'EN ERG AEC-RD 11 !
AEC-RD-11
A GEOLOGIC STUDY OF URANIUM RESOURCES IN PRECAMBRIAN ROCKS OF THE li'ESTERN UNITED
By: Roger C. Nalan David A. Sterling
Nay 1970 OPEl"~ AEC-RD-11 3 1972
UNITED STATES ATOMIC ENERGY COMMISSION GRAND JUNCTION OFFICE
RESOURCE DIVISION GEOLOGIC BRANCH
A GEOLOGIC STUDY OF URANIUM RESOURCES IN PRECAMBRIAN ROCKS OF THE WESTERN UNITED STATES
) Distribution of Uranium and Thorium in the Precambrian of the West-Central and Northwest United States
by
Roger C. Malan and David A. Sterling
May 1970
Grand Junction, Colorado
"This report wes prepared es an account of uork sponsored by the United States Government. neither the United Statea nor the United States Atanic Energy Commiaaion, nor any of their employees, nor any of their contractors, subcontractors or their employees make any uarranty, express or implied, or nnaumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information apParatus, product or process disclosed, or represents that its use vould not tnfr:Lnge privately~owned rights." CONTENTS
ABSTRACT • • l
INTRODUCTION 3
PRECAMBRIAN GEOCHRONOLOGY OF THE WEST-CENTRAL AND NORTHWEST UNITED STATES • • 3
Lower Precambrian 3
Middle Precambrian 10
Upper Precambrian • ll
PRECAMBRIAN METALLIZATION 12
DISTRIBUTION OF URANIUM AND THORIUM IN PRECAMBRIAN ROCKS, WEST- CENTRAL AND NORTHWEST UNITED STATES 13 Igneous rocks ...... 14 Lithologic subdivisions 14
Geochronologic subdivisions 14
J ' Geographic subdivisions 22
Metamorphic rocks •.••• 22
Lithologic subdivisions 22 Geochronologic subdivisions 27
Geographic subdivisions 28
DISTRIBUTION OF URANIUM AND THORIUM IN HIGHLAND SYS'rEMS 28
SAMPLE LOCALITIES WITH HIGHEST URANIUM AND THORIUM 28
Colorado ...... 33 Longs Peak-St. Vrain batholith 33 Cotopaxi-Texas Creek batholith 33 Pikes Peak batholith • • • • • 37
i. CONTENTS
SAMPLE LOCALITIES WITH HIGHEST URANIUM AND THORIUM - Continued
Wyoming • • • • • • • 40
Laramie batholith 40
Supergene enrichment in the Copper Mountain Locality, OWl Creek Mountains, Wyoming • • • • • • • • • • 44
SOLUBILITY OF URANIUM IN SILICIC IGNEOUS ROCKS DURING WEATHERING 46
SUMMARY AND CONCLUSIONS • .. • • • 0 • • .. 46
Distribution of thorium and uranium in Precambrian igneous rocks, ;rest-central and northwest United States • • • • • • 46
Distribution of thorium and uranium in Precambrian metamorphic rocks, west central and northwest United States • • • • • 48
Cenozoic basin favorabili ty, Rocky Mcuntains foldbelt and foreland 49
REFERENCES 51
APPENDIX • 55
Tabulation of analytical data, west-central and nortmiest United States ...... 55
- ii - ' '
ILLUSTRATIONS
Figure 1. Index map, Precambrian study • • 0 • 0 • • • • 0 • 0 4
2. Generalized geochronology of the Precambrian, west- central and northwest United States • • • • • • • • 8 3. Generalized geologic map of exposed Precambrian terrane in Wyoming and South Dakota • • • • • • . . 16 4. Generalized geologic map of exposed Precambrian terrane in Montana, Idaho and Washington •••• . . 17 5. Generalized geologic map of exposed Precambrian terrane in Colorado and northeast Utah • • • • • 18 6. Histograms showing frequency distributions of u, Th, and K in lithologic subdivisions of igneous rocks ...... 19 7. Histograms showing frequency distributions of u, Th, and K in geochronologic subdivisions of igneous
rocks • • • 0 • 0 • • • 0 • 0 • • • • • • • • 0 20 8. Histograms showing frequency distributions of U, Th, and K in geographic subdivisions of igneous rocks ...... 21 9. Histograms showing frequency distributions of U, Th, and Kin lithologic subdivisions of metamorphic rocks . . . • .. • ...... • • . . 25 10. Histograms showing frequency distributions of U, Th, and Kin geochronologic subdivisions of metamorphic
rocks 0 0 • • • • • • 0 0 • • • • 0 • 0 0 •
11. Histograms showing frequency distributions of U, Th, and K in geographic subdivisions of metamorphic rocks ...... • . . . . 27 12. Generalized geologic map showing locations of samples in the Long Peak-St. Vrain batholith, Front Range,
Colorado • • • • • • • • • • • • • • 0 0 • .. 0 • 13. Generalized geologic map showing locations of samples in the Cotopaxi-Texas Creek batholith, Fremont County, Colorado ...... 14. Locations of samples in the st. Peters Dome area, Pikes Peak batholith, Front Range, Colorado ••• 39
- iii - ILLUSTRATIONS
Figure 15. Generalized geologic map showing sample locations in the northern Laramie Range, Wyoming 42
16. Distribution of uranium in Precambrian rocks and in early Tertiary sediments in the central and northern portions of the Rocky Mountains foldbelt and foreland ...... • . . . . • . 49
- iv - TABLES
Table l. Summary of Precambri a.n geochronology in Wyoming 5 2. Summary of Precambrian geochronology in Montana. 6
3. Summary of Precambrian geochronology in Colora.do and Utah . • ...... • • • . . . • • . . • . . . 7 4. Summary of distribution of Th, U, and K in lithologic, geochronologic, and geographic subdivisions of Precambrian igneous rocks, west-central and northwest United States . .. • ...... 15 5. Summary of distribution of Th, U, and Kin lithologic, geochronologic, and geographic subdivisions of Precambrian metamorphic rocks, west-central and northwest United States • . • • • • • • • • • 23 6. Distribution of Th, U, and K by highland systems, west-central and northwest United States •••• 29 7. Summary of highland systems with greatest average uranium content, west-central and northwest United States ...... 31
8. Sample locations with highest uranium and thorium contents, >'lest-central and northwest United States 32
9. Sample da.ta., Longs Peak-St. Vrain batholith, central Front Range, Colora.do ...... 35 10. Sample data, Cotopaxi -Texas Creek batholith, Fremont County, Colora.do . . • . • . • ...... 38 11. Sample data., St. Peters Dome a.rea. of the Pikes Peak batholith, southern Front Range, Colora.do 41
12. Sample da.ta, northern Laramie Range, Wyoming 44
13. Sample data., Copper Mountain area, OWl Creek Mountains, Wyoming ...... • .. • • .. .. • .. 45 14. Distribution of thorium and uranium in weathering profiles ...... 46
- v - AEC-RD-11
A GEOLOGIC SWDY OF URANIUM RESOURCES IN PRECAMBRIAN ROCKS OF THE WESTERN UNITED STATES
Distribution of Uranium and Thorium in the Precambrian of the West-Central and Northwest United States
by
Roger c. Malan and David A. Sterling
ABSTRACT
This study of the distribution of uranium and thorium in lithologic, geochronologic, and geographic subdivisions of Precambrian rocks includes data on Colorado, Utah, Wyoming, South Dakota, Montana, Idaho,and washington.
The Precambrian geologic history of this region is divisible into four well-established sedimentary-volcanic cycles spanning the periods .8 to 1.2 b.y. ago, 1.4 to 1.7 b.y. ago, 1.8 to 2.5 b.y. ago, and prior to 2.6 b.y. ago. Most of the sedimentary-volcanic cycles are separated by major orogenies with mean ages of l.O b.y. (Pikes Peak event), 1.4 b.y. (Silver Plume-Sherman event), 1.7 b.y. (Boulder Creek event), and 2.6 b.y. (develop ment of Wyoming province).
In the west-central and northwest United States, the radioelement means for all Precambrian igneous, mostly plutonic, rocks are 29.3 ppm Th, 4.2 ppm U, and 3-4% K. Means increase from 13.7 ppm Th, 3.8 ppm U, and 2.1% Kin granodiorite-diorite to about 35.4 ppm Th, 4.9 ppm U, and 4.2% Kin granite. Thorium, uranium, and thorium/uranium correlate positively with potassium. ~uartz monzonite and granite account for 80 percent of the plutonic terrane at the present level of exposure.
Thorium and uranium in major age groups of plutonic rocks are greatest in rocks of therv 1.4 b.y. Silver Plume-Sherman event in Colorado and southern Wyoming (43.3 ppm Th, 5.3 ppm U) and in rocks of the~2.6 b.y. old Wyoming province largely in Wyoming (30.4 ppm Th, 4.1 ppm U). The high means of all plutonic rocks in Colorado (30.7 ppm Th, 4.4 ppm U) are similar to those in Wyoming (28.1 ppm Th, 4.0 ppm U).
The radioelement means for all Precambrian metamorphic rocks in the west central and northwest United States are 9.8 ppm Th, 2.3 ppm U, and 1.9% K. Metamorphic rocks of low to intermediate grade, principally Upper Precambrian Belt and Uinta supracrustal metasediments contain 11.8 ppm Th, 2.1 ppm U, and 2.0% K. Rocl~s of intermediate to high grade, largely of Middle and Lower Precambrian geosynclinal origin contain 8.2 ppm Th, 2.5 ppm u, and 1.9% K.
In metamorphic rocks, thorium and thorium/uranium ratios correlate positively and uranium correlates negatively with increasing age, independent of the potassium content. In contrast, thorium and uranium contents in igneous rocks closely correlate ;nth potassium but no time-related trend is evident.
-1- From Colorado and Utah on the south to Montana, Idaho, and Washington on the north, the mEan thorium content of metamorphic rocks increases slightly but uranium, potassium, and the thorium/uranium ratios exhibit no systematic variation ;rith geographic location.
The four mountain ranges in which the mean uranium content of all Precambrian rocks combined is greater than 4 ppm include the Seminoe-Shirley Mountains, the Granite Mountains, the 01<1 Creek Mountains, all in central vlyoming and the Front Range in Colorado. The strongest determinant of the average uranium and thorium in various ranges is the aerial extent of silicic igneous rocks relative to other rocks. The silicic igneous rocks characteristically contain about twice as much uranium and thorium as intermediate igneous rocks and metamorphic rocks.
Reconnaissance sampling indicated 19 locations 1vi th greater than 8 ppm U and/or 50 ppm Th including seven in Colorado, ll in Wyoming, and one in Montana. All are believed to be igneous or metaigneous and nearly all are quartz monzonitic or granitic in composition. Additional sampling in the localities of the anomalous reconnaissance samples indicates that the mean value of' 57 ppm Th in the southern half of the Longs Peak-St. Vrain batholith in the central portion of the Front Range, Colorado and the mean value of' 7.0 ppm U in the Cotopaxi-Texas Creek batholith in the northern Wet Mountains, Colorado are the highest of all mean values in large areas of exposed Precambrian terrane in the • Certain Tertiary intracratonic foldbelt and foreland basins may possess greater than average favorability for stratiform uranium rleposits in Tertiary sandstones as inferred from these additional data on the distribution of uranium in the provenances of the sandstones. -2- INTRODUCTION This report, the third in a series on uranium and thorium in Precambrian rocks of the •~estern United States includes the results of radiometric and geologic reconnaissance and sampling of exposed Precambrian terrane in Colorado, Utah, Wyoming, South Dakota, Montana, Idaho, and Washington (fig. 1). The first report (Malan and Sterling, 1969) included the results of studies in New Mexico, Arizona, southern Nevada, and southern California. The second report (Malan and Sterling, 1969a) was primarily a synthesis of the results of past studies on the distribution of uranium and thorium in the Precambrian of the western Great Lakes region with some additional nevr data and interpretations included. A final report will summarize AEC studies of the distribution of uranium and thorium in the Precambrian of the western United States. Field work included radiometric and geologic reconnaissance of exposed Precambrian terrane. About 260 bulk rock samples that are representative of major lithologic units of greatly differing facies and age were collected. These samples were analyzed for parts per million (ppm) uranium and thorium and percent potassium by the gamma-ray spectrometry method in the laboratory of Lucius Pitkin, Inc., contractor for the U. S. Atomic Energy Commission at Grand Junction, Colorado. PRECAMBRIAN GEOCHRONOLOGY OF THE WEST-CENTRAI, AND NORTHWEST UNITED STATES Isotopic age dates of Precambrian rocks in the west-central and northwest United States range from about .9 to greater than 3.0 billion years (b.y.). The four well established revolutions of Precambrian age in North America are all represented in the west-central and northwest United States as indicated by age data maxima of l.O b.y., 1.4 b.y., 1.7 b.y., and 2.6 b.y. In the following geochronologic revievr, the Precambrian in the west-central and northvrest United States is divided into the Lovrer, Middle and Upper informal time subdivisions of the u. S. Geological Survey (James, 1958). As used in this report, these subdivisions are time equivalent to the Early (>2.5 b.y.), Middle (1.7 to 2.5 b.y.), and Late (1.7 to .6 b.y.) subdivisions of the Precambrian as applied by Goldich, et al. (1961) in Minnesota. Precambrian geochronology in Montana, in Wyoming, and in Colorado, the states in the west-central and northvrest United States with the most extensive exposures of Precambrian rocks is summarized in Tables l, 2, and 3. Lovrer Precambrian The oldest knovrn continental crustal terrane on the North American continent largely formed during the period 2.5 to 2.9 b.y. ago. The largest of these regions of ancient continental crust is the Superior province in the central and southern parts of the Canadian Shield. Smaller regions of similar age include the Slave province in the northvrestern portion of the Shield and the Wyoming province, largely in Wyoming (fig. 2). - 3 - "' -0 (f)- '0 -"' ·~·· i -"'"' i u ·- r- _____c! J 0 ' 0:: i i c ! i ______.·· 0 ~ i ./ .0 i i ,. E 0 '1' u a:"' tfJ L. •• ! -0 j c l .!e / ~ .0-" , ·;: ;;; c .2 -"' 0 ]; E 8 c...~ en Q - I I J c.ClClO · ·- ~ 0:: 0:: 0: -4- TABLE J. SUH!I:ARY CF PRZCAMBRIAl'~ GEOCHRONOTOOY IH HYOJriiNG Age (b.y.) Hind River Range Medicine :Bow Range Laramie Range Sweet•rater Range Bighorn Range .60 1.00 Plutonism-Sherman Event Plutonism-Sherman Event (southern) 1.50 Plutonism-Older Granite Plutonism-Laramie Anorthosite? Metamorphism-Medicine Metamorphism-Idaho ~ Bow Quartzite & Deep Springs Fm. (southern) Lake Fm., Idaho Springs Fm. 2.00 Sedimentation-miogeo Sedimentation-eugeo synclinal synclinal (southern) Plutonism-Baggot Rocks Granite Metamorphism-gneissic complex Plutonism-Laramie Batholith Plutonism-Sweetwater Granite 2.50 (northern) Hetamorphism-gneissic 1>fetamorphism-gneissic complex complex Plutonism-Louis Lake Batholith Netamorphism-gneissic complex A Plutonism-granite I " Metamorphism-gneissic I complex 3.00 t ·~ Sedimcntation-gr~acke,shale SedimenLatlon .---:f'dil"'er.t,-.,.til"l'l Sedinentation Sedimentation and iron formation I I t j, I t f " ? TABLE 2. SUMMARY OF PRECAMBRIAN GEOCHRONOLOGY IN MONTAll A Age Gallatin, Ruby, (b.y.) Beartooth Range Little Belt Mts. & Tobacco Root Mts. Northwestern Montana .Go 1.00 Metamorphism-Belt Series I Sedimentation 1. 50 t "' Plutonism-Dillon Granite Metamorphisffi-gneissic complex Metamorphism-Cherry Creek Gneiss Metamorphism 2.00 i 1' i Sedimentation Sedimentation Sedimentation J i t Metamorphism(?) ~ ? 2.50 Metamorphism-Pony Gp. Plutonism-Stillwater Complex Metamorphism-gneissic Complex .r\ t Sedimentation Sedimentation 3.00 t Sedimentation ,, t \' ? ? ? TABLS 3. SUJ.i!-:ARY OF ?RECAl,ffiRIAI' GEOC'rtr\OHCLOGY III COLORll.DO A-se llnco!r.pa.':;;;-re (b.y.) ?ro~t 3:a.'1ge Park RanJSC SeY!l.tch Pan13e 31aCK Cun~.-cn Ileedle t:ts. ''lc.te:u \ 1:1'-'0! vs. " LOJ · 'c: ~i":-orn':1 is··- Plutonis~-Pikes Peak Event Uinta ·ts ,;;p t '(';-;' -=·.t.-:- i "1 Plutonism-Silver Plume and j Sher:ran Events Plutonism~St. Kevin Granite :a'lto:Jis '-C·u-acanti and P1 uto':liS'n-.Solu:; G!'anite and Plutonis'•·-G!'an:_te a::< ~ Vernal ~lesa Quartz 1·1onzonite Electra Lake Granite Vernal I·lesa ';·:artz 1. 5C ''et<.vr.orph imr -Uncompahgre !·:onzonite Plutonis:-J··Granite & 'J-rar.o'li::>:rite 'J'lartzi te :.~et011:0:rphisl 1 -sn~is'lic Ple M 0 N T A N A \ .,~~ --. 1 Belt Mt5., ' \ J ~--/ ~- ~ 0 \ 1 l I I lA)4" I 10> ~Mts~"'" _l_ ~--~- ~---~- Fi 9 u r e :. Generalized est- Central and GeochronologyNorthwest Unitedof the St ap tesrecambrion • -8- The isotopic age dates of 2.5 to 3.0 b.y. obtained on samples from these provinces are ages of metamorphism and anatexis of intermediate to basic volcanics and related sediments. Detrital zircons in granitized areas yield dates as great as 3·5 b.y. (Catanzaro, 1967), but crustal history greater than 3.0 b.y. is uncertain and is largely unresolved. In the Wyoming province the mean age in the Beartooth Mountains is about 2.7 b.y. (Gast, Kulp, and Long, 1958; Catanzaro and Kulp, 1964). Similar dates have been obtained in the Wind River Range (Giletti and Gast, 1961; Bassett and Giletti, 1963) and in the Bighorn Mountains (Gast, Kulp, and Long, 1959; Giletti and Gast, 1961). However, Heimlich and Banks (1968) believe that the granitic complex in the north half' and the gneissic complex in the south half of the Bighorn Mountains developed contemporaneously about 3.0 b.y. ago. The mean age of metamorphism and granitization in the Wind River Range is about 2.7 b.y. (Giletti and Gast, 1961; Bassett and Giletti, 1963). The age of deposition or of metamorphism of graywacke, slate, and iron formation at the southeast end of the range is about 2.9 b.y. (oral communication, z. E. Peterman, u. s. Geological Survey). Age dates near the margins of the Wyoming province (fig. 2) tend to be somewhat younger. Armstrong (1968) calculated an age of 2.5 b.y. for gneiss in the Green Creek complex of the Albion Range in southern Idaho along the inferred western margin of the Wyoming province. Catanzaro ( 1967) reinterpreted data of Catanzaro and Kulp ( 1964) and concluded that the older of two periods of metamorphism in the Little Belt Mountains in central Montana at the northern margin of the Wyoming province is somewhat greater than 2.45 b.y. Catanzaro (1967) believes Giletti and Gast's (1961) mica dates of 1.5 to 1.8 b.y. in metamorphic rocks from southwest Montana have been affected by radiogenic daughter loss during later metamorphic overprint and that gneiss, schist, and amphibolite in the Pony Group may be as old as 2.7 b.y. The extent of the Wyoming province is not accurately defined. However, in the Medicine Bow Mountains in southern Wyoming, extensive mapping and age-dating, particularly by Hills and others (1968), indicate the margin is coincident with the major, northeast-trending Mullen Creek Nash Fork shear zone. North of this shear zone, a 2.4 b.y. quartzo feldspathic gneiss complex is intruded by the 2.34 b.y. Baggot Rocks Granite (Hills and others, 1968). Both units are overlain by more than 35,000 feet of Middle Precambrian miogeosynclinal metasediments. South of the shear zone, a Middle Precambrian eugeosynclinal facies is predominate. The Stillwater complex, a Bushveld-type mafic to anorthositie intrusive in the Beartooth Range of southern Montana (fig. 2) has attracted con siderable attention in recent years because of its possible great - 9 - antiquity and because of recent discoveries of copper and nickel in the basal ultramafic layers, Kistler, Obradovich, and Jackson (1967) cal culated an age of 3.5 to 4.0 b.y., one of the oldest igneous rock dates in the world. However, Kistler, Obradovich, and Jackson (1969) later concluded that the complex was either emplaced or thermally metamorphosed about 2.6 b.y. ago. If this later date indicates !lletamorphic overprint, then the age of emplacement might be as great as 3.8 b.y. (Kistler, Obradovich, and Jackson, 1969). Dating of metasedimentary rocks below the Stillwater complex suggest the age of sedimentation· or the time of intrusion to have been 2.73 b.y. (Powell, Skinner, and Walker, 1969). Younger dates of 2.33 b,y, (Schwartzman and Gilleti, 1968) and 2.45 b.y. (Fenton and Faure, 1969) also have been calculated for the complex. Middle Precambrian Middle Precambrian, metamorphic and igneous rocks are extensively exposed in the western United States. The isotopic overprint left by the major 1.6 to 1.8 b,y, orogeny, culminating the Middle Precambrian, forms the most extensive geochronologic province in North America. During the period 1.8 b.y. to 2.5 b.y. ago, extensive geosynclinal sedimentation and volcanism occurred in vast regions surrounding the Lower Precambrian Superior-Slave-Wyoming continental crustal provinces. This sedimentary-volcanic cycle was culminated by the 1,6 b.y. to 1.8 b.y. Hudsonian orogeny of the Canadian Shield and correlative events in the United States. The Colorado Front Range is one of the largest and most intensively dated areas of exposed Precambrian rocks in the United States (fig. 2), The mean age of (l) metamorphism of eugeosynclinal sediments and volcanics of the widespread Idaho Springs metamorphic complex and (2) syntectonic catazonal granodioritic plutonism of the Boulder Creek event is about 1.7 b,y, (Peterman and Hedge, 1968; Peterman, Hedge, and Braddock, 1968; Hedge, Peterman, and Braddock; 1967; Hutchinson and Hedge, 1967; Hutchinson and Hedge, l967a; Wetherill and Bickford, 1965). Similar mean ages of metamorphism and plutonism apply to Precambrian exposures in (l) the Uncompahgre Plateau (Hedge and others, 1968) and the Black Canyon (Hansen and Peterman, 1968) in western Colorado, (2) in the Needle Mountains of southwest Colorado (Silver and Barker, 1967; Bickford and others, 1967), (3) in the Medicine Bow Mountains in southern Wyoming (Hills, Gast, Houston, and Swainbank, 1968), (4) in the Black Hills of South Dakota (Goldich and others, 1966), (5) in the little Belt Mountains in central Montana (Burwash, Baadsgaard, and Peterman, 1962), and (6) in southwest Montana (Giletti, 1966) (fig. 2). In the Medicine Bow Mountains of southern Wyoming, Hills and others (1968) concluded that the chloritic shist, metaconglomerate, quartzite, and siliceous marble of the Deep Lake Formation and the tillite, con glomerate, metasiltstone, mudstone, and sandstone of the Libby Group north of the Mullen Creek-Nash Fork shear zone comprise more than 35,000 feet of miogeosynclinal metasedimentary rocks. These meta sediments unconformably overlie a 2.4 b,y. old basement near the - 10 - inferred southern margin ~f the Lower Precambrian craton of the Wyoming province. These metasediments may be correlative with the Huronian and Animikie mioge~syncl inal sections along the southern crat::mic margin of the Lower Precambrian Superior province in the Great Lal Unper Preca~brian In the west-central and north;rest United States, the neriod from 1.6 b. y. to .6 b.y. ago. comprising the Upper Precambrian, is characterized by the following success ion of events: ( l) restricted miogeosynclinal sediment aticm early in the period, (2) widespread orogenesis with a mean age of 1.4 b.y., (3) wcdespread supracrustal sedimentation in the Beltian geo syncline, and (I,) restricted plutonism with a mean age of J.O b.y. In the west-central and northwest United States, the only kno;rn record of a sedimentary cycle between the 1.7 b.y. and the 1.4 b.y. orogenies i.s in southwest Colorado (fig. 2) where at least 8,000 feet of quartzite, slate, and schist comprise the Uncomnahgre Formation. This formation overlies a 1.7 b.y. old basement and it is intruded by 1.47 b.y. granite (Bickford and others, 1967; Si.l ver and Barker, 1967). Time correlative metasediments are present in central Arizona and in north-central New Mexico. Age date maxima indicate that vast areas were subjected to plutonism with a mean age of J .I, b.y. in the west-central and southwest United States. This period of ~rogenesis extends northeastward through the central United states (~·1uehl berger, Denison, and Lidiak, 1967). but it is not recognized north ~f a northeast-trending line through southern Hyoming and southern Minnesota. In Colorado and southern Wyoming (fig. 2) this well-dated event includes (l) the Silver Plume and Sherman Granites of the Front and Laramie Ranges (Wetherill and Bickford, 1965; qutchinson and Hedge, l967a; Hutchinson and Hedge, 1967b: Peterman and Hedge, 1968; Peterman, Hedge, and Braddock, 1968; Hills and others. 1968); (2) the Laramie anorthositic complex recently dated at 1.35 b.y. (oral communi cation, Z. E. Peterman, U. S. Geological Survey. 1969); ( 3) the St. Kevin Granite in the Sawatch Range. central Colorado (Pearson and others 1966); (4) quartz monz~nite and granite in the Uncompahgre Plateau (Hedge and others, 1968) and in the Black Canyon (Hansen and Peterman, 1968) in western Colorado: and ( 5) quartz monzonite nlutons in the Needle Mountains, southwest Colorado (Bickford and others. 1967; Silver and Barker, 1967). Low energy marine sedimentation in the great Beltian geosyncline (fig. 2) extending from Alaska to Mexico was the latest Precambrian event of regional importance in the western United States. The Belt Supergroup and its correlatives, the Uinta Group in Utah, the Grand Canyon Series and the Apache Groun in Arizona and the Pahrump Series in California and Nevada comprise 10,000 feet to more than 40,000 feet of predominately - ll - siltite, argillite, quartzite, and subordinate carbonate rocks of shallow marine origin. The thickest section is in the north in western Montana and northern Idaho. In this area, the Beltian metasediments thin to a depositional edge tc the east; they are thickest 300 miles to the west near the Phanerozoic overlap. The provenance was a highland to the west now collapsed and covered by Phanerozoic sediments and volcanics. Age dating of Belt metasediments by Obradovich and Peterman (1968) indicates discontinuous sedimentation from about 1.3 b.y. to about .9 b.y. ago. In most areas, the Belt Supergroup unconformably overlies a metamorphic complex about 1.8 b.y. old. Locally in southwestern Montana, near a source area of considerable relief, basal conglomerates of the La Hood Formation overlie the unconformity. In the west-central and northwestern United States, plutor,ism with a mean age of l.O b.y. (Peterman and Hedge, 1968; Hutchinson and Hedge, 1967; Hutchinson and Hedge, l967a) is recognized only in Colorado (fig. 2). Quartz monzonite is predominate in the large Pikes Peak batholith and in smaller plutons in central Colorado. The configuration of the widespread angular unconformity at the base of Cambrian strata suggests epeirogenic uplift and peneplanation in late Precambrian time in much of west-central and northwest United States. Hovrever, Cambrian strata conformably overlie Belt strata in many places. The northeast-trending Transcontinental arch survived as a weakly positive land mass element of this late Precambrian regional uplift until Pennsylvanian time (Eardley, 1962). In general, thick geo synclinal sediments accumulated west of the arch and thinner plat form sediments were deposited east of the arch. Local alkalic igneous activity near the time boundary of the Precambrian and Cambrian occurred at the 550 m.y. old Iron Hill syenite complex near Gunnison, Colorado and at the 580 m.y. to 655 m.y. old McKinley Mountain albite syenite stock near Canon City, Colorado (Jaffe and others, 1959). PRECAMBRIAN METALLIZATION In the west central and northwest United states, metallic mineral deposits of Precambrian age are far less important than those of Mesozoic and Cenozoic age. With the exception of some sedimentary iron deposits, all Precambrian metallic mineral deposits appear to be genetically related to magmatism. Principal types of deposits are gold-quartz and lead-silver veins; magmatic segregations of chromium, copper-nickel, and titanium-iron; sedimentary iron deposits; and disseminations of thorium-uranium-rare earths in pegmatites. - 12 - Veins High temperature tourmaline-bearing gold-quartz veins occur in 1.6-1.8 b,y. old mafic metamorphic rocks in scattered locations in the southern part of the Sawatch Range and in the Front Range in Colorado {Boyd, 1934). Similar deposits in rocks of similar age sometimes contain subordinate amounts of gold, platinum, palladium, and silver in the Sierra Madre, Medicine Bow, and Hartville Uplift areas of southeastern Wyoming. Lead isotope age-dating indicates several of the major vein deposits of lead-silver in the Coeur d'Alene mining district in northern Idaho are 1.2 to 1.4 b.y. old {Cannon, Pierce, Ant.reiler, and Buck, 1962). Wall rocks are lower Belt metasediments of generally similar age (Obradovich and Peterman, 1968). Magmatic Segregations Mafic to ultramafic zones in the lower Precambrian Stillwater complex in the Beartooth Range, Montana {fig. 2) are being explored for copper and nickel deposits. Other zones in this layered igneous complex have been mined for chromium. Segregations of titaniferous magnetite occur in mafic dikes in border facies of the Laramie anorthosite in the Laramie Range in southeastern Wyoming. Iron Deposits In the west-central and northwestern United States, some of the most impor tant metal deposits of Precambrian age are sedimentary iron deposits in metamorphosed sedimentary-volcanic sequences at Atlantic City in the southeastern part of the Wind River Range, Wyoming and at Sunrise in the Hartville Uplift, Wyoming. The Atlantic City deposits are in the Lower Precambrian rocks and the Sunrise deposits are in Middle Pre cambrian rocks. Pegmati tes Thorite-bearing veins in the Powderhorn district south of Gunnison, Colorado and in the Wet Mountains, Colorado may be genetically related to alkalic igneous intrusions of latest Precambrian age { "-' 600 m.y.) {Edwards, 1966, p. 138). At Powderhorn, the alkalic c~mplex is enriched in niobium and titanium. Thorium, uranium, and rare earths are erratically dispersed in widely scattered Precambrian pegmatites particularly in Colorado and in Wyoming. Several occurrences have been explored in the Sangre de Cristo Range and in the Front Range, Colorado and in the Sierra Madre, Owl Creek and Granite Mountains, Wyoming but none have been economically profitable for uranium. Lithium-bearing radioactive pegmati tes occur in the Sawatch Range northeast of Gunnison. - 13 - There is an unusual occurrence o~ uranium in ~ractured Precambrian granite near a xenolith o~ graphitic schist and quartzite in the Seminoe Mountains Wyoming. One small shipment was made. DISTRIBUTION OF URANIUM AND THORIUM IN PRECAMBRIAN ROCKS , WEST-CENTRAL AND NORTHWEST UNITED STATES Field work for this phase of the Precambrian study consisted o~ radiometric and geologic reconnaissance and the collection o~ 265 bulk samples repre sentative of major lithologic units in the Precambrian in Colorado, Utah, Wyoming, South Dakota, Montana, Idaho, and Washington. These samples were analyzed by the gamma-ray spectrometric method in the laboratories o~ Lucius Pitkin, Inc., contractor ~or the u. S. Atomic Energy Commission at Grand Junction, Colorado. A rapid identi~cation o~ rock type in each sample was made through ~eldspar staining techniques and estimation o~ percentages o~ major rock-~orming minerals. All the samples are located on generalized geologic and geochronologic maps o~ the Precambrian (~igs. 3, 4, 5). Locations and all analytical data for these samples are tabulated in the appendix. Igneous Rocks The distribution o~ thorium, uranium and potassium in lithic, geochronologic, and geographic subdivisions o~ Precambrian igneous rocks in the west-central and northwestern United States are summarized in table 4 and illustrated by histograms in ~igures 6, 7, and 8. Lithologic Subdivisions In table 4A, igneous rocks are subdivided into (l) granites, (2) quartz monzonites, and (3) granodiorites, diorites and a few more basic phases. ~uartz monzonites and granites account ~or nearly 80 percent o~ all bulk reconnaissance samples o~ igneous rocks indicating the silicic nature o~ the presently exposed Precambrian igneous terrane in the west-central and northwest United States. Thorium and to a lesser extent uranium correlate well with advancing magmatic stage and with potassium, similar to trends in igneous rocks in the south western United States (Sterling and Malan, in press) and with the general enrichment o~ thorium and uranium in later phases o~ the crystallization process in all magmatic series. Thorium increases ~rom a mean o~ about 14 ppm in granodiorites, diorites, etc. to a mean o~ about 35 ppm in granites; uranium increases ~rom about 4 ppm to about 5 ppm in these same groups of igneous rocks (table 4A). The mean thorium, uranium, and thorium/uranium ratio in granodiorites, diorites, etc. , are closest to estimates o~ the average composition (dioritic) and thorium-uranium contents (10-12 ppm Th, 2-3 ppm U) in the entire continental crust (Phair and Gott~ried, 1964; Heier and Rogers, 1963). Mean thorium-uranium ratios increase to 7 to 9 in quartz monzonites and granites because o~ the much greater increase in thorium relative to uranium in advanced magmatic stages (table 4A). - 14 - TABLE 4. S~MRY OF DISTRIBUTION OF TH, u, AND K IN LITHOLOOIC GEOCHR A. Lithologic Subdivisions No. Samples ppm Th ppm U % K Th(U Granites 19 35.4 4.9 4.2 7.3 Quartz monzonites 71 32.9 4.2 3.7 7.9 Granodiorites, diorites, etc. 24 13.7 3.8 2.1 3.6 B. Geochronologic Subdivisions Depth of Formation and Predominate No. Age (b.y.) Rock Type* Samples ppm Th ppm U ~ Th/U .08 - 1.08 1. 16 19.8 2.7 4.0 7.2 1.35 - 1.50 2. 37 43.3 5.3 3.8 8.2 1.60 - 1.80 3. 15 10.4 3.4 2.5 3.0 2.30- 3.00 4. 46 30.4 4.1 3.3 7.0 *1. Epizonal; predominately quartz monzonite. 2. Epizonal to mesozonal; predominately quartz monzonite. 3. Mesozonal to catazonal'; predominately granodiorite. 4. Catazonal (?); extensive granitization with gradationally migmatized gneissic mantles probably formed at deep levels, predominately quartz monzonite. Other Data Age No. Group Source Samples ppm U Th(U 1. Gottfried and Phair, 19641 30 4.9 5.2 2. Gottfried and Phair, 19641 53 60 5.2 6.8 .3. Gottfried and Phair, 19641 52 13.4 165 2.6 5.2 4. Gottfried and Phair, 19642 21 15.7 22 2.3 6.8 4. J. A. S. Adams, 19693 366 28.1 279 3.4 5.1 8.3 C. Geographic Subdivisions No. Samples ppm Th ppm U ~ Th(U Colorado 51 30.7 4.4 3.7 7.0 Wyoming-South Dakota-Montana 63 28.1 4.0 3.2 7.1 Other Data No. Source Samples Colorado Gottfried and Phair, 19641 135 255 4.8 6.0 Wyoming Gottfried and Phair, 19642 21 15.7 22 2.3 6.8 Wyoming J. A. s. Adams, 19693 366 28.1 3.4 8.3 279 5.1 lsampling restricted to Colorado Front Range. 2 sampling restricted to Wind River and Bighorn Ranges. 3 sampling restricted to Granite Mountains and Laramie Range. - 15 - ~r· .:~---- ~l~ < ~F'.;,.-- ---..------1--a;------wvr.u-;;:;-;:-----MONTANA ----r-I ------T------o~ I o ~r-- i~10 ~ ~~· Zo ~~~ < • 0 L---, ..-J t I I I ' I I 1""~ ( I I --~---~~ l r'-- tI \ ~ ._ _l_ 1 I Cosper "' I I • I I 0: t._ I I ···~J ~~-·- I ("· "1 ~---~ I -Ll I I I : I Cheyenne• I YOMING INEBRASKA L , WYOMING ---..lr- J! COLORADO ... Ui'AH !COLORADO -)--- I I P l 0 ~ I l I ~ I U~ptt '""'~' Uo \I<>Oil IOO .. ~Oiot< (O"orol>>l 1< I ll 0 J 0'"0111) U\looro~lo """' ol I Figure 3. Generalized Geologic Mop af Exposed Precambrian Terrane in Wyoming and South Dakota " c c : ;;. j ' ' ~ '1 • • c : 2 " 0 2 0 c 0 c ,.-0 ; I c 0 .0' E 0 u ·~ a. -0 ~ •c ,.0 z• •u ~ •N 0 c •c "' -17- ",~· \-- ~ ~ ') ' ~~~i't_:-~-~' J toe• WYOMING 1 -~\~_11~,.~? '---- ~- cOLoRADO ' Q 0 ::y,./"-r:;-11 s1,1 lll't_9W'I7- '-'~ "" J 3?tr~ v~ r ~~~ , ; ~ I 1 r------/-, I l, ' I --~-~~' ~ -~ .i' - '" - (r · , I ____r a; i I ~-__[ --lr _j· I ~--L_____ [------,-- , i l; .~,~,, """,;" c::J ...... ' .. ,. r~l L- ~ .... '""""'" '"'W";:::,:::ii:,::•:::::·,·~ :':".i:"' I .. _.,,. ,,_,,.,,_, ood cor t .. , .. ''"''" \.___ w-~-~- I " f------ 10 0 I() 20 J() 40molot I " t L_l - - Je· Figure 5. Generalized Ge'Oiogic Map of Exposed Precambrian Terrane in Colorado and Northeast Utah. Gronitu Ouarll Mcnzonitn Gronod1onte Diorite U• 19 X• 4G6 ppm u 1 j f Th/U• 7,0 Tll/U• l9 Thill• 3.6 ' /j. 71 U• 24 I"''" X•2929ppmn j i• 3293ppmT/l I lf• 13.69ppm Th Th " " U• 114 ~·344%~ K Fig. 6 Histograms Showing Frequency Distributions of U, Th,and K in Lithologic Subdivisions of Igneous Rocks -19- All Age Comboned 06- 1.06 b. Y 135 !SOb y ~- (.oa- 3.0 b)i) ~- {Epi~onol) Epozoool Mesozonol Mesozonal- Cotozonol ~~esozonol- Colozonol " 'P El4 N 'iG ~' ·~ if•419ppmU if• 2Hpp"'U X•34~ 00 ,u u .L ' " 5 10 15 "'0 ' 1 1 T>/UI •70 H/U•7Z Th/U>62 Th/u'I 30 n/u•7ol j N• 114 j II' 37 N• 15 l ,. " X• 29.29ppm Th ·(: ... Y•4333ppmTh I y, oo.H 00., n ·M Ju '"""··,. lllmL 20 •o 60 so 100 120 'l20 •o 20 40 00 60 " ~ ,_, ,, fl'IG l 11'37 !1>1~ "' 46 X• 32ll% K L t D F"b'"'" t_nb ''"" ' Fig. 7 Histograms Showing Frequency DistribL..tions of U, Th, and K in Geochronologic Subdivisions of Igneous Rocks 25 ~ All Stote> Comb,n•d I 20 COLO. WYO. S.D. " N• 51 i= 442 ppm U 1 1 1 Th/U • 70 Tti/U • 70 TII/U• 71 " .0 l l '0" '0 '0 N• 114 N• 51 N' 63 X= 29,29 ppm Th X• 30 12. ppm Th X: 26.14 ppm Til Th 15 0 .0 N: 63 N• 114 N: 51 " )(,3690/.,K '0 X: 324°/oK " X•344°/0 K '0 " •" 5 5 K 0/o K 4 5 2 3 4 Fig. 8 Histograms Showing Frequency Distributions of U, Th, and K in Geographic Subdivisions of Igneous Rocks -21-- Geochronologic Subdivisions In table 4B, igneous rocks in the west-central and northwest United States are grouped into the four major orogenic periods in which they were formed as based on isotopic age dating. These orogenic episodes were reviewed in the geochronology section of this report. The depth zone of formation of plutons and the predominate rock type at the present level of exposure of the plutons also are indicated in table 4B. Irregularities in the distribution of thorium and uranium contents are evident in table 4B that are not obvious in the lithologic subdivisions in table 4A. For example, the mean thorium and uranium contents in quartz monzonites in table 4A are 32.9 ppm Th and 4.2 ppm U; in table 4B, predominantely quartz monzonitic batholiths of mean age 1.0 b.y. vary in mean thorium content from about 20 ppm to about 43 ppm Th and from about 2.7 ppm U to 5.3 ppm U. Our analytical data from random reconnaissance sampling indicates that the highest average contents of thorium and uranium are in 1.35 to 1.50 b.y. old batholiths represented by the Silver Plume-Sherman event in Colorado and southern Wyoming. Data from other studies (Gottfried and Phair, 1964; J. A. S. Adams, written communication, 1969) are tabulated in the second part of table 4B. These data are from samples predominately from the Front Range in Colorado (Gottfried and Phair, 1964) and from the Granite Mountains and Laramie Range in Wyoming (J. A. S. Adams, written communication, 1969), whereas our reconnaissance sampling was randomly distributed throughout most highland systems in the region of this study. Nevertheless, the data from the different sources for time-correlative igneous events are in general agreement. Geographic subdivisions Thorium and uranium contents of igneous rocks in Colorado and in Wyoming, South Dakota, and Montana are tabulated in table 4c. In the Wyoming, South Dakota, and Montana group, 55 of the 63 samples are from Wyoming. Mean thorium and uranium and the thorium/uranium ratios in the two geo graphic groups are remarkably similar, namely 30.7 ppm Th and 4.4 ppm U in Colorado compared to 28.1 ppm Th and 4.0 ppm U in the Wyoming, South Dakota, and Montana group. Data from other studies in a limited number of ranges in Colorado and Wyoming are included in the second part of table 4c. Sample population is greater in these other studies but areal bias in sampling precludes a direct comparison with our data. Metamorphic Rocks The distribution of thorium, uranium, and potassium in lithologic, geo chronologic, and geographic subdivisions of Precambrian metamorphic rocks in the west-central and northwest United States are shown in the summaries in table 5 and in the histograms in figures 9, 10, and 11. - 22 - TABLE 5. SUMMARY OF DISTRIBUTION OF Th, U, AND K IN LITHOLOGIC, GEOCHRONOLOGIC, AND GEOGRAPHIC SUBDIVISIONS OF PRECAMBRIAN METAMORPHIC ROCKS, WEST-CENTRAL AND NORTHWEST UNITED STATES A. Lithologic Subdivisions Metamorphic Grade No. Samples ppm Th ppm u % K Th/U Intermediate to high grade 70 11.8 2.1 2.0 5.7 Low to intermediate grade 81 8.2 2.5 1.9 3.2 B. Geochronologic Subdivisions Age (b.Y.)* Environment** No. Samples ppm Th ppm U % K Th/u .8 - 1.3 l. 46 8.2 2.7 1.9 3.0 1.4 - 1.8 2. 21 9.0 2.5 1.3 3.7 1.8 - 2.5 3· 40 10.1 2.4 2.2 4.2 2.5 - >3.0 4. 44 11.6 1.6 1.8 7.3 Other Data Age (b.y.) Source No. Samples ppm Th ppm u % K Th/U 1.8 - 2.5 Gottfried ~d 15 16.6 Phair, 1964 13 4.7 3.5 *Interval of accumulation of sediments and volcanics; extensively metamorphosed near end of each period. *l<· l. Supracrustal shallow marine arenaceous, calcareous, and argillaceous metasediments (Beltian miogeosyncline). 2. Miogeosynclinal (?) quartzite, slate, metavolcanics, etc. 3. Intermediate to high grade metamorphic complex formed from eugeosynclinal sediments and volcanics; includes miogeosynclinal quartzite, metacarbonate, slate, etc. in southern Wyoming. 4. Primeval crust (?) - migmatized gneissic complex; extensively granitized; remnants of greenstone, graywacke, schist and sedimentary iron formation. C. Geographic Subdivisions No. Samples ppm Th ppm u %K Th/U Colorado-Utah 47 9.1 2.4 1.7 3.8 Wyoming-South Dakota 49 9.5 1.8 2.0 5.2 Montana-Idaho-Washington 55 10.7 2.6 2.0 4.1 Other Data Source Colorado Gottfried and 15 16.6 1 Phair, 1964 13 3·5 1 Sampling restricted to Colorado Front Range. Lithologic Subdivisions In table 5A, the 151 bulk reconnaissance samples representative of major metamorphic units in the west-central and northwest United States are subdivided into 81 samples of lmr to intermediate metamorphic grade and 70 samples of intermediate to high metamorphic grade. The first group includes several samples from the Belt Supergroup and the Uinta Group that are only slightly recrystallized. Other samples in this group usually retain some vestige of their original sedimentary or volcanic ong~n. Rocks of intermediate to high metamorphic grade formed at deeper levels and comprise variably migmatized gneissic complexes. In general, low to intermediate grade metamorphic rocks were derived from recrystal lization of miogeosynclinal and platform sediments while intermediate to high grade rocks formed from thick accumulations of eugeosynclinal sediments and volcanics. In metamorphic rocks of intermediate to high grade, thorium (11.8 ppm) is somewhat higher and uranium (2.1 ppm) is slightly lower than in rocks of low to intermediate grade (8.2 ppm Th and 2.5 ppm u, table 5A). These variations result in thorium/uranium ratios of 5·7 for intermediate to high grade rocks and 3.2 for low to intermediate grade rocks. The higher ratio is in the expected range for intermediate to acidic igneous rocks while the lower ratio is characteristic of ratios in sedimentary rocks. Thorium and uranium in both these groups of metamorphic rocks are close to the estimated abundance of thorium and uranium in the continental crust. Thus geosynclinal accumulations composed of clastic contributions from the erosion of highly differentiated, silicic upper continental crust in existing land masses and basic volcanics and volcaniclastics of lower crust or upper mantle origin comprise a "mix" approximating the mean abundance of thorium and uranium in the entire crust. Geochronologic Subdivisions In table 5B, metamorphic rocks are subdivided into the four major periods of accumulation of the sediments and volcanics from which they formed. In general, the sediments and volcanics were metamorphosed near the end of each of the periods. Small but systematic changes in mean uranium and thorium contents appear to be time-related in metamorphic rocks (table 5B); uranium and thorium in igneous rocks do not exhibit these trends (table 4B). In the metamorphic rocks, the mean thorium content and the thorium/uranium ratio increase with increasing age, whereas uranium decreases. These trends seem independent of the variations in mean potassium content; in contrast, there is a high degree of correlation of uranium and thorium ;ri th potassium in igneous rocks (table 4). Thorium/uranium ratios of 3.0 to 4.2 in the three younger groups of metamorphic rocks are characteristic of ratios in many sediments, in volcanics, and in intermediate stage plutonic rocks; the high ratio of 7.3 in the oldest metamorphic rocks is characteristic of ratios in acidic plutonic rocks. - 24 - All Metamorphic Rocks Combmed lntermed1ote to h1gh grade Low fa Intermediate grade Metamorphic Rocks Metamorphic Rocks 15 N • 70 N • 81 X•206ppmU X•254ppmU Th/U•43I Th/U•I 5.7 Th/U• 3.2 1 1 15- 1 N= 151 N= 70 w- N= 81 X• 983 ppm Th X= 11.75 ppm Th X= 6.16 ppm Th ppm Th I '0 '0 '0 N · 151 N • 70 N • 81 X•189%K X= 2.02%K X: 187%K 5 K "lo K 2 Fig. 9 Histograms Showing Frequency Distributions of U, Th,ond K in Lithologic Subdivisions of Metamorphic Rocks -25- All Ages Comb1ned (10-30 by) .8-L3b_y 1.4-LSby 18-25 bY, 25-3.0by. '"''~~yn~;;lnOI to •holl, (MI0900.JOOHnoo; I~U9ocoyMioncl tc (Ptomll,.o oru•l; Quor!Zooe and peldoc; Quort:o.. , low!O mt09000)n:hnol, •nlermodooto to 1'1•~ ; "' 151 N' 44 -,:, 1 ~s I l TO/U N• '~' tl' 21 X• S63~~mTh 'L'''Oeemn '0 " 20 30 11'151 'l' 4~ N' z, ... 40 tl•44 0 " X• 16!1%K X• 190%K l X• 133%~ X• 2.20%K j•I61%K t ' K 'b~LJo '1krfl)!d p z ~ I 2 3 4 5 ·wmuGoI 2 3 4 5 .. , 3 4 Fig. 10. Histograms Showing Frequency Distributions of U, Th ond K in Geochronologic Subdi.visions of Metamorphic Rocks ------ I •I I' !l" I ~ -27- As previously referred to, other studies have indicated that uranium and to a lesser degree thorium decline as metamorphic grade increases. In table 5B, the two older groups underwent intermediate to high grade metamorphism, whereas the two younger groups underwent lOiof to intermediate grade metamorphism. Thus the lower uranium contents in the higher grade rocks of the older groups are in agreement with this concept but the higher thorium contents are opposed. These interesting relationships suggest that something additional to metamorphic grade and lithologic composition may exert control on the distribution of thorium and uranium in metamorphic rocks. Geographic Subdivisions Metamorphic rocks in the west-central and northwest United States are divided into a southern area including Colorado and Utah, a central area including Wyoming and South Dakota, and a northern area including Montana, Idaho, and Washington (table 5C). The thorium content increases slightly from south to north but uranium, potassium, and the thorium/uranium ratios exhibit no systematic geographic variation. Distribution of Uranium and Thorium in Highland Systems Analytical data for all samples in the seven states covered in this report are tabulated in the appendix. From these data the mean contents of thorium and uranium in various mountain ranges or groups of ranges (figs. 3, 4, and 5) in the west-central and northwest United States are calculated in table 6. Data from other studies are included (Gottfried and Phair, 1964; J. A. S. Adams, written communication, 1969). These means are based on analyses of igneous and metamorphic rocks combined; this provides a basis for evaluating the various highland systems as sources for uranium in detritus in surrounding basins. Some correlation might be expected between the dis tributions of anomalously uraniferous highlands and basins mineralized with uranium if the source of the uranium was in the Precambrian crystalline rocks in the highland provenances. Also, basin sediments not known to be mineralized with uranium but which were derived from highlands anomalously high in uranium might be favorable exploration targets. The four mountain ranges with a mean uranium content greater than 4 ppm include the Seminoe-Shirley Mountains, the Owl Creek Mountains, and the Granite Mountains all in central Wyoming, and the Front Range in Colorado (table 7). Silicic igneous rocks constitute a high percentage of the Granite and Seminoe-Shirley Mountains and a lower percentage of the Owl Creek Mountains and the Front Range. In other mountain ranges in the west-central and northwest United States, the percentage of silicic igneous rocks is generally lower than in these four most uraniferous ranges. Silicic igneous rocks (quartz monzonite and granite) typically contain nearly twice as much uranium and thorium as metamorphic rocks and intermediate igneous rocks. Thus a crude assessment of the uranium content of a given range may be made if the ratio of silicic igneous terrane to metamorphic terrane plus intermediate to basic igneous terrane is known. However, some notable exceptions exist such as the low uranium content of 3.0 ppm in the predominately silicic igneous terrane of the Laramie batholith in the north half of the Laramie Range, Wyoming. - 28 - 'TABLE 6. DISTRIBUTION OF Th, U, AND K BY JITGHLAND SYSTEMS, WEST-CEl'ITRAL AND NORTHWEST UNITED STATES ' Colorado Mountain Range No. Samples Mean Mean Mean or Area Igneous Metamorphic --Total ppm Th ppm u L!. Th/U l. Front (AEC data) 31 6 37 35.5 3.9 3.07 6.5 1 (USGS data) 135 15 150 22.7 1 5.0 255 13 268 4.5 Weighted averages of combined data (AEC and USGS) 166 21 187 23.3 5·3 286 19 305 4.4 31 6 37 3.07 2. Sangre de Cristo 1 2 3 7.9 2.2 2.42 3.6 3· Sawatch 14 3 17 24.6 3.0 3.60 8.2 4. Wet 9 1 10 16.8 3.8 3. 73 4.4 5· Needles-San Juan l 4 5 13.1 3.4 2.03 3·9 6. Park-Gore-Tenmile 4 6 10 13.2 2.9 2.72 4.6 Weighted averages of all Colorado data (AEC and USGS) 232 22.3 5·1 350 4.2 82 3.13 Montana l. Pre-Belt of south- 6 14 20 13.5 1.8 1.68 7.5 western Montana 2. Belt Supergroup of 23 23 7.9 ..1.:2: 1.87 2:.1 western Montana Total 6 37 43 Weighted Averages 9.8 2.3 1.78 4.3 Idaho-Washington N. Idaho ll ll 9.8 3.0 2.33 3·3 E. Washington 3 3 11.8 3.:1. 2.99 ..2.:.! Total 11+ 11+ Weighted Averages 10.2 2.8 2.47 3.6 South Dakota Black Hills 2 6 8 9.2 3.1 2.50 3.0 Utah Uinta-Wasatch 9 9 7.8 1.7 1.10 4.6 lArea 1'1eighted average - 29 - 'TABLE 6. DISTRIBUTION OF Th, U, AND K BY HIGHLAND SYSTEMS, WEST··CENTRAL AND NORTHWEST UNITED STATES (Cont'd) Wyoming Mountain Range No Samples Mean Mean Mean or Area Igneous Metamorphic Total ppm Th ppm U % K Th/U -- '-- l. Beartooth 4 3 7 13.1 2.6 l. 52 5.0 2. Bighorn AEC data 6 3 9 23-5 l.l 2.24 21.8 USGS data 10 -10 17.9 1.4 --12.8 Total 16 3 19 20.6 1.3 2.24 15.8 Weighted averages 20.6 1.3 2.24 15.8 3· Granite2 Primarily igneous 282 25.3 4.8 3.50 5-3 4. Hartville 1 1 2 12.2 1.4 2.03 8.7 5· Laramie AEC data 15 15 9.6 1.8 3.01 5-3 J .A.s. Adams data3 87 37.0 3.1 11.9 Total 102 Weighted averages 33.0 3.0 11.0 6. Medicine Bow 13 ll 24 13.1 2. 4 2.18 5-5 7 )' OWl Creek 8 2 10 14.8 4.7 2.65 3-l J. Seminoe-Shirley ll ll 42.1 5.4 3-70 7.8 9- Sierra Madre 2 4 6 6.3 1.8 1.19 3·5 10. Teton-Absaroka 3 3 8.1 3.6 1.64 2.3 ll. Wind River 18 1 19 21.8 2.9 2.60 7-5 Weighted averages of all Wyoming data (AEC, USGS, J.A.S. Adams) 485 25.6 4.0 6.4 398 3-19 2primarily from J. A. S. Adams, written communication, 1969. 3Primarily for igneous rocks from Laramie batholith of N. Laramie Range. -30- TABLE 7. SUMMAFY OF HIGHLAND SYSTEMS WITH GREATEST AVERAGE URANIUM CONTENT No. Mean Mean Mean Highland System Samples ppm U ppm Th , 9b K Seminoe-Shirley Mts., Wyo. ll 5.4 42.1 3-7 Granite Mts. , Hyo. 282 4.8 25.3 5-3 3-5 Owl Creek Mts. , Hyo. 10 4.7 14.8 4.7 Front Range, Colorado 305 4.4 23.3 5.3 *Includes data from u. s. Atomic Energy Commission, u. s. Geological Survey, and J. A. S. Adams for igneous and metamorphic rocks combined. Localities With Highest Uranium and Thorium Contents T1venty reconnaissance sample locations with greater than 8 ppm U and/or 50 ppm Th are tabulated in table 8. All the rocks - 31 - TABLE 8. SAMPLE LOCATIONS WITH HIGHEST URANIUM AND THORIUM CONTENTS, WEST-CENTRAL AND NORTHWEST UNITED STATES Colorado Sample Range No. Location Unit Rock Type ppm Th ppm u Front D689 N. Cent.-3S-75W Silver Plume Granite 36.4 14.4 Granite Front D770 32-3N-72W Silver Plume Granite 29.4 13.3 Granite Front D769 12-1N-73W Silver Plume Quartz monzo- 104.2 .8 Granite nitic orthogneiss Front D78l 3-5S-76W Silver Plume Granite 94.6 5·9 Granite Needles B895 19-37N-7W Mt. Eolus Quartz 35·3 8.1 Granite monzonite wet D738 l8-19S-73VI Silver Plume Granite 23.8 20.9 Granite Sawatch D685A W. Cent. -9S-81W Silver Plume Quartz 98.9 5.2 Granite (?) monzonite Wyoming Bighorn D928 36-56N-88w Quartz 68.5 2.5 monzonite D929 18-54N-88w Quartz 57.0 2.5 monzonite Medicine Bow D790 l-l3N-79W Granodiorite 3·9 14.3 D792 9-14N-78w Sherman Monzonite 74.2 5·9 Granite D979 32-16N-83W Baggot Rocks Quartz monzonitic 57·9 1.3 Granite orthogneiss OWl Creek D930 SE-6N-6E Quartz 14.5 12.5 monzonite D938 33-40N-92W Granite 22.1 17.5 Seminoe-Shirley D992 Cent.-28N-83W Quartz diorite 73.6 23.4 Seminoe-Shirley F581 21-26N-83W Granite 38.6 9·5 Seminoe-Shirley D991 17-27N -83'tl Quartz 52.0 3·7 Seminoe-Shirley F583 l-26N-83W Quartz 65.7 2.5 monzonite Montana Gravelly E08o 15-6S-2W Quartz monzonitic 50.1 1.9 orthogneiss - 32 - Colorado The seven anomalous reconnaissance samples from Colorado are all from "-1.4 b.y. plutons of the Silver Plume event and its correlative, the Mt. Eolus Granite (table 8). The mean thorium and uranium contents of all samples from plutons of this event also are significantly higher than the means of all samples from either the ~1.7 b.y. Boulder Creek or the 1.0 b.y. Pikes Peak igneous events. Four of the Colorado samples contain more than 8 ppm u, and three contain more than 50 ppm Th. The majority of these samples are from the central and northern Front Range where the plutons of the Silver Plume event are most extensive. Additional sampling was done in three areas that '~ere anomalously uraniferous. These three areas include part of the Longs Peak-St. Vrain batholith in the Front Range, part of the Cotopaxi-Texas Creek batholith at the northwestern end of the Wet Mountains, and part of the Pikes Peak batholith at the southern end of the Front Range. Longs Peak-St. Vrain Batholith. The Longs Peak-St. Vrain batholith is a large pluton of Silver Plume granite about 30 miles long and 20 miles 'Tide in the northern part of the Front Range, northwest of Boulder, Colorado. The southern half of the batholith included in figure 12 is predominately a non-foliated quartz monzonite with few inclusions of metamorphic country rock and with a high gross radioactivity. As a result of the relatively high uranium and/or thorium in reconnaissance samples D769 and D77l, nine additional samples were collected from unoxidized exposures in deep highway cuts along a traverse between Ward and Lyons in the southern portion of the batholith (fig. 12). Thorium ranges from 28.2 to 112.7 ppm and averages 56.5 ppm (table 9). Uranium ranges from .8 ppm to 13.3 ppm and averages 6.3 ppm. These great variations in the thorium and uranium contents are reflected in the thorium/uranium ratios that vary from 2.2 to 130.2. The southern portion of the Longs Peak-St. Vrain batholith is enriched in both thorium and uranium but the average thorium/uranium ratio of nine indicates a some,rhat greater relative enrichment in thorium. The southern portion of the Longs Peak-St. Vrain batholith contains 46 percent more thorium and 21 percent more uranium than the averages in all 1.4 b.y. old igneous rocks in the western United states and 72 percent more thorium and 50 percent more uranium than the averages in all Precambrian quartz monzonites in the western United States (table 9). Cotopaxi-Texas Creek Batholith. The exposed portion of the 1.4 b.y. old Cotopaxi-Texas Creek batholith is 5 to 15 miles wide and 30 miles long. This pluton is at the northwestern end of the predominately metamorphic terrane of the Wet Mountains, between Canon City and Salida in central Colorado. The southern two-thirds of the batholith is sho'm in figure 13. The batholith is in fault contact with Paleozoic sediments on the west, and it is overlapped by Tertiary volcanics of the Thirty-nine Mile volcanic field on the north. - 33 - EXPLANATION Tertiary pi utons " Sample location j::::'"'"':i Paleozoic and Mesozoic sediments undivided N Precambrian •·c.- COLORADO Silver Plume (;ranite E!:·::;:;,~]~~ Boulder Creek Granodiorite llilllllllllllldaha Springs metamorphic cample. Seal o t Figure 12. Generalized geologic mop showing locations of samples in the Longs Peak-St. Vrain batholiths, Front Range, Colorado. -34- TABLE 9. SAN:PLE DATA, LONGS PEAK-ST. VRAIN BATHOLITH, CENTRAL FRONT RANGE, COLORADO Sample ppm ppm No. Location Rock Type Th u !_!._ Th/U D769 12-IJif -73W Quartz monzonitic 104.2 .8 4.19 130.2 orthogneiss F520 3l-2N-72W Quartz monzonite 60.9 6.6 4.37 9.2 F52l 20-2}[ -72'11 Quartz monzonite 67.1 2.5 4.48 26.8 F522 l8-2N-72W Quartz monzonite 60.1 6.0 4. 59 10.0 F523 9-2N-72W Quartz monzonite 46.9 8.0 4.65 5.9 D770 32-3N-72VI Granite 29.4 13.3 4.29 2.2 F524 34-3N-72W Quartz monzonite 112.7 2.9 2-53 38.9 F525 l-2N-7Zw Quartz.monzonite 28.2 9.9 4.31 2.8 F526 33-3N-71W Quartz :.1onzoni te 44.3 6.0 l+..lf 7.4 F527 22-3N-7lW Q,uartz monzonite 40.1 5.9 4.54 6.8 F528 25-3N-7lW Quartz monzonite 36.3 6.7 4.32 5.4 D77l 27-4N-73W Quartz monzonite 48.3 7.4 4.35 6.5 Average 56.5 6.;; 4.26 9.0 Average of 90 samples of ,.._, 1.4 b .y. old 38.6 5.2 3·8 7.4 igneous rocks Average of 71 samples of Precambrian 32.9 4.2 3-7 7-9 quartz monzonites - 35 - Now Maxi co P.M.j Sixth P.M. EXPLANATION E=:J Quaternary sediments 0 Sample location in Silver Plume Granite N ~ Tertiary volcanic flows e Coarse-grained gneissic phose ~ Paleozoic sediments @ Medium-grained massive phose Pre com brio n '!- ® Transitional phose; medium to COLORADO coarse-grained, slightly gneissic Silver Plume Granite • lilliiTII] Metamorphic complex olm--0,.-';"'~2:"'""mii3--mi4 mi 1es Scale Figure 13. Generalized geologic map showing locations of samples in the Cotopaxi- Texas Creek batholith, Fremont County, Colorado -36- Quartz monzonite is che predominant rock type in the cotopaxi-Texas Creek batholith (table 10). The present level of exposure in the Cotopaxi-Texas Creek batholith is probably somewhat higher than in the Longs Peak-St. Vrain batholith as xenoliths of metamorphic rocks are more numerous in the Cotopaxi Texas Creek batholith. Also, in contrast to the uniformly coarse-grained, massive phase in the southern part of the Longs Peak-St. Vrain batholith, samples from the southern part of the Cotopaxi-Texas Creek batholith are divisible into three phases based on megascopic textures. These are (l) a coarse-grained gneissic phase, (2) a mediwn-grained massive phase, and (3) a transitional phase with mediwn- to coarse-grained, slightly gneissic texture. The three .Phases, as indicated by symbols at sample locations in figure 13, appear to be randomly distributed. Detailed mapping might reveal whether ( l) the gneissic texture in phase l is a primary feature caused by locally greater friction of injection or (2) an early phase that was emplaced, metamorphosed, and subsequently intruded by the mediwn- grained, non-foliated phase. Contacts of these two phases are sometimes sha.rp but more often they are gradational zones represented by samples of the transitional phase in table 10. The range in the thoriwn conter,t of individual samples is from about 9 to about t,3 ppm but the range in the average thoriwn content for each of the three phases is only from about 24 ppm to about 29 ppm; the highest average is in the coarse-gratned, gneissic phase (table 10). Similarly the uranium content for individual samples is widely variable but the averages for the three phases only vary from about 6 ppm to about 8 ppm; the highest average is in the mediwn-graLned, massive phase. The average of all phases combined is about 28 ppm Th and 7 ppm U (table 10), about half the average thorium content and nearly the same average uraniwn content as in the southern part of the Longs Peak-St. Vrain batholith (table 9). Thoriwn to uraniwn ratios within the three phases vary from 3.6 to 4.4. The ratio for all phases codbined, 3.9, is less than half the ratio for all samples from the Longs Peak-St. Vrain batholith. Pikes Peak Batholith, The 1..0 b.y. old Pikes Peak batholith, comprises much of the southern portion of the Front Range in Colorado (fig. 2). Its exposed portion of about 1,700 square miles is the largest of all Pre cambrian batholiths in the western United States. The predominant rock types in this epi.zonal pluton are granite and quartz monzonite. The results of this study indicate that a portion of the Pikes Peak batholith in the St. Peters dome locality near Colorado Springs is enriched in thoriwn and uraniwn (fig. 14). This ~.ocality is characterized by numerous pegmatites containing rare earth, thoriwn, beryllium, and fluorite minerals. Alkali metasomatism of granitic country rocks is extensive. Eight samples from a traverse six miles long across the anomalous area contained 27 .l ppm to 46.7 ppm Th and 3. 5 ppm to 8.4 ppm U. The average thorium content of 33.9 ppm and the average uranium content of 5.9 ppm are each 44 percent greater than the average thorium - 37 - TABLE 10. SAMPLE DATA, COTOPAXI-TEXAS CREEK BATHOLITH, FREMONT COUNTY, COWRADO A. Coarse-grained gneissic phase Sample No. Location Rock Type ppm Th ~ Th/U D746 36-48N-llE Granodiorite 43.2 3.1 3-55 13.9 F507 3l-48N-l2E Quartz monzonite 20.7 4.0 4.05 5.2 F509 22-48N-.l2E Quartz monzonite 26.7 3.6 3.60 7.4 F512 7-l9S-73W Quartz monzonite 30.0 8.6 3.87 3.5 F506 l8-l9S-73H Quartz monzonite 29.4 16.4 4.18 i.8 F505 3l-19S-73H Quartz monzonite 23.0 4.0 3.60 ~ Average 28.8 6.6 3.81 4.4 B. Medium-grained massive phase Sample No. Location Rock Type ppm Th ppm U "{,_,_ K Th/U F50l 3-47N-llE Quartz monzonite 42.6 13.5 3-69 3.2 F502 30-48N-12E Granite 9.1 l.l 2.28 8.3 F503 6-4'7N-l2E Quartz monzonite 21.4 2.2 4.25 9.7 F508 3l-48N-12E Granite 36.8 4.5 5.16 8.2 F5ll 7-l9S-73W Quartz monzonite 29.4 3.6 4.39 8.2 D738 18-19S-73H Quartz monzonite 23.8 20.9 3.67 1.1 Average 27.2 7.6 3.91 3.6 C. Transitional phase; medium- to coarse-grained, slightly gneissic Sample No. Location Rock Type ppm Th ppm U %K Th/U F510 14-48N-12E Quartz monzonite 34.6 10.2 3·95 3.4 F504 14-47N-12E Quartz monzonite 14.2 2.0 3-75 7.1 Average 24.4 6.1 3.85 4.0 Heighted average of all phases combined 27.5 7.0 - 38 - TI4S TI5S N . .J R 68 W R67W EXPLANATION OE:=:=::E:=:==:i2=:=:=::J3 miles 1:' J Cretaceous sediments Scale ~~ b:-)F()I Precambrion 1 Pikes Peak Granite Denver • Sample location .. COLORADO Figure 14. Location of samples in the St. Peters Dome area, Pikes Peak bath o I it h , Front Range, Colorado. -39- and uraniwn contentr of all samples from the Pikes Peak batholith; and the thorium/uranium ratj o of 5.7 is essentially the same (table ll). In r,eneral the t\'lorium and uranium contents in samples from the St. Peters Dome locality are ff•.r more unitorm than in the southern part of the Longs Peak-St. Vrai.n batholith, in the Cotopaxi-Texas Creek batholith, and in most other plutons ·;hat we have sampled. Wyoming Ten of the ll anomalously uraniferous and/or thoriferous reconnaissance samples that were collected from Wyoming during this project (table 8) are i7,neous rocks from the 2.5 to 3.0 b.y. old Hycming geochronologic province. Rocks in this age range account for about 80 percent of the exposed Precru~brian terrfuce in Hyoming (fig. 2 and 3). One ·anomalously thoriferous sa.."'Tiple., D792, is from the 1.4 b.y. old Sherrtal ratholith in the Laramie R~~ge (table 8; fig. 3). Five of the Hyoming samples contain ~ore than 8 ppm U and seven contain more than 50 ppm Th. One igneous rock sarr.ple in the predominately metamorphic terrane of Montana. contained anomalously high thorium (table 8). None of our reconnaissance Sactples from Utah, South Da.l{ota, Idaho, or Washington contained more than 8 PP"' U or ~0 ppm Th. The e:>..'"Posed Precambrian· terrane in these states is dominantly metamorphic. J. A. S. Adams of Rice University has completed extensive sampling and 1;amma spectrometric analyses in the Precambrian in the northern Laramie Ra'lge ~'ld in the Granite Hountai ns under a research contract \d th the U. s. Aton-d.r. .Enerv..v Corrllnission. Some of the data from the Laramie Range is revie1.-tt::'i ar.d evaluated in the :folloHing sectian. Data on the Granite t-lountains are incomplete. A report including co;nplete data compiled under this research contract \>'ill be available at a later date. Laramie Batholith. The 2.5 b.y. old Lararnie batholith in the northern part of' the Lararrc:e Range is about 50 miles long and about 20 miles ·vride (fig. 15). An older metamorphic terrane composed of biotite and horn blende gneiss, tnl p;mati te, and amphibolite is exposed north al'ld south of the batholith (Condie, 1')69). Belts . 5 to 4 miles wide alone; the margins of the batholith are transitional between. plutonic and metam<:>rphic rocks. The southern metamorphl.c area is intruded by the 1.35 b.y. old Laramie anorthosite and related syenite. Farther south beyond the map area in Cigure l'', the 1.4 b.y. old Sherman batholith forms most. of the Laramie Ranf!e ln southern Hyoming (fig. 2). At the presen~ level or' exposure, Condie (1:;69) estimated that 74 percent of the Laramll" batholith is quartz monzonite, 14 percent is granodiorite, and 12 percent is granite. It is co;nparable in composition and age to the granitic terrane extensively exposed in other Hyoming ranges to the >rest and nortrMest (fig. 3). The locations (ng. 15) and the thorium, uranium, an-i potassiwn gamma ray spectrometric analyses for 44 samples from the northern "Laramie TABLE ll. SAMPLE 1 \TA , ST. PETERS DOME AREA OF THE PIKES PEAK BATHOLITH, SOUTHERN FRONT RANGE, COLORADO Sample No. Location Rock Type ppm Th ppm U % K Th/U F513 NW34 -·l4S-67W Granite 30.1 3.5 4.50 8.6 F514 NE32-14S-67W Granite 27.1 4.6 4.33 5.9 F515 SE32-lLS-67W Granite 28.5 4.2 4.16 6.8 F516 NE5-15S -67W Quartz monzonite 35.1 6.2 4.16 5.7 F517 SW8-l5S -67W Granite 33.6 8.4 4.08 4.0 F518 Nltll9-1;S-67W Granite 31.2 6.4 4.05 4.9 F519 NWl6 -153 -67W Quartz monzonite 46.7 6.4 4.33 7.3 D743 SW13-l~S-68w Quartz monzonite 38.5 7.1 3·83 5.4 Average 33·9 5.9 4.18 5.7 Average of 46 samples from Pikes Peak 23.6 4.1 4.0 5.9 batho1i th - 41 - ~Casper Cosper Mountain ~ 'Douglas .,. ~------NATRONA co. CARBON cO. EXPLANATION Pos't Precambrian sediments Sherman batholith Laramie anorthositic complu:; anorthosite and related syenite= ~!::€?$:1 Loramie batholith Gradational contact zonn of tht lllml!ll!l Laramie batholith Gntissic complex; includes miqmalillc lllillilliil and omphiboHflc foehn ii!Jiii!llill Amphibolite 0 Sample location e Sample with > 60 ppm Th 9 Sample with > 5 ppm U 0 10 mllu ...... "' .. ==c,~.~.7,,===±======• Figure 15. Generalized geologic map showing sample locations in the Northern Laramie Range, Wyoming. -42- Range (table 12) were provided by J. A. S. Adams, Rice University (written communication, 1969). The sample data are grouped under the Laramie batholith, the gneissic complex, and the gradational contact zones of the Laramie batholith in table 12. The average thorium and uranium contents of samples from the contact zones and from the gneissic complex are in the 20 to 25 ppm Th range and 2.5 to 3.0 ppm U range with thorium/uranium ratios of nine. The mean uranium content is typical of metamorphic rocks but the mean thorium content and the thorium/uranium ratio are at least twice as great as usual in metamorphic rocks (table 5). Thorium enrichment is also indicated in the silicic plutonic rocks of the Laramie batholith with a mean thorium content of nearly 50 ppm and an ex ceedingly high thorium/uranium ratio of 12 (table 12). The thorium in these plutonic rocks is somevrhat more than twice as abundant as in the metamorphic rocks; the mean uranium content of about 4 ppm is 60 percent greater than in the metamorphic rocks. Supergene Enrichment in the Copper Mountain Locality, Ovrl Creek Mountains, Wyoming. There is a striking example of supergene enrichment of uranium in Precambrian silicic igneous rocks in the Copper Mountain locality in the Ovrl creek Mountains, north-central Wyoming. In this locality, remnants of Eocene conglomerate and sandstone along the southern margin of the range overlie Precambrian silicic igneous rocks. These coarse clastic sediments host several uranium occurrences and small deposits. The Eocene host sedi ments are subjacent to a widespread dissected cover of Oligocene tuffaceous sediments of the White River Formation. Near Copper Mountain, exposures of Precambrian granite and quartz monzonite along a westerly trend tHo miles long are conspicuously stained vrith hematite. ·rhe extent of this alteration is essentially coincident 1·Ti th the distribution of the uraniurn occurrences in the remn6nts of Eocene coarse clastic sediments. Analytical data for tvro samples of relatively fresh, pinkish-gray quartz monzonite and three samples of quartz monzonite and granite exhibiting variable degrees of hematitic alteration are included in table 9. The uranium content of about 3·5 ppm in the unoxidized granite increases to 5.2 ppm in mildly altered rock, to 17.5 ppm in moderately altered rock, and to 93.1 ppm in severely altered rock. Thorium does not exhibit this systematic variation; the highest contents are in one sample of "fresh" rock and in the sample of the most altered rock. Thorium/uranium ratios vary systematically from a high of 10.1 in unaltered rock to a low of .6 in the most altered rock. The alteration and the anomalous uranium content of the granitic rocks and the mineralization in the superjacent Eocene sediments are believed to be genetically related. The data in table 13 strongly indicate that the anomalous amount of uranium in the altered granitic rocks is genetically related to the supergene hematitic alteration and that it is not syngenetic. OUr data do not resolve the question of origin of the uranium. It may have been derived from superjacent Oligocene tuffaceous sediments, from Precambrian silicic igneous rocks in the Ovrl Creek Mountains, or from both of these potential sources. - 43 - TABLE 12. SAMPLE DATA, NORTHERN LARAMIE RANGE, WYOMING* Laramie Batholith Gneissic Complex Sample No. ppm Th ppm u %K Sample No. ppm Th ppm U %K 78 17. 2.4 3.2 129 39· 6.8 4.9 85 6o. 3·2 3.1 135 24. 6.6 3.4 86 72. 4.3 3.6 138 42. 5.6 4.0 104 50. 1.2 4.3 148 12. l.l 3.2 109 36. 2.2 3.8 154 26. 3·9 4.7 115 64. 9·3 4.0 209 15. .8 4.2 121 67. 2.6 4.0 211 13. l.l 1.7 123 54. 1.8 2.4 214 14. 1.8 l.l 150 20. 1.4 l.O 216 15. .9 2.0 158 48. 30. 0.4 219 6.7 .7 1.4 162 15. 2.5 4.5 252 13. 2.6 3.9 163 53· 4.5 4.3 255 38. .l 3.7 166 53· 3.4 3.9 272 13. l.l 2.7 168 25. 1.7 2.3 273 44. -1.2 3.2 169 57· 1.8 5.8 Average 22.5 2.5 3.2 171 73. 2.3 3.7 Th/U = 9.0 174 66. 5·3 3·5 176 43. 1.3 4.6 Gradational Contact Zone of Laramie l8o 37· 4.1 4.2 Batholith 183 54. 2.5 3·9 186 104. 5.8 2.4 118 19. 2.1 3.0 224 16. .6 1.0 126 50. 4.0 3-9 226 65. 3·2 4.4 154 26. 3.9 4.7 228 70. 1.3 3.5 202 ~ _:2. 1.8 230 28. 1.3 1.7 237 37. 5.6 4.1 Average 24.4 2.7 3.4 Average 49.4 4.1 3.4 Th/U - 9,0 Th/U = 12.00 *Analyses by J. A. s. Adams, written communication, 1969. - 44 - TABLE 13. .ANALYSES OF SAMPLES FROM THE COPPER MOUNTAIN AREA, OWL CREEK MOUNTAINS , WYOMING ppm Th ppm u \i>K Th/U D939 Unoxidized Quartz monzonite 35.4 3.5 4.0 10.1 D935 Unoxidized Quartz monzonite 26.0 3.4 3.6 7.6 D936 Mild hematitic alteration Quartz monzonite 24.7 5.2 3.7 4.8 D938 Moderate hematitic Granite 22.1 17.5 4.9 1.3 alteration D937 Severe hematitic Granite 52.6 93-l 4.6 .6 alteration Solubility of Uranium in Silicic Igneous Rocks During Weathering Sampling was done in three locations in Colorado, one in Wyoming, and three in Arizona to test the solubility of uranium during the weathering of silicic igneous rocks. At each of the locations, samples from unweathered, uniformly radioactive granitic rocks in deep road cuts and from overlying residual detritus were collected and analyzed. Close agreement of chemical and radiometric (gamma-ray spectrometric) analyses for uranium in several of these samples indicates secular equilibrium. In most of the pairs of samples there are only minor differences between the contents of thorium and uranium in the residual detritus and in unweathered equivalents (table 14), within the probable range in variation of these elements in any relatively homogeneous igneous mass. Collectively, the average thorium content is only about two percent lower and the average uranium content is about nine percent lower in the residual detritus than in the unweathered samples. Thus within the vertical limits of sampling, most of the thorium and uranium probably are fixed in stable resistate acces sory minerals and in the crystal structure of major rock-forming minerals where they are not subject to leaching during disaggregation and oxidation of the granitic host rock. In some granitic terranes in New Hampshire (Richardson, 1964) and in Wyoming (Rosholt and Bartel, 1969), significant depletion of uranium to depths of 100 feet or more is established in the former area and is inferred in the latter area. However, other data from the Front Range, Colorado indicates no significant depletion of uranium from the surface to depths as great as )+ ,000 feet (Phair and Gottfried, 1964). These inconsistences may be influenced primarily by the ratio of soluble uranium along the grain boundaries of the major rock-forming minerals to insoluble uranium within major and accessory minerals. More studies are needed on the important aspects of solubilities and vertical distributions of uranium in granitic masses. - 45 - TABLE 14. DISTRIBUTION OF THORIUM AND URANIUM IN WEATHERING PROFILES Unweathered Residual Detritus Sec. Tl-rp. Range Rock Type ppm Th ppm U % K ppm Th ppm U ,,, K Laramie Range, 'tlyorr_t ng 3-12-72W Granite 9.7 ll.l 2.8 Front Range, Colorado 20-l2N-79W Quartz monzonite 6.2 44.7 6.!; 3· 70 22-3N-7lvf Quartz monzonite 5.9 37.7 4.8 h.73 ll-l8S-7lW Granite .6 16.1 l.O ::.87 Mazatzal Mts., Arizona SE-6N-8E Quartz monzonite 13.2 2.7 12.0 1.8 Graham Mts. , Arizona Center-llS-26E Quartz monzonite 20.9 4.29 3.7 3· 57 Sierra Prieta Mts., Arizona SE-l3S-3W Gra."!odiori te ...2..:.2 2.4 1.84 6.1 1.51 Average 20.8 3.4 3· 53 20.4 3.1 3.68 Average% deficiency in residual detritus vs. unweathered bedrock equivalents Th - 1.9% u - 8.8% SUMMARY AND CONCLUSIONS Distribution of Thorium and Uranium in Precambrian Igneous Rocks, West-Central and Northi'rest United States l. Thorium, uranium, and potassium correlate positively with increasing mag matic stage, a nearly universal condition in magmatic series throughout the world. 2. Igneous terrane is most extensive in Colorado and in Wyoming. Silicic phases are predominant over intermediate and basic phases at the present levels of exposure. The mean thorium and uranium in igneous rocks in Colo rado and in Wyoming are essentially the same. - 46 - 3. The Granite, O>rl ;reek, and Seminoe-Shirley Mountains in central Wyoming and the Front Ran;e in Colorado are the most uraniferous highland systems developed on Precunbrian rocks in the subject region. Silicic igneous terrane forms a large part of each of these ranges. 4. Geochronologically, thorium and uranium are significantly higher in~ 1.4 b.y. old silicic batholiths of the Silver Plume-Sherman event in Colorado and in~2.6 b.y. old silicic batholiths in Wyoming. 5. In general, thorium and uranium in Precambrian igneous rocks in the west central and northwest United States are slightly higher and the extent and number of localities with anomalous concentrations are greater and more widespread than in the southwest United States (Malan and Sterling, 1969). In the west-central and northwest United States, all reconnaissance sample locations with ~50 ppm Th and/or ~ 8 ppm U are in igneous rocks. Distribution of Thorium and Uranium in Precambrian Metamorphic Rocks, West Central and Northwest United States l. As a group, Precanbrian metamorphic rocks in the subject region contain about one-third as much thorium as igneous rocks (9.8 ppm vs. 29.3 ppm), about half as much uranium (2.3 ppm vs. 4.2 ppm), and about half as much potassium (1.9% vs. 3.4%). These metamorphic rocks formed from silicic detritus from the upper continental crust and from basic volcanics and related volcanigenic sediments that accumulated in geosynclines. The overall chemical composition of the metamorphic rocks is intermediate, probably near the dioritic average of the continental crust. 2. The effect of metamorphism on the distribution of thorium and uranium in the subject region is not definitive; lo;r to intermediate grade metamorphie rocks contain less thorium but more uranium than intermediate to high grade metamorphic rocks. In the southwest United States, both thorium and uranium are higher in the low to intermediate grade metamorphic rocks (Malru1 rood Sterling, 1969), a relationship that is recognized in other Precambrian metamorphic terranes (Yermolayev rood Zhidikova, 1966; Ji'ahrig rood Eade, 1968). 3. The average thorium content of Precambriroo metamorphic rocks in the subject region systematically increases with age but the average uranium content decreases. 4. The distribution of thorium rood urruoium in Precambriroo metamorphic rocks in the subject region exhibits no significruot regional geographic pattern. In contrast, thorium and urrooium in the metamorphic terrruoe of the southwest United States exhibit systematic geographic variations. ). No abnormal concentrations of thorium or urruoium were noted in the three most extensive areas of thick conglomeratic quartzites grossly similar to the basal Huronian urruoium host rocks in Ontario. These include Middle Precambriruo strata in the Medicine Bow Mountains, Wyoming and in the Needle Mountains, Colorado and Upper Precambrian strata in west-central Montana. - 47 - 6. In general, the thorium and uranium contents in Precambrian metamorphic rocks in the west -central and north~rest United States are lower and more uniform than in the southwest United States (Malan and Sterling, 1969). Anomalous concentrations of these elements are greater and more numerous in the metamorphic rocks of the latter region. Cenozoic Basin Favorability, Rocky Mountain Foldbelt and Foreland The Rocky Mountain foldbelt, on the unstable portion of the craton, is the most easterly diastrophic component of the mobile belt of the western United States. The northern two-thirds of the foldbelt and i t.s associated foreland coincide with the region of this study (fig. 16). Excluding placers in Precambrian conglomerate, the classic position of most of the vrorld 's stratiform uranium deposits in sandstone is on cratonic plat forms, in foldbelt or foreland basins that formed late in the history of mobile belts (Bilibin, 1955; McCartney and Potter, 1962). About one-fourth of the uranium resources of the United States are in early Tertiary fluvial sediments in Rocky Mountain foldbelt and foreland basins principally in Wyoming. Much of the remainder is in Mesozoic intracratonic basins in the tectonic foreland of the Mesocordilleran geanticline. The major districts of Tertiary age are in central Wyoming where Precambrian silicic plutonic rocks, extensively exposed in the cores of mountain ranges, supplied the host arkosic sediments. As previously reviewed and as indicated in figure 16, the Precambrian rocks in these ranges contain above average amounts of uranium. Thus, some of the uranium in the economic deposits may have been derived from these Precambrian rocks. Perhaps the Precambrian granitic provenances were of most importance in supplying favorable arkosic sediments and that the source of the uranium ;ras primarily in superjacent upper Tertiary tuffaceous sediments. In any case, the probability of ore discovery in Tertiary basins might be improved if basins are selected for exploration that have (l) a provenance enriched in uranium and (2) an upper Tertiary tuffaceous sedimentary section. All of the basins shown in figure 16 contain, at the least, occurrences of uranium in Tertiary sediments. The eastern half of the Wind River Basin, the Shirley Basin, the southern Powder River Basin and the northern Great Divide Basin all contain major uranium deposits (fig. 16). All are within or near a region of uranium enrichment in Precambrian Silicic igneous rocks. The greater Front Range (southern Laramie Mountains, Front Range, and northern Wet Mountains) is a large region of uranium enrichment in Precambrian siJicic igneous rocks (fig. 16). Our data indicate that this region and the central Wyoming region are the only two such regions of significant uranium enrichment in the Precambrian of the west-central and northYTest United States. Certain basins with Tertiary sediments derived from these anomalous provenances and with a present or past cover of upper Tertiary tuffaceous sediments should be favorable even though no important deposits have been discovered. These include: l. Southern Bighorn Basin 2. Hanna Basin 3. Laramie Basin 4. Western Denver Basin 5. North Park-Middle Park Basin 6. South Park Basin 7. Northern Raton Basin - 48 ------,---- ' N I T A ' N A I ' /~~, f------f' 'i '' f i ------f.--- ~ _J G ~-- \POWDER-\ i 1- RIVER -\ I I' D A ' H '' 'r ...... ""-\ ' I 0 ~ . " ., "" __ j__ I G y '' @ -----~----i g ~ B EXPLANATION Average Uranium Content in the Precambrian DENVER j (Generalized Boundaries) ; t i - 4-4.9ppm f t ; lli!iJlill! 3-3.9ppm i I D i 0 - 2-2.9ppm i I i kU?J!?:::j I - I. 9 ppm i I '< ' '< 1 ' 0 Not established ..._...._.;~ f-.-""r"-.... Major Tertiary Basins I ~~.J I •• •. Uranium deposits in Paleocene Eocene sediments ____ _j Figure 16, Distribution of Uranium in Precambrian Rocks ond in Early Tertiary Sediments in the Central and Northern Portions of the Rocky Mountain Foldbelt and Foreland -49- REFERENCES Armstrong, R. L., 196('., Mantled gneiss dome in the Albion Range, southern Idaho: Geol. Soc. America Bull., v. 79, p. 1295-1314. Bassett, W. A., and Giletti, B. J., 1963, Precambrian ages in the Wind River Mountains, Wyoming: Geol. Soc. America Bull., v. 74, p. 209-212. Bickford, M. E., Barker, Fred, Wetherill, G. W., and Lee-Hu, Chin-Nan, 1967, Precambrian chronology in the Needle Mountains, southwestern Colorado (abs.): Geol. Soc. America 1967 Ann. Mtg., New· Orleans, Program, p. 14. Bilibin, Y. A., 1955, Metallogenetic provinces and epochs, Gosgeoltekhizdat, Moscow (t;TO English translations in Library, Geol. Survey, Canada). Boyd, James, 1934, The Pre-Cambrian mineral deposits of Colorado: Colorado School of Mines D.Sc. thesis, unpub. Burwash, R. A., Baadsgaard, H., and Peterman, Z. E., 1962, Precambrian K-Ar dates from the western Canada sedimentary basin: Jour. Geophys. Research, v. 67' p. 1617-1625. Cannon, R. S., Jr., Pierce, A. P., Antweiler, J. C., and Buck, K. L., 1962, Lead-isotope studies in the northern Rockies, U.S.A., iQ Petrologic studies - A volume in honor of A. F. Buddington: New York, Geol. Soc. America, p. 115-131. Catanzaro, E. J., 1967, Correlation of some Precambrian rocks and metamorphic events in parts of Wyoming and Montana: The Mountain Geologist, v. !, , no. l, p. 9-21. Catanzaro, E. J., and Kulp, J. L., 196!,., Discordant zircons from the Little Belt (Montana), Beartooth (Montana), and Santa Catalina (Arizona) Mountains: Geochim. et Cosmochim. Acta, v. 28, p. 87-124. Condie, K. C., 1969, Petrology and geochemistry of the Laramie batholith and related metamorphic rocks of Precambrian age, eastern Wyoming: Geol. Soc. America Bull., v. 80, p. 57-82. Eardley, A. J. , 1962, Structural geology of North America: New York, Harper's Geoscience Series, 743 p. Edwards, Jonathan, Jr. , 1966, The petrology and structure of the buried Precambrian basement of Colorado: Colorado School of Mines Quart., v. 61, no. lJ, 177 p. Fahrig, W. F., and Eade, K. E., 1968, The chemical evolution of the Canadian Shield: Canadian Jour. Earth Sci., 5, p. 1247-1252. Fenton, M. D., and Faure, G., 1969, The age of the igneous rocks of the Stillwater Complex of Montana: Geol. Soc. America Bull., v. 80, p. 1599-1604. - 50 - Gast, P. W., Kulp, J. 1., and Long, 1. E., 1958, Absolute age of early Precambrian rocks in the Bighorn Basin in Wyoming and Montana, and southwestern Manitoba: Am. Geophys. Union Trans., v. 39, p. 322-334. lS59, Reply to Osterwald 's discussion of "Absolute age of -----=e~a~r~ly~P~r~e~c~am~brian rocks in the Bighorn Basin of Wyoming and Montana and southwestern Manitoba": Jour. Geophys. Research, v. 64, p. 1344- 1345. Giletti, B. J., 1966, Isotope age dates from southwestern Montana: Jour. Geophys. Research, v. 71, p. 4029-4036. Giletti, B. J. , and Gast, P. W. , 1961, Absolute age of Precambrian rocks in Montana and Hyoming: New York Acad. Sci. Ann., v. 91, p. 454-458. Goldich, S. S., 1966, Geochronology of the Midcontinent region, United States, 2. Northern region: Jour. Geophys. Research, v. 71, p. 5389- 5408. Goldich, S. S. , Iiier, A. 0. , Baadsgaard, H. , Hoffman, J. H. , and Krueger, H. W., 1961, The Precambrian geology and geochronology of Minnesota: Univ. of Minnesota and Minnesota Geol. Survey, Univ. of Minnesota Press, Minneapolis, 193 p. Hansen, W. R. , and Peterman, Z. E. , 1968, Basement -rock geochronology of the Black Canyon of the Gunnison, Colorado, in Geological Survey Research 1968: U. S. Geol. Survey Prof. Paper 600-C, p. C80-C90. Hedge, C. E., Peterman, z. E., and Braddock, W. A., 1967, Age of the major regional metrunorphism in the northern Front Range, Colorado: Geol. Soc. America Bull., v. 78, p. 551-558. Hedge, C. E., Peterman, z. E., Case, J. E., and Obradovich, J.D., 1968, Precambrian geochronology of the northwestern Uncompahgre Plateau, in Geological Survey Research 1968: U. S. Geol. Survey Prof. Paper bOO-C, p. C9l-C96. Heier, K. s., and Rogers, J. J. W., 1963, Radiometric determination of thorium, uranium and potassium in basalts and in two magmatic differ entiation series: Geochim. et Cosmochim. Acta, v. 27, p. 137-154. Heimlich, R. A., and Banks, P. 0., 1968, Radiometric age determinations, Bighorn Mountains, lvyoming: Am. Jour. Sci., v. 266, p. 180-192. Hills, F. A., Gast, P. W., Houston, R. s., and Swainbanlc, I. G., 1968, Precambrian geochronology of the Medicine Bmr Mountains, southeastern Hyoming: Geol. Soc. America Bull., v. 79, p. 1757-1784. Hutchinson, R. M., and Hedge, C. E., 1967, Precambrian basement rocks of the central Front Range and its 700 million year history: Gecl. Soc. America, Rocky Mountain Sec. Guidebook, 51 p. - 51 - l967a, Depth-Zone emplacement and geochronology of Precambrian ---p=lu_t.,.o_n_s-,-central Colorado Front Range ( abs. ) : Geol. Soc. America, Rocky Mountain Sec. 20th Ann. Mt., Program, p. 40-41. Jaffe, H. W., Gottfried, D., Waring, C. L., and Worthing, H. VI., 1959, Lead-alpha age determinations of accessory minerals of igneous reeLs (1953-1957): U.S. Geol. Survey Bull. 1097-B, p. 65-148. James, H. L., 1958, Stratigraphy of pre-Ke;reenalfan rocks in parts of Northern Michigan: U. S. Geol. Survey Prof. Paper 314-C, IJ2 p. Kistler, R. H., Obradovich, J. D., and Jackson, E. D., 1967, Isotopic ages of rocks and minerals from the Sti1l~ 1969, Isotopic ages of rocks and minerals from the Stillwater ----,;Cc-o-m-p""l-e-x, Montana: Jour. Geophys. Research, v. 74, p. 3226-3237. Malan, R. C., and Sterlinr;, D. A., 1969, An introduction to the distribution of uranium and thorium in Precambrian rocks includinp-, the results of preliminary studies in the southlfestern United States: U. S. Atomic Energy Cown. AEC-RD-9, 54 p., open file. l969a, Distribution of uranium and thorium in Precambrian rocks ---o~f~t~hce~Hestern Great Lakes region: U. S. Atomic Energy Comm. AEC RD-10, 25 p., open file. McCartney, H. D., and Potter, L. I., 1962, Mineralization as related to structural deformation, igneous activity and sed.imentation in folded geosynclines: Canadian Mining Jour., v. 83, no. 4, p. '33-87. Newhouse, H. H. , and Hagner, A. F., 1957, Geologic map of anorthosite areas, southern part of Laramie Range, Wyoming: U. S. Geol. Survey Mineral Inv. Field Studies Map MF 119. Obradovich, J. D., and Peterman, Z. E., 1968, Geochronology of the Belt Series, Montana: Canadian Jour. Earth Sci., 5, p. 737-747. Pearson, R. C., Hedge, C. E., Thomas, H. H., and Stern, T. H., 1966, Geochronology of the St. Kevin Granite and neighboring Precambrian rocks, northern Sa~ Peterman, Z. E., and Hedge, C. E., 1968, Chronology of Precambrian events in the Front Range, Colorado: Canadian Jour. Earth Sci., 5, p. 749-756. Peterman, Z. E. , Hedge, C. E. , and Braddock, W. A. , 1968, Age of Precambrian events in the northeastern Front Range, Colorado: Jour. Geophys. Research, v. 73, no. 6, p.2227-2296. - 52 - Phair, George, and Cottfried, David, 1964, The Colorado Front Range, Colorado, U.S. A., as a uranium and thorium province, In Adams, J. A. S., and 1 mrder, 'rl. M., eds., The natural radiationenvironment: Chicago, Univ. Chicago Press, p. 7-38. Powell, J. L., Skinner, W. R., and Walker, David, 1969, Whole-rock Rb-Sr age of metasedjmentary rocks below the Stillwater Complex, Montana: Geol. Soc. America Bull., v. 80, p. 1605-1612. Richardson, K. A., 1964, Thorium, uranium, and potassium in the Conway Granite, New Hampshire, U.S.A., in Adams, J. A. S. , and Lowder, W. M. , eds., The Natural radiation environment: Chicago, Univ. Chicago Press, p. 39-50. Rosholt, J. N. , and Bartel, A. J. , 1969, Uranium, thorium, and lead systematics in Granite Mountains, Wyoming: Earth and Planetary Sci. Letters, v. 7, p. 141-147. Schwartzman, D. W. , and Giletti, B. J. , 1968, "Excess" Argon in minerals from the Stillwater Complex, Montana (abs.): Am. Geophys. Union Trans., v. 49, p. 359. Silver, L. T. , and Barker, Fred, 1967, Geochronology of Precambrian rocks of the Needle Mountains, southwestern Colorado: Pt. I, U-Pb zircon results (abs.): Geol. Soc. American 1967 Ann. Mtg., Ne1tT Orleans, Program, p. 204. Sterling, D. A., and Malan, R. c., Distribution of uranium and thorium in Precambrian rocks of the southwestern United States: Am. Inst. Min. Met. Eng. Trans. (in press). Wetherill, G. W., and Bickfor-1, 11. E. 1965, Primary and metamorphic Rb-Sr chronology in central Colorado: Jour. Geophys. Research, v. 70, no. 18, p. 4669-4686. Yermolayev, N. P., and Zhidikova, A. P., 1966, Behavior of uranium in progressive metamorphism and ultrametamorphism as observed in the western part of the Aldan Shield: Geochemistry Internat., 3, p. 716-731. Young, G. M., 1969, Stratigraphical and sedimentological comparison o~ early Proterozoic rocks of S. E. Wyoming and the Great Lakes Region (abs.): Institute on Lake Superior Geology 15th Ann. Mtg., p. 45. - 53 - APPENDIX - 54 - , ... · APPENDIX. TABULATION OF ANALYTICAL DATA, WEST-CENTRAL AND NORTHWEST UNITED STATES COLORADO ppn Mountain Range sam;ele No. Sec.~· R~e Formation or Grou;e Rock 'IYPe eThOg eUsOa- ~ Reference Front Range D689 II. Cent.-35-75\i Silver Plume Granite Granite 41.4 17.0 4.44 D690 liE-15-75\i Boulder Creek Granite Monzonitic orthogneiss 16.2 .6 2.85 D69lA N. Cent. -11i-78w Boulder Creek Granite Quartz monzonite 5.5 1.0 4.62 D691Jl N. Cent. -1N-78W Boulder Creek Granite Quartz diorite 2.9 6.9 1. 72 D741 3-165-7111 Silver Plume Granite Quartz monzonite 48.4 5.2 4.01 D'T42 27-145-70\i Pikes Peak Granite Granite 23.1 2.9 4.17 D'/43 13-155-68W Mt. Rosa Granite Quartz monzonite 43.8 8.4 3.83 F519 19-15S-67W Pikes Peak Granite Quartz monzonite 53.1 7.6 1.18 D748 7-125-11E Trout Creek Augen Gneiss Quartz diorite 9·9 1.9 1.44 D749 18-llS-7211 Pikes Peak Granite Quartz monzonite 20.2 4.2 4.69 D750 26-95-7411 Silver Plume Granite Quartz monzonite 44.0 3.6 3.86 D751 35-8s-75W Silver Plume Granite Quartz monzonite 39.2 5·9 4.29 D752 14-75-75\i Silver PJ.ume Granite Quartz monzonite 20.5 2.5 3.60 D753 16-75-70\i Pikes Peak Granite Quartz monzonite 31.3 3.7 3.99 D754 36-75-711< Pikes Peek Granite Quartz monzonite 25.5 4.7 3.35 D755 6-78-7111 Pikes Peak Granite Quartz monzonite 44.9 3.3 4.36 D756 15-58-70\i Idaho Springs Quartz dioritic gneiss 5.4 3.5 .67 ~ D757 34-38-7211 Idaho Springs Granodioritic gneiss 13.6 3.5 2.40 ~ D758 13-48-7411 Boul.der Creek Granite Granodiorite ll.4 2.3 1.92 D759 13-48-7411 Boulder Creek Granite Granodioritic orthogneiss 7.1 3.1 2.65 D764 13-28-7111 Coal Creek Quartzite Quartzite 6.1 .6 .79 D765 14-28-7111 Coal Creek Quartzite Quartzite 3.8 1.6 .Q9 D766 9-28-7111 Quartz monzonitic gneiss 23.4 3.8 3.44 D767 36-lS-7211 Boulder Creek Granite Quartz monzonite 29.9 4.7 2.68 D768 6-lS-7211 Boulder Creek Granite Quartz dioritic orthogneiss 1.5 1.0 2.50 D769 12-lN-7311 Silver Plume Granite Quartz monzoni tic orthogneiss ll8.6 ·9 4.19 D770 32-311-7211 Silver Plume Granite Granite 33.4 15.7 4.29 D771 27-411-7311 Silver PJ.ume Granite Quartz monzonite 55.0 8.7 4.35 D772 22-511-7211 Silver Plume Granite Quartz monzonite 33.8 5.3 3.97 D773 4-511-7111 Idaho Springs Pegmatite .1 1.5 2.36 D774 8-511-70\1 Idaho Springs Quartzite 13.7 4.4 2.71 D775A 20-1211-7111 Sherman Grenite Quartz monzonite 43.5 7.3 3.38 D775B 20-1211-7111 Sherman Granite Quartz monzonite 50.9 7.6 3.70 D776 15-911-7211 Silver Plume Granite Quartz monzonite 33.5 2.5 3.62 D777 2-911-73\i Silver Plume Granite Quartz monzonite 40.7 6.6 4.17 D778 10-8N-75W Silver Plume Granite Quartz monzonite 15.5 5.0 3.56 D780 3-58-76\1 Idaho Springs Granodioritic gneiss 9.6 3.0 1.56 D781 3-58-7611 Silver Plume Granite Granite 107.6 6.9 3.34 D789 ll-1111-7911 Idaho Springs Syenodioritic gneiss _H ll 1.16 Aver;;e 29.0 4.6 3.07 e'l'h02 eU308 6.3 APPENDIX. TABULATION OF ANALYTICAL DATA, WEST-CENTRAL AND NOR'l.HWE3T UNITED STATES (Continued) COLORADO (Continued) ppm ppm l.fountain~ sem;ele No. Sec. Twp. R~e Formation or GrouE Rock TYPe elli02 eUaOs %eK Reference Front Range 30 samples Pikes Peak Granite Predominately quartz monzonite 29.3 5.8 Gottfried and Phair, 1964 (USGS data) 8 samples Shennan Granite Predominately quartz monzonite 27.4 6.7 Gottf'ried and Phair, 1964 45 samples Silver Plume Granite Predominately quartz monzonite 41.5' Gottfried and Phair, 1964 52 samples Silver Plume Granite Predominately quartz monzonite 6.12 Gottfried and Phair, 1964 52 samples Boulder Creek Granite Predominately granodiorite 15.33 Gottfried and Phair, 1964 165 samples Boulder Creek Granite Predominately granodiorite 3.14 Gottfried and Phair, 1964 15 samples Idaho Springs Formation Metamorphics undivided 18.6 Gottfried and Phair, 1964 15 samples Idaho Springs Fonmation Metamorphics undivided -- .2.:.!: Gottfried and Phair, 1964 Area weighted average 25.8 5.3 eTh02/ eU308 4.9 Sangre de Cristo D730 8-33S-70W Granodioritic gneiss 6.3 2.0 1.54 Range D731 12-38N-71W Quartz monzoni tic orthogneiss 13.6 3.2 4.11 D732 13-30N-71W Quartz dioritic gneiss 7.1 2.7 1.60 Average 9.0 2.6 2.42 eTh02/eU30a 3.5 Saguache Range D381 16-20S-2E Quartz monzonite 6.3 2.1 4.44 D676 w. Cent. -49N-2E Argillite 8.5 4.0 3.98 D677 S. Cent.-49N~)E Quartz monzonite 16.9 2.3 4.00 D678 NW-49N-6E Quartz monzonite 28.1 2.3 4.54 D679 SE-50N-6E Granodiorite 20.1 6.4 2.77 D680 S11-50N-7E Anthophyllite schist 21.0 3.2 4.12 D681 Cent. -49N-8E Quartz diori tic orthogneiss 9·7 1.8 1.42 D683 E. Cent.-14S-78W Granodiorite 12.7 2.3 2.74 D684 Cent.-9S-81W Granitic orthogneiss 18.3 9.0 3.35 D685A W. Cent.-9S-81W Quartz monzonite 112.5 6.1 4.o6 D685B w. Cent.-9S-81W Quartz monzonite 74.9 2.7 4.38 D686 s. Cent.-7S-80W Granodioritic orthogneiss 23.1 5.4 5.12 D687 Cent.-6S-81W Cross Creek Granite Quartz monzonite 21.3 1.9 3.22 JY747 1D-49N-9E Granodioritic gneiss 2.7 1.5 1.05 JY784 13-11S-80W Silver Plume Granite Quartz monzonite 45.7 5.1 3.94 JY786 5-11S-82W Silver Plume Granite Granite 23.7 1.1 4.87 D787 6-11S-83W Quartz monzonite 30.8 2.9 3.12 Average 28.0 ;. 5 3.60 eTh02/eUsOa 8.0 LArea weighted average from 7 batholiths. 2Area weighted average from 6 batholiths. 3Area weighted average from 2 batholiths. 4 Average from 1 batholith. APPENDIX. TABULATION OF ANALYTICAL nATA, WEST-CENTRAL AND NORmw!ST UNITED STATES (Continued) COLORAOO (Continued) ppn ppn Mountain Range SamJ2le No. Sec.~· R~e Formation or Grou~ Rock Tn>e e!lb.02 ~ %eK Reference Wet Mountains ll734 6-23S-69W Quartz monzonite 9.2 2.1 3.84 ll735 33-22S-69W Granodiorite 16.9 3.5 4.02 ll736 5-208-7011 Pikes Peak Gran! te Quartz monzonite 8.1 2.8 3.49 ll737 9-218-7111 Quartz monzonitic orthogneiss 18.5 1.2 4.71 ll738 18-19S-73W Silver Plume Granite Quartz monzonite 27.1 24.6 3.67 ll739 4-19S-73W Idaho Springs Quartz dioritic gneiss 10.3 3.7 2.22 Jl740 8-18s-71W Pikes Peak Greni te Quartz monzonite 13.5 1.2 3.88 Jl745A ll-18s-71W Pikes Peak Granite Granite 20.2 ·7 4.06 D745B ll-18S-71W Pikes Peak Gran! te Granite 18.3 1.2 3.87 ll746 36-48N-11E Silver Plume Granite Granodiorite 49.2 2:.1 3.55 Aver:,e 19.1 4.5 3.73 e'IhOa eUsOa 4.2 Needles-San Juan B883 26-37N-6W Vallecito Conglomerate Conglomeratic quartzite 11.7 2.5 .12 Mountains B885 4-37N-6W Vallecito Conglomerate Conglomerate 6.6 2.1 2.05 B890 8-43N-7W Uncompahgre Slate 7.5 2.3 1.90 B895 19-5711-7>1 Mt. Eolus Granite Quartz monzonite 40.2 9·5 4.36 C590 17-3911-BW Granodioritic gneiss 8.5 3.8 1. 73 Average 14.9 4.0 2.03 ....~ eTh02/ eU30a 3.7 Park-Gore-Tenmile C588 6s-8E Idaho Springs Quartz feldspar gneiss 23.4 4.6 2.92 Ranges C589 6S-8E Idaho Springs Biotite schist 3.8 1.8 2.67 D688 W. Cent.-6N-78W Idaho Springs Quartz dioritic orthogneiss 9.1 2.4 2.66 lJ692 NW-1N-82W Granodiorite 7·7 1.1 2.99 ll693 NE-1N-83W Tactite 3.4 1.2 2.03 D694 SE-6N-84W Granod1oritic flaser gneiss 18.5 3.6 2.37 ll695 cent. -7N-84w Quartz monzonite 31.9 4.2 3.81 IJ696 s. Cent.-lON-84w Quartz dioritic gneiss 6.5 3.0 1.42 ll782 3-8S-78W Idaho Springs Quartz dioritic gneiss 19.1 5.1 3.22 ll783 2-8S-78w Quartz monzonite 26.5 M 3.10 Average 15.0 3.4 2.72 eTh02/ eU30a 4.4 APPENDIX. TABULATION OF ANALYTICAL DATA, WEST-CENTRAL AND NORTHWEST UNITED STATES (Continued) ~ p;m Mountain Rge Sem.:21e No. Sec.~- R~e Formation or GrouE Rock !lY1le eTilOg- ~ ~ eK Reference Beartooth Range Ell6 31-58N-107W Quartz monzonitic orthogneiss 20.5 1.7 2.89 Ell7 8-57N-105ll Quartz monzonitic orthogneiss 37.1 2.2 2.40 Ell8 6-57N-1o41/ Quartz dia.basic orthogneiss 14.7 3.1 1.43 Average 24.1 2.3 2.24 e'lli02/eUs08 10.5 Bighorn Range ll921 6-4811-84\i Quartz dioritic paragneiss 6.0 .4 1,00 ll922 15-50N-84ll Quartz diori tic paregneiss 1.2 ,1 .60 ll923 15-50N-B4W Quartz monzonitic paregneiss 18.0 1.0 2.81 ll924 5-50li-83W Diallage gabbro < .1 <.1 <.01 ll925 13-53li-B4W Granodioritic orthogneiss 20.9 1.0 2.72 ll926 35-55N-B611 Granodiorite 30.5 2.3 2.68 ll927 29-56N-87W Quartz monzonite 20.5 .6 2.58 D928 36-56li-8BII Quartz monzonite 77·9 ;.o ;.81 D929 18-54li-BBII Quartz monzonite 64.9 3.0 3.97 10 sezn,ples Granite 20.4 1.7 --- Phair and Gottfried, 1964 Average 23.4 1.5 2.24 eTb02 /eUsOe 15.6 ' ~ Granite MOuntains D993 15-2911-8611 Sweetwater Granite Granite 53.1 2.8 4.;6 "' D994 36-29N-87W Sweetwater Granite Quartz monzonite 13.9 1.1 2.47 D995 25-29!1-8911 Sveetvater Granite Granite 55.1 2.6 4.o; 279 samples Sweetwater Granite Granite 28.8 5. 7 ;.52 Written communication, ------J. A. s. Adams, 1969 Average 28.8 5.7 3.52 e'lli02 /eUsOs 5.2 Hartville Uplift D907 15-3111-6411 Diabase <.1 < .1 .18 D909 7-3211-6;w Mica schist 27.7 3.2 ;.87 Average 13.9 1.7 2.03 eTn02 /eUs08 8.2 Laramie Range D794 11-14N-7211 She:rman Granite Quartz monzonite 21.1 4.0 3.94 D795 1-15N-71ll Sherman Granite Granite pegmatite 20.7 },0 3.91 D796 55-17li-72W Laramie Anorthosite Quartz diorite 1.7 .3 .68 D797 19-20N-7211 Laramie Anorthosite Granite 11.8 1.4 4.11 D798 16-20!1-7211 Laramie Anorthosite Monzonite 4.1 1.5 4.00 D799 21-2111-71\1 Laramie Anorthosite Diorite <.1 <.1 .68 D8oo 22-2111-71\1 Laramie Anorthosite Titano-magnetite < .1 < .1 <.01 D901 12-2111-7111 Laramie Anorthosite Quartz diorite 1.4 .2 .91 D902 1-2111-7111 Laramie Anorthosite Syenite .4 .3 ;.39 D905 14-3111-77W Laramie Granite Quartz monzonite 25.2 ;.; 4.21 APPE!lDIX. TABULATION OF ANALYTICAL DATA, WEST-CENTRAL AND NORmWEST UDITED STATES (Continued) ~(Continued) ppn PPl1 Mountain Range ssle No. Sec. ~· Range Formation or GrauE Rock "Y1'e e~02 eU;10e ~eK Reference Laramie Range IY;l05 5-30li-75W Laramie Grenite Quartz monzonite 22.5 7.1 3.77 (Continued) JY;Jo6 5-3011-7511 Laramie Granite Quartz monzonite 15.3 2.0 2.93 F585 20-13N-72W Shem.en Granite Quartz monzonite 15.7 2.2 4.62 F586 3-1211-7211 Sherman Granite Granite u.o 3.4 3.18 F587 3-12li-72W Shennan Granite Granite 12.6 3.3 4.78 87 samples Laramie Granite Predominately quartz monzonite 42.1 3.7 - Written communication, J. A. S. Ad ~ (Continued) P:!m P:!m Mountain Range SamJ2le No. Sec. ~· Range Fo:nna.tion or Gro:!!E Rock 'JYpe e~02 eU30s ~eK Reference OWl Creek !1950 SE-6N-6E Quartz monzonite 16.5 14.7 3.55 Monntains !1951 SE-6N-6E Quartz monzonite J2.1 4.9 2.22 !1933 SE-6N-6E Quartzofeldspathic parahornfels 1.8 .5 ·59 !1934 56-8N-1W Quartz monzonitic paragneiss ·9 <.1 2.56 !1955 29-401!-92\f Quartz monzonite 29.6 4.0 3.58 !1936 29-401!-92\f Quartz monzonite 28.1 6.1 3.65 !1938 33-401!-9211 Granite 25.1 20.6 4.92 !1939 33-401!-92W Quartz monzonite 40.3 4.1 5.96 !1940 1-40N-89W Quartz gabbroic orthogneiss 6.4 .1 ·99 !1941 10-40!!-88w Granodioritic orthogneiss 7.1 __,§_ ....:..§2 Average 16.8 5.6 2.65 eTh02 /eU30a 3.0 Rawlins Uplift !1987 17 -211!-87W Quartz monzonite J2.1 1.5 2.41 Seminoe-Shirley D989 7-251!-84\f Granodiorite 31.9 3.7 1.57 Mountains !J990 7-26N-83W Quartz monzonite 31.1 1.2 3.16 !1991 17-27N-83W Quartz monzonite 59.2 4.4 4.03 !1992 Cent, -28N-83W Quartz diorite 83.7 27.6 .30 F576 20-29N-83W Granite 48.5 3.7 4.21 0"' F579 22-28N-83W Quartz monzonite 36.9 3.1 4.94 F580 30-25N-82W Granite 18.3 2.7 4.71 F581 21-26N-83W Granite 43.9 11.2 4.23 F582 8-26N-81W Granite 45.0 4.8 5.15 F583 1-26N-83W Quartz monzonite 74.8 2.9 3.94 F584 14-26!1-83\f Quartz monzonite 54.1 4.8 4.51 Average 47.9 6.4 3.70 e'J!n02/eU30a 7·5 Sierra Madre I$61 30-141!-8611 Quartzite 9.6 2.0 .16 Range !1962 50-14li-86W Chlorite schist 1.1 .6 .o4 I$63 25-14!i-86W Phyllite 15.0 5.3 3.17 !1964 29-14!1-85" Granite 11.6 2.5 5.l2 !1965 27-141!-85\f Quartzite 1.3 <.1 .10 !1966 15-14!1-85\f Gabbro 4.8 ...!:.2 _,.2.§. Average 7.2 2.1 1.19 e'fn02 /eUs08 3.4 APPEIIDIX. TABULATION OF A!fALYTICAL DATA, WEST- CENTRAL AND NOR'IHWEST Uli!TED STATES (Continued) WYOMING (Continued) ppn Mountain R~ Sample No. Sec. Tvp. Range Formation or Group Rock 'IYPe eTh0-2 eU30s Ell2 l2-42N-105W Granite 51.5 2.9 3.48 Ell3 24-40N-1o6W Quartz monzonite 53.0 12.8 4.47 Ell4 24-40N-1o6W Quartz dioritic orthogneiss 19.3 3.3 1.35 Ell5 34-42N-1o8W Quartz monzonite 8.5 3.7 4.14 12 samples Granite 15.6 3.7 -- Phair and Gottfried, 1964 Average 21.2 3.5 2.60 eTh02/eU30a 6.1 SOUTH DAKOTA Black Hills 1910 33-3S-4E Black Hills Schist Micaceous quartzite 15.8 1.7 2.32 1911 15-3S-4E Black Hills Schist Phyllite 14.6 8.3 2.36 1912 21-1S-6E Black Rills Schist Phyllite 14.9 2.4 2.16 1913 3-2S-5E Harney Peak Granite Quartz diorite 1.6 2.9 1.99 1914 30-2S-5E Harney Peak Granite Quartz monzonitic pegmatite .1 ·9 2.95 1915 20-1S-5E Black Rills Schist Si1tite 16.3 2.9 1. 71 1917 16-211-2E Black Hills Schist Graphite schist 11.1 1.4 3.66 1919 6-4N-3E Black Hills Schist Graphite schist 9.6 8.1 2.87 Average 10.5 3.6 2.50 eT'n02/ eU30a 2.9 APPENDIX. TABULATION OF AUALYTICAL DATA, WEST-CENTRAL AND NOR'IHWEST UNITED STATES (Continued) ~ ppn ppn Mountain Range S~le No. Sec. Twp. Rans:e Formation or GrauE Rock T::rPe elliOg eU30s \leK Reference Uinta-Wasatch ])396 ,32-2N-22E Mutual Quartzite Quartzite 1.3 .3 .O'f Mountains F537 10-28-llW Mutual Quartzite Quartzite 1.2 1.2 .20 F538 22-28-llW Red Pine Shale Shale 22.7 3.2 2.95 F539 1-3S-1E Little Willow Formation Quartz dioritic gneiss 1.8 1.1 .71 F540 19-26-2E Big Cottonwood Formation Phyllite 11~.0 4.9 1.45 F541 19-26-2E Big Cottonwood Formation Quartzite 2.3 1.6 .16 F542 23-26-2E Mineral Fork Tillite Conglomeratic sandstone 4.4 1.6 .82 F543 14-26-2E Mutual Quartzite Quartzite 1.8 1.0 .81 F545 ll-2N-1E Farmington Canyon Series Quartz dioritic gneiss 30.8 3.0 2.77 Avere.ge 8.9 2.0 1.10 eTb02/eU30a 4. 5 ~ Pre-Belt of E076 23-66-4E Pony-Cberey Creek complex Quartz monzonitic gneiss 29.6 1.3 3.46 SW Montana; E077 15-56-4E Pony-Cherry Creek complex Granodioritic gneiss 6.3 1.5 .89 Gel.latin, E078 24-2S-2E Pony-Cherry Creek complex Granodioritic gneiss 10.3 ·3 .97 Madison, E079 ll-46-1W Pony-Cher.r,y Creek complex Granodioritic gneiss .7 < .1 .69 Gravelly, E080 15-6s-2W Pony-Cherry Creek complex Quartz monzonitic orthogneiss 57.0 2.2 4.20 'Ibbacco Root, ' Ruby, Highland, E081 7-6s-3W Pony-Cherry Creek complex Quartz gabbroic orthoamphibolite 1.2 .8 .46 Beartooth, end E082 20-46-4w Pony-Cherry Creek complex Quartz monzonitic gneiss 24.4 ).1 1.84 Absaroka Ranges E083 35-8s-6W Pony-Cherry Creek complex Granitic gneiss 45.0 3.6 4.05 E084 34-76-711 Pony-Cherry Creek complex Quartz gabbroic orthoamphibolite .2 <.1 • 74 E086 27-26-6W Pony-Cherry Creek complex Grenodioritic gneiss 1.8 ·5 1.26 EQ90 12-96-81! Pony-Cherry Creek complex Quartz monzonitic gneiss 33.6 5.3 3.83 EQ91 34-105-711 Pony-Cherry Creek complex Granodioritic gneiss 19.2 2.2 2.10 EJ.19 18-8s-20E Beartooth gneissic complex Granodioritic gneiss 17.2 2.9 1.48 El20 22-5S-15E Beartooth gneissic complex Granodioritic gneiss 3.9 3.9 1.26 El21 17-5S-15E Stillwater complex Quartz gabbro < .1 2.1 .01 El22 17-56-15E Stillwater a amplex Quartz diorite < .1 <.1 .03 El2) 22-46-10E Beartooth gneissic complex Granodioritic gneiss 6.9 3.3 1.20 El24 32-76-7E Pony-Cherry Creek complex Quartz dioritic gneiss 20.8 7.3 1.90 El25 35-ll6-2E Pony-Cherry Creek complex Quartz diorite ·5 < .1 .10 E835 10-26-8w Pony-Cherry Creek complex Biotite schist 29.2 2.2 ;;.08 3 samples Granite 19.2 ...!:2 -- Phair and Gottfried, 1964 Average 15.9 2.1 1.68 eTh02 / eU30e 7.6 APPENDIX. TABULATION OF ANALYTicAL DATA, WEST-CENTRAL AND NOR'mWEST UNITED STATES (Continued) ~(Continued) Pl'" ppn Mountain R~e Se.m~le No. Se=. ~· Ren~e Formation or Grou:e Rock~ e'IhOg eU30a ~ eK Reference Belt Supergroup E ~ F403 2-56N-2W Belt undivided Limestone 1.1 4.8 .31 F40i; 33-56N-4W Pre-Belt gneissic complex Granodioriti~ gneiss 7-6 2.5 1.04 F4Q9 34-50N-3W Belt undivided Quartzite 16.1 ).j 3./1 F410 2l-49N-1W Belt undivided Slate ll~. 0 3.6 2.74 .,4ll 12-47U~4E Belt undivided Chert 11.3 2.1 2-57 F412 j6-46N-5E Belt undivided Slate 19-> 4. -r ~~.40 pl~13 )6·17N-31W Belt undivided Quartzite 11.3 4.3 1.69 F' 1(. l5-21lf-21E Ravalli Group Biotite schi.st. 1), ) 4.1! 2.9) F417 16-211N-21E Ravall:l Group Q:uart:z;ite 7." 2.3 l. 75 FhJ.8 l-19N-21W flel.~ undivided Quartzite {.t. 2. ') 1.99 Fill9 2'7-19N-24E Ra.vs.lli Group Argillite 13.1.r. ....2.,2_ 2.)2 !,ve:r-ug» i ,_! '), ~ "?. >;_:. eTtC21 eUoCe ). ;) APPENDIX. TABULATION OF AliALY'l'ICAL DATA, WEST-CENTRAL AND NOR'IH"WEST UNITED S'XATES (Continued) WASHING !ION PJlln b!ountain Range S~le No. Sec, ~· Range Formation or Grou~ Rock= e~g- eUsOs ~ eK Reference F405 15-55N-44E l!elt undivided Phyllite 17.4 ).5 ).9) F406 35-59N-44E Belt undivided Ch1ori te schist 4.2 1.1 1.31 F4o8 4-24!i-44E Pre-Belt gneissic complex Quartz monzonitic gneiss 18.5 3.6 3.73 Average 13.4 2.7 2.99 eT'n02/eUsOs 5.0 .,."'