Reconnaissance of the Northwest Rim of the Colorado River Basin

RME -77(Pt. ~ ) / Subject Category :' GEOLOGY 'AND MINERA,LOGY

U NI TED STATES ATOMIC ENERGY COMM I SSION

RECONN.AISS ...-lliCE OF THE NORTHWEST RIM OF THE COLORADO RIVER BASIN, WAYNE AND GARFIELD COUNTIES, UTAH

By Robert C. Ge rhard

January 1955

Exploration Division Grand J unct ion Operations Office Grand Junction, Colorado

Tech n ic a l In formation Ser v i ce Oak. R i dge Te n nes s ee

UNCLASSI FI ED I. REC (o NNA l qSA CE OF THE NORYrI1rJEST Rill OF' THE- COLORA OO RIVER BASIN, .. WAYNE AND GARFIELD COUN TIES, UTAH .

.- ABSTRACT

About five mont hs ' f:eld work was devoted to examining the Salt Wash and Mossback outcrops i n a 1,0 O-square--mile area along the north-" . . west r"JTl of 'thE; Co oraclo River, Wayne and Garfield Counties, Utah.-

In the Little Rockies district, oxidized d~posits of vanadium- . _ uranium ore, associated chiefl ; with ca r bonized wood, logs, and plant '. . "~. fragments, occur in extremely small lenses in two horizons of the Salt ~~: Wash member of t he Morrison f ormation. Beca use of the small l~ri tic ular : .~. nature of presently known or ebodies, ?hysical ~xploration in t his dist r1c t ~

~ does not now appear to be econOIll:..ca.J..J.Y f easible. 0 -' • __ - . .. "In the Sout he rn Green River Desert, urap.ium m:i.n era liz~tion a Ssc 'cia ted.} ~ ~'~:' ~ ~' with carbon trash, asphaltite, and copper mi nerals occurs in the lower " -~ .: Mossback channel unit fillino paleochannels cut into the Moenkopi for.mation ~

-:-" ... : -- -."- INTRODUC TION

_::.... '~"; -:- Geologic reconP.ais sance was conducted to del i neate ground f~vorab l e '~ ~ .-:,= ~c-+ for exploratory drilling in r,he Salt \Aiash a nd Hossback s a nw.s tone~ . :'.'. '":".:..:' along the northwest r im of t he Color a do Ri ver, Wayne and Garf1~ld P ounties-;--_~ <" ·Ptah. As early as 19L5 t he Salt 1'1i ash depo'si ts of the Littl e Rockie; ·.. ~"~ .. ~ ~::"-' diSl.-rict were evalua ted by the TJnion Nines Development Corpo.ration til-· , - "--" ~ a detailed geologic report (1 ) . - . -, .' ." .. "- ~ ".

From Feb ruary t o July~ 19S3, field r econnai s sance wa s conduc t e d -' '--'"'~'r in this ar ea. As t:.me and ef fort were equal_y divided betWeen the $alt. Wash .and :Hossback €Jr.-pcs e re, t he s:rr...aller Salt 1;Jash out~ rop belt wa s wo ....ked in greater det~. il. This r econnaissance consisted of traver sing the rim with a scintillat i on cOL:TIte r , meas ~rr:'ng CI'oss-stra ta to det eriiine s edi- . mentary t rends, taking str atigraphic se ~ t:onsfcr facies st~dy, examining mines and prospects to est ablish ore guices, and mappL~g ore trends to determine t heir size, €xte n t ~ a. d P CCI'_c!.".ic r-alue. Geologic r econnaissan:e 0: the Mos sback exposures was performed in · two phases. First, a m re detailed investigation, including mapping and · channel sampling 0: ~nes; making radioactivity surveysJ detarmining channel sand limits and sedimentary trends; and examining the rim for paleochannels, _ranium miner~ s, limonite, logs, carbon trash, and copper staining, was carried outo

A regi onal recorxaissance made up the brief second phase. Prior to field study, an ai r su~vey was made to search for thick sands and . paleocha~~ els in the lower Mossback 5a~dstone of Millard Canyon and Elaterite Easin (figo 1). These outcrops were later investigated o~ the ground for anomalous radioactivity, uranium minerals, asphalt, copper stain, pyrite, logs and carbon trash.

LOCATION AND ACCESSIBILITY

The area covered by reconnai9s~~c e is a narrow strip about 15 miles wide and 65 miles long of the northwest rim of the Colorado . River Basin in Wayne and Garfield Counties, Utah (fig. 1). It covers approximately 1,000 square mi~es, lying between 110 andIll degrees west longitude. The area has not been su.bC.ivided by General Land Office survey.

The Dirty Devil River divides the ·region into two physiographic - .. uni t.s. One, stretching northeast from the Dirty Devil to the Green· River (fig. lh is the Southern Green River Desert. The other pr~sio graphic unit lies southwest from the Dirty Devil River in the southern Henr,y Mountains basin, referred to as the Little Rockie! district. It extends southward f-om the southern boundary of T. 33 S., R. 12 Eo, Salt Lake Base ~~d Meridian, Utah, to Hansen Creek. The Little Rockies Basin is bounded by Mount Holmes and ~o un t E:.lsworth on the ea.st and Mount Hillars on the north (rig. 2).

Access to botb the Southern Green River Desert and the Little Rockies district is by Utah State Hi ghwcS.y 24, a graded gravel road ex tending from Green River on Uo S. Highway 6-50 southwest to Hanksvilleo Localities in the Southern Green p~ er Desert are reached by traveling southeast from Temple crossroads ;~c·ion located on Utah Highway 24 for 50 miles over an unimpr6ved dirt a~d sand d~~e road to French Seep (fig. 3). Travel on this road r equire a four-wheel drive vehicleo Access to Mossback outcrops ir. Millard vanyon is gained by horseback down Outlaw Trail near French Seep. ~arts of Elaterite Basin may be reached by jeep on a new spur road branching east orf the trunk r oad which extends from French Seep to Hatch Canyon. Connecting jeep trails into Happy Canyon and South Fork, Hatch Canyon, were bu~ t fram t his trunk road.

- 5 - EMER'r - - ~ WAYNE

~ -: \\ - SOUTHERN GREENRIVER DESERT'

... . :::. - -. -

, ...... : .. ::. .. ' .. - -,

Figure I. Locat lQn of .the nor thwest rim, CO lorado ·River Wayne on<1 Garfield CountIes ,Utoh - 6 - . Jm ;',~ : ~ ' :- ,~ WOlt er Group R...--J WOOBRUFF SPRI :. : - 'qwoooru f ' Group J I

t ~ . • •• I I ·

• • • • ~r "" OLMES 6 • •

CROS S - STRATA MEASUREMENTS, , ~ ' o e l mont Group M1NERA ' IZEO OUT9WPS AT SHOOT A~ I NG AND WOODRUFF CL'AIM$

SWORT.H

Gr o up '-J

£ X P A NAT I ON

~----, ., Jm I Morr ison l __ -1 • • Unimproved rood

Mine or prosp ec CROSS - STRATA ME' ASUREMENT'S. - C)roup LITT L E ROC KIES O !STR ICT

S p r IO~

OCf 195"

Figure 2 l_oca1 :on map one Salt Wash trends , Little Hockles district'

Garf ield County, Utah .... ~ .-: - 1 - sou "'ERN GREE N '- Irlle for mo llo r:

R IV E R DESER

GRAND

Unimproved rood

TrOll

X ~"o specl

D CIOlm 9'O~P

~ Seep or SIH ln Q

li e

(!tICE ,.'s .GAOUP

I [ \ \ \1 I: / I J

Oct 19S4

F I ~ure 3 Lower Mossboc k facies and Channels, southern- .Gnutn River pesart

- ~3 . · · . Po i sor: Spr :':lg= : ;: nyon ( ~ i g 0 1 ) i s r eached by cont1:nuing south on _" " Utah 24 from i e.mP e ~~ o s sroads t o P.anksvil lej thence south 12 miles on Utah 95 , a s econaarJT road, t o the Wayne-Garfield County line; thence east down Po i son Spri ngs (3ox Canyon ; for about L5 mileso From Poison Springs Canyon jeeps can ~ ea ch the mouth of Happy Canyon by fording the Dirty Devil R~y er, but t ~av e~ sout h or north along the Dirty Devil is limited to foot t ~ai l s or horse t railso

The Little Rockies dist r i ct is accessible to t wo - wheel drive veh:cles during fair weather by t r aveling sout h from Hanksville on Utah 95 to North Wash junction (fig. - .I , thence sout h 5 miles to Trachyte Creek on an unimproved r oad, t hence 15 miles over t he Hogback to Woodruff Spri ngs or Star Ranch Spring. The Delmont claims, Shootering Canyon, and Hans en Creek all may be reached on spurs branching from the trunk road ext endi ng , from Woodruff Springs. -

In the Southern Gre en diver Desert, drinking wat er is obtainable at French Seep, flowing 1/2 gal lon per minute and at a seep in HapP7 Canyon flowing one gallon per minute . -T5. ter for drilling operations is not available from the- Dirty- -D evil Ri ver because of its deep, steep- . walled canyon.

Water for drilling and domest ic use is available at Woodruff Springs , Star Ranch, and Indian Spri ng ( fig~ 2 i ..J..r. t he Little Rockies dist ricto Flow at Woodruff Springs is about 25 galloHs per minute.

TOPOGRAPHY

The Southern Green Ri ver Desert cO ~ 9 is ts of r elat ively flat-l ying sediments whose surface r i ses gently sout hward to approximat e ly . 7~OOO ' feet above sea level. This surface is m&~tled with shifting eolian sands and dissected--by numerous, deep, straight-sided canyonso These closely ' spaced finger-like canyons have resulted from prolonged headward erosion by tributaries of the Green and Di rty Devi l Riverso They are floored mainly by red beds of the Moenkopi forma t ion. Mossback sandst one i8- exposed in the lower parts of the se ~anyon walls and forms benches, ~ thinly-covered flats, and spur s ext e ~ding out into t he canyons. In ' Poison Springs Canyon, it weathers i nto a narrow dark brown bench known as the "Black Jump~" In places ~ his bench grades into large masses of weathered Mo!sback talus bl ockso

Mount Hillars, Mount Holmes, and Mou.~t Ellsworth are the dominant topographic features of the Little Rockies distri~to They consist of igneous plugs and laccoliths partially covered with folded and faulted sediments. In Shootering and H~~ sen Creek Canyons the sedimentar,r _ beds dip about two to f our degrees west and the area is dissected by , numerous wash es and s ever al canyons . Some of the mesa surfaces are co v er~ with terrace gravels derived f~ om Mount Hillarso Deep straight-walled canyons have been cut i n.f. o the Salt Wa sh member ·of the Morrison formati oh, .which caps a continuous sheer cl iff sout hward from Shootering Canyono

- 9 - Mo st of the district i s at· an elevation 0: 5, 500 f eet. Surface relief increases moderately to t he weste

. eget ation is r elat i vely abundar.t i n t he higher Southern Gr een Ri ver Desert, and consists largel y of bunch grass, grea~ewood, sagebrush, cedar and pinon treeso The vegetation on the canyon floors and in the Little Rockies district is typical desert foliage.

GEOLOGY

This section of the Colorado!s nor t hwest r~ consists of Permian, Triassic, Jurassic, and Cretaceous s edimentar,y rocks exposed i n simple flexures 0 Cropping out between the Gr een and Dirty Devil Rivers, the older beds are flat lying or dip gentl y one to four degrees westward. from the Monument upwarp towards t he Henry ~ount ain s synclinal basin o Striking about N. 300 E. on the upwarp~ these rocks swing into a north-trending strike along the Dirty Devil Rivero Faulting is uncommon ex cept for · several sets of par allel gravity fault s in the South Fork of Hatch Canyon - and a few small en echelon faults in Poison Springs Canyon. . '.

In the 1ittl e Rockies district the Jurassic and Cretaceous sediments strike north-northeast and have a regional dip of two to seven ·degrees northwest towards the axis of the Eenry Hountains basino This structur al basin, formed after Upper Cretaceous deposition (2), is one of the. major folds of the Colorado Plat eau. Locally aroand Mount Hillars and the · Little Rockies, the sediments were forcibly intruded in mi ddle Terti ary time (2) by diorite porphyry laccoliths and thrust abruptl y upward·. The principal joint sets trend northeast and southwest.

Exposed along the Colorado R:ver i n the area st udi ed ar e the Permian Rico formation, the Cedar Mesa sand s one, Organ Rock, and White Rim sand stone members of the Cu~ler formation; the Triassic Moenkopi f or mation, Chinle formation (includi ng the Mo s sback sandstone memb er),and Wingate sandstone; the Jurassic Kayenta formatior-, lavajo sandstone, Carmel formation, Entrada sandstone , Curti s formation, Summerville ~ ormation, and Morrison formati on; and the ~r e ta ceou s ~kota sandstone and Mancos shaleo In the area examined the sedim€n ta ~ r ocks have been studied and mapped by Baker (3) and Hunt ( 2 and 4 )0

Li t tle Rocki es 0istrict

The Jurassic Mor rison format ~on exposed along t he southea st r im of the Henry Mountains basin, ~ons~s ts 0: t he upper E~~shy Bas in member and lower Salt Wash member . Eocause the Sa t Wash is t he ore-bear i ng member p it was t he prime object i ve of atudy i n +he Little Rockies distr ict o Measured sections r evealed that the Mo~risor. t hi ckens gradually t owards the southwest -

- 10 - Th e Sa: t -1~a s h member consi sts largely of light -gray to light y ellowi~h- brown, fin6- to ve ~ coarse- grained sandstone, with some thin interbedded wedge - sh ap~~ tongues of light gray, light green , and maroon mudstone r anging in thickness from several i r.ches to 50 feet.- Though mas sive -units some t imes oc cur, the sandstones are generally medium- to thi ck- bedded and cross-stratif iedc Because of its high percentage of quart -z, very- spa.rse feldspar, and calcite ce.ment g ~ad:gan (5) , i n this area, has termed the Salt Wash an orthoquartziteo The beddi ng, cross-stratification, and lenticular nature of these sandstones-, together with evidence of fossil wood and dinosaur bones, points towards a fluviatile origin.

The Salt Wash thi ckens gradually from about 400 feet at Farmer's Butt e to 525 f eet at Hansen Creek (fig. 2). Thi s southward thickening, usually at the expense of the B::-u shy Basin men.'Jer, is accompanied by a general i ncrease in grain size g Conglomeratic quartz sandstones and interbedded lenses of quartz sandstones and interbedded le ~ ses of quartz conglomerate are more common at Hansen Creek t han at Woodruf f Springso Lithofacies study (f i g. 4) has a_so revealed a gradual southwestward increase of quartz sand in the Salt Wa sh sectiono Sandstone i sol ith -, contours (isopercentage lines o~ sandst one, fig . 4) show thi s relation shipo ~ These features support preliminary observations by Craig (6) on Morrison stratigraphy of the Colorado P~ate au o

Cross-strata measurements of the Salt Wash in the Little Rockies d:s trict have been summarized st atistically (figc 2) through the use of the stereographic pr oj ect ion, a technique suggested by Pettijohn (7)0 The bulk of measurements delineateS a signif:cant sedimentary trend - about ~ No 5oPEo, and a minor t rend about Nc 28-4P W. These generalized trends haTe been plotted on t he lith of~ci e 8 map (fig. 4)g The sedimentary t rend s ~ lithofacies trends, and northeast thi nning of the sandstone accompanied by a parallel decr ease in sand grain size suggest the Salt Wash sands-- were deposited by a belt of trur~ streams flowing northeast over an alluvial plain of -low r eliefe Apparently the Sal t Wash streams transported sediment in a fan-shaped system of braided chap~el s which t ad its apex near the crossing of the Utah-Arizona state l ine by the Colorado Rivero Tributarieq to the t runk streams flowed from t he southeaet.

Southern Green Ri~e r Desert

The upper Triassic Mo ssback sandstone described herein is considered a basal member of the Chin:e fo~at io~ because it initiates a fluviatile environment of deposition pre_ceded by a regional unconformity and fo ... lowed by an eolian depositional environment that produced the Wingate sandston " As uranium mineralizatior. is known to oc cur in the Mossback sandstone of the Southern Green River Desert, the prime object ive of this reconnaissance was to examine t his sandst one. In t his area it is made up ~ arg e~y o ~ light gray and light br wnish-gr ay medium- to coarse-grained poor tc f air-sor ted sandstones, interbadded with conglomer atic sandstones and some ccnglomerates J and intercalated light to medium gray mudstones5

- 11 -- Pre -M

~ DEl. ~ONJ GROUP 5 T ~ £ X P L A N A T / -0 N

~ Mornson for';afion - - I'pr e~ .. ~(e - Mor~ls ori format Io ns 4 . -~ S i~ e and - dip l. ~~HOOTAR I N~ ' Vr- CANYON - Sedimentar y treno" . / ~~ r o , , ~5T Ore bo.d y' - 5 Ize (tons) - s S -70- Soli Wash Isclith 100 ( 5S .. MS

o S lrollgrophlC section / / I s c A E :' 2 · 3 4 5 r.l t U:$

Wash I!thofacies mop) .L ittle Rockies, di :tr"i:c·' -, CJ f le,C Coo " .' , U oh The cor~lome ra :ic beds con ~ain pe bbles of quartz , gray quartzite, brown chert, tan limestone , and some greer. and gray clay gal~so ._ These sedi ments, commonly ex.i1ibiti ng cross-stratification j occur in -rapidly inter fingering lenticular units. Th e bulk of the Chinle .formation, overlying . this basal sandst.one, ':"5 made up of gray, green» pale red" and. purple claystones and siltstones, with a few interbedded $an~stone lenses • . - Fossil wood is co~on th~~ugtout the Chinle. Most carbonaceous wood and fossil plant fragments occur in the Mossback membero

Throughout the area the Chinle formation ranges in thickness from 400 to 550 feet. The Mossback sandstone is continuous and is about 50 feet thick near the Green River and thickens southwestward to 125 feet in Happy Canyon, then thins westward to about -70 feet in Poison Springs Canyon and southeast to less than 60 feet near the Colorado River (figv -3)0

In the Mossback sandstone of the Southern Green' River Desert, ~wo recurrent units have been ~ecogr~ ized~

c 1. Upper blanket unit ~ A massiv e, dark-brown weathering con_ -:.; ,< glomeratic sandstone, in part cross-stratified; barren of _-. _- mineraliza tion ; a cont:.nuous well-cemented unit and·· a '. persistent _-' bench markero - - .

2. Lowe~ - channe l uni t ~ A ~ ig ht gray, fine- to coarse-grained, ' cross-strat ified sandstone with some interbedded conglomerate_ and mudstone; underlying the upper blanket unit, it fills paleochannels ~ uranium mineralization in the area occurs in " -..

this horizon. .- .... -:.. -- The most striking sedimentary featur es throughout the area are the lensing sandstones, mudstones , and c0nglomerates of the lower unit ~ which fills channels cut into the Mo enkopi mudstones. These channel ways range in size from scours 2r l feet wide to paleochannels 200 to 300 feet wide, 35 feet deep and 2 miles long. Most of them are about 15 to 20 feet deep, 100 feet wide, and c ~~ be traced 1,000 f eet along an outcrop 0 These sedimentary features (f:g. 3) have an east or northeast orientation, presumably indicative of the paleodrainage pattern. They contain more lenses of conglomerate and t.in mudstone wedges than other horizons of the Mossbackc

In examining thick sandstones of the l~~er channel unit , two distinct sandstone facies were foundz

1. Clayey quartz sands onE ~acie s~ Very light gray, fine- to medium-grained c ~aysy quartz sandstones~ thin bedded and . commonly cro85-strat.i!ied; because of its high clay content)} it has {ery ~ow pcros:ty and permeabilityo

2~ Quar tz sandstone facies ~ Light gray~ _ medium- to coarse- gra"ned sandstone9~ abundant calcite cement ; cross-stratification common; th: s ~acie s has l ow porosity a~d permeability because 0: ':"ts hi gh percent age 1 cal~i te cement c - 13 - The sharp b ou~ d a~y be ~wee n t he two ~a c i es trends northwest a8ross Elater i t e -

Basin and the head of ¥.i. llard Canyon ( figo· J) 0

UnANl v~ MINEP~LIZ ATiv N AND ORE .DEPOSITS

Salt Wash M embe~ of the Morrison Formation ......

Uranium minerals in the ~ i ttle Rockies district occur in two horizons of the Salt Wash membero Oxidized deposits of vanadium-uranium ore are associated chiefly with carbonized ~ood , logs, and pl ant fragments. It appears that deposition of the o ~e wa s controlled by the occurrence of carbon. In these bed ~ ed depcs.:.ts, which occur in one zone about ' 200 feet above the base of the Sal t Wash and :n ~~otre r zone · ~O to 'lOO feet above the contact, min eral~za t i on generally follows cross- stratification. or cuts across bedding- Th e orebodies are smali, t abul ar, limited, and irregular in extent, but ar e of good grade. . .

At Woodruff Springs ( ~ig ~ 2 ) mineralization is in the upper zone , .. about 200 feet above t he base of t he Salt Wash. The Walter claims '. exhibit low-grade min e ra l~ za· i on associated with c a r bo~~zed l egs in cr oss- ~~ ' stratified sandstone and mudstor.e : '= Ds es containing m.ascerated plant .....~>;~ fragments • Limonite and calcite cement are common" The logs are of 'ore .'~ grade, but their scattered distribution in barren sands'tone r enders the'.. ·.: '.:~ _ prospect unpromis ~ n g . ~- - ~ .-::- .. -- .. The largest oreb6dy found i n t he district is on the Woodruff' groupo -~ ' -~ .. : Here small rolls of carnotite, roscoelite, a..'1d hewettite are associated /;::~ ...~-~ with vegetal trash and carbonized wood i n a med ium- grained " friable, - --, ~: ~.~~ ,cross-stratified, quartz sandstor:e with i nt e rb~dded mud·st .one tongiies,o-' - :;'--,-":7.::;: Limonite is common to abundant . Silicified logs a~ e found on thes-e :claim·s in the upper third of the Salt Wa sha Most o ~ them ar e barren of minerali zation, but one log wi t h carn o tjt ~ stai ns yi elded 0.53 per ce t U30S and 0.53 percent V205.

In the Del Monte area ore deposits occur in extremely small, bigh~ ~;-_-.;.;, : grade lenses i n the lower ore zone about 90 to 100 feet above the base -> > :-:- ., of the Salt Wash member. A 50-ton orebody is considered to be a good- . - ' sized deposit on these claims. Car notite and hewettite minerals are associated chiefly with carbonaceous mat t er ~~d c~ay galls. Limoni te streaks are common. Because these small rich beds and lenses are not haloed by ore of a lower tenor, there is little possibility for developing large low-grade tonnage.

Production from ~hootering Canyon is significant for the Little Rockies district. On these ~laims ore deposits consi st largely of clust€rs of ''buttons," extremely smA_ l tabul ar bodies of hi gh-grade ore 25 feet square and 3 to 10 inches t hi ck o Paral:Lel bedding and cross- st r atificat ion are found i n the lower or e zon -= a::J 0U ~ 35 .t o 50 fe f- ~ · -a,bove t,h .::> Sal. - ~.:~ __ .. -.' Surmne ~v"11le contact. As at Delmont i uranium minpral.s .of C!l .l"not i t;.. , hewett :'te and probably rOBcoe:..:..te ·are a~~ocia . t eo. with -veget. al ~ "" a sh and , clay galls. - 14 On the L'l:::1<; - ~:.. ':" ice :2.a ::..ms c! Shootering Point, where erosion has s t ripped 0. f JT; c st. 0: -: ~'l e Sal t., \.Jash sand and has left 5 to 25 feet of barrer. sa ~cs:cr:e v e r: J~~ng t he ere horizon, open-pit stripping methods are usedo ?i t s r~ve . een d"~ w!l ere outcrops indica te a. sufficient density o ~ orebodieE. The ex:.remely sr.-lall ore deposits necessitate selective m:'~ing and s o ""~=-n§:j t-·.- ..a nd operations. About It miles down dip from the Lucky Strike :::la~~ s, these cl~ s~ers of ' buttons" have beer. mi. ed '0 :-," dr:'f:':'r.g i n tc b e. "tt sides of the canyon. Verti cal depth to the ore horizon is about 200 feet. On the canyon's north side the ore trend is about N. 60c E. ] ~losely paralleling the dominant sedimentary trend. These ri:h l: 'c uttons " are not ha.loed by significant amounts of ore.

As in the Trachyte e.nd rO r tr. ~l a s t c~.=-s ·-,ric ts (fig. 1), orebodl.es of the L1 ttle Rockies are essen"t:'a:ly lllog deposits. n These a.ccumulations of organic matter are probatly rela:.eQ t.., the sedimentary trends (fig .• 2) . Marked shifts in sedimentary t rencis :lave been observed by Stokes ( 8) in many mineralized Salt Wash d.is:ri~ ts of the Colorado Plateau~ and t!'i.:;) s~ ,· local accumulati ons of organic matt er may indicate such a shift • . in th~8 area a l ithofacies study indicates sar.dstone WAkes up 75 to 85 percent of the Salt Wash member ~ It al se reve als that t he o reb o~ size will vary inversely with the amo unt ~: sa r.d s ~o ~e in the stratigraphic section.

Mossback Member of the Chinle Foramti on

In the Mossback sandstone of t he Scut hern Greer: River Dese rt, mineralization of the copp€r- ~rani ~~ t ' ~ e is fairly common but known or~ deposits are rare. Uran ' m Qre is f ~ Un j i n the lower Mossback channel unit near the base of sanjstones ar.a c : n ~ lomer ~ tes ~il ~ ing paleochannels in the Moenkopi.

The only known pr oduc t i ve o: ebody i ~ the distr i c t (1953) is in Poison

Sprin(ss Canyon (fi g. 3). T ~ a r:::'um , 80 5so:ia:-e ..... cr.ie:::'y with carbonized logs and minor aspha1t ite, occurs ~~ cr~ ss -s : 4at i ~ied clayey q a~tz sandstone and limestone c onglomera ~ e filling a p£_eovhannel p This c h a~~pl . is about,l to 200 feet wide and 20 feet deep, has a sedime n ~ary trend of S. 670 W., and is expo,qed for several hundred f eet a._ong t!le rim. Large t alus blockS cover t he steep slope over much of the channel trendo Ore minerals are meta-autunite, meta-torbernite, an "'1i dent,if1ed yellow uranium sulfate, mineralized carbon trash, and occasic:;).a ~ l.y ttraniferous asphal tit e. Gangue minerals include abundant lim o~i t e, calcite, gypsum, jarosite, pyrite, galena, and brochantite and other copper rrdnera1s ~

Mapping of the ~ne and channel (fig. 5) revealed that drifting extended through the orebody .into barren cha~~e 1 sandstone. The orebody was mapped by scintillat ion surveys and assays of channel samples . Readings in excess of 700 cps were pr esumed t o indicate uranium con cent r ations in excess of 0.10 per c ~ ~t U3080 Originally about 40 tons

= 15 - r (,,~ ~~~ ~(.\.- v-~~ ------(, A lr m

._- -_. __ . --- .. _---- /11 r HANNEL SECTION f"

EXP L A IVA T IO N

'V1o sS boCk member. Chinle formo11on

Moenk0p' formo tlon

ConQlomerote

Sandstone ~I Muds tone

Sedimentary trend t I fsorod I,ne s (cps)

.02 Chemical ~ssoy U 3 Os

l' . Ore body

Figure ~ .. Plan F:>oison, 5,pri'rgs Canyon . I • of high-lime ore made up the deposit w~i ch was ~ to l ~ feet thi ck, tabular in shape, and has a limonite haloo

In spite of high radioactivity on outcrops$ other prospects in mineralized channels of Poison S pr~ngs Canyon have failed to produce ore. Mineralization and ~adioactivity decrease rapidly behind the rimso Limonite, jarosite, mineralized wood , si l~cified wood, and gypsum are abundant.

On Ekker's claims along the Dirty Devil River, high-grade mineralized logs are scattered through clayey quartz sandstones filling paleochannelso One sampled log assaying 50 71 percent U30e had a lime content of 32 06 percent. The high-lime, channel s~~dsto n es are barren or weakly mineralized but commonly contain limonite.

Uranium mineralization in Happy and Eatch Canyons is also controlled primarily by small channels and scours in the Mo enkopi formationo These . are filled with clayey quartz sandstones of the lower Mossback and contain- a mineral suite like that of Poison Springs Canyono Ore minerals, associated chiefly with carbonized logs, wood and vegetal trash, include meta torbernite, mineralized fossil wood , and some ur~~iferous asphaltiteo Also common are pyrite, galena~ marcasite, limonite, jarosite, gypsum, and copper oxides. Radiometric and chem ~ cal assays reveal this minerali zation is out of equilibrium in that the chemical assays are five times greater than the radiometric assaysc

Lower Mossback channel units in Mi llard Canyon and Elaterite Basin contain sparse amounts of carbon trash, carbonized wood, plant fragments, and silicified logs in the clayey quartz sandstone and quartz sandstone facies discussed above. Jarosite, limonite, gypsum, and copper oxides in the sandstone and underlying ~oenko pi mudstones are rare~ . These ~- - canyons appear to be barren of minerali zation, ~~d the outlook ~or fut~re ore discoveries is discouragingo

This area is also unfavorable for are deposition because of tightly cemented impermeable sandstone facies of the lower Mossback conglomerate (fig. 3).

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REFERENCES

1. Mastrovich, A. M., ?.eport on Little Rockies district, Henry Mountains·' area, Utah: Union M ~ nes Davel. Corp. report, 1946 (unp~b~ished ' rep~rt).

2. Hunt, C. B., Guidebook to the geology of Utah (no. 1): Utah Geo1 • . Soc., 1946.

3. Baker, A. A., Geology of the Green River ~- Cataract Canyon region, Eaery, Wayne and Garfield Counties, Utah~ U. S. Geol. Survq . Bull. 951, 1946. 4. Hunt, C. B., et al., Geologic map of the Henr,r Mountains region, Utah: U. S • .Geol. Survey Oil and Gas Investigations Map OM-131, 1952. 5. Cadigan, R. A., U. S. Geo1o Survey, 1953 (personal' COmmunication).

6. Craig, L. e., et al., Preliminary report on the stratigrap~ of tA~ Morrison and related formations of the Colorado Plateau regi9n: -~. U. S. Geel. Survey TEI-lSO, 19510 7. Pettijohn, F. J., Sedimentar,y rocks, New York, Harper & Broso, 19490 8. Stokes, W. L., Primary sedimentary trend indicators as applied to ore finding in the Carrizo Mountains, Arizona and New Mexico: U. S. Atomic Energy Comm., RME-3043 (pt. 1), 1953.

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