyrite, bornite, and molyb- ultramafic lamprophyre and lamproite li- denite were also detected in the Old Jim thology. Mine, determined by scanning electron 13. Phosphates. microscope backscatter imaging. There are several unusual minerals in xe- Fluorapatite, Ca5(PO4)3F, hexagonal, was identified in the Hutson, Davidson North, noliths in cores from within or near the Guilless, and DLP-2 core dikes. A rare oc- Coefield Intrusive Complex, including cores DLP-2 and DLP-3, and Davidson currence of monazite, (Ce,La,Y,Th)PO4, a REE phosphate, was detected by X-ray North and Minner cores. Some of these diffraction in core DLP-2 at 112 ft; irid- xenoliths contain both sodium- and potas- ium was also detected and confirmed in sium-rich minerals, including the sodium this core by scanning electron microscope and some unnamed garnets, which could analysis (Fig. 11). suggest a syenite facies. Calcium carbonate and calcium silicates could suggest 14. Zircon, ZrSiO , tetragonal. 4 an igneous calcite. A high-temperature Zircon was detected in the xenoliths of silicate, tridymite, was detected in several cores DLP-2 and DLP-3, where this study xenoliths. Additional spodumene, zircon, found several occurrences of zircon. Al- metal sulfides, and oxides, including ura- though zirconium concentrations were ninite, were also identified, but more anal- high in many dikes, zircon crystals are ysis is needed to determine any xenolith rare in high-alkaline fluids. source rocks. The presence of these min- 15. Other minerals. erals is significant because many of them Pure carbon, C, cubic, was detected in core have never before been noted in or de- DLP-3-332A, as well as a possible silicon scribed for the Western Kentucky Fluor carbide, but more work needs to be done spar District, and the variability of their occurrence indicates that the dikes repre- on these rare minerals. Spinel, (MgAl2)O4, octahedral, was also detected in four sepa- sent a wide spectrum of lithofacies of an rate dikes: Davidson-Midway, Minner 7, alkaline igneous complex. Many of these Clay Lick, and in the Pennwalt (597-V) rare minerals imply deep mantle sources core. A sodium tourmaline and abundant for the mantle-derived igneous rocks of calcite, dolomite, and another sodium the district, including depths near the carbonate were also detected at the Old wüstite-iron boundary in sublithospheric mantle rocks. 26 Results

REE in Dikes titanium magmas, similar to those that formed the Background. REE are enriched in magma melts, Coefield Intrusive Complex, have a high La/Yb depending on the degree of melting, fractionation, and Tb/Yb ratio (Fig. 13). Compared to other lam- and metasomatic influence and the final - petro proites (Rock, 1991), low values of barium, stron- logic lithofacies. Normally during fractionation, tium, zirconium, and lanthanum suggest that there low degrees of partial melting of mantle peridotite is unlikely to be a lamproite facies in this dataset. will enrich the LREE and in the presence of gar- Niobium-bearing rutile occurred in several net, buffer the HREE (Figs. 12–19). The La/Yb ratio dikes and is a pathfinder mineral for carbonatite is frequently used to measure the degree of frac- petrology (Mariano, 1989; Beattie, 1993; Green, tionation, enrichment, and depletion in an igne- 1995); it assists in melt partitioning of the incom- ous body; Kay and Mahlburg-Kay (1991) used La/ patible elements niobium, tantalum, zirconium, Yb, Tb/Yb, and Sm/Yb ratios to record degrees of hafnium, and yttrium. During fractional crystalli- melting and fractionation. zation, REE are enriched, but each of the incom- Carbonatites contain the most enrichment of patible elements are not easily fractionated and in- REE in the world, and their La/Yb ratios generally stead change during metasomatism, during which range between 100 and 1,000. According to Mitch- zirconium increases compared to hafnium and yt- ell (1986), some kimberlites have a La/Yb ratio of trium (Rudnick and others, 1993). Enrichment of 80 to 200, and Tappe and others (2005, 2006) stated these elements suggests carbonatite metasomatism that the La/Yb ratio should range between 70 and has enriched niobium (Fig. 18). Post-crystallization 130 for extremely fractionated magmas. High-tita- perovskite alteration to rutile/anatase is a measure nium kimberlites have La/Yb ratios greater than of late-stage CO2-rich alteration events (Haggerty 70 (Kononova, 1984) and an extremely fractionated and Baker, 1967; Haggerty, 1976) and indicates car- kimberlite body would have higher La/Yb ratios, bonatite formation. Niobium is of special impor- greater than 100 (Mitchell, 1986). Extremely high tance because it seems to increase in more evolved La/Yb ratios (greater than 100) have not been ob- rocks, as in the carbonatite at Magnet Cove, Ark. served in the Western Kentucky Fluorspar District, (Erickson and Blade, 1963), which contains higher which implies the lower La/Yb ratio and Ti/Eu niobium concentrations (4–9 percent) than the as- ratio represent a moderately fractionated, nonkim- sociated syenite-type rocks. berlitic source rock (Figs. 12–19). According to Liu Experimental data from partitioning studies and others (2011), La/Yb ratios for Chinese frac- related to ratios of U/Th and La/Yb (Beattie, 1993) tionated nepheline syenites range from 29.1 to 36.1, also suggest that melt excesses in the garnet stabil- much lower values and a much smaller range than ity field allow fractionation of thorium from ura- for kimberlites. Similar studies in the East African nium, and confirm some data shown in Figure 16 Rift (Eby and others, 2003) suggest that high-tita- that indicate increased thorium fractionation in the nium garnets increase Tb and Yb concentrations in Coefield Intrusive Complex. the source rocks because of garnet-present versus Discussion of Elemental Data From Dikes. Chon- spinel-present melting and fractionation (Rogers, drite-normalized REE patterns of the dikes ana- 2006). The presence of clinopyroxene and garnet in lyzed in this study (Figs. 12–19) show a family of a melt causes enrichment of LREE and depletion of alkaline dikes with variable enrichment of LREE. HREE (Hanson, 1980). Analysis of clinopyroxene Ratios of La/Yb are an estimate of the enrichment has been used to examine the La/Yb versus Ti/ of LREE (lanthanum) and HREE (ytterbium). La/ Eu ratios to discriminate between carbonatite and Yb ratios (Figs. 12–15) illustrate the set of ultra- silicate metasomatism (Rudnick and others, 1993; mafic dikes at the Coefield Intrusive Complex with Coltorti and others, 1999). The presence of plagio- values between 55 and 75, significantly higher than clase in a melt can produce a negative europium for the other analyzed samples. This same family anomaly. Titanium and silicon have been used to of dikes has LREE enrichment (Figs. 12–13) and a analyze kimberlite and lamproite facies, in which trend toward carbonated peridotite (Figs. 13–14). lamproite contains higher silicon and kimberlite contains higher titanium (Kononova, 1984). High- 31

Results 27

Legend in order of 1000.000 increasing distance from Hicks Dome

Hampton Joy-13 Sunderland T-5-76 Billiton Minner-4 100.000 Billiton Minner-7-277 Davidson North Davidson-Midway T-9-76 Billiton Lady Farmer

X Chondrite Stout T-8-76 Cardin 10.000 Billiton-Hutson BH-7 Maple Lake-1 Caldwell Creek

1.000 La Ce Pr Nd Eu Gd Tb Dy Ho Er Tm Yb Lu Y REE

Figure 12. Normalized REE concentrations of selected dikes in the Western Kentucky Fluorspar District. The moderate slope suggestsFigure 12. REE a plotlow of selectedpercentage dikes in the of WKFD the showing magma normalized melt REE and values fractionated. The moderate slope enrichment suggest a low ofpercentage LREE magma in all melt dikes. and fractionated Higher enrichment values of of the LREE LREE in all in dikes. the A complex metasoamtism, less garnet influence and or higher degree of melting and less fractionated enrichment may be explained by crossover values of Hampton Joy and Sunderland. Higher values of LREE in the CIC Coefieldindicate an enrichment Intrusive event Complex trending toward indicate carbonatite an values, enrichment while the Maple event Lake values trending reflect a depletedtoward mantle carbonatite composition ofvalues, total REE. Caldwellwhereas Creek the and MapleMaple Lake, Lake both of valueswhich are located reflectthe furthest a distancedepleted from Hicksmantle Dome butcomposition are located geospatially of total within REE. a mile A of complex each other, containmetasomatism, contrasting values less of REE. garnet Caldwell influence,Creek containing highor higherREE values (discusseddegree underof meltingcaption in Figure and18) and less Maple fractionated Lake containing lowenrichment values suggest maya reactivated be explained plumbing system, by one crossover containing a primitivevalues dike from (Maple the Lake) Hampton and the other Joy a metasomatically and Sunderland enriched dike dikes. (Caldwell Caldwell Creek). Creek and Maple Lake dikes, both of which are located farthest from Hicks Dome but geospatially within a mile of each other, have contrasting concentrations of REE. High REE concentrations at Caldwell Creek and low REE concentrations at Maple Lake suggest a reactivated plumbing system, one containing a primitive dike (Maple Lake) and the other a metasomatically enriched 32 dike (Caldwell Creek).

6.00 Davidson North Midway Lady 5.00 Farmer

Minners, 4.00 4, 7 Stout Cardin 3.00 Sunderland Hutson

Tb/Yb Coefield Intrusive Complex

2.00 Hampton Caldwell Creek

1.00 Maple Lake

0.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 La/Yb

Figure 13. 13. Plot La/Yb of La/Yb ratios vs Tb/Yb versus (light Tb/Yb to heavy ratios rare earth(light elements), to heavy showsrare earthfractionated elements) melt crystallization are indicative and ofmetasomatism fractionated of melthigh titanium crystallization alkaline ultramafic magmas in the WKFD. The linear trendand metasomatism from lower to higher of high-titanium La/Yb and Tb/Yb alkaline ratios at ultramaficCoefield and Midwaymagmas areas in theindicate Western carbonatite Kentucky metasomatism Fluorspar and District.the enrichment The linear of REE trend bearing from dikes in the CIC. lower to higher La/Yb and Tb/Yb ratios at Coefield and Midway indicates carbonatite metasomatism and the enrichment of REE- bearing dikes in the Coefield Intrusive Complex. 33

28 Results

16 sillimanite Legend in order of highest to lowest Sm/Yb ratio 14 Garnet= Grt, Spinel = Sp Grt-Sp fluoro-tetraferriphlogopite schorlomite, B-Lady Farmer 4 _ 341.5 12 wÜstite, Sp B-Minner-4 astrophyllite 10 B-Minner-7_277 Coefield Intrusive Complex Davidson_Midway-T-9-76 8

Sm/Yb andradite Grt Davidson North mixed facies 6 B-Hutson-7 spinel and garnet peridotite villiaumite Stout T-8-76 4 natrite increasing melt and carbonization Cardin 2 almandine Grt Sunderland-T-5-76

0 Caldwell Creek_1 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 Hampton Joy-13_277 La/Yb Maple Lake-1 _ 427

FigureFigure 14 Bivariate 14. Bivariate linear plot of linear La/Yb vs plot Sm/Yb, of showing La/Yb significant ratio versus changes inSm/Yb dike mineralogy ratio showsfor an evolving significant peridotite melt.changes Titanium in increases dike mineralogyin the melt during for calcium-titanium an evolving garnet crystallization,peridotite and melt. the metasomatism Titanium increasesor carbonization in ofthe peridotite melt increasesduring REEcalcium element-titanium ratios toward garnet the CIC crystallization,field. In this model, aand dynamic the melt metasomatism with xenocrysts of ordeep carbon seated mantle material, 34 evolvesization to a highof peridotite titanium garnet increases peridotite lithofacies, REE ratios containing toward enriched the values Coefield of La/Yb Intrusiveand Sm/Yb due Complex to melting infield. the garnet In the stability model field andhypothesized mantle metasomatism. in this study, a dynamic melt with xenocrysts of deep-seated mantle material evolved to a high-titanium garnet peridotite lithofacies containing enriched concentrations of La/Yb and Sm/Yb caused by melting in the garnet stability field and mantle metasomatism.

25.00 Davidson_Midway Davidson 22.50 T-9-76 Sunderland T-5-76 North Hampton Joy 20.00 13_277 Caldwell Creek_1 Cardin 17.50 B Hutson 7 15.00 Stout I-8-76 B-Minner 4 Ratio 12.50 B-Lady Farmer

Nb/Ta Nb/Ta 10.00 4_341.5 B Minner 7_277 7.50

5.00

2.50 Maple Lake 1_427 0.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 La/Yb Ratio high niobium > 100 ppm high calcium > 14% Figure 15.Figure Plot 15 of Plot whole of whole-rock-rock La/YbLa/Yb and and Nb/Ta Nb/Ta showing ratios elevated shows values in elevated both super chondriticconcentrations (>17.5 Nb/Ta) in and both sub superchondriticchondritic (<17.5 Nb/Ta) (greater niobium rich than ilmenite 17.5 and rutile fields. Titanium Nb/Ta ratio)niobium and rich subchondritic phases partially control(less fractionationthan 17.5 in Nb/Ta magma meltsratio) (Beattie, niobium-rich 1993, Green, ilmenite 1995) and theseand tworutile clusters fields. of data Titanium-niobium-richgive some insight into the mantle-sourced phases magmas in the WKFD. partially controlFractionation fractionation of ilmenite and in rutile magma suggests melts that magma (Beattie, was generated 1993; in Green,the super chondritic1995), meltand and these fractionated two clustersniobium to createof data higher give Nb/Ta some ratios in insight a super chondritic peridotite into the mantle(Sunderland-sourced and Caldwell magmas Creek). Thein thenear Westernchondritic and Kentucky sub-chondritic Fluorspar data with La/Yb District. >50 may Fractionation record a higher degree of ilmenite of partial melting and rutile(or remelting) suggests and metasomatism that of a garnet peridotite facies containing high La/Yb dikes (50-70) in the CIC. These sub-chondritic compositions may also represent mixing with a crustal component or depleted metasomatic fluids which magma was generated in the superchondritic melt and fractionated niobium to create higher Nb/Ta ratios in a superchondritic produced slightly enriched REE in the CIC dikes peridotite. peridotite (Sunderland and Caldwell Creek dikes). The near-chondritic and subchondritic data with La/Yb ratios greater than 50 may record a high degree of partial melting (or remelting) and metasomatism of a garnet peridotite facies containing dikes with high La/Yb ratios (50–70) in the Coefield Intrusive Complex. These subchondritic compositions may also represent mixing with a crustal component or depleted metasomatic fluids, which produced slightly enriched REE in peridotite in dikes of the Coefield Intrusive Complex. 35

8 Results 29

7 Maple Lake-1 _ 427

6 Caldwell Creek_1

4 B-Minner-4 B-Hutson-7 Sunderland 3 Stout Uranium (ppm) Uranium Davidson Midway Davidson North Cardin B-Lady Farmer 2 Hampton Joy 13 B-Minner-7

0 0.001.002.003.004.005.006.00 Thorium/Uranium

Figure 16. Bivariate diagram of whole-rock uranium/thorium element fractionation, which is thermal-inducing in magma melts; theirFigure partitioning 16 Bivariate is diagramindicative of whole of the rock degree uranium ofthorium partial element melting fractionation, and fractionation. which is thermal The inducing trend in line magma demonstrates melts and their thorium partitioning enrichment is indicative of the degree of partial andmelting uranium and fractionation.depletion during The trend these line demonstratesevents, and thorium increasing enrichment Th/U and ratios uranium toward depletion the during Coefield these events,Intrusive and increasingComplex, Th/U which toward is thethe Coefield site intrusion, which is the of highsite of-titanium high titanium garnets. garnet composition.Thorium fractionation Thorium fractionation from uraniumfrom uranium generates generates aa thermal thermal engine engine for further for metasomatism.further metasomatism. Fluoro-phosphate Fluoro mineralogy- is abundant in these dikes and probably accounts for most of the radionuclides, since only two zircons and one monazite were noted in core DLP-2, in the X-ray diffraction studies, and only small amounts of phosphate mineralogy is abundant in these dikes and probably accounts for most of the radionuclides, since X-ray diffraction 36 foundmonazite only twohave zirconsbeen noted and in other one investigationsmonazite in of corethese DLPdikes.- 2.

50 Davidson-Midway 45 Hampton Joy B-Minner-4 Sunderland B-Hutson-7 Cardin B-Minner-7 40 Davidson North Caldwell Creek_1 Stout B-Lady Farmer-4 35 Zr/Hf chondrite value 37.8

30 Zr/Hf 25 Zr/Y 20 Maple Lake 1

15 Stout B-Minner-4 Zr/Y and Zr/Hf Sunderland Davidson North B-lady Farmer 4 B-Hutson-7 10 Cardin Davidson-Midway Caldwell Creek_1 B-Minner-7 5 Maple Lake 1 Hampton Joy 13 0 Zr/Y chondrite value 2.52 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 La/Yb

Figure Figure17. Zr/Y 17 Zr/Y and and Zr/Hf Zr/Hf ratios ratios vsversus La/Yb showingLa/Yb ratios,super-chondritic showing dikes superchondritic in both sample sets dikes indicating in both mantle sample and metasomaticsets, which geochemical indicates enrichmentmantle in the WKFD. and metasomatic geochemical enrichment in the Western Kentucky Fluorspar District.

37 Results 30

Niobium-Yttrium 250 Caldwell Creek_1 200

150 DM Sunderland B-Minner4 Davidson North 100 BLF-4 Cardin BMN-7 Stout Niobium (ppm)Niobium 50 BH7 0 ML1 Hampton Joy A. 0 10 20 30 40 50 60 70 Yttrium (ppm) A

Titanium-Niobium 250 Caldwell Creek 200 BLF-4 150 B-Minner-4 Sunderland DM 100 Cardin Davidson North

Nioium (ppm)Nioium HJ Stout B-Minner-7 50 BH-7 ML1 0 0 5000 10000 15000 20000 25000 30000 35000 40000 B. Titanium (ppm) B Figure 18. A. Increasing niobium and yttrium concentrations suggest some variable degrees of partial melting and enrichment Figure 18 A.in Increasing a fractionated niobium titanium-niobium-rich and yttrium values suggest carbonatite either: near 1) some the Coefield variable degrees anomaly. of partialThe high-niobium melting and enrichment cluster around in a fractionated the dikes of titanium niobium rich carbonatite the Coefield Intrusive Complex became enriched in a melt and the high yttrium, niobium, and titanium concentrations suggest near the Coefield anomaly and 2) the high Nb cluster around the CIC dikes becomes enriched in a melt and the high Y, Nb and Ti suggest further alkaline mantle metasomatism in further alkaline mantle metasomatism in these incompatible elements at Caldwell Creek. Imenite was detected at Minner and these incompatiblein the Coefield elements Intrusive at Caldwell Complex, Creek. Ilmentite and abundant was detected niobium-rich at Minner rutile and (anatase, the CIC, brookite) and abundant was detectedniobium richat the rutile Davidson (anatase, North, brookite) was detected at Davidson North, Sunderland, Sunderland,Lady Farmer, Lady and Minner,Farmer, andand yttrium-fluoriteMinner dikes; yttrium-fluorite was detected atwas the detected Cardin dike. at the These Cardin enrichments dike. These are enrichments commonly associatedare commonly with enriched alkaline deposits in carbonatitesassociated or nepheline with syenite enriched source alkaline rocks. deposits B. Ti/Nb ratioin carbonatites showing increasing or nepheline Nb in syenite response source to increased rocks. B. differentiation Ti/Nb ratio shows of high increasing titanium magma. The most important data point niobium in response to increased differentiation of high-titanium magma. The most important data points in these plots are the in these plots are the Caldwell Creek values of Nb, Ti, and Y, which when combined with the high La/Yb ratio (Figure 12) are highest in the district. This suggest another source of Caldwell Creek concentrations of niobium, titanium, and yttrium, which, when combined with the high La/Yb ratio (Fig. 12) are high REE enrichmenthighest in in the the district. district. This This suggests implies that another another source carbonatite of high-REE or metasomatic enrichment alterationin the district event and was implies centered that inanother the southern carbonatite part of the district near the Tabb Fault System. Mapleor metasomaticLake and Hampton alteration Joy mayevent represent was centered less metasomatized in the southern dikes. part of the district near the Tabb Fault System.

Numerous dikes are enriched in LREE dikes. Maple Lake and Hampton Joy dikes have (Fig. 12); normalized values are shown for minor europium depletion, whereas Stout, Minner, Caldwell Creek, BLF-4 Lady Farmer, BMN-4 Min- and Cardin dikes have slightly positive europium ner, and BMN-7 Minner dikes (Figs. 12–13). Deple- anomalies, although not significant enough to be tion of LREE occurs at Maple Lake and Hutson used as a petrogenetic indicator. The range of raw 38

Results 31

Ti/Eu vs. Zr/Hf Distance from Hicks Dome 12000.00 Hampton Joy-13_277 Zr/Hf chondritic line 37.8 Sunderland-T-5-76 10000.00 B-Minner-4 8000.00 Ti/Eu chondritic line B-Minner-7_277 Davidson_Midway-T-9-76 6000.00

Ti/Eu Davidson North

4000.00 Cardin B-Lady Farmer 4 _ 341.5 2000.00 Stout T-8-76 B-Hutson-7 0.00 0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 Maple Lake-1 _ 427 Zr/Hf Caldwell Creek_1

Figure 19 FigureDiagram 19. of Ti\Eu Ti/Eu and and Zr\Hf Zr/Hf trace ratios element show ratios increasing showing increasing differentiation differentiation in the in magma.magma. The The Zr\Hf Zr/Hf ratio ratio indicates indicates increasing increasing Zr in the magma zirconium indicating in metasomatism,the magmawhich is super caused chondritic, by superchondritic Ti is elevated, and metasomatism. the Ti garnets crystallize Titanium in the is CIC,elevated, then the and Ti content the titanium decreases garnets during continued crystallize differentiation in the Coefield and Eu content increases indicatingIntrusive increasing Complex enrichment dikes, decreasing of REE in some the of titaniumthe dikes duringcontent late while stage thecrystallization europium in thecontent WKFD. increases. Several of these As the core melt analysis evolves, including increasing the Minner-4, Davidson- Midway, Cardinenrichment and Davidson of europium North indicate and that REE these occurs were thein somemost differentiated of the dikes rocks during and the late most-stage enriched crystallization in REE that were in the analyzed Western in the Kentucky district, which Fluor suggest a low degree of partialspar melting.District. The Several high titanium, core analyses, low REE dikes including are the Hutson for the and Minner Sunderland-4, Davidson in Livingston-Midway, County. Cardin, Hampton and Joy and Davidson Maple Lake North are somewhatdikes, indicate unique and contain lower La/Yb,that low these Ti/Eu. wereHampton the Joy most is closest differentiated to Hicks Dome rocks and Mapleand the Lake most is the enriched furtherest in from REE Hicks that Dome were in southernanalyzed part in ofthe Crittenden district. CountyThe high-titanium, but Maple Lake is less differentiated.low - REE dikes are the Hutson and Sunderland in Livingston County. Hampton Joy and Maple Lake dikes are unusual because they have low La/Yb and Ti/Eu ratios. The Hampton Joy dike is closest to Hicks Dome and Maple Lake is the farthest from Hicks Dome, occurring in the southern part of Crittenden County, but Maple Lake is less differentiated than Hampton Joy.

REE data (Fig. 4), such as concentrations of lantha- These data, along with the abundance of titanium num (3.3–118 ppm), cesium (6.6–257 ppm), europi- alteration and magnesium enrichment in many um (0.12–5.27 ppm), and ytterbium (0.3–4.2 ppm) dikes, might be an avenue to examine the altera- also indicates extensive fractionation and metaso- tion mineralogy as a pathfinder to REE anomalies matism, which occurred prior to intrusion of the (Fig. 19). For example, and based on the limited dikes. Total REE concentrations for these dikes sample set, the higher magnesium values near the range from 41 at Maple Lake to 1,320 at Caldwell Coefield Intrusive Complex and the ilmeno-mag- Creek. netite/leucoxene alteration in the Clay Lick (T- The Caldwell Creek dike is somewhat unusu- 798a) dike area indicate that some areas are more al in that it has the highest REE values (Fig. 12), but altered than other dikes in the district, but more is not located in the Coefield Intrusive Complex, research is needed to determine any correlation be- and it has the highest niobium, yttrium, and tita- tween regional zonation and REE in dike alteration nium values of the samples analyzed (Fig. 18). The patterns. Caldwell Creek dike is altered, containing clays Only moderate elemental zinc (10–353 ppm) and carbonates, and is located near the Maple Lake was detected in the dikes. The most zinc-enriched dikes, which contain yttrium fluorite and calcite. dike was Sunderland, which contained 353 ppm, The enrichment of REE is primarily a frac- whereas the dike at Hutson Mine, which was pri- tionation event, whereas high values of titanium, marily a zinc mine, only contained 10 ppm zinc. niobium, phosphorus, thorium, and zirconium Some molybdenum was noted in the Old (Fig. 12) also suggest a metasomatic enrichment. Jim dike, and iridium was noted in core DLP-2 at 32 Results

112 ft, in a monazite phosphate; this was confirmed ures 20 through 23. These patterns suggest two dis- by scanning electron microscope analysis (Fig. 11). tinct low-value REE signatures in fluorite, assum- Iridium, osmium, and ruthenium were noted in ing the REE values were within the fluorite crystal core BH-7 at 74 ft, according to X-ray diffraction. structure and not in the fluorite inclusions. One The presence of iridium and other metals could im- pattern shows enrichment of MREE (Figs. 20–22) ply that there could be phases of platinum group and matches Trinkler and others’ (2005) data on elements in the Western Kentucky Fluorspar Dis- MREE enrichment in several of the fluorite sam- trict. ples. The second pattern, seen in dark purple fluo- U/Th ratios (Fig. 16) show a decrease in ura- rite from the Davenport Mine, shows some enrich- nium and enrichment of thorium toward the Coe ment of LREE; a duplicate analysis was performed field Intrusive Complex, another indication of to confirm the analysis. thorium fractionation from uranium during meta- Fluorite in dikes was detected by X-ray dif- somatism of the magma. fraction as sodium fluoride, yttrium fluoride, During fractionation in an alkaline melt, the cadmium fluoride, and an unnamed REE-bearing incompatible elements, including zirconium and fluoride, in addition to calcium fluoride. Many of hafnium, will increase only slightly in the remain- the Kentucky ore-stage fluorites contain REE, but ing melt, because of their similar ionic properties, the values are low compared to those from the so the higher, above-chondrite values of zirconium purple fluorite at the Rose Mine (Burruss and oth- and hafnium and zirconium and yttrium indicate a ers, 1992b) and the Hicks Dome fluorite (Hall and carbonatite metasomatic influence (Figs. 15–19), as Heyl, 1968). Dark purple fluorite from the Daven- previously discussed in Eby and others (2003) and port Mine has high LREE values and other purple Pearson and others (2004). Some of the dikes in this fluorite from the Western Kentucky Fluorspar Dis- study have higher Zr/Y and Zr/Hf ratios (Figs. 17, trict shows a slight increase in La/Yb ratio at com- 19) compared to chondrite values, and the zirco- parable Tb/Yb ratios, suggesting that purple fluo- nium and hafnium values are compatible with the rite is slightly more enriched in REE than yellow values related to carbonatite sourcing described fluorite (Figs. 20–21). by Chakhmouradian (2006). Carbonatites can be Uranium and thorium concentrations in the a metasomatic influence on a mantle magma, and fluorite were also determined because these radio- the enrichment of some of the incompatible ele- nuclides are associated with igneous processes and ments (titanium, zirconium, hafnium, niobium, they have a potential contribution to fluorite col- tantalum, uranium, and thorium) (Beattie, 1993) oration. The uranium and thorium concentrations confirms this (Figs. 15–19). Many of the incompat- were very low, many samples below the detection ible elements were concentrated above chondrite limit, but some values were of interest. The Daven- values and may have helped concentration of tita- port deep purple fluorite contained the highest tho- nium and fractionation of thorium and uranium. rium concentrations: 10.7 and 13.1 ppm (Fig. 22). The wide range in concentration of elements In contrast, dark purple fluorite from the Joy Mine in the analyzed dikes suggests a heterogeneous had a high uranium concentration (3 ppm) but low mix of ultramafic rocks resulting from complex thorium concentration (Fig. 23) and high barium- metasomatic reactions, perhaps both silicate and strontium concentration. carbonatite, which directly affects the rocks’ REE content (Figs. 16–20). These metasomatic processes Discussion of REE in Fluorite are somewhat gradational, and significant overlap Analysis of REE in ore-stage fluorite indicates creates high variability in REE; iron, niobium, ti- two REE phases (Fig. 20). Five fluorites showed tanium, carbon, and calcium values allow for REE MREE enrichment: the Joy purple, Hastie-Victory enrichment in some of the dikes. dark and light yellow, Big Four, and Eagle Babb purple. The Davenport purple fluorite was one REE in Ore-Stage Fluorite sample, split and analyzed at two different times, Rare earth elements in fluorite were analyzed, to show enrichment in LREE. The REE patterns at and normalized REE patterns are displayed in Fig- Joy and Davenport indicate two mineral-forming 42

Results 33 REE in Fluorite-SGS Normalized 100.00 Legend in order of highest normalized REE values of MREE and LREE

JoyJoy purplePurple 10.00 HASTIEHastie yellow YELLOW

Victory-HastieVictory-Hastie dark Dk yellow Yellow

BigBig Four X Chondrite EagleEagle BabbBabb purple Purple 1.00 Davenport DAVENPORTMine_DUP_PUR1 MINE_DUP_PUR1 Davenport DAVENPORTMine_DUP_PUR2 MINE_DUP_PUR2 Victory-HastieVictory-Hastie purple Purple

0.10 KLONDIKEKlondike II light II-Lt yellow Yellow La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y REE Figure 20. REE patterns of fluorite from the WKFD. One group is enriched in MREE, irrespective of color; in decreasing order of MREE abundance these are Joy Purple, Hastie Yellow, Victory Hastie FigureDark Yellow, 20. Eagle Patterns Babb Purple, of and REE Big Four. in fluoriteA second group from composed the ofWestern two Davenport Kentucky Mine samples Fluorspar show an enrichment District. in LREE.One A thirdgroup group is shows enriched depleted inREE, theMREE, Hastie irrespectivePurple and ofKlondike color; II light in yellow. decreasing The variation order between of the MREE two enriched abundance, fluorite sample thesesets suggest are a highJoy temperature purple, differentiated Hastie yellow, fluorine rich Victory fluid, one-Hastie fraction enriched dark inyellow, LREE and anotherEagle low Babb purple,temperature and enriched Big in Four.MREE. It A is alsosecond possible group that both composed carbonatite and MVTof two fluids Davenportmixed. Some fluorites Mine with samples elemental values is enriched near the lower in limitLREE. of detection A third may representgroup fluidsis depleted depleted in 43 inREE REE:and or may the contain Hastie analytical purple oscillation and errors Klondike as shown in II the light Klondike yellow. yellow and The Victory variation Hastie purple between values. the two enriched-fluorite sample sets suggests a high-temperature-differentiated fluorine-rich fluid, one fraction enriched in LREE and another low-temperature fraction enriched in MREE. Both carbonatite and MVT fluids may have mixed. Some fluorites with elemental values near the lower limit of detec tion may represent fluids depleted in REE.

Hastie purple 3.5 Hastie dark yellow 3 Joy Mine purple 2.5 Eagle Mine purple Big Four purple 2 Klon Hastie yellow

Tb/Yb dike 1.5 light yellow 1 trend lines Davenport purple 0.5

0 0 5 10 15 20 25 La/Yb

Figure 21. Ratios of REE in fluorite. La/Yb and Tb/Yb ratios were plotted to characterize REE distribution in colored fluorite from the Western Kentucky Fluorspar District. These limited data suggest that purple fluorite is slightly more REE-enriched compared to yellow. The Davenport purple may have formed from a separate fluid phase strongly enriched in LREE.

Figure 21. Ratios of REE in fluorite. La/Yb and Tb/Yb were plotted to characterize REE distribution in colored fluorite from the WKFD. These limited data suggest that the purple fluorite is slightly more REE enriched compared to yellow. The Davenport Purple may have formed from a separate fluid phase strongly enriched in LREE (see Figure 21).

0 0 0.5 1 1.5 2 2.5 3 3.5

Figure 22. Uranium-thorium concentrations in fluorite showing high uranium Joy Mine fluorite and high thorium Davenport Mine fluorite. The wide variance in U- Th values between Davenport and Joy fluorite might suggest more fractionation with higher LREE vales at Davenport. Previous studies by Beattie, (1993) suggest high garnet facies may influence Th-U fractionation.

3.5

2.5

2 Tb/Yb 1.5

0.5

0 0 5 10 15 20 25 La/Yb

Figure 21. Ratios of REE in fluorite. La/Yb and Tb/Yb were plotted to characterize REE distribution in colored fluorite from the WKFD. These 34 limited data suggest that the purple fluorite is slightly more REE enrichedResults compared to yellow. The Davenport Purple may have formed from a separate fluid phase strongly enriched in LREE (see Figure 21).

14 Davenport Mine_DUP 12 Davenport Mine_PUR 10

Thorium (ppm) Thorium 4

2 Joy Hastie yellow below detection limit 44 0 0 0.5 1 1.5 2 2.5 3 3.5 Uranium (ppm)

Figure 22. Uranium-thorium concentrations in fluorite show high uranium in fluorite from the Joy Mine and high thorium in fluorite from theFigure Davenport 22. Uranium-thorium Mine. The concentrations wide variance in fluoritein uranium showing and high thorium uranium concentrations Joy Mine fluorite inand fluorite high thorium from Davenport the Davenport Mine fluorite. and JoyThe wideMines variance in U- might suggestTh values betweenmore fractionation Davenport and with Joy fluoritehigher might LREE suggest values more at fractionation Davenport. with A previoushigher LREE study vales atby Davenport. Beattie (1993) Previous suggest studies by that Beattie, high (1993)- suggest garnethigh facies garnet may facies influence may influence thorium-uranium Th-U fractionation. fractionation.

Purple fluorite YellowPurple fluorite fluorite Yellow fluorite

Davenport Joy

Figure 23. Y/Yb ratios place the Western Kentucky Fluorspar District fluorites in the MVT hydrothermal category and conflict somewhat with the REE signature previously discussed. Several fluorites analyzed in this study had concentrations below de tection limits, so these data might be skewed; more analyses should be completed to determine genetic sourcing of the fluorite. The dark purpleFigure fluorite 23 Y from -Yb the elemental Davenport ratioMine and place other the purple WKFD and yellowfluorites fluorites in the fit MVTmostly intohydrothermal the MVT and categoryhydrothermal and shows some conflict with the categories, REEbased signature on available previously data and analytical discussed. techniques. However, Baseline several compositional fluorites data analyzedfor MVT and in carbonatite this dataset data fromwere below detection limits of analytical Makin and others (2014) and Möller and others (1998). equipment, so this data might be skewed and more analytical work should be completed to determine genetic sourcing of the fluorite. The Davenport mine (DM) dark purple and other purple and yellow fluorites fit mostly into the MVT and hydrothermal category based on available data and analytical techniques. Baseline compositional data for MVT and carbonatite data from Makin and others, (2014) and Moller and others, (1998).

Conclusions

During initial pre-Cambrian continental rifting, mantle upwelling, carbonatite metasomatism and magmatic intrusions occurred along basement faults near the SCLM of the NMRZ. This mantle upwelling introduced mafic and ultramafic plutons into the rift complex but upward mobility of the magma melts stalled due to lithostatic pressures above the SCLM during early Paleozoic. Sub- lithospheric de-lamination of the crustal materials may have contaminated the mantle melts during structural uplift. The enriched REE and variant elemental chemistry of the dikes in this study suggests the petrology of the melts was differentiated and metasomatized by the stalled mantle melts in early Paleozoic. These partially differentiated alkaline mantle fluids are carbonate rich, and fractionated into

at least two different melts during the Paleozoic, one high titanium, carbonatite type, CO2 and magnesium rich, another siliceous melt which is considered minor and poorly defined. These mantle fluids were intruded as dikes along initial fractures and faults during the structural extension phase in

late Paleozoic (Permian, 272 Ma). The CO2 rich fluids were a volatile, late stage carbon dioxide differentiate, which mixed with and was enriched with fractionated REE fluids, which then mixed with Results 35 episodes or variously timed and differently en- fluid, which would occur at these subcontinen- riched fluids in the district: one enriched in MREE tal lithospheric mantle depths. During the ascent, and one enriched in LREE. The light yellow fluorite the gaseous phase would expand and be enriched from the Klondike II Mine had the lowest concen- with REE and fluorine from the fractionated melts tration of REE (less than 1 ppm) and could have or metasomatized magmas. This gaseous phase formed from a very late-stage depleted-REE fluid would mix with MVT basinal brine fluorite to form or was lower temperature or was sourced differ- the hydrothermal mineralization. There may have ently. The high uranium content in the Joy Mine been various short-term pulses or phases of gas mi- purple fluorite suggests a fluorite source that was gration and mineralization that would not be mea- less metasomatized and fractionated than the Dav- surable by dating techniques. enport Mine purple fluorite, which was higher in The sampled Kentucky fluorites had low val- thorium, lower in uranium, and had a higher La/ ues of REE (Fig. 20) compared to other carbonatite Yb ratio, indicating LREE enrichment (Figs. 21–22). fluorite values from other parts of the world (Yang The Joy Mine fluorite had a higher Tb/Yb ratio and others, 2003; Xu and others, 2012); however, (HREE) (Fig. 21), as did Hastie Mine purple and as previously mentioned, no samples from the yellow, Eagle, and Big Four purple fluorites, com- Coefield Intrusive Complex were analyzed.- Con pared to Davenport purple fluorite. No fluorites firming the lack of a carbonatite influence are the from the Coefield Intrusive Complex were sampled yttrium and ytterbium concentrations in fluorite during this study, because sampling and elemental (Fig. 23); however, crustal sourcing from delami- analysis had already been conducted. Higher REE nation might influence some of the yttrium- con values in fluorite might be expected near or within centrations. The Joy Mine fluorite had the most the complex area. enriched REE (with a europium anomaly) and also The genetic origin of fluorite is the subject of were high in barium and strontium; these values much debate (Möller and others, 1998; Xu and oth- plot in the MVT field, suggesting mantle mixing ers, 2012; Makin and others, 2014). High-temper- with crustal material. The Davenport fluorite has ature fluids generally are more enriched in LREE an LREE carbonatite signature but also plots in the than lower-temperature fluids and will show a MVT field; duplicate samples are needed before negative europium anomaly; lower-temperature any definitive conclusions can be drawn. The Dav- fluids are depleted in LREE and show a positive enport and Joy Mines have higher ytterbium con- europium anomaly, according to Möller and others centrations than other fluorites in the district, but (1998). Möller and others (1998) used Tb/Ca ratios concentrations are still low compared with other to determine genetic origins, but the analytical lim- carbonatite fluorite (Möller and others, 1998), such its of detection in this study required Y/Yb ratios as at Mato Preto, Brazil (Santos and others, 1996). to be used, as a better estimate of genetic origin. Further analysis and paragenetic studies could de- An origin from either carbonatite fluids or MVT lineate which fluid types were the primary genetic fluids can be estimated from Y/Yb ratios (Fig. 23) carriers of REE. and using the techniques of Makin and others Assuming a carbonatite origin, a carbonatite (2014). The raw-data ratios of Y/Yb for several dike and carbonatite fluorite should have similar samples—the Davenport, Joy, and Hastie fluorites REE signatures because of their similar genetic ori- (Fig. 23)—indicated that most values were fully in gins. Fluorite from the Davenport Mine is LREE the MVT range. Variations in trace elements may enriched and is comparable to concentrations from be the result of disparate origins of fluorine, or the Davidson Midway and Cardin dikes, which are variously timed enrichments, depending on the near the Davenport Mine fluorite. The enrichment, original supply of fluorine in this complex system. indicated by steep negative slope in plots of LREE For example, during the ascent of upwelling car- concentration from the dikes near the Davenport bonatite-type magma, a gaseous CO2-fluid phase fluorite mine (Figs. 12, 20–21), show that both dike would exsolve from a parent magma (Plumlee and fluorite compositions are enriched in LREE. and others, 1995). This fluid phase would have to The Joy fluorite has high MREE values, however, be from a dense, high-pressure, supercritical CO2 and the Hampton Joy dike contains somewhat of 36 Conclusions a moderate carbonatite-type enrichment in LREE. Conclusions These data indicate that the partitioning and frac- During initial Precambrian continental rift- tionation of REE in the Davenport fluorite had to ing, mantle upwelling, carbonatite metasomatism, have occurred prior to mineralization and that and magmatic intrusions occurred along basement the Davenport fluorite might be closely associated faults near the subcontinental lithospheric mantle with carbonatite. of the New Madrid Rift Zone. This mantle upwell- Based on fluorite paragenesis of ore-stage ing introduced mafic and ultramafic plutons into fluorite from the Western Kentucky Fluorspar Dis- the rift complex, but upward mobility of the mag- trict, Hayes and Anderson (1992) suggested that ma melts stalled because of crustal lithostatic pres- there may be several stages of fluorite mineraliza- sures above the subcontinental lithospheric mantle. tion. Variant fluorine fluids, thermal influences, or Sublithospheric delamination of the crustal materi- remobilization of fluorite may cause these stages. als may have contaminated the mantle melts dur- Based on the REE analysis in this study, thermal ing structural uplift. The enriched REE and variant influences may have created an early-stage, high- elemental chemistry of the dikes in this study sug- temperature, LREE-enriched, dark-colored fluorite gest the petrology of the melts was differentiated with a negative europium anomaly (Davenport and metasomatized by the stalled mantle melts in Mine fluorite) and a later stage, MVT ore-stage, the early Paleozoic. These partially differentiated paragenetically correlatable phase, slightly en- alkaline mantle fluids are carbonate-rich and frac- riched in MREE, with a positive europium anoma- tionated into at least two different melts during ly, with both yellow and purple coloration, which the Paleozoic: one high-titanium, carbonatite-type, would include fluorites from the Joy and Hastie CO2- and magnesium-rich, and another siliceous Mines. Based on the rare-element fluorite mineral- melt that is considered minor and poorly defined. ogy in dikes, other elements besides calcium were These mantle fluids were intruded as dikes along abundant in the melt, which allowed other types initial fractures and faults during the structural of unusual fluorites to precipitate, such as sodium, extension phase in the late Paleozoic (Permian Pe- cadmium, yttrium, and REE fluorides. These ele- riod, 272 Ma). The CO2-rich fluids were a volatile, ments were available and sourced from MVT flu- late-stage carbon dioxide differentiate that mixed ids and fractionated melts, either during fraction- with and were enriched with fractionated REE flu- ation or metasomatism or during hydrothermal ids, and then mixed with MVT basinal brine fluids reactions. As these fluids began to ascend with the to form the concentric zonation pattern of the al- CO2 fluid degassing, there was mixing with the tered dike-mineral sequence. Most of the fraction- various fluids, which lowered the temperature of ation of the REE component occurred in the mantle later intrusive fluids. The fact that only some dikes during mantle upwelling, and was brought to the were altered and mineralized with MVT minerals surface via the volatile event along preferential ex- (mid-stage sphalerite) suggests two phases of ig- isting pathways in the Coefield Intrusive Complex neous intrusion fluids—an initial intrusion of the and surrounding areas. Most of the alteration of dark-colored dikes, prior to or coincident with the the dikes and mineralogy occurred during the mix- initial MVT mineralization, and a second phase of ing and ascent with CO2-rich volatile fluids during CO2-rich alteration fluids that mixed with MVT a second event, which explains why there are two fluids to create the lighter-colored dikes associated parallel dikes in many areas: one only slightly al- with reddish sphalerite mineralization. Based on tered and the other more severely altered.. The the paragenesis, the mid- to late-stage purple fluo- timeframe for two events is unclear—whether it rites would be expected to have been deposited or was one long event or two events—but isotopic altered with the second-phase fluids. Additional dating should help answer this question. After the microchemical work on these fluorites would help intrusion of massive amounts of igneous dike and explain the REE concentrations. fluorite material, the fault system collapsed, which Conclusions 37 formed many of the grabens in the district. The differences, and LREE enrichment suggest that the complexity of the district illustrates that the ther- fractionation occurred. Future work should be con- mal and mineral zonation is more complex than ducted to confirm the zoning of clinopyroxenes for earlier workers described. further clarification. In addition to the Coefield Intrusive -Com plex, another area of interest is the Caldwell Creek Dike Petrology and Mineralogy dike in southern Crittenden County. The Caldwell The mineral composition and geochemical Creek dike has the highest REE concentration an- data indicate that there are both alnöite and aillikite alyzed in the district, and its high iron, titanium, lamprophyres in the Western Kentucky Fluorspar niobium, and yttrium contents suggest extensive District, that some dikes are more evolved than metasomatic alteration of the dikes in this area, and others, and that some dikes in the Coefield Intru- are indicative of another area of potential REE con- sive Complex trend toward carbonatite and kim- centrations in the district. This study’s dataset sug- berlite (Figs. 5, 13–14). Alkaline ultramafic intru- gests that there are other thermal influences on the sive rocks in the district consist of a multi-mineral igneous and mineralization system besides Hicks suite of titanium garnets, fluorites, base metals, Dome. More work is needed on the entire district and rare mantle xenoliths. Titanium garnet, altered to find other thermal centers besides the Coefield ilmenite-magnetite oxides, niobium rutile, anatase, Intrusive Complex and the Maple Lake–Caldwell and REE-bearing perovskite have been identified. Creek dikes. These other centers disturb the re- Rare ultra-high temperature and pressure miner- gional patterns in both mineralogy and elemental als such as schorlomite, astrophyllite, wüstite, and chemistry, including the REE content. moissanite have been detected in xenoliths that Overall, the petrology, mineralogy, and el- occur in breccias, suggesting deep-mantle carbon- emental chemistry seem to confirm the evolution- atite metasomatism in a subcontinental lithospher- ary model discussed at the beginning of this report. ic mantle. Several carbonatite-type REE minerals Although a traditional carbonatite has not been ob- have been detected in this study’s small sample served on the surface, mineralogical and elemental set, and other indicator minerals such as fluoro-tet- analysis (Fig. 5) suggests that there are carbonatites raferriphlogopite, fluoro-phosphates, and sodium- in the subsurface and that they had a profound ef- and REE-bearing fluorides occur in the dikes, as do fect on the igneous dike chemistry and mineralogy titanium- and barium-rich micas. on the enriched REE in the Coefield Intrusive Com- Many of the xenoliths contain calcite, dolo- plex and upon the variant REE enrichment of fluo- mite, and magnesite, which could be igneous car- rite in the Western Kentucky Fluorspar District. The bonates; further research and isotopic dating are volatile component (carbon dioxide degassing) al- needed for confirmation. The presence of the high- tered both the igneous dikes and some of the MVT temperature silicate tridymite, unusual uranium mineralization in the district. The presence of high minerals, various metals and sulfides, chromium magnesium in the Coefield Intrusive Complex con- garnet, nickel phlogopite, barium biotite, and un- firms the alteration of the ferro-magnesium source usual carbon minerals such as moissanite is worthy melts in basement rocks and is an indicator of al- of future research. teration pathways for REE enrichment. Many of the igneous dikes in the Western Ken- Rare minerals associated with carbonatite oc- tucky Fluorspar District are carbonate- and oxide- cur in dikes in the district, and are similar to the rich, and include phosphates, magnetite, fluorite, Magnet Cove, Ark., and Aillik Bay, Labrador, Can- niobium rutile, perovskite, various titanium ox- ada, suite of minerals; enrichment in the incompat- ides, uranium-thorium oxides, fluoro-REE-bearing ible elements also suggests a carbonatite metaso- phosphates, and the base-metal-bearing minerals matic influence on the dikes. The higher titanium sphalerite, galena, native iron, and barite. The al- concentrations in some dikes suggest higher tita- teration minerals calcite, dolomite, biotite, phlogo- nium mineral concentrations or that titanium has pite, ankerite, garnet, chrysotile, lizardite, chlorite, been fractionated from europium to form the anom- and clay minerals including kaolinite, vermiculite, alies (Fig. 19). Zonation patterns (Plate 1), mineral and brucite also occur in the dikes and are common 38 Conclusions accessory minerals in carbonatites. The presence of lithofacies in the magma melts is responsible for fluorite and sphalerite in the altered dikes suggests the enriched LREE in the complex, and the variable that base-metal-rich MVT fluids and CO2-rich al- garnet chemistries might affect fractionation by alteration fluids mixed during the Permian mineral- lowing the more incompatible elements to incorpo- ization event. rate into the garnet, and would raise the Th/U and Rare minerals indicative of fractionation and Zr/Hf ratios to those found in the complex area metasomatism of REE are niobium rutile and its (Figs. 16–17, 19). polymorphs, anatase and brookite. The high nio- Certain areas of the district, such as the Coe bium in rutile and high La/Yb ratio in the Coefield field Intrusive Complex and the Lady Farmer, Intrusive Complex also suggest an overprint of Caldwell Creek, Sunderland, and Midway areas, a high level of carbonatite metasomatism on the have slightly elevated LREE concentrations. The fractionation event. The rare fluorides suggest that raw data for any REE showed concentrations be- abundant sodium, cadmium, REE, and yttrium tween 16 and 570 ppm, and the total REE concen- were available in the melt to replace calcium in the tration did not exceed 3,700 ppm for all 12 of the fluorine structure in an alkaline fluid. Fluoro-tetra- dikes analyzed. The La/Yb ratio for the Western ferriphlogopite is a rare mica, and its presence sug- Kentucky Fluorspar District varies from 10 to 70, gests an evolving magma melt. The abundance of and the carbonated high-titanium, garnet-perido- unusual garnets suggests a complex fractionation tite portion of the district (in the Coefield Intru- environment; some parts of the district are rich in sive Complex) has La/Yb ratios between 50 and calcium and titanium garnets, which may have fa- 70, which is within the range of alkaline lampro- cilitated the enrichment of the LREE. Sphalerite is phyres, carbonatites, and nepheline syenites and used as a correlation mineral to determine the tim- trends toward carbonatite and kimberlite in some ing of CO2 alteration fluid mixing with MVT miner- areas. al fluids during a mid-stage paragenetic sequence. High Ca/Al, La/Yb, Zr/Hf, and Nb/Ta ratios The abundant REE-rich perovskites/loparites sug- of some dikes clearly show an enrichment above gest enriched fractionation and emplacement in primitive mantle values and indicate a fraction- REE in a carbonatite environment. The presence of ation and metasomatic enrichment in the Coefield potassium feldspar and barium-rich mica suggests Intrusive Complex and surrounding areas (Figs. 15, that there also are other lithofacies, because of the 17). High magnesium values around the complex gradational changes of these rocks and alteration confirm earlier work on magnesium enrichment in and MVT mineralization overprint on the dikes. the Minner area (Heck and others, 2006). Scatter diagrams (Figs. 12, 14, 19) depict some late-stage car- REE Analysis in Dikes bonatite-type enrichment, but none of the analyses Plots of chondrite-normalized REE concen- in this study demonstrated any economic deposits trations for alkaline ultramafics and fluorite in the of REE; more work on remaining dikes that were Western Kentucky Fluorspar District (Figs. 12–19) not analyzed in this study is warranted. show a family of dikes that have negative slopes; The highest REE concentrations in the West- LREE enrichment in whole rocks is 100 times high- ern Kentucky Fluorspar District were at Caldwell er than for chondrite, which is indicative of par- Creek; samples from this location were very altered tial melting of the sublithospheric mantle sources. and weathered. Although the clay dike sample The linear, increasingly higher-temperature posi- from Caldwell Creek looks solid and intact, there tive trends of La/Yb versus Tb/Yb ratios and La/ may have been some enrichment by mechanical Yb versus Sm/Yb ratios in dikes in the district weathering. REE content at Caldwell Creek is the (Figs. 13–14), reaching maximum values at the Co- most enriched in the district, whereas REE values efield Intrusive Complex, Midway, and Caldwell at the nearby Maple Lake Dike are the lowest in the Creek area, indicate classic fractionation of the al- district (Fig. 12). Caldwell Creek dikes may repre- kaline ultramafic body, undersaturated with silica, sent another area similar to the Coefield Intrusive trending toward carbonatite and enrichment of Complex, which underwent carbonatite metaso- REE in the Coefield Intrusive Complex. Garnet Conclusions 39 matism; Caldwell Creek could be more enriched Carbonatite Metasomatism and than the Coefield Intrusive Complex. Incompatible Element Ratios The Caldwell Creek and Maple Lake dikes High concentrations of the incompatible ele- are the farthest from Hicks Dome and are located ments titanium, niobium, zirconium, hafnium, yt- within a mile of each other south of the Tabb Fault trium, vanadium, rubidium, uranium, thorium, System. Their close proximity to each other illus- potassium, and beryllium indicate magma melt trates a problem of two extreme REE compositional metasomatism in the mantle. These elements are variations in a small geographic area and suggests incompatible during partial melting and fraction- that there may be more than one center of thermal ation of the mantle and are usually the last to enter influence or mineralization (besides Hicks Dome) late-crystallizing phases during the evolution of a in the Western Kentucky Fluorspar District, or that magma melt. Hicks Dome fluids were established in multiple Combined results using La/Yb, Nb/Ta, Tb/ pulses: one enriched and one depleted in elements Yb, Sm/Yb, Zr/Y, Zr/Hf, Nb/Y, and Ti/Eu ra- and CO2 volatiles. The use or reuse of an estab- tios indicate fractionation and REE enrichment in lished plumbing system may still be required by the district and suggest niobium enrichment of a variant or episodic fluid movement and may help high-titanium garnet-present melt sourcing of dif- explain the variable dike chemistry in a small area. ferentiated magmas or variously timed metasoma- High LREE concentrations in the Coefield tized fluid movements. These processes influence Intrusive Complex suggest a carbonatite phase of the distribution of REE and imply that there may metasomatism, and high concentrations of HREE be higher concentrations of LREE in the district, at Caldwell Creek, Hampton Joy, Sunderland, and possibly related to fractionation of garnet-present Cardin dikes may represent overall variability and melt dikes in the central part of the district near chemistry of garnets in the magma melt. The high- the Coefield Intrusive Complex and Midway and er LREE and rare minerals at Billiton Minner, Lady Caldwell Creek areas. Farmer, and Davidson Midway dikes are the result Raw niobium concentrations range from 1 of titanium garnets in the melt, a high tempera- to 199 ppm, which suggests high-titanium, deep- ture, fractionation, volatile carbonatite metasoma- seated alkaline mantle-melt influence. Magma tism. At the lower end of the LREE spectrum is the generation in the superchondritic melt fraction- Hampton Joy dike, which has high calcium and ated the niobium to create a higher Nb/Ta ratio aluminum, and is the closest of the dikes to Hicks but lower La/Yb ratio in a superchondritic silicate Dome in this study; in contrast, the Hutson dike and carbonatite-enriched peridotite (Fig. 15) at the is farther from Hicks Dome and has high calcium Sunderland, Hutson, and Caldwell Creek areas. and low aluminum. The Hutson dike has higher The subchondritic Nb/Ta and high La/Yb ratios titanium and niobium, but slightly lower REE than in the Coefield Intrusive Complex may reflect the Hampton Joy dike. The variance in these ele- higher-temperature (or remelted) carbonatite flu- ments suggests complex fractionation and meta- ids mixing with crustal contaminated or depleted somatism, thermal effects on fluid chemistry, and metasomatic fluids. The high-titanium dikes reflect late-stage alteration events. some degree of partial melting, with high La/Yb These fluoride and carbonate melt fluids ratios (50–70) in the Coefield Intrusive Complex, also increased Tb/Yb ratios (Fig. 13), increased which represents carbonatite mantle metasoma- uranium-thorium mobility and thermal influ- tism, and produced slightly enriched LREE and ence, extracted and mobilized REE, and support depleted HREE in basement peridotite (Figs. 12– the chondrite-normalized dike signatures shown 13). Increasing niobium (Figs. 15, 18), yttrium, and in Figure 12. Fluoro-phosphates are abundant in ytterbium concentrations, and increasing Nb/Ta these dikes and probably account for most of the ratios (Fig. 17) indicate increasing differentiation uranium-thorium radionuclides, because only two of magma melts, whereas decreasing titanium and zircons and one monazite were noted in core DLP- increasing europium concentrations (Fig. 19) indi- 2, and only small amounts of monazite have been cate a late-stage differentiate enrichment in REE noted in other investigations. as the titanium elements crystallized in minerals 40 Conclusions

(schorlomite and rutile) and that a carbonate vola- others (2013), demonstrating that the perovskite tile phase mixed with peridotite dikes at the Co- partition coefficients are higher in carbonate melts efield Intrusive Complex. and that they fractionate trace elements such as zir- Because zircon crystals are more soluble in al- conium, hafnium, and REE in the carbonate melts kaline melts (Wilke and others, 2012), they would more efficiently than in silicate melts. not be expected to be identified by X-ray diffrac- The uranium decline curve and increasing tion; in fact, only two zircon crystals were noted Th/U ratio (Fig. 16) support metasomatism trend- in our extensive X-ray diffraction analysis. High ing toward a carbonatite in the Coefield Intrusive zirconium concentrations were recorded in many Complex dikes. The fractionated dikes signify a dikes, however, Zr/Y ratios (Fig. 17) are fairly con- deeper-asthenosphere fractionated and metaso- stant during fractional crystallization because of matized magma melt that also demonstrates an their similar atomic features, but this ratio varies increasing uranium/thorium thermal influence during magma melting and can be used to mea- on fluids and REE in the Coefield Intrusive Com- sure the degree of melting (Nicholson and Latin, plex. The thorium concentration at Caldwell Creek 1992). The Zr/Y ratios for the Western Kentucky is 17.5 ppm, whereas at Maple Lake it is 0.8 ppm; Fluorspar District range from 4 to 15 (Fig. 17), com- uranium values are nearly identical at Maple Lake pared to a Zr/Y chondrite ratio of 2.52; most of the (6.78 ppm) and Caldwell Creek (5.99 ppm), also Zr/Y ratios are greater than 10. Likewise, Zr/Hf suggesting a weakly defined trend toward carbon- ratios (Fig. 17) for the district range between 37 atite. and 45 and are superchondritic (greater than 37.8), Several of the Ti/Eu versus Zr/Hf ratios indicating enriched zirconium and a metasomatic shown in Figure 19, including for the Minner-4, enrichment event in the higher-temperature gar- Davidson-Midway, Cardin, and Davidson North net facies. Higher zirconium concentrations im- dikes, indicate that these were the most differenti- ply a high degree of melting and metasomatism; ated and metasomatized rocks in the samples ex- the fractionated melt trends toward a more alka- amined and the most enriched in REE that were line and carbonated peridotite melt, with higher analyzed. Carbonization of peridotite and REE REE values in the Coefield Intrusive Complex and concentration in perovskite indicate that various lower values in the peripheral zones (Fig. 17). The mineral carriers could concentrate the REE. Hamp- high yttrium concentrations (3.2–62) are evidence ton Joy, Hutson, and Sunderland dikes do not have for differentiated REE in alkaline ultramafic rocks, a significant carbonatite LREE signature, but have possibly indicating low-yttrium parent material a more uniform distribution of REE. and high-yttrium alkaline fractionated material. The lone dike that is most primitive and not Dikes in the Coefield Intrusive Complex con- highly differentiated is the one at Maple Lake in tain REE in perovskite, and, as shown in Figures 18 the southern part of Crittenden County; it confirms and 19, raw titanium values are high in some of the a primitive, porphyritic, un- or very weakly meta- dikes, ranging from 0.04 to 3.3 percent (Figs. 4, 18), somatized lamprophyre mantle dike with low Zr/ and many dikes contain visible rutile. The normal- Hf, Nb/Ta, and La/Yb ratios (Figs. 17–19). The ized Ti/Eu ratios range from 2,824 to 10,967, and Caldwell Creek dike is almost the opposite of the the enrichment of europium during differentiation Maple Lake dike, in that it has the highest REE, ti- is indicated by the data shown in Figure 19. The Ti/ tanium, niobium, zirconium, and yttrium concen- Eu diagram (Fig. 19) shows the variable influence trations in the sample set and the highest La/Yb of garnet content in the melt or increased fraction- ratio (Figs. 12, 18). These two dikes, located with- ation-differentiation of carbonate and silicate mag- in a short distance of each other, could provide a mas, where the carbonate magma trends toward snapshot and explain the complex relationship carbonatite and has lower Ti/Eu ratios (higher between fractionation, metasomatism, and evolu-

REE). The higher-REE perovskites in the Coefield tion of CO2 fluids that have intruded the district. Intrusive Complex are examples of a carbonatite Caldwell Creek is also a potential data point for mineral phase that fractionates REE. Results from another REE anomaly in the southern part of the this study confirm experimental work by Beyer and district, with increased lanthanum, ytterbium, ti- Conclusions 41 tanium, niobium, and thorium concentrations. In falling within the MVT category. Ratios of Y/Yb contrast, the Maple Lake dike is a depleted primi- are used to measure the origin of fluorite (Makin tive mantle, perhaps suggesting two generations and others, 2014) and suggest a genetic MVT and of intrusions that are using the same plumbing hydrothermal origin for most of the fluorite in this systems. The Caldwell Creek dike is near the Tabb study. A low Y/Yb ratio falls into the MVT genetic Fault System, which has produced about 70 per- category (Fig. 23), which conflicts with some of the cent of the fluorite mined in the Western Kentucky REE carbonatite signature data. The MREE enrich- Fluorspar District; much more work is needed to ment (Fig. 21) in the Joy purple fluorite suggests further understand the type of magma melts and hydrothermal sourcing; it is not a typical carbon- metasomatism in this area. atite fluorite LREE signature—most carbonatite The trace and incompatible-element ratios fluorite contains significant enrichment of the LREE suggest that a primary district-wide fractionation- fraction. The Y/Yb ratio indicating genetic origin metasomatic event focused CO2 and high-tempera- (Fig. 23) shows that the Joy fluorite plots closest ture fluids toward the Coefield Intrusive Complex to the carbonatite category, however. Because of and possibly other areas such as Caldwell Creek. barium, strontium, and REE’s similar ionic val- The fractionated alkali-rich melt would have crys- ues, high concentrations of barium and strontium tallized slowly, causing enrichment of the La/Yb (greater than 5,000 ppm) in the Joy Mine fluorite portion of the REE, whereas the higher-tempera- may have influenced this fluorite’s REE signature ture, more volatile metasomatic event would have by displacing some of the REE elements. caused enriched La/Yb, Zr/Hf, Ti/Eu, and Nb/Ti The plot of U/Th ratio in fluorite (Fig. 22) sug- ratios (Figs. 17, 19). gests a diverse enrichment in two distinct uranium and thorium sources in fluorite at the Joy and Dav- REE in MVT-Stage Fluorite enport Mines and may suggest silicate-carbonatite REE in the MVT-stage fluorite are only slight- fractionation in the presence of garnet. These dif- ly enriched with LREE and MREE (Fig. 20). Based ferent fluorites suggest that the Davenport fluorite, on the uniform distribution of REE in fluorite, the with its high thorium concentration and La/Yb ra- REE is assumed to be within the crystal structure tio, was sourced from a carbonatite melt whereas of the fluorite and not as microscopic inclusions the Joy fluorite, with its high uranium concentra- within the fluorite. One fluorite sample from the tion, might be sourced from more of a silicate fluid. Davenport Mine is enriched in LREE (Fig. 20); the Conflicts in fluorite genetic sourcing may be other, a Joy Mine fluorite sample, is enriched in the result of different fluorite inclusions being ana- MREE. These two values suggest a differentiated lyzed or cross-contamination of various fluorites REE source of fluorite deposition, where early fluo- during mixing of two or three fluorine fluids, MVT rite fluids were enriched in LREE and later- fluo fluids, carbonatite, and silicate fluids during transit rite fluids were enriched in MREE. The Joy and and final deposition. A larger sample set and better Davenport Mine dark purple fluorites have the analytical capabilities would be of great value for highest REE concentrations in the fluorite samples future research. analyzed for this study (Fig. 21). Based on thermal All raw-data concentrations for REE in fluorite influence on fluorite deposition ö(M ller and others, were under 15 ppm and total REE did not exceed 1998), the Davenport fluorite would be high-tem- 31 ppm. Purple fluorite has higher REE values than perature and have a carbonatite LREE signature yellow fluorite (Fig. 21). Trace-mineral concentra- whereas the Joy would be a later-stage, cooler-tem- tions, including REE, seem to decrease in abun- perature fluorite depleted in LREE and enriched in dance away from Hicks Dome, except around the MREE. The oxidizing effect of CO -rich fluids may 2 Coefield Intrusive Complex, which has a hetero- have lowered the fluid temperature and influenced geneous melt of enriched REE. Generally, across the later Joy fluorite composition. the district, large-scale vertical and horizontal pat- Several of the purple and yellow fluorites fall terns of MVT-stage hydrothermal fluid movement into the MVT or hydrothermal category (Fig. 23). that mixed with igneous-dike alteration fluids is Use of the Y/Yb ratio results in most of the data evidenced by the variation in content of sphalerite 42 Acknowledgments and REE in fluorite. Limited fluorite samples were Appreciation is also extended to Jason Back- analyzed during this preliminary study, and no us, KGS laboratory manager, for his assistance fluorite samples from near the Coefield Intrusive in sample preparation, thoughtful discussion on Complex, but current data suggest that the hydro- preparation and analytical techniques, and super- thermal origin of the fluorite is responsible for the vision of much of the analysis; to SGS Laboratories low REE concentrations compared to typical car- of Canada for final analytical work; and to Thomas bonatite REE concentrations. Brackman, director of the geophysical laboratory at Northern Kentucky University, for use of their Acknowledgments scanning electron microscope. I would like to thank the many people who Thanks also go to other KGS colleagues: Bran- assisted in this investigation by providing mine don Nuttall, for help with ternary diagrams; Terry access, samples, analysis, or thoughtful discussion Hounshell, for cartographic work on maps and and reviews of this manuscript. Special apprecia- diagrams; Scott Waninger and Richard Smath for tion is extended to Robert Trace, whose field and field work, sample collection, scanning, -and da mine notes and guardianship of cores and igneous tabase work; and Tom Sparks, for assistance with dike samples have provided a wealth of informa- creating the minerals and dike databases. tion. Thank you to mining industry profession- Special thanks go to Tim Hayes, research ge- als Don Hastie and Jim Watson of Hastie Brothers ologist and fluorite expert with the U.S. Geologi- Mining; Ryan Prosser of Rogers Group Inc.; and cal Survey, and Craig Dietsch, igneous petrologist William Frazier, Boyce Moody, and Buddy David- and associate professor of geology at the Univer- son for access to mines, data, and cores. sity of Cincinnati, for their thorough reviews of Finally, students Jason Heck, using the UK the manuscript and insightful discussion. I thank scanning electron microscope microprobe; Han- Brett Denny, research geologist with the Illinois nah Utterback, using the Northern Kentucky Uni- State Geological Survey, and Kentucky Geological versity scanning electron microscope; and Jerrad Survey colleagues Matt Massey, research geologist Grider at UK also contributed to this project, as did and igneous petrologist; Meg Smath, editor; David David Moecher, chair of the Department of Earth Harris, head of the Energy and Minerals Section; and Environmental Sciences at UK, who discussed and Jerry Weisenfluh, interim director, for their the manuscript with me and allowed the use of the kind and thoughtful reviews and considerable pa- department’s scanning electron microscope micro- tience in helping develop this manuscript. probe. References Cited 43

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Samples of altered and unaltered intrusive dikes Top row, altered, from left to right: • Hutson Mine mica peridotite, BH-7_74, pebble breccia • Hutson Mine mica peridotite, BH-7_125, altered • Midway (Davidson dike), T-9-76, porphyritic, altered • Sunderland lamprophyre, T-5-76, altered • Little Hurricane lamprophyre, 597-V, altered Bottom row, unaltered, from left to right: • Hutson Mine shaft mica peridotite, T-10-76 • Stout lamprophyre, T-8-76 • Minner alnöite, BMN-4 • Guilless Mine lamprophyre, T-1-76 • Clay Lick East mica peridotite, T-1136