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May 27, 1968 PREFACE

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May 27, 1968 PREFACE A srr lDY OF 'T'H ~ KI11JfBERLirr1E IN ELLIO't'rn CCU TY, K~ 1 TJCKY Frank H. Fowler Geology 570 May 27, 1968 PREFACE This paper i s pr sented as a fulfillment of the requirement for Geology 570, the Senoir Thesis. This investigation was suggested by my thesis advisor, Dr. c. H. Shultz, who mad possible the actual fi ld study of t he outcrop. The kimberlite outcrop was visited in December, 1967 and subsequent library and laboratory study was conducted during the Wi nter and Spring quarters 1968. Dr. Shultz also provided thin sections of the rock samples collected at , h site, and provided access to photomicrograph equipment. His advice and introduction to references was also greatly appreciated. Dr . Faure supervised the X- ray i nvestigations. i i CONTENTS ABSTRAC'r • • • • • • page 1 INTRODUCTION • 2 Location and History GENERAL GIDLOGY • 3 l'utroduoticn Stratigraphy Structure PETROGYDY • • • • • • • • • • • 4 Outcrop Hand Specimen Thin Section Hea.vy Mineral Concentrate Ca.lculat d Chemical Analyses DISCUSSION • .. • ·• • • • • • • • • • 12 Relation to Regional Occurrences of Si milar Intrusives Comparison with Kimberlites of Siberia and South Africa Method Q~ Intrusion Garnet and Olivine Evidence for Formation of Kimberlite Magma and its Condition Upon Intrusion CONCLUSIONS • •· . • • • • • • • • • • • 16 REFERENCES CITED • • . • • • • • • • • • • • • 17 iii Figures Plate, 1, tipre. l • • • Sketch map ct llli.·o'tt OolUt-· lentucq, showing relative position of kim\erlit• (l!Od.iti•d trom Koenig 1'9'6'). Plat.• l; ftll:r 1 2 , • • Kap ·ahow.f.ng outero.pa -&ltd pattem &f kim'b,erlit.e Pla.te ! , Pipre l • • • heah eur~aoe o - kimber11ie "har4ba.llk·8 with i1 ·estone and shale inclusion. Plate . ~ . i'ipre 1 • • • Photomi.cropapb or general s•oti:Qtl or k'imberl:lte sho-S.:". ·. large r.otnlded. oliv:ine, and nall .e\ihe4ral olivine -80 ·,,· . ~ : e,,- opaque ilmenite., map.et!t• t and perovl4d. te in matrix of serpent'.in• ani ca~bonate . • • Phc»tomicrograpll ef :perovslcite alteratien rim u-ouad ilmenite, .s.erpentiit:iaat!.on. of oliv.lne, and mapt1-te in gro-UJ!ldmass of serpentin.e and carbonate. Plat• 4, ·· pre l • • • Photonricro,graph :slloWitlg •BA17 f~actt;tre pattern of' large ilmenite phene,c17sts. Plate: 4, rtp.r·• 2 ,. • • Photo 1orograJ'h &t kel.,.Phitio reaction rim around pnet, with .· gnetite' :in se~eatine and carbonate e;n>udmass,. I.B4u of i•f"ract1o:n ttt Ga.set , Arraage4 tn'\e Groups Acu»rtilt• -..o· Coler. '!'-&ale l • .,, . Chemioal. AJtalyses af lim'berlites •. • • • • • 11 iv The El,lio·'tt County di tremes are basal tic kimberlites occurring a radially arranged groups of apophysis type intrusions centering around large eutc~p ·o.i1 Hamilton Creek. An explos.i ve :fluidization intrusion of a gas.-aolid irlure is indicated by the lack of stnotural d.ef'oJ'fb:tion and contact eta.morphism of the country rock. TThe outcrops have identical mineralogy 'but vary in percent composition of inerals and inclusions because of ditterenoes in the degree o·f alteration, intrusive oonditions, a.nd stratigr&plly ·o.f the country rock. In·clusions of probable upper mantle material, Precambrian basement material, and local •11 rock occur indtH3&ting the probable souroe of the kimberli te as the upper mantle. The rela.tionshi . bet een garnet color and pyrope content is apparently a result of one color being the first melted fraction of the upper mantle While t he other is _the residual garnet caught up by the magma as it i ntruded. Olivine phenoor7sts are of· two ages indicating a pa.use in the intrusive a quence which could, according to Bard t (1965); account for the abseno• of diamond. The 269 m. y . age (Zartman, et al. 19'67) of - .,...._. th~s intrusion corresponds to that of the ultrabasic mica-peridotites of the Kentuelt7-Illinois fluoFspar district. Both lie on one of several deep crtt.eta.1 fa-.ilt zones of the east.em. United St.ates eraton along which intrusion a.ppar.ently took place at various tiJJtes throughout Paleozoic and Mesozoic time. 1 . 2. INTRODUCTION The kimb rlites of Elliott County wer the first igneous rocks diseovered in Kentucky. A. R. Crandall of the Kentucky Geological Survey found the intrusives in the valley of Ison Creek around 1881. J . S. Diller, also of the Kentucky Geologic Survey, was told of the outcrop and published sever&l reports of his investigat~ons of it before 1900. Later, Crandall (1910) described this intrusive as a "crater-like dike" with arms radiating north, est, and · southwest from the main body. Diller referred to the rock as a peridotit e until Lewis (1888) coined the term "kimberlite• 1 for the d.iamantiferous plugs of 'the Kimberley area of South Africa to which. these rocks are nearly identical. A kimberlite, as defined by Lewis, is a porphyritic peridotite comp0ssed essentially of olivine and its alt eration products. In addition, J1hl ;gopite, ilm.en .te, pyrope, diamond , perovskite, and other minerals re present in var,ing amounts. Chemically, kimberlit s are oharact r i z d by lo Si02 and Al203 content, high. gO , fairly high Ti02 and C02, pres ne of P205, and AI2o3 greater than K20 and Na.20 combined. Kimberlite therefore is a notably magnesium-rich ultrabasic rook• The o•terop being studied is located in northeastern Kentuoky in Elliott County. ore :precisely, it occupies the southwest corner of the south est 1/9 of t he Willard geologic quadra.ngl , 83°00' west longitude- 38°07' 30" north latitude (Plate 1, Fig. 1) . Exposures sporadically dot the ridg b tween Ison Creek and Hamilton (Hambleton) Creek for about a mile east of the Ison- Johnson School ( Plate 1 , Fig. 2) . Wi t hin the last few years drilling has be· n done at the largest out crop, labeled "mine" {Plate 1 , Fig. 2) , to determinepossible economic value of t he rook, but although there is a continuing a.ttemp't to promote a mining op ration, nothing of outst anding economic i mportance seems to have been fotind. Recently a magnetic survey was conducted i n an attempt to establi.sh th otual ext nt and form of the i ntntsions. This paper is a petregra io study of this group of intrusives to gain additional infor.rnation concerning the origin a.nd manner of implacement of this kimberlite in pa.rtiottlar and o:f all kimberlites in general. Plate 1 co. ROWAN /' I ,..J ,nr' / ,,/ ~ ~ , ,) I ' I I ~ r- '"""'\ , MORGAN CO. ~ , , .. _ ,..r--._ .... r\."-,v-'( LAWRENCE CO. 1----------, \ _....,..__ ___ '- I .... ...__, LEGEND \ 1 .......... ) I Figure 1 Sketch map of Elliott County, Kentucky, showing relative position of kimberlite (modified from Koenig 1956). 3~ 0 01'30" --~·~~~~~M~~it);),~~~~~~~~~~-:-- rsoNV.,,,e QtAacl . Figure 2 Map showing outcrops and pattern of kimberlite in area between Ison Creek and Hamilton Creek. 0 I MILE GENERALE GEOLOGYE Introduction Elliott County is characterized by steep hills forming even-crested ridges which are separated by narrow alluviated stream valleys. The topography is mature with average elevation between 700 and 1100 feet. Limited farming and grazing is done in the larger valleys, while the streams cutting the ridges are narrow and deep. t Stratig raphy The region is underlain by a sequence of nearly flat lying Middle Pennsylvanian beds of the upper half of the Breathitt Formation. This consists of a typicalp coal measure sequence predominantly of sandstones, witht interbedded siltstones,t shales, thin coal beds with underclay and limest ones. Sandstone members of this formation cap the hills accounting for the even-crested ridges of the area. The region is a part of the Allegheny Plateau physiographic province • • Structure Elliott County is located on the west flank of the Parkersburg Synclinorium. Regional dip is to the south and southeast at a very small angle. The dip is reversed locally by faults, small domes and basins associated with the regional structure.r The intrusives are on the upthrown side of the, Little Sandy Fault, a high angle normal fault extending east-west for about 12 miles, located one mile south of the outcrop area. This fault is part of the more extensive Rough Creek­ Kentucky River fault zone which connects the Elliott County diatremes with the mica-peridotites of the western Kentucky-southern Illinois fluorspar district. K~Ar and Rb-SrS dating (Zartman,,!i !!.• 1967) shows these two intrusive complexes to be of similar age, around 269 m.y., Late i Pennsylvanian-Early Permian. TThe EElliott County diatremes show no obvious ·relation to the faults in the area except possibly as pre-existing subsurface zones of weakness along which intrusion took place. Evidence of minor doming or fracturing in the immediate vicinity of the intrusions is very slight or entirelyt lacking. 4. PE'l.'ROGRAPHY Outcrop The kimberlite bodies are best exposed in and on the banks of steep stream valleys. The most obvious exposure is 0. 25 mile south of the Ison- Johnson School. This is a r ough ridge of nhardbank" on the west facing bank of the str eam. On the opposite bank, erosion is less rapid and the outcrop consi sts of "yellow- ground" with residual grains pf garnet and ilmenite scattered through the soi l . Additional outcrops were difficult to locate due to their smal l size, apparently radial distribution, and r esidu l seil cover. Although the rook appears in hand sample to be r elatively resistant, it act ually weathers at about the same rate as the country rook. his inhibits recognition of additional exposures or tracing existing ones topographically. The local extent, identical mi neralogy, and roughly radial outcrop pattern of the& small isolated outcr ops i ndicate that they may be part of the same in· rusi on at depth.
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