l.'· .'· / ll. fof\1~ AEC-RD-10 UNITED STATES ATOMIC .ENERGY COMMISSION "l GHAND JUNCTION OFFICE
HESOURCE DIVISION l GEOLOGIC BRANCH l J OPEN FILE J J MAY 2 5 1971 A GEOLOGIC ST1J1JY OF URANI\J!>! m:SOlifc~E:S IN PRECAMBRIAN ROCKS j OF THE WESTERN UNITED STATES
J Distribution of Uranium and Thorium in Precambrian Rocks of the Western Great Lakes Region J by ] Roger C. Malan and David A. Sterling J J J ] ] J July 1969
J Grand .)'unction, Colore.do J ''~L'c: ;";~·ill ·,·:·.;; r:r';·:ro·J ~.;,;'I~ :l({'(':ilrl! r,l \'."'1111 spnmwrd hy 1~1C Un:lr< ~::.11;':; l;c;·n;;~i'ICnl. flr.i!I!Gr :;,:! :: .. ii.;,l ;;:::t.'.; ;;, r :; [;:Ji[:',J ;:L,;r_; ;\!,ln:ir. Cnu:.r C::;r;II1L$'1:(;n, nnr ~r.y r1J lil,·il rn:nL;Y8'~:i, r:nr :1ny nl :Ui c:Jn!rJ(:,!:~. f.t.l'':i:;.,;.-:.•... ,: .. r·r 11~,:;; ~~··;·l''>'~t'':l. rrrJii .. ~ ar.y w.\rr~r.ty, llx~u;,:·.; err irllphc:l, (lf J D~~n::1c:: '·"1 ),~.:::;1 li::iJ:Liy t'•r re:.pt1!1~.ii•i:l:y ICir ti.(! i':'ii•r;:~v. e,'mp'e[,~rw::s nr r:~··f::lr:,·:.~ ul .l:;y inlor· n,:1!illi1 ,'i'~,Jrttill.:., piotll!<:t or prot:n$:: dJ:>r:losec, or rcpe:>vi\l~ th:~t ~~~ us(: woullf ll'.lt iJ,Irirl!;~ prlv::tciy j U':dwd 11;::1tS." ; '
DISTRIBUTION OF UPJI.NiliM Al'ID THOlliUM IN PRECAMBRIAN ROCKS OF THE WESTERN GHEAT LAKES REGION ] ' ,-l TABLE OF CONTENTS i ] Page ,- ABSTRACT •. 1 1 J INTRODUCTION 2 i Previous Uranium Investigations 2 J Current Uranium Exploration Situation 2 ; PRECJI.MBRIAN GEOCHRONOLOGY OF THE WESTERN GREAT LAKES 4 J' SUJ.1NARY OF PHECAMBRIAN NETALLOGENESIS, GREAT LAKES REGION 9
DISTRIBUTION OF URANIUM AND THORIUM '3 ll Radioactive Granitic Rocks ll
~ Veins in Slate ll J Monazite Placers I 13 l Uranium in Iron Formations 13 Thoriferous Hyperalkalic Complexes 13
J Keweenawan Felsite Dikes 13
] .uraniferous ~artz Pebble Conglomerate 13 Cambrian Franconia Formation 14
J Formational Background Level& 14 J UHAl'IIUM RESOURCE OUTLOOK 16 Animikie. Series 16
J Granitic Rocks 21 J Sioux ~artzite 21 CONCLUSIONS .•.•.•.•.•.•.•.•.• 22
J REFERENCES • • • 23 J i. J J u.·: • > ,J LIST OF ILLUSTRATIONS J
J Figure l Index Map - Precambrian Study . • • • • 3 Figure 2 Generalized Geologic and Geochronologic Map of J the Precambri,m, Western Great Lakes Region •• 5 Figure 3 Generalized Lower and Middle Precambrian Paleo ] geologic and Metallogenetic Map, Southern Canadian Shield. • • . . . • • • . • . • • • • • 10 J J
J LIST OF TABLES
Table 1 Generalized Correlations of Precambrian Strati J graphic Units Referred to in Text .••••.• 6 ] Table 2 Uranium and Thorium Occurrences in the Western Great Lakes Region • • . . • • . 12
Table 3 Distribution of Uranium and Thorium in Selected J Precambrian Lithic Units, \ole stern Great Lakes
Region ...... a o • • • • b • • • • • 15 J Table 4 Comparison of Thorium and Urariium Contents of l Huronian and Animikie Strata • . • • • • • • 18 J J J J J
J ii. J J J .. ] AEC-RD-10 A GEOlOGIC ST\IDY OJ' 1,iRAl'Hill~ RESOURCES IN PRECAMBRIAN ROCKS J OJ' THE WESTEr& illfiTED STATES .
Distribution of Uranium and Thorium in Precambrian Rocks J of the 1Vestern Great Lakes Region
J by J Roger C. Malan and David A. Sterling J J -----ABSTRACT Private prospecting and investigations by the U. S. Atomic Energy Com mission during the 1950's resulted in the discovery of several uranium J and thorium prospects in Precambrian rocks in the western Great Lakes region of the United States. In \visconsin and in upper Michigan, · ] Lo>rer, Middle, and Upper Precambrian silicic and hyperalkaliccpluton·ic rocks contain anomalous amounts of disseminated radioactive minerals. In upper Michigan, Middle Precambrian metasediments of the Animikie ] Series contain uranium veins in slate, monazite placers in conglomerate and irregular concentrations of ·uranium in iron formation adjacent to slate. l 1Vhile none of these prospects contain reserves that are economically mineable at present, some may contain important.~ong range, low grade resources of thorium and uranium. For example, 'limited sampling J indicates that masses of silicic igneous rocks in northeastern 1Vis consin may contain 50 to 100 parts per million U308. This is greater than the uranium content in any of about 250 bulk ·samples of Ijre J cambrian igneous rocks from the 1Vestern United States that have been analyzed in this pPoje~t.
J A potentially great resource of thorium may exist in the monazite placers in conglomerates of the Goodrich Quartzite (Animikie Series) near Palmer in upper Michigan, but the uranium content is very low. J Anomalous amounts of uranium in sparse outcrops of other conglomeratic quartzites of the Animikie warrant additional study, but extensive J till cover precludes systematic sampling. · J J
J - l - J l J' . •. ·~ ------INTRODUCTION :] Previous Uranium Investigations Initial investigations for uranium in the extensive Precambrian terrane in the ;restern Great Lak.os region (fig. 1) ;rere carried out by the Jones l and Laughlin Ore Company under contract with the U. S. Atomic Energy Conunission from April 30,. 1951 through June 30, 1953. L. P. Barrett ] was the senior investigator under this contract. Investigations were continued directly by the U. S. Atomic Energy Commission through the Ishpeming, Michigan Sub-Office of the Division of Raw Materials under 0 the direction of L. P. Barrett from 1953 to 1958. The investigations by the U. S. Atomic Energy Commission in the western ] Great Lruces during the 1950's included examinations of numerous radio active occurrences, a1.rborne and ground radiometric reconnaissance of favorable lithologic units, hydrogeochemical reconnaissance and elec J trical and seismic geophysical surveys (Illsley, 1958; Kinnaman, et al., w-ritten communication, 1958; Smith and Fickel, ~rritten communication, 1957). Superior Oil Company and the U. S. Geological Survey (Stead, J et al., 1950) did extensive airborne radiometric reconnaissance. Superior Oil and many individuals and small groups also did consi-derable ground radiometric prospecting. Shallow drilling and dozing were done J at a few selected prospects by pri-vate interests, but no economically exploitable uranium deposits were discovered.· J Current Uranium Exploration Situation One. two-week field trip was.made to the western Great Lakes region in J September 1967 for the following purposes: l. Assess the level of uranium prospecting and exploration J effort in that region. 2. Ex,amine the most significant prospects that were discovered J during the acti-vity of the 1950's. 3. Collect bulk samples of selected lithic units for establishing J background U and Th. 4. Compare geologic emrironments in the Precambrian of the J western Great Lrutes region with environments in the uranium districts in Canada.
] The western Great Lakes region of the United States has attracted very little attention during the current uranium exploration boom. Kerr McGee Corporation has made a few brief reconnaissance examinations J through its Toronto, Ontario office; in 1967, they ai:!quired a state lease on the quartz-calcite-pitchblende vein prospect in the Michiga~e Slate Formation of the Middle Precambrian P~imikie Series on Green's ] Creek ncar Palmer, Michigfu,, about 15 miles southwest of Marquette , '. )' . J - 2 - J ] L__ L__ L__j l_j Ll.J L__j L..Jj L_j L_j L_j L_j :.....:._] L_j L_j L..J :....:.:....J L_j L_____j L_____j . .__ 1 i.--
I ) . "'I .r· 'bD s t9 ~. f
lnekx Mop· Precornbrion S1udy riillJ RD-9 ~ RD-10 Q RD-11
Figure I. Distribution of Precambrian Rocks in the Western United Slates 'J' .·. '-I In 1'l68 ~ · rt locr::.l g:::-·c.)UP, th~_~ Hard.1-rood Mining Company, Hardwood, Michigan, acquired a sLate leas~:; on the o1d Felch pl~ospect, alias Isham prospect, ] nbod lf5 miles soutlw·cst. of Marquette. R. C. Vickers (1953) collected sari"1plcs at this prospect from ;.j, .radiometrically anomalous biotite schist xen~lith in r.· -·"de granite tl1at contained O.Ol
j PRECA!\1BRI/\N GEOCHRONOIO:.:;y OF THE ViESTERL"T GREAT LAKES
Figure 2 is a generalized geologic and geochronologic map of the Pre- J . camorian of the western Great L-akes region that was constructed from compilations by Goldich, et al. (1961) and Bayley a.-od Muehlberger (1968). The geology of this region he.s been studied by scores of investigators J during the past J.OO yea.rs particularly in the areas of the Middle Pre cambrian sedimentc-.r.-y· iron for.uat.ions of Michigan, Minnesota, and Wisconsin and in the UPP''r Precambri •' • I 0 J 0[][][l~[J000[J ~ .... , ~ "'''~~rll 14 0 J •! -~ •. ~· ;f•• .0 :n ~ ~i ,, ~ .. ''.! ; 0 J 0 D ; .~ J l .. 0 ·~ ~. 0 0 u 0 ~ t J 3: n ~ ... 0 J , ~ __ 0 I ~ ] ' ~ / "n 0 (' 0 ~ 0 J / 0 ----~ ' " ~ J ~ ~· " ] N ., 0 J i;: J --,.. ~ r ·------"" ' '\._/ ' -~---~- --- , 0 J . ~ 1 no 0 0 ~ ~ : 2"- 0 , " 0 g 0 ~ 0 TABLE 1. GENERALIZED CORRELATIONS OF PRECAMBRIAN STRATIGRAPHIC UNITS REFERRED TO IN TE',(T UNITED STATES CANADA .---,---Age_ I Minnesota Hisconsin-Nichi~e-~~ r IElliot Lpe' ~~:;:~;-l 1.1 b.y. Duluth Gabbro I i Keweenawan·Series · Nonesuch Shale H Portage Lake Lava Series QJ §"' Sioux Quartzite 1.4 b.y. Elson ian Orogeny •M 1.7 b.y. Penokean IOrogeny ~"' I Hudsonian Orogeny I ~~ I s:: Animikie Series Animikie Series (Marquette Range, Mi·~h.) $1 ol I •.-i Michigamme Slate H Upper ~I I .g Goodrich Quartzite ol rl I "'QJ liD,; Negaunee Iron Formation Huronian Series H p., ~ Middle S iamo SJ.a te :;;: Ajibik Quartzite Cobalt Group -- Lorra.in Formation Wewe Slate I Lcwer Kona Dolomite Bruce Group I Mesnard Quartzite Ten Mile Formation 1 j Matinenda Formation I 2.5 b.y. Algoman brogeny r---1 Kenoran Orogeny Knife Lake Group s:: H al QJ .s:: Laurentian Orogeny ~ Ji!"' Keewatin Group ·-J . ' 'Jc . .. 'I 'rhe olde;:;t expo;seJ roch:s :l.n th.?- ·1·rcstern Gr2at. Lakt~S region are basic volcnn:Lcs and sediments m~Ltnro.rphoced to grc.:..:r.;stone and metasediments of the Kc>Jt·:at:Ln Groupo l_l'h8 IC~~etv2.tin ~·rts affected by foldin~ and minor ] plutonism durine; the poo1·l.y def:i.necL, unr•"li.D.bly d'ltcd Ia.u:centian orogeny more than 2.5 b.y. ac,o. Msta.;:;edimcnts of the Knife Lake Group ;lith a minim1im ac;~ of' 2.5 b .y .. unconform"'bly overlie the Ke ] The boundary between the low-8r and Middle Precambrian is defined by the great Algoman orogeny (Kenoran orogeny of the Canadian Shield) about 2.5 b. y. ago. The region that l·ras af!'ected by this orogeny is named the J Superior Province of the C&>adian Shield. Synkinematic granite and gneiss «ere generated in large areas of Minnesota and upper Michigan, and the -l Lo~ l Follol·ring the Algoman orogeny_, miogeosynclinal quartzose, argillaceous, and ferruginous sediments 10,000 to 20,000 feet thick ·and eugeosynclinal gray1mcke, chert, and _·basic volcanics of undetermined thickness were J deposited in northeast-trending geosynclines at least 300 miles wide through Minnesota, Wisconsin and upper Michigan. These sediments and volcanics comprise the A>imikie Series. The northwestern margin, based J on the present distribution of these sediments, bisected Minnesota along a northeast line (fig. 2) >rith the Algoman Mountains to the north1-rest as the provenance. Facies range from miogeosynclinal in northeastern Min J nesota to eugeosynclinal in eastern central Minnesota (Goldich, et al., 1961)·. Paleozoic cover and syntectic 1.7 b.y. old granite and gneiss obscure ·its southeastern limit, but infolded remnants of this sedimenta;r-y J sequence are distributed as far south as the Baraboo Range in south central Hisconsin. l The minimum and maximum ages of the Animikie sedimentary cycle are 1.7 and 2.5 b.y. The imprinting of the 1.7 b.y. Penokean orogeny precludes precise age dating. In southern Ontario, the Middle Precambrian sedi J mentary cycle is represented by the Huronian Seri'es which conta:i.ns higher energy sediments, in part continental. No sedimentary iron deposits J characteristic of the Middle Precambrian Animikie sedimentary cycle in J - 7 - J J J·· .. l uppe·r Michienn and Minnenota ar-:! p:r\?s.:::nt; but fluv:ial, pyritiferous, quart~". pebble conslomeratcs in the: bD-,sa.l 1-Iuronio.n in the Elliot Lake district. contain th0 ~;~rld' z larc;c,>t uran:ium deposits. The strati J c;rctphic relationship of the Animilde Series of Minnesota and upper Michic;an to the belt of Huronian sediments fr-om Sault Ste. Marie northeastt.rar(l to Sudbury and beyond is not established (James, 1958; 1 Barrett, H-ritten communication, 1956). The I During the Penol,ean orogeny (mean age - l. 7 b .y.), syntexis and meta 'l morphism affected large areas of the Animikie sediments and the subjacent Keewatin and Algoman basement complex in a w·ide belt from Marquette in upper Michigan south~ J No sedimentary record for the 1.7 to 1.4 b.y. interval exists in the western Great Lakes region. The i.4 b.y. Elsohian orogeny is reflected by scattered dates in the granitic and felsic metamorphic terrane in J central vlisconsin (fig. 2). Its northern extent in l Following the Elsonian orogeny, a record of sedimentation is preserved J in outcrops of the Sioux Quartzite 'in south>restern Minnesota and adjacent South Dakota (fig. 2). As much as 5,000 feet of predominately fine- to medium-srained, marine (?) sandstone with thin interbedded mudstone and J a thin basal quartz pebble conglomerate accumulated in an elongate westerly trending trough from southwestern Minnesota to central South Dakota. Age dating indicates folding and recrystallization to quartzite and argillite J about 1.2 b.y. ago (Goldich, et al., 1961). J J - 8 - _I l J• . ' 'l From about 1.2 to l.O b .y. ac;o as much as 30,000 feet of flood basalts (l-ihite, 1960) and 20,000 fe"t of conglomerate, shale, and sandstone accu mulated to form the Keweenm;an Series in the northeast-trending Keweenawan J trough (fit>. 2). This trough perhaps of l'ift ori&in is expressed as a south to southh·est-trending grav-ity high in the subsurface for several hundred miles beyond the southern limits of exposure in east central J Minnesota. In the Ke1veenaw Peninsula of upper Michigan, copper production through 1964· from the middl.e Kel;e.:cnawan Portage Lake Lava Series and the upperKe11eenawan Nonesuch Shale has been about 410 million tons of ore J containing about 5.9 million tons of copper (Ensign, et al., 1968; Hhite, 1968). J The Duluth Complex west of Lru'e Superior consists of great multiple gabl>roic sills that intruded the Keweena,,an Series and older units about J l.l b.y. ago. Cratonic stability and peneplanation prev-ailed from about 1.0 b.y. ago to about • 5 b .y, ago l-lhen early 'Paleozoic epicontinental seas encroached J upon part of the western Great Lakes region. J l The general distribution of major metal districts in the Lower and Middle Precambrian of the United States and Canada is sho"'n in figure 3. The region between Chibougamau on the northeast and the Cuyuna iron range J on the southwest is one of the foremo;;t metallogenic provinces in the . 11orld; the total gross value of production and reserves is in the tens of billions of dollars. lower Precambrian (Archean) metallization in :1 this province is primarily represented by base metal sulfide and by auriferous deposits in the complex of billion dollar districts between Lake Huron and Jarr~s Bay (fig 3). The two principal types of these J Lower Precambrian deposits are (1) strata-bound syngenetic (?) sulfide deposits in volcanic and sedimentary sequences that were metamorphosed during the Algoman (Kenoran) orogeny 2.5 b.y. ago and (2) structurally J discordant gold and copper bearing epigenetic deposits in igneous and metamorphic rocks of similar age (Goodwin, et aL , 1966). J Middle Precambrian (lmver ·prot.er.o?_<;>·1:c:) metallization in this province is lithophile in character and is best represented by the Elliot Lake uranium-thorium placers and the Michigan and Minnesota sedimentary iron J deposits. Late Precambrian metallization is primarily represented by magmatic J segregations (?) of copper in ba.sic flo11s of the lo1Ver Keweenawan Portage Lake Series and by stratiform disseminations of copper in the J upper Keweenawan Nonesuch Shale, all in upper Michigan (fig. 2). J J - 9 - J J LJ ___·r i_.. __ L...-..J L__...l L.....J L.__l L___.L_jL_jL.JL.JL.J~LJLJLJL_j ___j L- L- L- ~ I ~ 1-t: ~ ..,... .: ~ James Boy 0 100 200 300 miles . ~~__,...,...,.-~=-~- ....:,;;:::":,:,<· . --1 / I 1 / Hajor provenance( 2.5b.y.Superior gaoctironologic province) Q..-chi!:lou')amau of Uiddle: Precambrian Huronian and Ani~ikie sediments Q . I Motooom1 0 ? 0 Liffla l.o."''~LGC 0 / ., '1...----?. 0 Porcupine I - EXPLMi.\ TI D!l- --. 6 0 0 1 0 tO tlorar.do -o 0 0 • 0 TirruMnJ (.).: Jr::iri.lcr.d / Placer uraniur:-thnriu;;~ deposi~s in I ..,..:.,to' Lo:C., _ ' ~/ ---- 0 hip.h energy, fluvial clastics of :i.,o~ ¢ .,, o P o/ lo!iddle Preca;;;brian Huronian Series /. ...J.O~ . C-el>olt 7 o o/ = Sedir:ientary iron dep~sits in lo~ energy shelf znd niogJ:osyncl ina! / Scuff Sta · /sudbury :.c.~rie Elliot Ll:l~ll ,..-/ sediments of ~iddle PreCa~brian v\)"-,\~ ~Lo:.o Animikie Ser.ies. =~rqueUo 0 Cu-Hi rnagnatlc segregations in basic Iron River prutons of ~iddle Preca~brian. Menornin&Q Lake 0 - Huron Stratiform sulfide and iron d~posits 2nd vein Au-Cu deposits in m!ta ~orphosed Lo~er Precaahrian volc2nic and sedir.Jt!nts Of ''Greenstone Belts" -APproximate ~ean position of Widdle Precambrian continental nar2,in Figure 3. Generalized Lower and Middle Precambrian Paleogeologic and Metallogen.etic Mop, Southern Canadian Shield I .. l J Several dif:Ccrent types of uran:twn and/or thorium occurrences were dis covered during the 1950's in .~ variet-y- of' host roclts in the Precambrian of' Hisconsin and upper Mlcohigan (L. P. Barrett, writ'cen communication, J 1958). The types. and the locations of the principal occurrences are shown in table 2 and figure 2. l Radioactive Graniti'c ~££~~ l•oost of the oceurrences in Penoltenn and El.sonian granite and gneiss are l in ferromae;nesian zones hi predominately quartzose feldspathic gneiss, but a fe~< are in ma.ssive phases of coarse grnnite. The strongest anomaly of this type is on the Anklsm farm near Big }'alls about 20 miles north J northeast from Waupaca, Wisconsin (fig. 2) (King, 1960). Sparse amounts of fluorite, pyriteS> magnetite_, ilmenite, zircon, thorite (?), apatite, l uraninite, and multiple oxide m1.ner>lls (?) are concentrated in biotite schlieren in the granite. Several shallo~< prospect pits and drill. holes indicated erratically distributed thin zones usually containing 0.01 to 0.02t, UJ08. The best sample contained 0.08% UJ08. This property was l examined by the writers in October 1967. The average of two composite samples of granite country rock in the vicinity of the prospect is 77.2 ] ppm eTh02 and 65.7 ppm eU308 as determined by gamma spectrometric assay. No presently economic source of uranium appears to exist at this pros pect; however, additional sampling ;rould provide bet-ter information on the distribution of thorium and uranium in the host granite mass. Much J of the surrounding terrane is covered with glacial till but scattered small outcrops of similar granite as far as two miles from the prospect J exhibit high background radioactivity. The nearest area of age dating is about 12 miles south where a 1.4 b.y. date was calculated. J The second most anomalous gra.nite examined b;~r the ~ L. P. Barrett, written communication, 1958, has reported other anomalous J granites of Kenoran or Penokean age south of the Marquette Range. Samples of uraniferous granitic gneiss from an undisclosed location in northern · J Minnesota were submitted to'the U. S. Atomic Energy Commission in 1968. ] Veins in Slate There are a few u:;:-anium vein type prospects in the upper Animikie Michigamme Slate in the Marquette syncline (fig. 2). The best known J of this type are Ford Mot9r Company's Huron River prospect (Vickers, 1955a) and Kerr-McGee's Greens Crec'k prospect (Vickers, 1955b) near J Palmer,Michigan. At these prospects, fault 'breccia zones are weakly J - 11 - J l L_j L._j L._j L._j L._j L_j ___j L_j ._,_, __ : L._j L_j L._j L._j L_j I ' "__j ~ L- L- L- ~ ---' TABLE 2. URANIUM AND THORIUM OCCURRE1TCES ill THE HESTE?J/ GREAT LftY.ES REGION Type Principal localities ------References Segregations in granite and gneiss of Penokean and Hisconsin Elsonia'l age Big l''alls King, 1960 Michigan Felch Vickers, 1953 ·Republic Quartz-calcite-pyrite-uraninite veins in upper ftnimikie Michigan ,_, Michiga~~e Slate Huron~-River Vickers, 1955a 1\) Gre-;;ns Creek Vickers~ 19550 Monazite placers in upper Animikie Goodrich Quartzite Michigan Palmer Vickers; l956a Segregations in upper Animikie iron formation Michigan Iron River Range Marquette Range Barrett, 1952 Thorium-rare earth multiple oxide segregations in Hisconsin syenite complex Hausau Vickers, 1956b Keweenawan felsite dikes Michigan Bergland Beroni and Patterson, 1956 ~~e~tz pebble conglomerate (float) Hisconsin Mt. McCaslin J -]·! minerali'Led 1 Monazite placers occur in the Goodrich Quartzite in the upper part of ) the Animikie Series in the Pulraer area of the :Marquette Range (fig. 2). Vickers (l956a) concluded that a large lovr. grade thorium resource rri.ay l be present in this area.. The area of' Goodrich outcrop ·is limited. j The iron ore ·companies do not sample the Goodrich .in exploration and development holes drilled into the underlying Negaunee Iron Formation l of the middle Animikie, the principal source of iron ore in the Mar quette Range (table 1). Thus Vickers' considerations are based on limited data. The uranium content in the Goodrich outcrops that have J been sampled is very 101< (table 3). (Vickers, 1956a). ' J Urnn:Lllltl. in Iron Formations 1. P. Barrett (written communication, 1952) reported localized concen ·] trations of uranium rarely exceeding 0.20"/o U308 in the· upper Animikie ! iron formations in the Marquette and Iron River ranges of Michigan (fig. 2). These concentrations are ·in oxidized iron formations and ] are closely associated 1 Thoriferous Hyperalkalic Complexes J The thorilli~-bearing minerals cyrtolite and allanite occur in a syenite complex intruding Penokean or Elsonian granite. and Animikie quartzite near Wausau, Wisconsin (fig. 2) (Vickers, l956b). Considerable surface ) trenching in a few locali'cie s indicated that· only a low grade thorium I resource might exist. ] I Keweenawan Felsite Dikes The contact zone of a felsite dike intrusive into lo1 J Table 3 Sllilli~arizes the results of our limited sampling for establishing the background level.s of urani.um and thorium in selected formations in the western Great Lakes region. Recent thorium analyses of samples of J Goodrich Q.uartzite by the U. S. Geological Survey (verbal communication, M. Staatz, 1968) and the results of sampling by the Geological Survey of Canada in the source area of the uranium host sediments at Elliot J Lake (Roscoe and Steacy, 1958) are included. General conclusions based on our limited sampling are: 1 1.· Granitic rocks that contain anomalous amounts of thorium and/or uranium include those near Big Falls, Wisconsin; Republic, Michigan and New Ulm, Minnesota. More study J and sampling of these granites should be done. 2. The Goodrich Q.uartzi te is enriched in thorium. (table 3), J but exposed portions do not appear to contain significant J amounts of uranium. J - 14 - J I L.....J :L...J L._j L...J L....:.J :.____] L_j ''----[ l_:_: ~~~~~w_ji...... :.JL___JL___jl___jl___jL...J TABLE 3. DISTRIBUTION OF URANIUM AND THORIUM IN SELECTED PRECAMBRIAN LITHIC UNITS, HESTERN GREAT LAKES F.EGION Gamma Spectrometric Analys~s lf eTh02 eU308 eK N~. Description location (ppm)_ (ppm) Sample ----- ~i')f'li Upper ~~eca.mbrian Sioux Quartzite AAC 297 Quartz pebble conglomerate New Ulm, 1~inn. ll.O 1.9 0.71 AAC 298 Quartzite Jasper, Hinn, 4.5 6.5 0.04 Elsonian plutons AAC 296 Syenite Hausau, Wise. 4.5 2.5 4.22 AAC 295 · Granite Big Fallil, Hisc. 93.1 104.7 5.83 AAC 295H Granite Big Falls, Wise. 61.4 26.7 4.87 Middle Precambrian Penokean plutons AAC 293 Granite Republic :1 Mich. 102.4 14.7 5.22 Animikie Series (Han1uette Range) Michigarmne Slate AAC 291 Argillite Palmer, Mich. 8.9 22.3 .75 Goodrich Quartzite AAC 292 Conglomeratic quartzite Palmer, Mich. 60.0 8.7 3.03 lo;rer Goodrich Y 37. 72. 46. 55. 1-' \Jl 45. 90. 386. 67. Upper Goodrich Kf 79. 988. 170. 933. 851. Siamo Slate Palmer, Mich. 28.5 6.6 4.82 Ajibik Quartzite Negaunee, Mich. 15.5 12.4 3.60 J.!esnard Quartzite Palmer, !1ich. 2.4 10.7 0.28 Lo;.;er Pre.'!ambrian Kenoran plutoy AAC 299 Quartz monzonite New Ulm, Minn. 51.6 5.1 0.35 Pre-Huronian 3 26 samples Granitic Elliot Lake area, Ont. 27.6 ll.O l/ Analyses by R. ¥. Droullard, U. S • .Atomic Energy Commission, 1968 ~ P~alyses by Carl Bunker, U. S. Geological Survey, Denver, Colorado, 1968 ]/ Roscoe and Steacy, 1958; values are arithmetic means; Th02 range.= 7 to 95 ppm, 11303 range= 3 to 30 ppm ,, J Jl 3. The l·'i.lchiga;YnT!e Slate :• the .',j ibik Quartzite and the Mesnard ! Quartzit.e l~'ormations of t.h:.::: 1\nimikie Series contain signif ..1 icantly high b!!.cl,ground levels of uranium ranging from 11 ·,- to 22 ppm (table 3). The thori.um to uranium ratio in the Michig,o,,nme is about .4; tr.ore interestingly, the thorium to ure.ninm rat·lo in the Meward Q,uartzite at the base of the Arlimilde Series is .2. l1 l U:RANIIDI RESOURCE OUTLOOK l.J ------·- 'f The uranium rE!sources in Middle P:r·ec&.mbr:i.an (lower· Proterozoic) rocks ) are of foremos·t importe.n<:? in th•-' non-Communist portion of the world, accounting I'or about. 50 p-ercent of' the reserves a.vailable at· $10.00 jl or less per pound U308 (Uranium Rc:r;ources, Joint Report, ENEA and IAEA, 1967). These resourc,;,s ar-e mairtly in two districts, the Wit \.ratersrand district of' South Africa and· th~.~ Elliot Lake· distric·t of' Onta.rio 3 Cnnadao The latter diatrict is the free World's foremost ] uranium distriet. Elliot L.s.l<:e po-oduced one billion dollars gross ' value of ore wit-hin five years from the inception of' mining, a world record in met.s.l mining~ The r~acogni tion of critical en;rironmental ~~ factors that controlled the localization of uranium in Elliot Lake is of paramount importance in the seareh for similar districts. J If the environment and ore controls at Elliot Lake, Ontario, are appli cable as exploration guides for urs:aium deposits in the Precambrian of the western Great Lakes region of the United States, the most favorable J targets should be basal conglomerat.,s in the low·er part of the Animikie Series of Middle Precamb:cian age. The great uranium resource at Elliot Lake, variously estimated a.s 500,000,000 to 750,000,000 pounds U308 J reserves phts production, i3 in bas."'l conglomerates of the Middle Pre cambrie.n (lo·;rer- Proter-ozoic) Huronian Series which. may be correlative, in part, ~rith the Animikie (.Jam<:s, 1958). The easternmost exposures J of Animikie strata ar-e at Marquette, Michiga.n, where Paleozoic strata overlap the Precambrian; the Elliot Lake distr-ict is about 200 miles east of Marquette. In the western Great. Lakes region, the basal con ] glomerates of the An~.mikie are not known to be mineralized with uranium; however, exposures are sparse because of' the extensive till cover. J T110 conditions a,re somew·hat encouraging despite the apparent absence of significant urani.um conce<1trations in the sparse outcrops of the J conglomeratic facies of the Animikie Geries. 1. 'In thz 1950's, high grade.pyr:i.tic quartz pebble conglomerate ] floB.t w·as disco;rered in the Mt. McCaslin ar-ea o±' northeast W'isconsin. As previously r·<:vie·;rsd, t-he aource of this float may be in th.:o Animikie of northes.stern Wisconsin or in upper J i"Iichigan o J - 16 - J I J 2. The extensive monazite plo.·~ers in the upper .Animikie Goodrich ] Quartzite ne;J.r Palmer:; Nichigan indicate heavy minerals were being .::oncentr-:so.t.ed by a sed:l.m\;nt.ary plo.(•:ering process; ·the ;.'~:rob able method o:f :format.io;-, o:f th•' Elliot JJake depon:lts (Tic·:·· ] 1969; Hosco"', 1957; Ros•:oe and SteE.cy, 1958). In the i•fu· .. .:.•c: · Formation (b~'ts&.l Hu:ron:Lao) in the Elliot Lake district, the thorium to uranium r::;.tio in 229 sample;> of non .. ore-bearing quartzite and l conglomerate is L8 (Ro.scoe and Steacy, 1958) (table 4). South east><·ard a·way f1•om the district and toward the depocenter o:f the Huronian basin or geosynclinE: J thorium increases and uranium l decreases in rapidly thickening lower Huronian quartzose units. In tre.nsgressive Huronian qt:artzose formations stratigraphically abo·.re the ne.c:erow :fall.. ·lin« depositional environment o:f the uranium J depo.~its, tho:rh;m to uranium ratios incr.ease to about 5 in the Ten Mile For·mation and about. 12 in the .Iorrain Fo:t'mation (Roscoe and St.ea.cy, 1958) (table 4) 0 In 89 samples o:f ore-.. bearing con l glomerates~ thorium to uranium ra.t:ios a:ce .l~ (Roscoe and Steacy, 1958) (t:abie 4) o The ., in the Huroni>J.n :i.s not duplicated in the Animikie o However, the J increr:-.se in thoriwn to uranium rat.i.os :!.n ascending stratigraphic positions in the Animikie and in the Huronian is remarkably similar (table 4)o Because o:f the low sample populations in J the .i\nimilde, the statistical signi:f:!.cance o:f this relationship cannot be tested. J In Ontario, thor'i.um in monazite conc>Jntrations is common in the discontinuous Huronian sediment:•ry belt from Sault Ste. Marie eastw·ard to Sudbury and thence northeastwa.rd to the Lake Mistas ] sJ.n:t areae Economic ura.nium concentrations are known only in the Elliot Lake-Blind F.iver locality and the Agnew Lake locality. In the U 0 S. portion of the west·ern Great 1-!l.kes region, critical J conditions controlling detrital a;::cumulation o:f uraninite may have existed in localiti·es where eoarse clastic Animikie sedi ments accumulated. The possibility o:f uranium concentrations ] in subsur:fa,ce Animild;:, conglomerates cannot. be discounted at this· time because of certain similarities in the distribution o:f radio>lctive mincerals in the, Huronian at Elliot Lake and in J the Animilde in upper Michige.n, namely, (1) monazite is locally concentrated in both Silries and (2) whil:~ the u:t'anium content is low in outcropping areas of bas.~l Animikie conglomerates, J the uranium to thorium ratio exhibits the same increase :from upper to lower Animikie as in the Huronian at Elliot Lake, J Roscoe and Steacy (1958) have postula.ted the sequence o:f events in the :formation o:f the Elliot Lake deposits. The salient points are: J 1. Deep we>J .. thering o:f the Lower Precambrian (Archean) granite and greenstone highland north and northwest o:f the Elliot Lake area J during'the early Middle Precambrian (lower Proterozoic). J - 17 - J ' . 1'ABLE 4. COMPARISON 01" THORIUM AND URANIUN CONTENTS OF HURONIAN AND ANIMIKIE STRATA No. Th02 Samples (ppm) Huronian Series (Elliot I,uke are&) "}:/ Cobhlt Group Lorrain ·Formation Quartzite or grit 1 50 5 10. ~uartz pebb~e conglomerate 3 570 47 12.1 Bruce Group Ten Mile Formation ~uartzite or grit 1 20 6 Quartz pebble conglomerate 6 490 90 Matinenda Formation Quartzite or grit 82 41 21 1.9 Quartz pebble conglomerate 147 610 370 1.7 Quartz pebble conglomerate 89 680 1,600 .4 within an ore zone Pre-Huronian granitoid rocks in Huronian 26 11. 2.5 provenance Animikie Series (Marguette Range, Mich~gan) !:!£per Michigamme Slate 1 8.9 .4 Goodrich Qual:'tzi te (Upper) · 6 604.2 (Lower) 9 95.3 8.7 . 11.0 Middle Siamo Slate 1 28.5 6.6 4.3 Ajibik Quartzite 1 15.5 12.4 1.3 Mesnard Quartzite 1 2.4 10.7 .2 lJ Roscoe and Steacy, 1958 - 18 - tJ :1 . 2. Uplift and rapid denudrttiotl or the deep regolith. Resistant vein quart.z in greenstone regolith and felsic detritus in eranite regolith I·T8re transported by streams flowing south J Y!ll.rd to southea.st.1·m:rd to form the quartz clasts and arkosic matrix of the baso.l conglomerate.3 of the Huronian along the l continental ma1·gin. 3. Monazite, brannerite and uraninite di~tributed in the granitic _regolith were transported and concentrated by placering action l of streams parti.cularly along a fall. line trend in the physio graphic profile of the continental margin. l U-Pb age dates younger than the host. sediments for the Elliot Lake de -posits and the abundance of pyrite have led some researchers to favor an epigenetic hydrothermal origin (Davidson, 1957) or biogenic precip-· J itation of uranium deriYed from weathered granite and transported in solution (Derry, 1960). Geologists of the Geological Survey of Canada and the Ontario Department of Nines >rho have carried out detailed studies l of the Elliot Lake district during the past 15 ·years favor a placer origin (Roscoe and St.eacy, 1958; Robertson, 1969); they believe the U-Pb post host rock age dates reflect resetting of isotopic clocks during minor re l mobilization of the uranium by 10'<0' intensity, post ore, thermal events (Robertson, 1969). ] The question of the or~gln of the great concentration of pyrite, averaging . nearly 15 percent, in the Ell.iot Lake ores is unresolved. S. M. Roscoe J offers t1-To alternate explanations (ver·bal communication, 1967): 1. Sedimentary iron clasts in the conglomera.te host rocks were J altered to pyrite by deuteric solutions or during diagenesis. 2. Pyrite was introduced by hydrothermal post ore solutions. J Sedimentary iron clasts are present in the Cobalt Group, the upper group of the Huronian Series, but th·~Y are essentially absent in the -subjacent Bruce Group of the Huronian. If pyrite in the uranium host rocks of the J basal Bruce Group is an altera.tion product of sedimentary iron clasts, some transition phases might be expected but none have been observed J (verbal communication, S. N. Roscoe, 1967). As previously mentioned, the extensive high-energy, near-source clastic facies of the lower part of the Huronian north of Lake Huron in southern J Ontario does not appear to be duplicated in the U. S. portion of the western Great Lakes. In the United States, sedimentation probably time correlative with the Huronian sedimentation contains chemically precip J itated sedimentary iron formations and other facies indicative of a low energy, shelf or miogeosynclinal environment. S. M. Roscoe (verbal communicat).on, 1967) has concluded from these relationships that the ] lower Proterozoic continental margin extended westward from Sudbury through Elliot Lru J - 19 - J I .. '(I l J~a~;,:e Michic;an nnd t.he LaJ..,~l Fr\~': ..:wlb.r.l.an Keweenawan t:fough (.fig. 3). Roscoe thus concludc'd l.hat. t.h2. r;otential :fo:t· Elliot Lake type deposits ' in the United :3bttrard parallel but 50 to 100 miles northl J - 20 - J J '_ j .. . . ] Granitic- Rocks ] As pre~\riously reYieived 'J certain ar-cns of granitic rocks that were generated during the Alcomart (2.5 b.y.), Penokean (1.7 b.y.) and Elsoninn (1.4 b.y.) oroe;·.mies il.re enr}.ched in thorium and/or uranium. The fe11 bulk sampl-es of these anomalous granites that have been analyzed J by gamma spectrometry contain 52 to 102 ppm Th02 (77 ppm Th02 average) and 5 to 105 ppm u3o8 (38 ppm U308 averag.9) (table 2). The uranium content in sparse ,;a.mpling of a qw'-rtz monzonite in the Big Falls area J in northeast w'isconsin is much greater than in any Precambrian plutonic rocks that have -been sampled in the southw-estern United States (Malan and Sterling, 1969) or similar rocks that have been sampled in the J 1wst cent:ral and no:rth>·!Gstern Unit.;:d States (Malan and Sterling, in preparation), J Large volum•"s of Animikie sedimoonts such as the slightly uraniferous Mi.chiganrne Slate may have be•3n assimilated by magmatic activity during th·-~ :Pr~nokean and Elsorlia.n orogenies; uranium enrichment of the melt. J as 3U6gested by Van Wambeke (1967) in other parts of the world may have result,~d. In the Elliot Lake district, Hu:ronian sediments were assimilated by the Penokean (1. 75 b.y.) Cutler batholith. The Cutler J granite contains two to three times more ur·anium than the pre-Huronian ] Algoman granites (verbal communication, S. M. Roscoe, 1967). In unsampled areas in 1-lisconsin and upper Michig:9.n, large volumes of Penokean or Elsonian granites muy contain significantly more uranium and thorium than the small areas that were sampled. More s:9.lllple data J 11ould provide a better b.<;.sis for comparison of these granites 11ith those in the Western United st.. !J.tes where our sampling is more extensive J and systematic·. In a later re:port, we hope to rank the granites throughout the 11estern United States and, hop1~fully in the western Great Lakes region, on the basis of their average contents of uranium ] and thorium. J Sioux Q,uartzi te The Upper Precambrian Sioux Q,uar-tzit. ., of southeastern Minnesota and southern South Dakota is p1•edominately a thick section of quartzite J and argillite largely co'\Tered by Pleistocene till and Cretaceous sediments. N.~arly all exposures are quartzite; however, a quartz pebble basal conglomerate is exposed locally near New Ulm, Minnesota. J A sample of the conglomerate eonteined 11 ppm Th02 and 2 ppm U308, A sample of subjacent Algoman (2.5-2.7 b.y.) quartz monz~nite contained 52 ppm Th02 and 5 ppm U308· Thc~seresults are not in themselves en- J couraging; ho11cver, three gr·ou~1d we.ter. samples from wells in the Sioux Quartzite at Fulda, Minnesota a.i'ld at Sioux Falls, South Dakota contain 5 to 10 ppb U. These are by far the most anomalous water samples from J the Precambrian of the western Great Lakes region that were analyze·d · by the u. S. Geological S~rvey (Scott and Barker, 1962). J J - 21 - J I .J' ] ------CONCI~USIONS J 1. +he num2rous occurrences of uraniu1n and tho:r·ium in diverse environ ments in the 1festern Gres.t Lakes region are inadequately explored. J Exploration is greatly handicapped by extensive till cover with l sparse outcrops. 2. Thes0 known Occurrenc.es include irregular masses of anomalously uraniferous srani te _q uranium Yeins in slr<..te, monazit0. placers, J local concentrations of uranium in iron formation, thoriferous aJ.h:alic complexes~ uraniferous f\;:lsite dikes:J and ur.s.ni:ferous J quartz pebble coi)Glomerate i'l.oat. 3. Tvro envi::.:-onm2nts contain presently· un~t~onomic, large, low-grade resources of pos;sible importanr~e later in this century. These J include (1) irreg·dar masses o:f anomalously uraniferous granite l and (2) extensive thorium-bearing monazite placers. 4. There are similarities between the distribution o:f trace amounts o:f thorium and uranium in the Arlimikie Series in upper Michigan J and the Huronian Series in t:1« Elliot Lake district, Ontario. While the results of superficial explo1·ation in upper Michigan during the 1950's >Te::-e not encoura.ging, more detailed geologic J and geochemical studies :for blind stratiform or vein-type deposits in the Animikie Series are warranted~ J 5. The high-grade float boulder o!' pyritic quartz pebble conglomerate from northeastern Wisconsin is one o:f the most interesting uranium occurrences in the western Great Lakes region. The boulder prob J ably is a glacial erratic from th.?. Huronian of the Elliot Lake distri~t, Ontario or :from the Animikie o:f northeastern Wisconsin J or upper Michigan. J J J J J J - 22 - J ,'\ I " ' J '• e ,] ----·--HFFERENCJW ] Bayley, H. lv., and Muehlberg2r, W. R., 1968, Basement rock map of the United States:. U. S. Geol. Survey and Univ. of Texas. Beroni, E. P., and Patterson, B. A., 1956, P. A. Burke and associates J property near Bergland, Michigan: U. S. Atomic Energy Comm. open· !l file Prelim. Reconn. Rept. Ish-1, lli"lpub. Catanznro, E. J., 1963, Zircon ages in southwestern Minnesota: Jour. 'l Geophys. Research, v. 68, p. 2045-2048. Davidson, C. F., 1957, On the occurrence of uranium in ancient con ] glomerates: Econ. Geology, Y. 52, p. 668-693. Derry, D. R., 1960, Evidence on the origin of the Blind River uranium l deposits: Econ. Geology, v. 55, p. 906-927. Ensign, C. 0., et al., 1968, Copper deposl.ts in the Nonesuch Shale, Hh:i.te Pine, Nichigan, in Ridge, J. D. , ed. , Ore deposits of the J United St•~tes, l933-19'b7, Am. Inst. Mining Metall. Eng., p. 460-482. Goldich, S. S., Nier, A. 0., Baadsga.ard, Halfdan, Hoffman, J. H., and J Krueger, H. H., 1961, The Precambrian geology and geochronology of Minnesota.: Univ. of l'iir.n ] Grout, F. FQ, Gruner, J. W.. , Schwartz:! G. M.. , and Thiel, G. A., 1951, Pre-Cambrian stratigraphy of Minnesota: Geol. Soc. America Bull., J v. 62, p. 1017-1078. Hurley, P. M., Fairbairn, H. W., Pinson, W. H., Jr., and Hower, J., 1962, Unmetamorphosed minerals in the Gunflint ]'ormation used to test the J age of the Animikie: Jour. Geology, v. 70, p. 489-492. Ills1ey, C. T., Bills, C. W., ru"ld Pollock, J. W., 1958, Some geochemical J methods of uranium exploration, in Survey of Raw Materials Resources: United Nations, New York, Proc. Second Internat. Conf. Peaceful Uses J Atomic Energy, 1958, v. 2, p. 126-130. ' James, H. L., 1958, Stratigraphy of pre-Keweenawan rocks in parts of J Northern Michigan: U. s. Geol. Survey Prof. Paper 314-C, 42 p. King, J, W., 1960, Report of examination, LHtle Wolf Mining and Minerals, Inc., Anklam Property Big Falls, i'laupaca County, Wisconsin: U. S. J Atomic Energy Comm. open file rept. ' J - 23 - J I i 1': ·-1· Leith, C. K., 1934, The pn,-Cnmbrio.n: Geol. Soc. America Proc. 1933, J p. 151-180. Leith, C. K., Lund, R. J., and Leith, A., 1935, Pre-Crunbrian rocks of the Lalw Superior region: U. S. Geol. Survey Prof. Paper 184, 34 p. J l·lalan, R. C., and Sterling, D. A .. , 1969, An introduction to the distribution of m·anium and thorium in Precambrian rocks including the results of J preliminary studies in the southwestern United States: U. S. Atomic Energy Comm. AEC·-HD-9, 5!f p., open file. J !-!alan, R. C. and Sterling, D. A., Distribution of uranium and thorium in the Precambrian of the l ----~~ 1968, Geology of the iron ores of the Lake Superior Region in the ] United States, in Ridge, J. D., cd., Ore deposits of the United States, 1933-1967, Am. Inst. Mining Metall. Eng., p. 489-505. J Peterman, Z. E. , 1966, Rb-Sl' dating of Middle Precambrian metasedimentary rocks of Minnesota: Geol. Soc. America Bull., v. 77, p. 1031-1043. J Robertson, J. A., 1969, Geology and uranium d~posits of the Blind River area, Ontario: ODM reprint of paper, 7lst Annual Meeting, Canadian J Inst. Mining Metall., Montreal. Roscoe·, S.M., 1957, Geology and uranium deposits Quirke Lake-Elliot Lake, '] Blind River anoa, Ontario: Geol. Survey Canada Paper 56-7. Roscoe, S.M., and Steacy, H. R., 1958, On the geology and radioactive deposits of Blind RiYer Region, in Survey of raw material resources: J United Nations, Ne1·r York, Proc. second Internat. Conf. Peaceful Uses Atomic Energy, 1958, v. 2, paper 222, p. 475-483. J Scott, R. C., and Barker, F. B., 1962, Data on uranium and radium in ground water· in the United States, 1954 to 1957: U. s. Geol. Survey J Prof. Paper 426, 115 p. Stead, F. if., Davis, F. J., Nelson, R. A., and Reinhardt, P. W., 1950, Airborne radioactivity survey of parts of Marquette, Dickinson, ·and J Baraga Counties, ·Michigan: U. S. Geol. Survey open-file map. Uranium Resources, Revised Estimates, Dec. 1967, A joint report by the J European Nuclear Energy Agency and the International Atomic Energy Agency, 22 p. J VanHise, C. R., and Leith, C. K., 1911, The geology of the Lake Superior region: U. S. Geol. Survey Mon. 52, 641 p. · ] - 24 - J I . - Vickers, R. C., 1953, Leitch and Isham No.· 2 claim near Felch, Michigan: u. S. Geol. Survey open file Trace Elements Prelim. Reconn. Rept. D-673, unpub. l955a, Geology of the Huron River pitchblende occurrence, Baraga ----~C~o~unty, Michigan: U. S. Geol. Survey open file.Trace Elements Inv. Rept. 303, unpub. -----;;-:--:l955b, Greens Cret'k uranil;m occu::-rence, Marquette County, Michigan: U. S. Geol. Survey Trace Elements Memo Rept. 566, 12 p., unpub, Vickers, R .. C., l956a, Geology and monazite content of the Goodrich Quartzite, Palmer area Marquette County, Michigan: U. S. Geol. Survey Bull. 1030-F. ------~l956b, Airborne and ground reconnaissance of part of the syenite complex near Wausau, Wisconsin: U. S. Geol. Survey Bull. 1042-B. vn1ite, 1'1. s., 1960, The Keweenawan lavas of Lake Superior, an example of flood basalts: Am. Jour. Sci.,, v. 258A (Bradle;y- Volume), p. 367-374. 1968, The native-copper deposits of Northern Michigan, in Ridge, J. D., ed., Ore deposits of the United States, 1933-1967, Am. Inst, Mining Metall. Eng., p. 303-324. ' - 25 -